Understanding the drivers of global ionospheric variations during geomagnetic storm

Dejene Ambisa

dc.contributor.author	Dejene Ambisa
dc.date.accessioned	2023-07-03T12:11:00Z
dc.date.available	2023-07-03T12:11:00Z
dc.date.issued	2023-06
dc.identifier.uri	http://ir.bdu.edu.et/handle/123456789/15444
dc.description.abstract	The behaviour of the Earth’s ionosphere during 17-18 March 2015 geomagnetic storm has been investigated by different studies. However, the spatio-temporal evolution of the drivers of global ionospheric effect and characteristics of large scale travelling ionospheric disturbances (LSTIDs) during storm has not yet been investigated, using multi-data sources, in detail. Therefore, in this dissertation drivers of the ionospheric storms and effect of energy deposition hemispherical asymmetry on the amplitude and velocity of LSTIDs are investigated during the 17-18 March 2015 space weather event. The investigation is carried out using multiple experimental data from different sources including: (1) Global navigation satellite system (GNSS) derived TEC data, (2) field-aligned currents (FACs) data from Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) (3) thermospheric neutral com position data from GUVI/TIMED satellite and (4) geomagnetic field measurements from International Real-Time Magnetic Observatory Network (INTERMAGNET) and SuperMag and (5) hemispherical power (HP), an estimate of the total hemispheric energy flux deposited into auroral region, from Coupling, Energetics and Dynamics of Atmospheric Regions (CEDAR) Madrigal database. To visualise ionospheric storm effect percentage deviation in vTEC was computed with respect to the quiet-time backgrounds. Attributes of LSTIDs are determined considering a longitude range of 20 degrees over the America, Europe-Africa, and Asia-Australia sectors. The time series of vTEC is fitted with fourth order polynomial in order to remove the diurnal variability of the ionosphere. The difference between fitted and the original vTEC then give the detrended TEC or ∆TEC. Furthermore, ∆TEC was binned within 10 x 5 min latitude/time to detect the existence of LSTIDs. The cross-correlation method (CCM) is applied between time series of change in TEC (∆T EC) at different lati tudes to estimate the meridional velocity of LSTIDs. The time lag obtained from the CCM method is used in estimating velocities of LSTIDs in all sectors of both hemi spheres. Our results revealed that the northern hemisphere high-latitude ionosphere, the American-Canada-Greenland sector, responded about 12 hours earlier than the southern hemisphere high-latitude ionosphere, resulted from hemispherical energy imbalance as detected from hemispherical Power. The positive ionospheric storm ob served in the high-latitude regions is found to be due to solar wind energy deposition at high latitude. Interestingly, it is found that the northern hemisphere positive iono spheric storm shifted to the mid-latitude and disappeared there whereas the southern hemisphere ionospheric positive storm shifted to mid-latitude and then farther to the v low-latitude with time. This spatio-temporal evaluation of positive ionospheric storm is found to be due to the spatio-temporal enhancement of the [O]/[N2] ratio. Also, the mid (Europe-African) and low (Brazilian) latitudes positive ionospheric storms prevailed due to Prompt Penetration Electric fields (PPEF), Disturbance Dynamo Electric Fields (DDEF), and enhancement of the [O]/[N2] ratio. Moreover, the nega tive ionospheric storm, observed at the northern hemisphere high and mid-latitudes in the American and Asian sectors, is linked to the reduction of [O]/[N2] ratio. We also observe that the amplitude of LSTIDs are larger in the northern hemisphere than the geomagnetic conjugate regions in the southern hemisphere which may partly be accounted for by hemispherical energy imbalance during storm time. In addition, on average higher meridional LSTIDs velocities are observed in northern hemisphere in all sectors.	en_US
dc.language.iso	en_US	en_US
dc.subject	Physics	en_US
dc.title	Understanding the drivers of global ionospheric variations during geomagnetic storm	en_US
dc.type	Dissartation	en_US