VALIDITATION OF EEF MODEL DRIFT VELOCITY
USING C/NOFS SATELLITE MEASUREMENTS AT
QUIET CONDITIONS OVER BAHIR DAR
A THESIS SUBMITTED TO
THE SCHOOL OF GRADUATE STUDIES OF
BAHIR DAR UNIVERSITY
IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE IN PHYSICS
BY
Tebikew Gashu Tadesse
BAHIR DAR UNIVERSITY
BAHIR DAR, ETHIOPIA
SEPTEMBER 2017
c Copyright by Tebikew Gashu Tadesse, 2017

BAHIR DAR UNIVERSITY
DEPARTMENT OF
PHYSICS
The undersigned hereby certify that they have read and
recommend to the Faculty of Science, School of Graduate Studies
for acceptance a thesis entitled “VALIDITATION OF EEF
MODEL DRIFT VELOCITY USING C/NOFS SATELLITE
MEASUREMENTS AT QUIET CONDITIONS Over Bahir
Dar” by Tebikew Gashu Tadesse in partial ful llment of the
requirements for the degree of Master of Science.
Dated: September 2017
Advisor:
 Dr Melessew Nigussie(PhD)
Examination Commitee:
 Dr Ramudin R (PhD)(External examiner)
Dr Tsegaye K (PhD)(Internal examiner)
Dr Gebire Egizeabiher K (PhD)(Chairman)
ii

BAHIR DAR UNIVERSITY
Date: September 2017
Author: Tebikew Gashu Tadesse
Title: VALIDITATION OF EEF MODEL DRIFT
VELOCITY USING C/NOFS SATELLITE
MEASUREMENTS AT QUIET CONDITIONS
Over Bahir Dar
Department: Physics
Degree: M.Sc. Convocation: September Year: 2017
Permission is herewith granted to Bahir Dar University to circulate and
to have copied for non-commercial purposes, at its discretion, the above title
upon the request of individuals or institutions.
Signature of Author
THE AUTHOR RESERVES OTHER PUBLICATION RIGHTS, AND
NEITHER THE THESIS NOR EXTENSIVE EXTRACTS FROM IT MAY
BE PRINTED OR OTHERWISE REPRODUCED WITHOUT THE AUTHOR’S
WRITTEN PERMISSION.
THE AUTHOR ATTESTS THAT PERMISSION HAS BEEN OBTAINED
FOR THE USE OF ANY COPYRIGHTED MATERIAL APPEARING IN THIS
THESIS (OTHER THAN BRIEF EXCERPTS REQUIRING ONLY PROPER
ACKNOWLEDGEMENT IN SCHOLARLY WRITING) AND THAT ALL SUCH USE
IS CLEARLY ACKNOWLEDGED.
 iii

Dedication
This work is dedicated to my father Gashu Tadesse and
my mother Shashitu Bitew.
iv

Table of Contents
Table of Contents
 v
List of Tables
 vii
List of Figures
 viii
Acknowledgements
 ix
1 Introduction
 1
1.1 Background of the Thesis . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Motivations of the Thesis . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3 Objectives of the Thesis . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.4 The Structure of the Thesis . . . . . . . . . . . . . . . . . . . . . . . 6
2 The Earth’s Ionosphere
 7
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2 The Formation of the Ionospheres . . . . . . . . . . . . . . . . . . . . 8
2.3 The ionization process and production rate in the ionosphere . . . . . 11
2.4 The layers of the ionospheres . . . . . . . . . . . . . . . . . . . . . . . 16
2.5 The variations of the ionospheres . . . . . . . . . . . . . . . . . . . . 20
2.5.1 Diurnal variations . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.5.2 Latitudinal variations . . . . . . . . . . . . . . . . . . . . . . . 21
2.5.3 Seasonal variations . . . . . . . . . . . . . . . . . . . . . . . . 22
2.5.4 Geomagnetic activity/storms/ . . . . . . . . . . . . . . . . . . 23
2.5.5 Longitudinal Variations . . . . . . . . . . . . . . . . . . . . . 23
3 IONOSPHERIC EQUATORIAL ELECTRIC FIELD MODEL DRIFT
VELOCITY
 26
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
v

3.2 The EEF Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.3 The CHAMP Satellite Measurements . . . . . . . . . . . . . . . . . . 29
3.4 The C/NOFS Satellite Measurements . . . . . . . . . . . . . . . . . . 31
3.5 A Real-Time Forecast Service for the Ionosphere . . . . . . . . . . . . 32
3.6 The Equatorial Ion Vertical Drift Velo city (E × B) in the Ionospheres 34
4 DATA AND ANALYSIS METHOD
 43
5 RESULTS AND DISCUSSIONS
 46
5.1 Diurnal variations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
5.2 Monthly variations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
5.3 Seasonal variations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
5.4 Longitudinal variations . . . . . . . . . . . . . . . . . . . . . . . . . . 52
5.5 Model validiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
6 CONCLUSION and RECOMMENDATIONS
 57
6.1 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
6.2 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Bibliography
 59
vi

List of Tables
4.1 The number of days in months used from C/NOFS satellite measure-
ment data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
vii

List of Figures
2.1 Schematics of photoionization and impact ionization. . . . . . . . . . 9
2.2 An il lustration of the geometry related to the solar radiation (I) when
penetrating a slab of thickness dz in the Earth’s atmosphere at a zenith
angle  . The distance to the source and to the ground is s and z
respectively. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.3 Normalized Chapman production function versus reduced height and
solar zenith angle   . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.4 The vertical structure of the ionospheric layers. . . . . . . . . . . . . 17
5.1 September equinox daily variations of the equatorial vertical drift velocity. 47
5.2 June solstice daily variations of the equatorial vertical drift velocity. . 48
5.3 Monthly variation of equatorial vertical drift velocity. . . . . . . . . . 50
5.4 The seasonal variation of the equatorial ionospheric vertical drift velocity. 52
5.5 The longitudinal variation of the equatorial vertical drift velocity . . . 53
5.6 The validations of the equatorial vertical drift velocity with its C/NOFS
satellite measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . 56
viii

Acknowledgements
About everything thanks to the almighty and gracious God, as man propose Go d
dispose; next to this I would like to give my heartfelt gratitude for my advisor Dr.
Melessew Nigussie who helped me while I was selecting the topic and also for this
constructive criticism, suggestions, technical assistance and encouragement that he
gave me from beginning up to the completing of this thesis. I would like to thank all
of the sta  in physics department lectures for their help and support throughout my
education, you are a credit to the university. I would like to thanks all of my fellow
postgraduate students who have make my time in the department so enjoyable, thanks
for the fantastic memories. I would like acknowledge my family and friends for their
never ending support and encouragement throughout my intellectual endeavors. I
am also delighted to express my deepest respect to my parents for providing their
ultimate moral support and motivation to continue my education and instilling in me
the self belief that anything is possible with a little hard work. Finally, my heartfelt
gratitude goes to wonderfully my lovely friends; for her continued patience, support
and encouragement throughout the courses of this research program.
Tebikew Gashu
Bahir Dar, Ethiopia
September, 2017.
ix

Abstract
The equatorial ionospheric vertical ion drift velo cities (Vz) are important for the
understanding of the equatorial ionospheric dynamics. In this study the equatorial
electric  eld and World Magnetic Models have been used to compute the electric and
magnetic  elds, respectively. These parameters in turn used to compute the vertical
drift velo city. The drift velo city has been computed for di erent day, month, season,
and longitudes. Our result indicates that the peak of Vz is maximum in Asia during
June solstice and September equinox with a values of 65 m/s and 60 m/s respectively
at 11:00 LT and minimum in North America during December solstice and March
equinox with a comparable values of 10 m/s at 9:00 LT times. Similarly, in Ethiopia
the peak Vz with amplitudes of 15-20 m/s during September and March equinox
and 10-15 m/s during December and June solstice seasons at 11:00 LT times. Thus
the day time equatorial vertical drifts have largest amplitudes between 11:00 LT and
19:00 LT with typical values of 15-25 m/s that shows our model result is in a good
agreement with other equatorial ground-based observations over India, Brazil, Peru
and Kwajalein.
Key words: EEF Model Derived Vz, C/NOFS satellite measurements and Geomag-
netic Real-Time model.

Chapter 1
Introduction
1.1 Background of the Thesis
The ionosphere is the electrically charged portion of the atmosphere, located be-
tween approximately 50 km and 2000 km above the Earth’s surface. The ionosphere
was discovered when it was observed that the radio waves can propagate over large
distances and one had to assume the existence of an electrical conductive layers in
the upper atmosphere which could re ects the waves. In this region, the ionizing
radiation from the Sun causes electron and ions to exist in a su cient quantities that
they a ect the propagation of radio waves (Kleusnberg and Teunissen, 1996).
The ionosphere is a very sensitive and dynamic system controlled by many parame-
ters. It is formed when the energetic electromagnetic and particle radiation from the
sun and space ionize air molecules that creating a weakly ionized plasma in the upper
atmospheres. The layer of the ionosphere is also formed by the extreme ultraviolet
(EUV) and x-ray radiations from the Sun and has characteristic variations with the
time of the day and latitudes. At high latitudes there is a natural light displays in
the sky that is called aurora, which displaces lights caused by electrons and protons
striking the atmosphere at high speeds. The particles come from the magnetosphere
1

2
and spiral down the magnetic  eld lines of the Earth. These particles produce a
spectacular array of lights and when they strike the atmosphere that produced ion-
ization. The behavior of the ionosphere can vary quite signi cantly with time (Sun
spot cycle, seasonally and diurnally) and geographical lo cations (polar, aurora zones,
mid latitude and equatorial regions).
The ionosphere is a central region of the geosphere. Within the ionosphere, the
equatorial region is one of the most complex, hosts to numerous instabilities, inter-
actions and still unresolved questions regarding dynamics. The equatorial ionosphere
and thermosphere constitute a coupled system with its electro dynamical and plasma
physical pro cesses being responsible for a variety of ionospheric phenomena pecu-
liar to the equatorial region. The equatorial ionosphere is more susceptible for most
important electrodynamical phenomena such as the equatorial electro jet (EEJ), equa-
torial ionization anomaly (EIA), equatorial spread F (ESF) plasma instabilities, tidal
behavior of thermospheric winds and tides etc which in uenced by the regional ge-
omagnetic  eld, its declination and the proximity of the magnetic to the geographic
equator (Prof. Rao, 2006).
The structure of the ionospheres are studied by various ionospheric models developed.
One of these models are the equatorial electric  eld (EEF) model which derived from
the magnetometer measurements of near-polar orbiting satellite (CHAMP). As they
cross the magnetic equator by recovering a clean signal of the EEJ current and mo d-
eling the observed current to determine the electric  eld present during the satellite
passes the equator. Such data is measured from the ground-based coherent scatter
radar at Jicamarca, Peru and a horizontal  eld measurements from West African
Magnetometer Network Magnetic Observatory Chains (Alken and Maus, 2009).

3
In the ionospheric E region, neutral winds, gravity and plasma pressure gradients
drive large scale current systems (Heelis, 2004). In this region, the eastward compo-
nent of the electric  eld at the magnetic equator drives vertical E × B electron drift
until polarization charges accumulates at the upper and lower boundaries of the E
region which is a non conducting strip. The result is a strong vertical electric  eld
which drives an enhanced zonal electron drift within about ±3 degrees of the mag-
netic equator under quiet conditions. In the E regions of the equatorial ionospheres
there are two layers of currents responsible for the quiet solar daily variations in the
Earth’s magnetic  eld (i.e., the world wide solar quiet and the EEJ). The worldwide
solar quiet current systems of the Earth’s ionosphere produces an electrostatic elec-
tric  elds directed east-west (down-dusk) in the equatorial day side of the ionosphere
(Fuller-Rawell, 2011). At the magnetic dip equator, where the geomagnetic  eld is
horizontal, this electric  eld is results in an enhanced eastward current  ow within
±3 degrees of the magnetic equator which is called EEJ. The EEJ is the intense
ionospheric current  owing eastwards within the narrow strip  anking the dip equa-
tor responsible for the observed enhanced horizontal magnetic  eld intensity at the
magnetic equatorial neighborho od (Chapman, 1951). Its current distributions are
determined from the CHAMP satellite measurements by removing  rst the magnetic
 eld contributions from other sources and then using the results independent of the
satellite altitude and ambient  eld geometry (Luhr et al, 2004; Mano j et al, 2006).
Thus the day time eastward EEF in the ionospheric E region plays an important
role in equatorial ionospheric dynamics. It is responsible for driving the EEJ current
system, equatorial vertical ion drifts and the EIA. In order to its importance, there is
a much interest in accurately measuring and modeling the EEF measurements with

4
full temporal and special coverage of the equatorial ionospheres.
The equatorial vertical plasma drifts are driven by the complex dynamo processes in
the ionospheric E and F regions. The neutral winds on the day side causes positive
and negative charges to accumulate at the down and dusk terminators, respectively,
giving rise to the EEF (Heelis, 2004). This  eld is eastward in the day side and
westward on the night side. The EEF in combination with the Earth’s magnetic  eld
driver ion drifts which are typically upward and westward during the day time and
downward and eastward at night.
The accuracy measuring and predictions of the vertical plasma drifts is important for
the study of many physical processes in the low latitude ionosphere, including the
EIA (Appleton, 1954; stole et al, 2008), upper F region electron density structure
(Su et al, 1995), the EEJ (Forbes, 1981; Alken and Maus, 2007) and the forecasting
of the low latitude ionospheric weathers. In order to model the quiet time vertical
plasma drifts in the F region by using observatory and satellite data sources (Scherlies
and Fejer, 1999) of a combined measurements from the Jicamarca incoherent scatter
radar (ISR) with observation from the Atmospheric Explorer E (AE-E) satellites to
produces a quiet time empirical vertical drift models at all longitudes, seasons, local
times and solar  ux values (Fejer et al, 2008).
In the Earth’s ionospheric F region, between 200 Km and 800 Km altitudes, the day
time distribution of electrons and ions as a function of altitude, latitude, longitude
and local times are determined by ionospheric pro duction, loss and transport mech-
anisms. production is primarily through photoionization of atomic oxygen by solar
EUV (  < 91.1nm) radiation and loss is through charge exchange of O+ ions with N2
and O2 to give NO + and O +
2 , followed by recombination with electrons. Transport

5
of ionization perpendicular to B is due to E × B drifts and transport parallel to B
is due to am-bipolar di usion and the components of the neutral wind parallel to B.
At low latitudes the primary transport mechanism is via E × B drifts in the vertical
and meridional plane. At the magnetic equator, these E × B drifts upward in the
day time and primary downward at night. The day time upward drifts are respon-
sible for pro ducing crests in the F region peak electron density (Nmax) at ±150 to
180 magnetic longitude (i.e., called equatorial anomaly) (Hanson and Mo ett, 1966;
Anderson, 1973).
1.2 Motivations of the Thesis
At the magnetic dip equator, the east-west electric  eld generated in the E-region
dynamo gets mapped to the F-region along the highly conducting  eld lines and lifts
the plasma to higher altitudes in the presence of the horizontal north-south magnetic
 elds (Martyn, 1947). Recently, several works have been carried out to study the
di erent aspects of the equatorial ionospheric vertical plasma drifts using the C/NOFS
satellite measurement magnetometer data. These include a model simulation study
carried out to predict the diurnal, monthly, seasonal, longitudinal and time variation
of the EEF model derived ionospheric plasma drift velocities in the Peruvian sectors
(Alken and Maus, 2007). The strength of the equatorial vertical drift is not the
same for di erent EEJ zone magnetic sectors. This suggests that the need for the
ionospheric studies to be carried out in the Ethiopian sectors especially at Bahir
Dar (11.60 N and 37.380 E) regions. Furthermore, expanding on their studies to our
knowledge, no work was done over the sector in examining the EEF derived vertical
plasma drifts under the quiet conditions in relation to the horizontal component of

6
the Earth’s magnetic  eld.
1.3 Objectives of the Thesis
The main signi cance of this research is the use of C/NOFS satellite measurements
to determine the characteristics of ionospheric vertical ion drift velocity distributions
at the equatorial solar quiet conditions which focus on the validitation of EEF model
ionospheric vertical drift velocities. In order to test this hypothesis, the following
research objectives have been set:-
• To estimate the ionospheric vertical ion drift velocity using the EEF and World
magnetic  eld model.
• To validate the drift velocity model against the C/NOFS satellite measurements.
• To characterize daily, seasonal, monthly and longitudinal variations of the equatorial
ionospheric vertical ion drift velocity.
1.4 The Structure of the Thesis
The structure of the thesis is organized into six chapters. In this chapter we de-
scribe brie y about the general background of the thesis. In chapter two the Earth’s
ionosphere and its formation, variation and layers were described. The EEF model,
CHAMP satellite measurements, C/NOFS satellite measurements and the vertical
ion drift velocity derived from the EEF model has been described in chapter three.
In chapter four, the method of analyzing and the data obtained was stated. The
result and discussion of our work has stated in chapter  ve. Finally, our conclusion
and recommendations have been stated in chapter six.

Chapter 2
The Earth’s Ionosphere
2.1 Introduction
The ionosphere is the region of Earth’s upper atmosphere, from about 50 Km to
2000 km altitude that includes the thermosphere and parts of the mesosphere and
exosphere. It is ionized by solar radiation, plays an important part in atmospheric
electricity and forms the inner edge of the magnetosphere. It has a practical im-
portance because, among other functions, it in uences radio propagation to distant
places on the Earth, telecommunication, and satellite tracking Earth observation from
space and satellite navigation. The ionosphere is the layer of Earth’s upper atmo-
sphere that contains neutral and ionized constituents which dealing with a mixture
of thermal and gravitationally bound charge carrier gasses (P r  
olss, 2004). This is
important to:-
• Enables the  ow of electric currents, there by leading to magnetic  eld perturba-
tions and electro dynamics heating e ects.
• In uence the dynamics of the upper atmosphere by producing /slowing down/ ther-
mospheric winds.
 7

8
• Modi es the electromagnetic waves, whether it is by refraction, re ection, attenu-
ation or rotation of the plane of polarization (P r  
olss, 2004).
The ionosphere is also the constituent of the Earth’s atmosphere which becomes in-
creasingly rare ed and can support free electrons for short periods. This region has
the properties of a gas and plasma which exhibit some increasing e ects. The neutral
atoms and molecules, N2, N, N O, O2, O, H and He are ionized by the impact of the
EUV and X-ray radiation, emanating from the Sun (P r  
olss, 2004). This layer of the
atmosphere is controlled by:-
• The radiation of the sun and coupling with the neutral atmosphere.
•The solar wind, Earth’s magnetic  eld and the interplanetary magnetic  elds.
• The high variability of the density of the charged particles.
The ionosphere is the radiation from the sun contains su cient energy at short wave-
lengths to causes appreciable photoionization of the Earth’s atmosphere at high alti-
tudes, resulting in partially ionized regions. Within the ionosphere, the recombination
of the ions and electrons proceeds slowly (due to low gas densities) so that fairly high
concentrations of free electrons persist even throughout the night.
2.2 The Formation of the Ionospheres
The outer edge of the Earth’s atmosphere is subjected to extremely harsh solar radi-
ations, which consists of a broad frequency spectra of neutral oxygen atom, under the
e ect of UV, losses of an electrons and disintegrating into ion (Brekke, 1997 2nded.).
This positively charged oxygen ion is highly unstable and sensitive that tends to at-
tract the free electrons when they are at close proximity. The upper levels of this
layer have less ions compared the lower levels. Therefore, the processes of ionization

9
and recombination are greater at lower levels. This leads to the formation of the
ionosphere of the Earth’s atmosphere. The ionosphere is formed when the energetic
electromagnetic and particle radiation from the sun and space ionize air molecules,
creating plasma in the upper atmosphere by the incident solar radiation interacting
with and removing electrons, from di erent gasses. Di erent wavelengths of solar
electromagnetic energy in the UV and x-ray radiation parts of the spectrum ionize
di erent component gasses in the atmosphere. A single ionospheric layer may be
regarded as being formed by a speci c wavelength interacting with a single species of
the air molecules.
Figure 2.1: Schematics of photoionization and impact ionization.
.
Thus the grade of ionization depends on the intensity and the wavelength of the in-
coming radiation as well as the composition of the atmospheres. So the ionization
production processes are takes places into three ways such as:-

10
• Photoionization of the thermospheric gases by solar EUV and X-ray radiations
(photons). The ionosphere is mainly formed by the photoionization which is the
physical process in which an incident photon ejects one more electrons from an atom,
ion or molecule of the neutral atmosphere (Brekke, 1997 2nded.). The predominant
gases (O, N2 and O2) of the ionosphere and their photoionization /non-dissociative/
processes have written in the general form:-
 (2.1)
x + photon(  = 103nm)   x+ + e
Where X atom/molecule in the upper atmosphere photon = hc
  for example:-
O+
2 + e
  (  = 103nm)   O+
2 + hc
2 + e
N2 + hc
  (  = 80nm)   N+
O + hc
  (  = 91nm)   O+ + e
• Ionization by the photoelectrons and scattered/re-emitted/ radiation, but particu-
larly charge exchange reactions/attachment/ written in the general form as
 (2.2)
M + e   M-
Where M atom/molecules For example:
O+ + N2   N O+ + N
O+ + O2   O+
2 + O
• Impact ionization which is the precipitation of the energetic particles plays the
ionization production at the polar latitudes. The precipitating energetic electrons

11
produce additional ionizing photons within the atmosphere by the process i.e. called
the bremstrahlung or braking radiation. The upper atmosphere can be ionized by the
incident energetic particles that play at high latitudes. For the precipitating energetic
electron process represented as:
X + eprecipitate (E = 12eV )   X + + edetached + eprimary (2.3)
Where X is energetic particles.
2.3 The ionization process and production rate in
the ionosphere
The solar radiation acting on the di erent compositions of the atmosphere with height
and generate layers of the ionization and the ionized particles in the ionosphere are
producing during the day time through the absorption of the solar extreme UV and
X ray radiation by the atmosphere species. The ionosphere coexists with the upper
portion of the neutral atmosphere and receives a considerable energy and momentum.
Let us take a horizontal plane from the ionosphere which is aligned in the horizontal
atmosphere and visualize that the atmosphere has a single constituents of the particle
density (n). Let the solar radiation be monochromatic intensity (I) and have time
dependent angle called zenith angle which is the angle with the vertical ( ). The
solar radiation penetrates that ideal strati ed medium with distance ds and travels
through the atmosphere a slant path, the intensity decreases by the amount of dI.
Now if the absorption cross section of the neutral particle is (d) then we can write
the equation
 -dI
 (2.4)
ds = dnI .
If C electrons are produced per unit absorbed energy, then the rate of pro duction of

12
Figure 2.2: An illustration of the geometry related to the solar radiation (I) when
penetrating a slab of thickness dz in the Earth’s atmosphere at a zenith angle  . The
distance to the source and to the ground is s and z respectively.
the ion in a unit volume is
 Q = -C dI
 (2.5)
ds = C dnI.
The photoionization production reaches a peak where dQ
ds = 0, which on simpli cation
dQ
ds - C d2n2I = 0
ds = d
ds (C dnI) = Cd(I dn
ds + n dI
ds ) = Cd(I dn
ds + n-dnI) = CdI dn
( dn
I ds )m
nds )m + ( dI
where the subscript m denotes that the value at the peak. The slant height s is related
to the vertical height z as s = -z sec   and so that
( dn
nds ) = (-dn
ndz ) cos   = cos  
H where H = ( -dn
ndz )-1
is the scale height which the mean distribution height of the gas.
( dn
nds ) = dn = cos  
H

13
 (2.6)
dHmnm sec   = 1
In the expression, Hmnm sec   yields the total number of the atoms (Nm(x)) in a
column of unit area of cross section with base at the level of maximum pro duction
lying along the slant path. Thus the peak of the production o ccurs at the height
where dNm(x) = 1 or Nm(x) = 1
d . Now, if the intensity in the top of the atmosphere
is I8 then the equation (2.4) on the integration becomes
Is
 -dI
8 dnds
I = s
I8
 (2.7)
 Is = I8 exp(-Tz )
H ). The peak produc-
where the optical depth (Tz ) = d sec  nm(z), nm(z) = n0 exp( -h
tion rate Qm can be derived from the equation (2.5) by substituting for the nm from
the equation (2.6) and for Im from equation (2.7), gives
Qm = CdnmIm = Cd(Hmd sec  )-1(I8 exp -Tz )
where Tz = 1 for the peak value
 (2.8)
 Qm = cI8 cos  
Hm exp 1
Let us consider the distribution of the number of density of the gas follows exponen-
H ), from the Barometric distribution law, then according
tially decay i.e. n = n0 exp( -h
to the equation (2.6) the peak pro duction rate occurs at the height hm, hence
dH n0 exp( -hm sec  
H ) (2.9)
H ) = 1ordHn0 sec   = exp( hm sec  
As we know the variation intensity I with di erent height can be obtained from the
equation (2.7) on simpli cation gives
I = I8 exp[-dn0Hm sec   exp( -h
H )] (2.10)

14
Figure 2.3: Normalized Chapman production function versus reduced height and solar
zenith angle   .
The distribution of the pro duction rate from equation (2.9), ( 2.10) and
H ) is given by
nm(z) = n0 exp( -h
Q = CdnmI = Cdn0I8 exp[ -h
H - n0dHm sec   exp( -h
H
H )], where h = z - z0
Qm = Cd cos   exp -1
H
Cd = Qm H exp 1
cos  
H )]
Q = Qmn0H d sec   exp 1[exp -h
H - n0dH sec   exp( -h
H )]
Q = Qm exp[1 + hm -h
H - exp( hm -h
H is a reduced height.
since z = hm -h
Thus the production function of the Chapman function is
 (2.11)
Q = Qm exp[1 - z - exp(-z)]

15
This is shows that the pro duction layers corresponding to all wavelengths and solar
zenith angles have the same shape in terms of the normalized quantities z and Q. It
is convenient to express Q in terms of Q0 and h0 instead of Qm and zm corresponding
to the vertical radiation, but in terms of Q0 and s0 corresponding to the vertical
H and
radiation (  = 0). Then substituting Qm = Q0 cos  , exp zm
H = sec   exp z0
H , we get the pro duction function for the vertical incidence as
y = z-zo
 (2.12)
Q = Q0 exp[1 - y - sec   exp(-y)]
For very large y (y 0 or z zo) the vertical pro le takes the form
 (2.13)
Q = Q0 exp( -z
H )
This means that at the maximum height we will get maximum ionization, the ion-
ization pro le decay determined by the scale height of the ionizable constituent. Due
to the height (about z scale height above the peak), Iz ˜ I8 so that the pro duction
of ionization depends more on the ionizable constituents and less on the intensity of
the ionizing radiations. For every small y (y 0 or z 0), the production function
becomes
 (2.14)
 Q = Q0 exp[1 - sec   exp -y ]
And the pro le decreases very rapidly with height below the altitude of the peak
production. The maximum production is encountered at   = 0, i.e. when the sun is
shining overhead. Then also the maximum is encountered at lowest altitudes. When
the zenith angle is increases the maximum rise at higher altitudes and the maximum
value decreases. (Brekke, 1997 2nded.).

16
2.4 The layers of the ionospheres
There are di erent layers in the ionosphere occurs due to the maximum ionization
production at di erent altitudes. Based on the mean vertical electron density pro les,
the ionosphere is divided into D, E and F layers. In the vertical structure of the
ionosphere, the density of the ionosphere (day time) increases with altitude, reaches
a maximum and then decreases for further increases of altitudes. Thus the layer
below and above the ionospheric peak are the bottom side and topside ionospheres
respectively (Brekke, 1997). The electron concentration of the ionospheric layers
varies with the exposure of di erent types of radiation, recombination and transport
processes and none of the layers behave exactly like the ideal Chapman layer with
respect to variations in altitude, time of day and latitude. Besides, none of the layers
disappear totally when the sun is below the horizon, because of the scattered radiation
and transport mechanisms which can transport plasma from a sunlit to a dark region
of the atmosphere.
1 The D layer
It is the inner most layers located from 60 km to 90 km above the surface of the Earth
which is weakly ionized and composed of the molecular ions of O+
3 ,
2 , N +
2 , N O+, NO -
Hydrated ion (H3O+(H2O)n) dominated. The ionization here is due to the photoion-
ization of the NO by the H-Lyman series of a radiation (  = 121.5nm) which is a
very strong spectral line, penetrates down into the D layer and has enough energy
to ionize NO that founds in a small amounts. In addition, high solar activity can
generate hard X-rays /cosmic rays/ (  < 1nm) that ionize N2 and O2. In this layer,
the electron density increases from less than 107m-3 to 1010m-3 which have not a
distinct peak and disappears at night. Both the ion production and recombination

17
Figure 2.4: The vertical structure of the ionospheric layers.
processes are highly complicated, so a large number of the complicated and highly
positive and negative ion is formed and the recombination processes are depends on
both the height and temperatures.
Thus this region is characterized as a comparatively dense atmospheres, collision dom-
inated which is the collision between ion, electrons and neutral particles frequently
dominated. As the radio waves passing through causing the electron to move and
collide with the neutral molecules, giving rises to their energy so that the collision
increases the strength of the radio wave frequency decreases.
2 The E layer
It is the middle layer stretches from 90 km to 150 km above the surface of the Earth
which contains O2, N2, O ions. It is pro duced by the ionization of the molecular
and atomic oxygen and molecular nitrogen by X-rays (1nm <   < 10nm), Lyman ß

18
radiation (  = 102.6nm) and ultraviolet radiation (100 <   < 150nm) disso ciating
O2 and N2 to O+
2 disappears quickly by charge exchanges i.e.
2 and N+
2 . N+
N +
2 + O2   O +
2 + N2
N +
2 + O   N O+ + N
So that O+
2 and N O+ are dominating ions. The loss process is the dissociative
recombination of the E layers.
O2 + e   O* + O* and N O + e   N* + O *
And the continuity equation gets into the standard form:-
dne
 (2.15)
e
dt = q - aeffn2
Thin sporadic layers appears in the E layer due to many other things, the incidence
of the metal ions (i.e. N a+, Mg + and F e+) with a long life time which a ected
by dynamic processes. The sporadic -E (Es) layer can be extremely thin and dense
layers. They are not associated with the normal E layer and occur more occasionally
both day and night.
Thus the E layer of the ionosphere is characterized as:-
• Can only re ect radio wave having frequencies lower than about 10MH z and may
contribute a bite to absorption on frequencies above it.
• Weakens at night because the primary sources of the ionization are no longer present.
• Increases after sunset as the height of the E-layer maximum which can travel the
radio waves by re ection from the layers.
3 The F layer
It is the topside layer of the ionosphere extended from 150 km to 1000 km above
the surface of the Earth which contains the O + dominated. It is the densest point
of the ionosphere which implies the signal penetrating of the layers will escape into

19
space. At higher altitudes, the number of the oxygen ion decreases and lighter ions
such as hydrogen and helium become dominate. Then the extreme ultraviolet solar
radiation (10nm <   < 90nm) ionize atomic oxygen. The F layer consists of one
layer at night but during the day a deformation of the layer often forms F1 and F2
in the pro les. The F2 layer remains by the day and night responsible for most sky
wave propagation of radio waves, facilitating high frequency (HF, short wave) radio
communications over long distances. The primary ions of O+ and N+
2 are reacting
with the neutral atoms and molecules become:-
O + hv   O+ + e
photoionization of O
N2 + hv   N +
2 + e
photoionization of N2
O+ + O2   O+
2 + O
O+ + N2   N O+ + N
charge exchange/attachment of O+ and N +
2 ions N2 + O   N O+ + N
The most important ions are O+, N O+ and O+
2 . These recombines to
O+ + XY   X O + Y
X O+ + e   X * + O * where X and Y can be O and N. The continuity equation for
O+ is given by
 d
dt [O+] = q -  [O+][X Y ] = q - ß[O +] (2.16)
Where ß =  [XY ]. The factor ß will in a certain height be approximately constant
because the neutral density [XY] do es not change signi cantly during the ionization
processes (the ionization rate is small). The continuity equation becomes
d
 (2.17)
dt[X O+] = ß [O+] - a[X O+]ne

20
since [O+] + [X O+] = ne . By combining these equations (2.16) and (2.17) we get
dne
 (2.18)
dt = q - a[X O+]ne
At high latitudes (> 200K m) where the O+ is the dominant ion and the loss rate
becomes proportional to the electron density
[O +] [XO +]   [O+] ˜ ne
 dne
 (2.19)
dt = q - ßne
In the lowest part of the F layer the X O+ ion is dominant and we get a loss propor-
tional to the square of the electron density.
[O +] [XO +]   [XO +] ˜ ne
 dne
 (2.20)
e
dt = q - an2
Thus the F layer deviates from an ideal Chapman layer. This deviations results from
complicated recombination processes and forms the divergence term which usually
not negligible. The continuity equation should be
dne
 (2.21)
dt = q - a[XO +]ne - v. ne
2.5 The variations of the ionospheres
The ionosphere is varies greatly because of the:-
• Changes in the sources of the ionization(i.e. Sun ).
• Changes in the neutral parts of the upper atmosphere, responds to solar EUV
radiations. This occurs in the atmospheric regions of the thermospheres.

21
• Charged particles responding to the neutral atmosphere in the thermosphere.
The ionospheric variations mainly occur when the:-
2.5.1 Diurnal variations
The ionosphere varies over the 24-hour period between the day and night time and
over the 11 year cycles of solar activities which illustrates changes in the F region
maximum electron densities on the shorter time scales. Solar x-ray radiation can
increase dramatically when a solar  are o ccurs; this increases the D and E region
ionization. As the Earth rotates with respect to the sun, the intensity of the solar
radiation increases and the ionization also increases to maximum at around noon.
During the afternoon, the ionosphere begins falling due to electron loses and with
darkness the ionosphere becomes higher. Through the night, its maximum frequency
gradually decreases, reaching their minimum just before downs (sibanda, 2010).
2.5.2 Latitudinal variations
As the latitude increases, the intensity of the radiation and daily production of free
electrons decreases, since with increasing latitude the solar radiation strikes the at-
mosphere more obliquely (Sibanda, 2010). With respect to geographical location, the
ionosphere may be characterized broadly into three regions (i.e. low, mid and high
latitude) that have di erent properties. In the low -latitude region, the ionosphere is
distorted with a depletion of electron density over the geomagnetic equator and large
enhancement occurring around ±20 north or south of the magnetic equator. This is
due to the ’fountain e ect’ an electrodynamics lifting of the plasma drifts upwards
until the pressure and gravity forces are high enough and the plasma is then forced
back through the magnetic  eld lines to higher latitudes. As a result the geomagnetic

22
 eld runs horizontally over the geomagnetic equator causing strong electromagnetic
forces that leads to abnormally large electrical conductivity over the equator and a
strong electric current (an electrojet) that  ows in the E and F regions. In the mid-
latitude region, the ionization is produced almost entirely by UV and X-ray emissions
from the sun, and depleted again by the chemical recombination processes. The inter-
action of the equatorward propagating disturbance with the ionospheric plasma and
constituents of the neutral atmosphere a ects the movements of ions and the balance
between pro duction and loss of ions in the regions (Garcia-Fernandaz, 2004). In the
high-latitude region, the electron densities are considerably lower than in the lower
latitudes since the solar radiation strikes the atmosphere at more oblique angles. The
high latitude ionosphere is rich in plasma instabilities because of its susceptibility to
the external in uence that caused by the geomagnetic  eld runs nearly vertical and
the magnetic  eld lines connect to the outer part of the magnetosphere that driven
by the solar wind (sibanda, 2010).
2.5.3 Seasonal variations
As the Earth revolves around the sun, the ionosphere varies throughout the year due
to the solar zenith angle of the sun varies with diurnally and seasonally. It determines
by the hemisphere which the sun is overhead. It is summer on the hemisphere where
the sun is overhead and winter on the other hemisphere. The sun is overhead at the
equator around the time of the equinoxes. This seasonal cycle causes a corresponding
seasonal and special variation in the global ionospheric structures (sibanda, 2010).
The D, E and F1 region electron densities are greater in summer than in winter (Mc
Namara, 1991).

23
2.5.4 Geomagnetic activity/storms/
Geomagnetic storm is the depressions of the geomagnetic  eld due to an enhancement
of the trapped particle population and the asso ciated ring current intensi cation. It
is occurs due to the solar wind and the concentration of the charged particles in
order to pro duces the polarized electric  elds. Geomagnetic storms are the result
of a huge amount of charged plasma’s coming from the sun by means of solar wind
and entering into the magnetosphere of the Earth which caused by the changes of
the solar wind parameter and due to the coupling theory of the magnetosphere and
ionosphere, the geomagnetic storms turns in to ionospheric storms. They are a major
disturbances in the Earth’s magnetosphere that occurs when the IMF turns southward
and remains so far a prolonged periods of time which is measured by changes in the
disturbance storm time (DST) index. The geomagnetic storm is said to be occur when
the geomagnetic induces exceeds certain thresholds as a result worldwide disturbance
of the Earth’s magnetic  eld happens. It arises from the Earth’s magnetic  eld
and plasma environment response to changes in the solar wind plasma properties
which mainly in uenced by the changes in the solar wind IMF from north to south
hemispheres, facilitating easier access to the Earth’s magnetic domain. This may last
for one or more days which is greater seems like to larger geomagnetic storms during
the equinoxes
2.5.5 Longitudinal Variations
The longitudinal variations are considered to be due to a combination of the orien-
tation and strength of the geomagnetic  eld as well as the tidal winds in the lower
thermosphere. The variations in tidal winds due to non migrating tides may in uences

24
the dynamo generated electric  elds and currents resulting in the observed longitudi-
nal variations of the solar quiet current functions. The longitudinal variations of the
equatorial plasma drifts exist at di erent local times and seasons. The factors that
contribute to the longitudinal variations of the EEF and E × B plasma drifts are:-
• The thermospheric wind variations which drives the ionospheric dynamo
•The magnetospheric electric  eld variations with universal time which penetrates
from high latitude to the equator.
•The variations of the geomagnetic  eld strength and declination which controls
the zonal and meridional wind corporate or opposes one another in distributing the
plasma’s.
•The geographic latitude of the magnetic equator
•The geomagnetic  eld and solar cycle dependent conductibility.
Batista et al, (1996); Hartman and Heelis, (2007) both described the longitudinal
variations of equatorial plasma drift associated with the longitudinal variations of the
magnetic declination’s. Deninov et al, (1998) and Walker, (1981) also found that the
longitudinal variations of equatorial E × B plasma drifts that related to longitudinal
variations of geomagnetic  eld strength along the equator.
These geomagnetic  eld measurements commonly observed during the geomagnetic
quiet perio ds that referred to as the geomagnetic daily variations or solar quiet vari-
ations. This regular variation of the geomagnetic  eld o ccurs due to the:-
•Earth’s rotation and its orbital movement around the sun.
•Orbital movement of the moon.
The most prominent regular variations of the geomagnetic  elds are:-
1/ Diurnal variation (solar daily variations)-this is occurs when the:-

25
• Flowing of the electric current in the E layers of the day side ionosphere. The
electric current in the Earth’s crust produced by the electromagnetic induction is
contributed to the variations (Lanza and Meloni, 2006).
•Time of the year, solar activity and geomagnetic latitudes. Due to its relativity small
intensities the diurnal variation is only visible in magnetograms on days when there is
no stronger magnetic disturbance in the magnetosphere. Those days are called solar
quiet days (Sq). The corresponding days when the magnetic  eld is active i.e. called
solar disturbed days (Sd) (Lanza and Meloni, 2006).
2/Lunar variations:- it occurs when the gravitation of the moon causes atmospheric
tides (Jankowski and Suckor , 1996).
3/Yearly variations:- this occurs due to the Earth’s orbital motion around the sun
and its tilting with respect to the plane of its orbits. According to the geomagnetic
observations in leivogor, the perturbation in the geomagnetic  eld also varies with
the seasons of the year (Lanza and Meloni, 2006).

Chapter 3
IONOSPHERIC EQUATORIAL
ELECTRIC FIELD MODEL
DRIFT VELOCITY
3.1 Introduction
Ionospheric models are a mathematical description of the ionosphere as a function of
location, altitude, day of year, phases of sunspot cycle and geomagnetic activity. Geo-
physically the state of the ionospheric plasma may be described by four parameters
such as electron density, electron and ion temperature, since several species of ions
are present i.e. ionic compositions (Schunk and Sojka, 1992). Models are usually
expressed as computer programs. The model may be based on basic physics of the
interaction of the ions and electrons with the neutral atmosphere and sunlight. It may
be a statically description based on a large number of observations or a combination
of physics and observations. The EEF model is one of the ionospheric models which
describes mainly in this paper with C/NOFS satellite measurements of vertical ion
drift velocity comparatively.
 26

27
3.2 The EEF Model
The Earth’s ionosphere is created by energy from the sun being imparted to neutral
molecules in the upper atmosphere when this energy is absorbed by a molecule; an
electron is separated from the molecule leaving a free electron and ion. The collisions
of this ionized particles with the neutral winds  owing in the ionosphere drives a
current which moves across the geomagnetic  eld as in a dynamo and central to the
electrodynamics of the equatorial ionosphere. This tidal wind interaction with the
geomagnetic  eld is responsible for the atmospheric electric  eld that together with
the wind system drives the ma jor phenomena under quiet conditions.
The EEF is created in the ionosphere by wind driven currents in combination with
the earth’s magnetic  eld which builds up a charge at dusk and down  eld geometry.
Consequently, an eastward electric  eld along the magnetic equator responsible for
driving many interesting phenomena in the ionosphere. The eastward component of
the EEF is particularly important at the equator since it is responsible for driving
the EEJ current system, the equatorial plasma fountain and EIA. This electric  eld
is a fundamental parameter in any model describing equatorial ionospheric electro
dynamics. But direct measurements of the EEF have been restricted to a very few
ground-based radar (Chau and Kudeki, 2006) and a small number of satellite mis-
sion (Fejer et al, 2008; de la Beaujardiere and the C/NOFS Science De nition Team,
2004).
The EEF model is developed by the (Alken and Maus, 2010b) from the CHAMP
satellite magnetometer measurements at all longitude by modeling the EEJ current
system using the empirical inputs for the conductivity and wind  eld constraining re-
sults. This method has the advantage of implicitly including longitudinal di erences

28
directly in the model since the CHAMP mission ended in 2010; this method cannot
currently produce Real-Time EEF estimates. However, the upcoming swarm satellite
mission will use this approach to model global EEF values in near Real-Time. Alken
and Maus, (2010a) extended their previous studies of the EEF modeling method to
work with ground-based horizontal magnetic  eld di erence ( H) measurements by
using a directed CHAMP satellite over  ights to produce a unit climatological EEJ
latitudinal current pro les and using  H to determine the magnitude of the pro le
at any given time.
The ionospheric electric  eld plays an important role on the plasma distribution and
dynamics of the equatorial and low latitude thermosphere (Fejer, 1997; Scherlies and
Fejer, 1999). At the magnetic equatorial latitude the day time eastward electric  eld
gives rises to an upward E × B drift velocity which across the magnetic  eld lines
toward higher latitudes and then the plasma di uses downwards along the magnetic
 eld lines under the in uences of gravity and pressure gradient force results the forma-
tion of a plasma fountain centered at the magnetic equator. Sherlies and Fejer, (1999)
presented the  rst comprehensive study of global empirical model of the quiet time
F-region equatorial vertical drifts based on combined ISR observations at Jicamarca
and ion drift meter (IDM) measurements on board the AE-E satellites. Their study
presents local time, season, solar cycle, and longitude e ects on quiet time equatorial
F-region vertical plasma drifts.
Thus the EEF model is a global climatological model which primarily responsible
for driving vertical drifts in the F-region that expects the seasonal and longitudi-
nal structures from the CHAMP satellite measurement data bases. The longitudinal
structure of the EEF mo del can be in uenced by the longitudinal variations in the

29
conductivity, the geomagnetic  eld and the neutral winds.
3.3 The CHAMP Satellite Measurements
The challenging mini satellite play load (CHAMP) satellite measurements are used
to determine the equatorial electrojet current distributions, which was launched on
15 July 2000 into a circular, near-polar orbit inclination 87.50 with an initial altitude
of 456 Km. By the end of 2009 it has decayed to 310 Km.The local times of the orbit
changes by 1 hour in 11 day requiring about 130 days for covering all local times
(Reigber et al, 2002). It has been making high quality (accuracy) of the magnetic
 eld about 0.1 nT measurements.
The  rst observation made about the EEJ was in Huancayo (peru) in 1922, attributed
to a narrow ionospheric current of about 300 Km in width  owing over the dip equa-
tor. During the day time, the eastward polarized  eld is generated by the global scale
dynamo at the magnetic dip equator which gives rises to a downward Hall current.
Due to the presence of the nonconducting boundary a strong vertical polarization
 eld opposes the downward  ow of the current. This  eld in turn gives rises to the
intense Hall current which (Champ, 1951) named EEJ. The EEJ phenomenon has
been given various attention and has attracted many scientists in the past and recent
times (Okeke and Hamano, 2000).
The EEJ is a narrow belt of intense electric current in the ionosphere con ned to
about ±3 around the dip equator. This indicated on a magnetogram as an enhance-
ment of the solar daily variation of the horizontal component of the magnetic  eld H
and solar quiet day variations. The abnormally large amplitude of variations in the
horizontal components measured at the equatorial geomagnetic observatories. The

30
sources of data to study the EEJ are the observations by radar, rocket, satellites and
geomagnetic observatories.
Generally, the equatorial ionosphere is highly dynamical, unpredictable and charac-
terized by the existence of intense equatorial plasma bubbles associated irregularities.
This is leads to:-
•All the radio communication system utilizing the Earth space propagation path and
e ects on satellite navigation systems.
• A signi cant di erence in the structure and e ects on radio propagation of the
ionosphere at the equatorial electrojet and accompanying equatorial anomaly, greater
absorption and geomagnetic  eld orientations being nearly horizontal.
This equatorial irregularities mainly characterized by:-
• Start right after sunset when the upward drift velocity exceeds 15 m/s to 20 m/s
(or 30 m/s to 45 m/s for solar maximum).
• Form plum-like structures extending o ccasionally above 1000 Km.
• Smaller scale  eld aligned irregularities are observed within these plums.
• Plums are generated by the Rayleih-Taylor instability mechanisms; smaller irregu-
larities are generated in a hierarchy of instabilities.
Thus at the magnetic equator the primary causes to increase the altitude after sunsets
are:-
• The decay of the bottom side ionosphere in the absence of pro duction by solar
ionizing radiation.
• An increase in upward drift velocity E × B.

31
3.4 The C/NOFS Satellite Measurements
The Communication/ Navigation Outage Forecasting System (C/N OF S) satellite
was launched in April 2008 as an Air Force Mission to Forecast ambient plasma den-
sities and irregularities in the equatorial ionosphere (De La Beaujardiere et al, 2004).
The instruments on the satellite measures the electric  eld, plasma characteristics,
neutral winds and the strength of scintillation producing irregularities. During the
C/NOFS satellite mission author laboratory, the primary purposes of the C/NOFS
satellite is:-
• To forecast the presence of the ionospheric irregularities that adversely impact com-
munication and navigation systems. A satellite scheduled for launch in May 2005 into
a low inclination (130), elliptical (375 × 710 Km) orbit, is the most signi cant com-
ponents of the C/NOFS program.
• Complementary ground-based measurements are also critical to the success of the
mission.
The C/NOFS science objectives may organize into three categories:-
a. to understand the physical processes that active in the background ionosphere and
thermosphere in which plasma instabilities grow.
b. to identify the mechanisms that trigger the plasma irregularities responsible for
signal degradation.
c. to determine how the plasma irregularities a ect the propagation of electromag-
netic waves.
The C/NOFS satellite is the  rst satellite only dedicated to forecasting ionospheric
irregularities and radio wave scintillation’s. It is equipped with sensor that measures
the following parameters:-

32
• Ambient and  uctuating electron densities.
• Ion and electron temperatures.
• Alternating (ac) and direct (dc) current electric  elds.
• Magnetic  elds and Neutral winds
• Ionospheric scintillation
• Electron content along the lines of the sight between C/NOFS and global positions
system (GPS).
Thus the sensor suite on C/NOFS is richer than on any previously  own equatorial
satellites. A broad range of the ground-based measurements will complement the
space data. In addition, the data from several other satellites and ro cket experiments
will augment the C/NOFS observations. Several campaigns are planned to validate
operational forecasts, acquire data to achieve the science goals and the theoretical
models.
3.5 A Real-Time Forecast Service for the Iono-
sphere
The equatorial ionospheric zonal electric  eld exhibits temporal variations on time
scales ranging from a few seconds to several months. While the wind forced dynamo
current system in the day side ionosphere is the causes of the diurnal (once occur in
24 hours) component of the equatorial ionospheric electric  eld variations are due to
the interaction of the solar wind with the magnetosphere. The so called disturbance
electric  eld component of the equatorial zonal electric  eld has two parts:-
1/ Promote-penetration

33
It is the immediate response of the equatorial zonal electric  eld to solar wind varia-
tions.
2/ Disturbance dynamo
It is the delayed e ect often arriving 4 to 5 hours after a large variation in the solar
wind parameters (Fuller and Rawal, 2011).
The equatorial zonal electric  eld is a primary driver of the EIA and electron densities
irregularities. Both of these features strongly a ect radio and communication signals
as they pass through the ionosphere. Temporal variability in the zonal electric  eld
posses di culties for forecasting degradation radio signals when passing through the
ionosphere. Continuous prediction of the zonal ionospheric electric  eld for all local
time and longitudes can provide a key to improved forecasts of space whether condi-
tion for communication and navigation in the equatorial region. The Real-Time model
is available at http : //W WW.geomag.us/models/P P EF M/RealtimeE F.html.
The main components of the web applications are:-
1. Cloud based infrastructure
2. Real-time data harvesting, pro cessing and storing
3. Web interface for regular uses
4. Programmatic access suitable for automated queries. The programmatic access to
the Promote-penetration model is particularly suitable for Real-time incorporation
into space whether models.

34
3.6 The Equatorial Ion Vertical Drift Velocity (E×
B) in the Ionospheres
The term drift velocity is the average velocity that a particle such as an electron
attains in a material due to an electric  eld. It can also be referred to as axial
drift velo city. In general, an electron will propagates randomly in a conductor at the
Fermi velocity. An applied electric  eld will give this random motion a small net  ow
velocity in one direction. The Earth’s ionosphere is an electrically conductive region
which responds to the thermospheric winds in order to push the ionosphere along the
inclined magnetic  eld lines to the altitudes and the composition of the thermosphere
that a ects the rates of ions and electron recombination. The electrons and ions are
created from the solar energy that swept up by the winds of the upper stratosphere
and move initially in the direction of wind  ow, as they attempt to cross lines of  ux
of the Earth’s magnetic  eld. A force perpendicular to the wind direction is applied
to the charged particles by the lines of  ux. This results in the ions being de ected
in one directions and the electrons in the other directions (which is one west and the
other is east). The de ecting force due to the magnetic  eld is
F = qV × B
 (3.1)
Where F-force, q- amount of charge, B -magnetic  eld  ux density and V - velocity
of the charged particles.
The net e ect of the de ection is the current  ow directed in the east-west directions
which is called the EEJ. This is driving by the day time eastward EEF in the iono-
spheric E regions in order to determine the equatorial ion vertical drift velo cities. The
Earth’s magnetic and electric  eld interaction with the neutral wind and the ionized

35
particles of the lower ionosphere generates an electric  eld which encircles the globe
above the magnetic equator. Above the equator there are two  elds, both parallel
to the surface of the Earth. The magnetic  eld is aligned magnetically south to the
north and at all points above the magnetic equator parallel to the Earth’s surface.
During the day time, the electric  eld is directed from magnetic west to magnetic
east along the magnetic equator and at all points parallel to the Earth’s surface. The
interaction between these perpendicular  elds and the free electrons, which are cre-
ated by the ionizing energy that produced a conditions called the fountain e ect. It
is the electrodynamics lifting of the free electrons above the magnetic equator. Thus
the electric  eld is given by
 E = F
 (3.2)
q
Then substituting equation (3.1) in to equation (3.2) we get
 (3.3)
E = qVe × B
q = -Ve × B
Where the minus sign indicates the velocity of the electrons When we crossed this
equation (3.3) with B obtains
 (3.4)
E × B = (-Ve × B) × B
Where the velo city Ve is perpendicular for both E and B So by applying the triple
product rule the equation (3.4) become
E × B = Ve(B · B) - B(B · Ve ) = Ve (B )2
since B · Ve = 0
 (3.5)
 Ve = E × B
B 2
The Earth’s ionosphere has a unique behavior governed by the di erent physics,
principles and laws. Some of the quantitative laws that controls the characteristics of

36
the ionospheres are chemical, dynamical and conservational energy. The chemical
process controlled the production and loss of ionization in lower ionosphere, but
the dynamic pro cess controls the movement of the ionization in above layers of the
ionosphere. In the ionosphere the rate of change of the ionization of the neutral
atmosphere by the solar radiation obtained by applying the equation of continuity,
conservation of mass and conservation of energy. This is necessary to introduce the
elements of the neutral atmospheric and magnetospheric physics which in uenced by
the process originates from the continuity equations given below
dne
 (3.6)
dt = Q - L - · (neV)
Where Q- rate of production per unit volume, L- rate of loss of ionization per unit
volume, ne - density of electrons, · (ne v)- Loss of ionization due to transport with
velocity. The motion of charged particles in the ionosphere is mainly expressed by
the pressure gradient force, the gravitational force, the electric  eld and the collision
between particles. From Newton’s 3rd law of dynamics, we have the conservation of
the momentum for the jth ion species which write in form:
 jdVj
 (E + Vj × B) - Sj = k j jk(Vj - Vk) (3.7)
mj
dt = - Pj +  jg + qj j
In order for as a simplicity, the force of viscosity, coriolis, acceleration, centripetal
acceleration, tides and waves are not included in this equation:
dpj
 (3.8)
dt + · ( jVj) = (pj - Lj)mj
 = njKBTj where (Vj)- ion velocity vector, (mj )- ion mass E =
since pj =  j KB Tj
mj
- f, · J = 0 = · B, ( j)- mass density, qi- ionic charge × B = µ0J; since ne =
Si nj, (pj ) -pressure of the ion species j, (g) -acceleration of gravity and ( jk)- collision

37
frequency between ion and species j and k and (Vk)- neutral wind velocity vector.
The steady state  uid velocity of each species may be found from the momentum
equations which move the ion species in plasma in the presence of an electric and
magnetic  eld by setting the time derivative equal to zero and neglecting the pressure
and gravity terms can be expressed as
 dVi
ni mi
dt = nie(E + Vi × B) - ni mi in(Vi - Vn) (3.9)
 dVe
neme
dt = ne e(E + Ve × B) - neme en(Ve - Vn) (3.10)
Where the neutrality is maintained only a single charge q = e is involved. Here the
E  eld is one would measure in an Earth  xed reference and it also neglected ion-ion
and ion-electron collisions frequency as with small compared with the ion-ion and ion-
electrons collisions frequencies at least in the lower part of the ionosphere (E-region).
Approximately the ion neutral collision frequency is found
2 where mn mean neutral molecular mass or  in =
 in = 2.6x10-15(nn - ni)(mn)- 1
kN2 · [N2] + kO2 · [O2] + kO · [O ] for ion densities in the E-regions.
Similarly, the electron collision frequency is given by
2
2
e
Ve =  en +  ei = 5.4x1010nn · T 1
e
 )]neT - 3
e + [34 + 4.18 ln(T 3
ne
The steady state solution of the ion momentum equation (3.9) is
ni e(E + Vi × B) - nimi  in(Vi - Vn) = 0 (3.11)
dt = 0
since dVi
And for the electron is equation (3.10) can be
-nee(E + Ve × B) - ne me en(Ve - Vn) (3.12)

38
Where me mass of the electrons
The ion velocity can be derived from equation (3.9)
 (3.13)
Vi = Vn + e
 (E + Vi × B)
mi in
Similarly, the electron velocity from equation (3.10) can be
 (3.14)
Ve = Vn - e
 (E + Ve × B)
me en
By adding and subtracting a term Vn × B in the bracket on the right side of the
equation(3.13) and rearranging we get
 (E + Vn × B + Vi × B - Vn × B)
Vi = Vn + e
mi  in
 (E + Vn × B + (Vi - Vn) × B),
Vi - Vn = e
mi  in
since E = E + Vn × B and Vi = Vi - Vn (the E  eld and ion velocity measured
from the Earth’s reference frame).
 E + e
Vi = e
 (E + Vi × B) = e
 Vi × B (3.15)
mi  in
mi  in
mi in
Similarly, by the same procedure, the electron velocity becomes
 E + e
Ve = e
 (E + Ve × B) = e
 Ve × B (3.16)
me en
me en
me  en
Since Ve = Ve - Vn and E = E + Vn × B
Let us now, the neutral wind can be neglected, the ion velocity from equation (3.13)
is
 and  i = eB
 (E + Vi × B) since Vn = 0 (neutral wind velocity), Ki =  i
Vi = eB i n
 i
mi
 i n
(angular gyro frequency)
 E + e i
 E +  i
Vi = e i
 Vi × B =  i
 Vi × B = Ki
B (Vi × B) (3.17)
B E + Ki
eB in
eB  in
B  in
B in

39
Then equation (3.15) solved replacing Vi and E by Vi and E’ which forming Vi × B
from equation (3.17) we get
B (Vi × B) × B
 E +  i
Vi × B = [  i
 Vi × B] × B = Ki
B E × B + Ki
 i n
 in
Since (A × B) × C = (A · C)B - (A · B)C
B [(Vi · B)B - (B · B)Vi]
Vi × B = Ki
B E × B + Ki
Vi × B = Ki
B B2Vi
B E × B + Ki
B (Vi · B)B - Ki
Vi × B = Ki
B B Vi (3.18)
B E × B + Ki
B (Vi · B)B - Ki
And by taking a dot product of the equation (3.15) with B we get
 E · B + e
Vi · B = e
B (Vi × B) · B
 (Vi × B) · B = Ki
B E · B + Ki
mi  i n
mi  i n
Since (A × B) · C = (A × C) · B = (B × C) · A
B (Vi · (B × B)) But B × B = 0
Vi · B = Ki
B E · B + Ki
 (3.19)
Vi · B = Ki
B E · B
Thus equation (3.18) becomes
Vi × B = Ki
B )2(E · B)B - KiBVi
B E × B + Ki
B ( Ki
B E · B)B - KiB Vi = Ki
B E × B + ( Ki
So equation (3.17) becomes
B )2(E · B)B - KiViB]
Vi = Ki
B E + Ki
B [Ki
B E × B + ( Ki
i
Vi = Ki
B B Vi
B E + ( Ki
B )2E × B + ( Ki
B )3(E · B)B - K2
Vi = Ki
i Vi
B )3(E · B)B - K 2
B E + ( Ki
B )2E × B + ( Ki
Solving for Vi , we derive that
Vi + K 2
B )3(E · B)B
i Vi = Ki
B E + (Ki
B )2E × B + (Ki
Vi (1 + K 2
B )3(E · B)B
i ) = Ki
B E + ( Ki
B )2E × B + ( Ki
Vi = 1
 [Ki
B )3(E · B)B] (3.20)
1 + K 2
B E + ( Ki
B )2E × B + ( Ki
i

40
This equation represents a decomposition of Vi into three orthogonal components
with respect to E and B. The  rst term in the brackets in equation (3.20) represents
the component along E, the last term represents the component along B and the
middle term represents the component along the direction perpendicular to both E
and B. Similarly, by neglecting the neutral wind  n = 0, the solution of the electron
velocity is obtained from the equation (3.14)
Ve = 1
 [Ke
B )3(E · B)B] (3.21)
1 + K 2
B E + ( Ke
B )2E × B + ( Ke
e
 .
 and  e = eB
Since Ke =  e
me
 e n
As the altitude dependence of the ion velocity direction, we will neglect all other forces
except the electrostatic  eld E and as the E  eld and B perpendicular (E · B = 0)
then equation (3.20) becomes
 E × B
 Ki
 (3.22)
i
Vi = 1
1 + K 2
B E + K 2
1 + K 2
B 2
i
i
At the altitude where the ion neutral collision frequency is much smaller than the ion
gyro collision frequency then the ion move at the velocity in a plane perpendicular to
the magnetic  eld B. Hence Ki 1
 (3.23)
Vi = E × B
B2
In a Cartesian coordinate system (x,y ,z) where B = B z and E = E y. The E × B
drift will be in positive x direction. The ion velocity will make an angle Ti with the
applied electrostatic  eld E i.e
 (3.24)
 tan Ti = Ki =  i
 in
As the velocity rotates clockwise when seen along the B and  in increasing along B.
In the ionosphere at about 125 Km altitude  in =  i and Ti = 450. As the altitude

41
lower down in the ionosphere where  in >  i , the ion velocity will be increasing along
E as the collision frequency increases. The ion velocity in the D region is parallel to
the E  eld in the absence of other forces. Above 250 Km the ion velocity is very close
to the E × B direction in the absence of any other forces. The magnitude of the ion
velocity from equation (3.22) is given by
2
i
Vi = [( Ki
1+(Ki )2 )2 + ( K2
1+(Ki )2 )2 E2
B2 ] 1
 E
B
 E
B = sin Ti
 (3.25)
Vi = Ki · (1 + K 2
2
i )- 1
This equation is used to derive the angle between the electric  eld and the ion velocity
at di erent heights. Since Ti = 900,
 E
B = E
 (3.26)
Vi = sin Ti
B
At the upper atmosphere the ion velocity is given by Ti = 900
 (3.27)
Vi = E
B
Similarly, for the electron velocity, equation (3.21)
 E
 E × B
 (3.28)
e
Ve = - Ke
1 + K 2
B + K2
1 + K 2
B 2
e
e
 at 90 Km, Te = 900 close to the E × B direction Since  en
tan Te = -Ke = -  e
 e n
decreases above 90 Km, Te will become increasingly close to the E × B drift from
equation (3.27) the magnitude of the electron velocity to be
 E
B , as Te = 900
Ve = Ke (1 + K2
2 E
B = - sin Te
e )-1
 (3.29)
Ve = E
B
(Brekke, 1997 2nd ed)
Therefore, the electrons are moving in the E × B direction above 90 Km when there

42
are no other forces than the E  eld is applied. Above 250 Km the electrons and
ions are E × B drifting at the same speed when the E  eld is only applied force.
In a collision less plasma, the ions and electrons move together at the velocity of
B2 perpendicular to the ambient magnetic  eld B in response to an applied
Vi = E×B
electric  eld. This implies that the plasma drifts are inversely proportional to B. when
the electric  eld is the same for all longitudes (E × B) if the ion drifts are the same for
all longitudes. Therefore, the perpendicular electron velocity is independent of both
its mass and charge. Indeed, a parallel derivation of the perpendicular velo city for
the ions results in identical equations of the equation (3.5) which is the ion becomes
 (3.30)
Vi = E × B
B2
For the Earth’s orientation of the magnetic and electric  elds the perpendicular ve-
locity is vertical upwards during day time and downward during night time. Thus the
e ects of the vertical ion drift velocity in the ionosphere is causes to move the vertical
electron density pro le up during the day and down during night with respect to the
solution without plasma drifts and depends strongly on the neutral winds in the E
region that stimulates for di erent tidal diurnal and semidiurnal modes.

Chapter 4
DATA AND ANALYSIS
METHOD
The ionosphere is the region of the upper atmosphere and located approximately be-
tween 50 km to 2000 km above the Earth’s surface. The ionosphere is the born of
the interaction between solar radiation, Earth’s atmosphere and magnetic  elds. So
B2 can be measured by
the motion of the plasma convicting at a velocity Vi = E×B
a variety of techniques including coherent and incoherent radars, digisonds, satellite
and rockets etc. The convection patterns can also be derived from the equivalent
currents based on the ground magnetometer data.
Then in order to study the validitation of EEF model drift velocity using C/NOFS
satellite measurements at quiet conditions, we have used the vertical plasma drift data
obtained from the C/NOFS satellite measurement system at the Bahir dar radar ob-
servatories (11.60 N and 37.380 E). The receiver measures and records data for every
second for 24 hours and takes a one minute average values. The C/NOFS satel-
lite data from October, December, February and June months in 2011 years for the
days have been gathered. These measured data have not includes all o  the days of
the given months and also do es not covered all o  the months of the years. They
43

44
Table 4.1: The number of days in months used from C/NOFS satellite measurement
data
 Month days
Feb 1
June 3
Oct 7
Dec 1
have not a continuously measured data gathered. After the data has been received
from the source of the calibrated C/NOFS satellite data measurement software and
such data sets have been grouped separately into seasonal bins representing June
solstice (June-August), December solstice (December-February), September equinox
(September-November) and March equinox (March-May) conditions taken during Ge-
omagnetically quiet days (K p = 3) have been used.
Similarly, the E ×B vertical drift velocity of 2011 is plotted using the calibrated data
obtained from the website of the Geomagnetism Real-Time model of the ionospheric
electric  elds on a real time basis using the solar wind data from the Advanced Com-
position Explorer (ACE) satellite
(http : //W W W.geomag.us/models/P P E F M/RealtimeEF.html) in the Real-Time
EEF model calculation of the electric  elds. From this mo del, we obtain the values of
the horizontal component magnetic  eld intensity (B), the electric  elds (E) and the
observation times which accounts for the variations the vertical plasma drift velocity
at quiet times and loads 365 days of the years data then MATLAB co de has been de-
veloped by importing the calibrated C/NOFS satellite and the Real-Time model data
for the days of each month has been plotted as shown in the results stated in chapter
5 in order to show the geomagnetic storm conditions of the Earth’s ionosphere and
drive the vertical plasma drift velocity (Vz) using the equation(3.27) stated above in

45
chapter 3. Thus, using these data to characterize the diurnal, monthly, seasonal vari-
ations of the Vz with time. Besides, in order to show the longitudinal variations of the
Vz at di erent geomagnetic lo cations of North America (54.52600 N and 105.25510
W), Asia (34.04790 N and 100.61970 E) and Bahir Dar, Ethiopia (11.60 N and 37.380
E) then using this values and inserting in to the Real-Time Geomagnetism website
calculation mo del to obtain their values which loads their result into the MATLAB
code and plot the graph in chapter 5.

Chapter 5
RESULTS AND DISCUSSIONS
In this study the ionospheric equatorial vertical drift velocity data has been obtained
from the C/NOFS satellite measurements at Bahir Dar stations (Geographic latitude
11.60 North and longitude 37.380 East) in the year 2011. The study presented the
diurnal, monthly, seasonal and longitudinal variation of the equatorial vertical drift
velocity.
5.1 Diurnal variations
Figures 5.1 and 5.2 show the diurnal variations of the vertical drift velocity estimated
for Bahir Dar region. In  gure 5.1, the  ve day results show almost identical values.
This is a good evidence that the models used to compute these velocities are clima-
tological (Alken, 2009). The diurnal variation shows similar pattern; double hump
structures that is two maxima at around 11 and 19 LT with peak values of 20 m/s and
25 m/s respectively, however, the evening peak values is greater than the day time
peak value. It is evidently the e ect of the Pre-Reversal Enhancement (Rishbeth,
1971). At the Sunset terminator, the eastward E  eld is enhanced before the E  eld
becomes westward during night time. This phenomenon is called PRE. It causes an
46

47
enhanced upward E × B drifts in the post-Sunset sector. Thus it a ects the plasma
bubbles generation signi cantly by lifting the ionosphere to higher altitudes leads to
a small ion-neutral collisions (Abadi et al, 2015). The depleted values in between
13 and 17 LT might be due to the decay of the ionization that a ects the strength
of the electric  elds. Similarly,  gure (5.2) also shows the three day results almost
identical values around 17 m/s with one maxima structures. But the Pre-Reversal
Enhancement Vz peaks is decrease compared to September equinox quiet days with
peak values nearly 5 m/s. Farely et al, (1986), the less pronounced Pre-Reversal En-
hancement in Vz occurs during the non- equinoctial months due to di ering sunset
times in the two hemispheres.
Figure 5.1: September equinox daily variations of the equatorial vertical drift velocity.
Thus the daily variations of the ionospheric vertical drift velocity exhibits where the
ionization is signi cantly higher during the day and lower at night. Due to the losses

48
of the electron during the afterno on, the ionosphere begins to falling and with dark-
ness the ionosphere became higher which its maximum frequency gradually decreases
that reaching their minimum just before down through the night. The day time drifts
have largest amplitudes between about 11:00 and 19:00 local time with typical values
of 20 m/s and 25 m/s respectively at quiet periods. The drift exhibits morning and
evening reversals from downward night time to upward day time and vice versa. The
morning reversal times and the day time drifts indicate just little variations with the
phases of the solar cycle.
Figure 5.2: June solstice daily variations of the equatorial vertical drift velocity.
The enhanced electric  eld responsible for the post sunset enhancement of the F re-
gion vertical plasma drift is generated by the F region dynamo driven thermospheric
winds. This F region dynamo driven polarization  elds can operate only during night
time as these shorted out by the large E region conductivity during the day time

49
(Rishbeth, 1971). The constant eastward F region wind can account for the Pre-
Reversal enhancement of the equatorial electric  elds (Farley, 1986). They showed
that the post sunset enhancement of the F region vertical plasma drift is a direct con-
sequence of the rapid decrease of the E region conductivity after sunset compared to
the F region/electron density irregularity is generated/. This variation occurs when
during 19:00-20:00 LT hours after Sunset and within 19:00 LT hours either before or
after sun rises which is highest during sunset time and less during sun rise periods.
Therefore, the occurrences of the Pre-Reversal enhancement of the ionospheric verti-
cal drifts due to the variations of the:-
• F region neutral winds /thermospheric winds/.
• Changes in the ratio of the E to F region conductivity.
• E region dynamo contributions.
• E ects of the lack of the symmetry between the hemispheres.
• Non-coincidence of the geographic and dip equators.(Farley et al, 1986).
5.2 Monthly variations
The monthly variations of the ionospheric vertical drift velocity as shown in the
 gure 5.3 for the same regions. The monthly variation peak occurs in both equinox
season and a minimum during December solstices seasons (Su et al, 2006). As it can
be seen from this  gure, the two maxima structure ionospheric equatorial vertical
drift velocity is lies in September and March equinox months especially in October
and April months with amplitude value that reaches to 15-20 m/s at 11:00 LT and
minimum in December solstices months with its peak values of 10-15 m/s at 11:00
LT time. This Vz is depleted in between 13 and 17 LT due to the decay of the

50
ionization that a ects the strength of the E  elds. On the other hand, the Pre-
Reversal enhancement drift velocity is maximum in October, November and April
months with peak values of 15-25 m/s at 19:00 LT time and minimum for the rest
of the months of the year with values below 15 m/s at this time and goes to the
negligible e ect in June and December solstice months. This variation comes from
the increment of the Pre-Reversal enhancement electric  elds (Rishbeth, 1971). As we
Figure 5.3: Monthly variation of equatorial vertical drift velocity.
know that the location of the satellite at the solstice in orbit is provides the maximum
tilt on hemisphere towards the sun (perihelion) which receives more direct and longer
duration of the light than do es the opposite hemisphere (aphelion) (Fayose et al,
2012). Then since Ethiopia is located on the northern hemisphere which is tilted
towards the sun (winter solstice in Ethiopia) gets higher solar radiations. On the
other side, the summer solstice in Ethiopia gets weak radiations of the suns energy.

51
5.3 Seasonal variations
The study of the ionospheric equatorial vertical drift velocity at Bahir dar station has
been grouped into four seasons such as spring (March-May), summer (June-August),
autumn (September- November) and winter (December- February). As the  gure
5.4 indicates the two maxima structure vertical drift velocity is recorded in autumn,
spring and summer seasons that is in September and March equinox and June sol-
stice with peak values of 15-20 m/s at 11:00 LT quiet time while minimum in winter
(December solstice) with comparable amplitude values nearly 15 m/s at 11:00 LT
time (Fejer et al, 1991). On the other hand, the PRE peak Vz values between 10
m/s and 15 m/s lies in September equinox but minimum in June solstice seasons with
peak values nearly 5 m/s. This is because the sun shines directly over head on the
equator which causes high ionization during September and March equinox but the
Earth become tilted towards or away during the solstice that causes to decreases the
emissions of solar radiation to the Earths ionospheres (Su et al, 2006).
This seasonal variations of the ionospheric equatorial vertical drift velocity are arises
due to the alignment of the Earths magnetic  eld with the solar day terminator. When
the Earth’s magnetic  eld become aligned with the solar day terminator around the
location of the receivers, then the local eastward electric  eld and the magnetic  eld
makes perpendicular to each other. As a result, the upward E × B drift velocity
gets its maximum value and then forms the right spread F. These vertical drifts are
strongly enhanced just after sunset but shows no comparable feature near sunrises
which termed the PRE of the vertical drift or equivalently of the eastward electric
 eld components (Kelley, 2009 2nd ed.). So these seasonal variations of the Vz charac-
terized by longitudes results from the di erences in magnetic declination angles and

52
the thermospheric wind pattern variations.
The equatorial Vz shows large day to day, seasonal and solar activity variations
(Woodman, 1970; Fejer et al, 1970a, 1989, 1991). The peak of the PRE of Vz in-
creases linearly with solar  ux during equinox and summer and saturate for high  ux
levels during southern hemisphere winter (Fejer et al, 1997). This velocity decreases
as the magnetic activity changes from quiet to moderate condition between 13 and 17
LT but increases well above the quiet time values for high magnetic activities around
19 LT.
Figure 5.4: The seasonal variation of the equatorial ionospheric vertical drift velocity.
5.4 Longitudinal variations
The longitudinal variations of the equatorial vertical drift patterns obtained from
our empirical model for the quiet day conditions using (11.60N and 37.380E Bahir

53
dar, Ethiopia), North America (54.52600N and 105.25510W ) and Asia(34.04790Nand
100.61970E) during June and December solstice and September and March equinox
at the same time and days presented in the  gure 5.5, shows two and one maxima
structures of the Vz. The peak equatorial vertical drift velocity maximizes in the
Figure 5.5: The longitudinal variation of the equatorial vertical drift velocity .
Asia region with drift amplitudes around 65 m/s and 60 m/s during June solstice
and September equinox at 11:00 LT time but minimum during December solstice and
March equinox in North America sector with amplitudes of 10 m/s at 9:00 LT times.
On the other hand, the June solstice the peak vertical velocity reaches 40 m/s at
11:00 LT in the North American regions. This velocity is decreases goes from the
quiet time to the moderate time between 13 and 17 LT due to the decay of the ion-
ization. Besides, the PRE vertical drift velocity is maximum in October with peak
values around 10-60 m/s and minimum in December with peak values 10-15 m/s and

54
February nearly 5 m/s peak values but negligible June months. So the midday and
afternoon June and December solstice vertical drifts are anti-correlated in the regions
of the large magnetic declination (Walker, 1981 and Deminov et al, 1988). During
the December solstice, the vertical plasma drifts are more strongly correlates with
the geomagnetic  eld strength and declination.
Similarly, in the African sector especially in Ethiopia the solar radiation is directly
overhead and there is high solar activity and ionization which leads to a strong mag-
netic  eld strength causes to decreases the vertical drift velocity with amplitude val-
ues of 10-15 m/s in the March equinox and December solstice and 15-20 m/s during
September equinox and June solstice at 11:00 LT corresponding to the other longi-
tudinal drift velo city measurement sectors. This longitudinal variation happens due
to the displacement of the Geomagnetic and Geographic equator, the large di erence
in the magnetic declination angles and magnetic  eld strength along the magnetic
equators. (Walker, 1981 and Deminov et al, 1988).
Thus the equatorial electric  eld plasma drift and associated phenomena vary with
longitude at a given local time and seasons. The day time equatorial vertical drift
velocities have much larger longitudinal and seasonal dependence in the western hemi-
sphere than in the eastern hemisphere. As the Earth rotates due to the tilt of the
magnetic dipole and other factors (Luhr et al, 2004), the magnetospheric electric  eld
varies with universal time which suggested the longitudinal variations of the distance
of the magnetic equator from the northern and southern magnetic poles that leads to
explain the longitudinal variations in the strength of the EEJ.

55
5.5 Model validiation
The equatorial ionospheric E × B plasma drifts have been studied extensively with
the incoherent scatter radar and satellite at Jicamaraca, ionosonde and other space
receiver techniques (Fejer, 1991, coley and Heelis, 1989 and Fejer et al, 1995; Abdu et
al, 1981 and scherlies and Fejer, 1991). These measurements suggests that signi cant
longitudinal variations in equatorial plasma drifts exists at drift times and seasons.
This study is uses the C/NOFS satellite measurement and the Geomagnetism Real-
Time model solar wind ACE satellite website
(http : //W W W.geomag.us/models/P P E F M/RealtimeEF.html)at Bahir Dar in
Ethiopia to validiate the Vz. The results on the diurnal, seasonal, monthly and longi-
tudinal variations were presented in the  gure 5.6. This shows that the vertical drifts
for all seasons characterized by upward enhancement followed by a downward reversal
(scherlies and Fejer, 1999). The enhancements have peak velocity in the ranges of
20-25 m/s that occurs around 19:00 LT during quiet periods (i.e, a perio d of minor
solar forcing). During periods of quiet geomagnetic activity there is considerable,
unexplained variability in the density and structure of the equatorial ionosphere. In
order to predict the response to geomagnetic storms, it must be predict the conditions
in the ionosphere. The average quiet peak E × B drift is typically 15-25 m/s occurs
at 11:00 LT and 19:00 LT times (Rishbeth, 1971). This indicates that the C/NOFS
satellite measurement and the Geomagnetism Real-Time model drifts are in goo d
agreement during October and February with peak values of 20-25 m/s and 15 m/s
for December months but slightly di er in Junes with comparable peak values.
The quiet time vertical plasma drifts are driven by a complex interaction of E and F
region electro dynamics processes (Richmond, 1995). This may vary signi cantly with

56
the time of the day, diurnal, seasonal, longitudinal and solar cycles. At the equatorial
latitudes the F-region electrodynamics plasma drifts are upward and westward during
the day and downward and eastward at night.
Thus this C/NOFS vertical drift velocities are in a goo d agreement with the ISR and
AE-E satellite measured drift velo city which is westward from about sunrise to late
afternoon with peak magnitudes between about 20 m/s and 40 m/s close to no on and
vary signi cantly with season and longitudes (Fejer et al, 1997).
Figure 5.6: The validations of the equatorial vertical drift velocity with its C/NOFS
satel lite measurements.

Chapter 6
CONCLUSION and
RECOMMENDATIONS
6.1 Conclusion
The ionosphere is one of the most interesting layers in the atmosphere which plays
a crucial role in the modern day communication and responsible for various natural
phenomena. It is said to be responsible for lightning, propagation of radio waves and
ionizing the atmosphere by solar radiation, extended from 50 km to 2000 km vertical
stretch which roughly overlaps the thermosphere and exospheres.
The ionospheric electric  eld plays important roles on the plasma distributions and
dynamics of the equatorial and low latitude thermosphere. At the equatorial latitudes,
the ionospheric electric  eld drive the EEJ and the F region plasma motions and
a ects the thermospheric neutral winds, the development of the Appleton anomaly,
the composition of the low latitude ionosphere and protonsphere and the generation
of E and F region plasma instabilities.(Fejer, 1997).
The dynamics of the equatorial ionospheric F region vertical E × B drift velocity
applying data obtained from the C/NOFS satellite measurement at Bahir Dar for the
periods of the solar quiet time conditions. The estimated mean seasonal values of
57

58
drift velocity are 15-20 m/s during September and March equinox period and 10-15
m/s for the period of December and June solstice at 11:00 LT times. Besides, the
PRE vertical drift velo city reaches with amplitude values of 15-25 m/s at 19:00 LT.
In Asian regions the equatorial vertical drift velocity reaches with its peak values of
65 m/s but in North American regions this drift velocity becomes 40 m/s due to the
longitudinal variations of the equatorial vertical drift velocity with its geographic and
magnetic equator latitude, thermospheric neutral wind, geomagnetic  eld strength
and declination variations from season to seasons. Therefore, the day time equatorial
vertical drift velo cities have large amplitudes between about 11:00 and 19:00 local
times with typical values of 15-25 m/s.
Finally, our results are found on the average to be comparable agreement with vertical
plasma drift measurements carried out using ISR and AE-E satellite measurements at
Jicamaraca radio observatory and HF radar measurements in Peruvian sector which
carried out the C/NOFS satellites measurements at Bahir Dar in Ethiopia equatorial
region at quiet periods with the models.
6.2 Recommendations
Since this thesis only focused on the quiet time Vz variations over Bahir Dar re-
gion and have not studied the whole Ethiopian ionospheric equatorial Vz. We rec-
ommended that studies should be better to take in all satellite receiver stations in
our country. Even the greatest recommendation will focus on studying the whole
Ethiopian ionospheric equatorial Vz by adding the C/NOFS satellite measurement
stations in order to cover the whole area of our country. And also we recommended
that to study the Vz and PRE variations at disturbed conditions.

Bibliography
[1] Abadi et al, (2015), E ects of Pre-Reversal Enhancement of drift
on the latitudinal extension of plasma bubbles in the southeast Asia,
http://doi.org/10.1186/s40623-015-0246-7
[2] Abdu et al, (1981), Magnetic declination control of the equatorial F region
dynamo electric  eld development and spread F, J. Geophys. Res., 86(A13),
11,44311,446, doi:10.1029/JA086iA13p11443.
[3] Anderson, (1973), A theoretical study of ionospheric F region equato-
rial anomalyI. Theory, Planet. Space Sci., 21, 409419, doi:10.1016/0032-
0633(73)90040-8.
[4] Alken, (2009), A quiet time empirical model of equatorial vertical plasma drift
in the Peruvian sector based on 150 km echoes,J. Geophys. Res., 114, A02308,
doi:10.1029/2008JA013751.
[5] Alken and Maus, (2007), Spatio-temporal characterization of the equatorial
electrojet from CHAMP, rsted, and SAC-C satellite magnetic measurements,
J. Geophys. Res., 112, A09305, doi:10.1029/2007JA012524.
59

60
[6] Alken and Maus, (2008), Improved horizontal wind mo del HWM07 enables
estimation of equatorial ionospheric electric  elds from satellite magnetic mea-
surements.Geophys.Res.Lett.35.
[7] Alken and Maus, (2009), Electric  elds in the equatorial ionosphere drived
from CHAMP satellite magnetic  eld measurements, National Geophysics
Data center, NOAA E/GC1,325 Broadway, Boulder, co80305-3328, USA.
[8] Alken and Maus, (2010a), Relationship between the ionospheric eastward elec-
tric  eld and the EEJ, Geophs, Res.lett,37L04104, doi:10.1029/2009GL04189.
[9] Alken and Maus, (2010b), Electric  elds in the equato-
rial ionosphere derived from CHAMP satellite magnetic  eld
measurements,J.Atmos.sol.Terr.phys.72,319-326,doi:10.1016/j-jastp-
2009.02.006.
[10] Appleton,(1954), The anomolous equatorial belt in the F2-layer. J. At389 mos.
Terres. Phys. 5, 348.
[11] Batista et al, (1996), Equatorial ionospheric vertical plasma drift model over
the Brazilian region, J. Geophys. Res., 101, 10,887.
[12] Brekke, (1997), Physics of the Upper Atmosphere. Wiley published asso ciation
with Praxis Publishing.
[13] Brekke, (19972nded.), The Physics of the Upper Atmosphere,John Wiley and
Sons Ltd.

61
[14] Champ, (1951), The EEJ as detected from the abnormal electric current dis-
tribution above Huancayo and eleswhere Archmeteol, Geophys.Bio climatol
A4.368-392.
[15] Chau and Kudeki, (2006), Statistics of 150 Km echoes over Jicamarca based
on low power VHF observations,Ann Geophys,24.
[16] Coley and Heelis, (1989), Low-latitude zonal and vertical ion drifts seen by
DE 2, J. Geophys. Res., 6751.
[17] De la Beaujardiere,et al, (2004), C/NOFS: A mission to forecast scintillations,
J.Atmos.sol.terr.phy,66,1573-1591, doi:10.1016/j.jastp-2004.07.030.
[18] de la Beaujardiere and C/NOFS Science De nition Team, (2004),C/NOFS: A
mission to forecast scintillations, J. Atmos. Sol. Terr.Phys., 66(17), 15731591,
doi:10.1016/j.jastp.2004.07.030.
[19] Deminov et al, (1988), Longitudinal variations of the electric  eld in the day
side equatorial ionosphere, Geomagn.Aeron., 28, 57 60.
[20] Farley, (1986), The Pre-Reversal enhancement of the zonal electric  eld in the
equatorial ionosphere. J.Geophys. Res. 91, 13723-13728.
[21] Fayose et al, (2012), Variation of Total Electron Content [TEC] and their
E ect on GNSS over Akure,Nigeria.
[22] Fejer et al, (1989), Equatorial F region vertical plasma drifts during solar
maximum, J. Geophys. Res., 94, 12,049-12,054.

62
[23] Fejer et al, (1991), Average vertical and zonal F region plasma drifts over
Jicamarca, J. Geophys. Res., 96, 13,901-13,906.
[24] Fejer, (1991), Low latitude electrodynamic plasma drifts: A review,J. Atmos.
Terr. Phys., 53(8), 677 693, doi:10.1016/0021-9169(91)90121-M.
[25] Fejer, (1995), Global equatorial ionospheric vertical plasma drifts mea-
sured by the AEE satellite, J. Geophys. Res., 100(A4), 5769 5776,
doi:10.1029/94JA03240.
[26] Fejer et al, (1997), Empirical models of storm time equatorial zonal electric
 elds, J. Geophys. Res., 102,24,047-24,056.
[27] Fejer, (1997), The electrodynamics of the low latitude ionosphere resent results
and future challenging,J.Atmos.sol.Terr Phy,59,1456-1482.
[28] Fejer et al, (2008), Quiet time equatorial F region vertical plasma drift
model derived from ROCSAT-1 observations,J. Geophys. Res., 113, A05304,
doi:10.1029/2007JA012801.
[29] Forbes, (1981), The equatorial elctroiet,Res,Geophys.space 19(3).
[30] Fuller-Rawal, (2011), Storm time response of the thermosphere iono-
sphere system in Aermony of the Earth’s Atmosphere and Iono-
sphere, IAGA spec.sopron Book ser.vol2 edited by Abdu and Panchava,
Dordreht,Netherlands,doi:1o.1007/978-94-007-0326-1-32
[31] Prof.Rao, (2006), Characteristics of the Indian equatorial ionosphere lecture
notes, department of physics Andhra universty,Visakhapatnam, India.

63
[32] Garcia-Fernandaz, (2004), Contributions to the 3D ionospheric sounding with
GPS data,Ph.D. thesis, Universitat Polit‘ecnica de Catalunya, Spain.
[33] Goodman, published online. 27 dec. 1999, Doi: 10.1002/047134608 x.w1254.
1999 John wily and logins.
[34] Hanson and Mo ett, (1966), Ionization transport e ects in the equatorial F
region, J. Geophys. Res., 71, 55595572.
[35] Hartman and Heelis, (2007), Longitudinal variations in the equa-
torial vertical drifts in the topside ionosphere, J. Geophysics
Res,112,A03305,doi:10.1029/2006JA011773.
[36] Heelis, (2004), Electrodynamics in the low and middle latitude ionosphere,A
tutorial,J.Atmos.sol.Terr.phy,66.
[37] Jankowski and Suckor , (1996), Guide for magnetic measurements and ob-
servatory practice. Warszawa:International Association of Geomagnetism and
Aeronomy
[38] Kelley, (20092nd ed.), The Earths ionosphere, Plasma physics and Electro-
dynamics, Cornel University College of Engineering school of Electrical and
computer Engineering, Ithaca, AY.
[39] Kleusberg and Teunissen, (1996), Lecture notes in Earth sciences: GPS for
geodesy, Springer.
[40] Lanza And Meloni, (2006), The Earths magnetism. An introduction for Geol-
ogist, Wurzburg, springer.Matsushita, S. : 1969,. Radio sci, 4; 771-776.

64
[41] Luhr et al, (2004), No on-time equatorial electrojet:Its spatial features
as determined by the CHAMP satellite, J. Geophys.Res., 109, A01306,
doi:10.1029/2002JA009656.
[42] Manoj et al, (2006), Evidence for short spatial correlation lengths of the noon-
time equatorial electro jet inferred from a comparison of satellite and ground
magnetic data, J. Geophys. Res., 111, A11312, doi:10.1029/2006JA011855.
[43] Martyn, (1947), Atmospheric tides in the ionosphere. I. Solar tides in the F2
region. Proc. Roy. Soc. London A 189, 241260.
[44] McNamarca, (1991), The ionosphere communications surveilance and direction
 nding, krriegner publishing campany, Malabor,Florida.
[45] Okeke And Hamano, (2000), Earth planets space 52; 237-343
[46] Richmond, (1995), Ionospheric electrodynamics using magnetic apex coordi-
nates, J.Geomagn.Geoelectro,47,191-212.
[47] Prolss, (2004), Physics of the Earth’s space environment:an introduc-
tion,springer.
[48] Reigber et al, (2002), CHAMP mission status,Adv. Space Res., 30, 129134.
[49] Rishbeth, (1971), Polarization electric  elds produced by winds in the equa-
torial F region, Planetary and Space Science, 1357-369.
[50] Schunk and Sojka, (1992), Approaches to ionospheric mo deling,Simulation and
prediction, Advance in space research, 12(6),pp:317-326.

65
[51] Sherlies and Fejer, (1999), Radar and satellite global equatorial F region ver-
tical drift model, Utah state University, Logan.
[52] Sibanda, (2010), Challenges in Topside Ionospheric mo deling over South
Africa, Rhodes University.
[53] Stolle et al, (2008), Estimating the daytime Equatorial Ionization Anomaly
strength from electric  eld proxies, J. Geophys. Res., 113, A09310,
doi:10.1029/2007JA012781.
[54] Su et al, (1995), Comparison of satellite electron density and temperature mea-
surements at low latitudes with a plasmasphere-ionosphere model, J. Geophys.
Res.,100, 14,591 14,605.
[55] Su et al, (2006), Distribution characteristics of topside ionospheric density
irregularities: Equatorial regions versus mid-latitudes, J. Geophys. Res., 111,
A06305,doi:10.1029/2005JA011330.
[56] Walker, (1981), Longitudinal structure of the F-region equatorial anomaly:
A review, J. Atmos. Terr. Phys., 43(8),763 774, doi: 10.1016/0021-
9169(81)90052-0.
[57] Woodman, (1997), vertical drift velocitis and eastward electric  elds at the
magnetic equator, J.geophsics. Res,75,6249-6259.

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Declaration
I hereby declare that this Thesis is my original work and has not been presented for
a degree in any other university, and that all sources of materials have been duly
acknowledged.
 Name: Tebikew Gashu
Signature: ——————————–
Date: ———————————-
This thesis has been submitted for examination with my approval as a University
advisor.
 Name: Dr.Melessew Nigussie(PhD)
Signature: ——————————–
Date:
�2礼�