Characterization of the Varia-tions of Energetic Electrons Flux in Earth’s Outer Radiation Belt

Geletaw Behailu

dc.contributor.author	Geletaw Behailu
dc.date.accessioned	2023-05-03T13:03:29Z
dc.date.available	2023-05-03T13:03:29Z
dc.date.issued	2023-02
dc.identifier.uri	http://ir.bdu.edu.et/handle/123456789/15232
dc.description.abstract	Earth’s radiation belts composed of two toroidal belts of energetic electrons and ions surrounding the Earth. Particularly, the outer radiation belt lies at geocenteric radial distance between 3RE and 7RE (where RE is Earth radii in the equatorial plane) consists of primarily of high energetic electrons (0.1−20 MeV ). The flux of energetic electrons in outer radiation belt is highly dynamic in space and time. Those high energy electrons are potentially hazardous during space missions causing radiation damage to spacecraft instrumentation. Therefore, it is important to characterize the nature of the variations of energetic electrons flux in this region. Thus, this dissertation fo cuses on three interconnected research efforts implemented to understand the energetic electron flux variations in outer radiation belt. First, we implemented an effort to investigate the effect of geomagnetic storm in the vari ations of energetic electrons flux in Earth’s outer radiation belt. we used Relativistic Electron - Proton Telescope (REPT) energetic electrons flux observations from the Energetic particles, Composition and Thermal plasma (ECT) instrument suite of the Van Allen probe satellites. This work focuses on analyzing the effects of geomagnetic storm on radiation belt energetic electron fluxes based on solar wind and IMF parameters as well as magnetic indices for the period from 2013 - 2018. The results illustrated that in all selected geomagnetic storm events the energetic electrons flux enhancements have been observed in the recovery phase and depletion of fluxes occurred in the main phases for energy channel of 2.1 MeV and 3.4 MeV . The energetic elec tron fluxes post - storm (recovery phase) were increased dramatically in the outer radiation belt region, with maximum at L ∼ 3.5. Moreover, for considering geomagnetic storm in 2013 using different energies from 1.8 MeV up to 7.7 MeV , with L shell of 1 − 6, we have obtained the energetic electron fluxes were shown enhancement during the recovery phase and deep depletion during the main phase of the storm. The second study attempts to characterize the causality and timing of the solar wind and IMF parameter activities on the outer radiation belt environment based on three tools: time shifted cross correlation, mutual information, and transfer entropy statistical analysis. The Van Allen Probes mission measurements of multi-MeV electrons flux data in the period from January 01, 2017 to December 31, 2018 have been used. The results indicate that the information transfer from solar wind and IMF parameters into multi-MeV electrons flux is dependent on the kind of driving parameter, range of L-shell, and energy of electrons. The result identifies the rank of driving parameters based on their maximum values in the correlation and information transfer analysis. Thus, solar wind velocity is the dominant driving parameter for the variation of multi MeV electrons flux in the outer radiation belt. Given three ranges of L-shell (∼ 4, ∼ 4.5 and ∼ 5), with decreasing L-shell values the maximum information transfer from driving parameters into electron flux decreases and the lag time increases. Such dependency analysis can help to ix select the model parameters that influence the variation of multi-MeV electrons flux and improve the existed models of the dynamical system. The third study has been intended in evaluating the performance of SNB3GEO energetic elec tron flux model in predicting the observations of LANL and GOES-13. In forecasting relativistic electron fluxes, SNB3GEO model provides relatively reliable and easily interpretable prediction output. Although the performance of this model was evaluated with respect to other models (such as Relativistic Electron Forecast Model (REFM)), its prediction accuracy never assessed with respect to experimental measurements except those used in model development (i.e. GOES-12, GOES-13). In this work, we implemented evaluation of the prediction performance of SNB3GEO using two experimental measurements, which are LANL and GOES-13. The daily averaged rel ativistic electron flux data from 01 January 2013 to 31 December 2016 have been used to analyze the forecasting performance. Correlation Coefficient (CC), Normalized Root Mean Square Error (NRMSE) and Prediction Efficiency (PE) have been used as performance evaluation quantifier. The results indicated that SNB3GEO provides a more accurate forecast when it is compared with GOES-13 than LANL observations. The four years average values of CC; NRMSE and PE, when the model performance has been evaluated with observations of GOES-13 are 0.896; 0.497 and 0.792, respectively, whereas the average values are CC = 0.739; NRMSE = 0.706 and PE = 0.450, when the model performance evaluated with respect to observations of LANL. Such prediction performance evaluation of SNB3GEO will contribute for further improvement of the model used to predict energetic electrons fluxes in Earth’s outer radiation belt. Thus, in this dissertation the above three case studies are the main research findings.	en_US
dc.language.iso	en_US	en_US
dc.subject	Physics	en_US
dc.title	Characterization of the Varia-tions of Energetic Electrons Flux in Earth’s Outer Radiation Belt	en_US
dc.type	Thesis	en_US