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2019 
Using Relativistic Electron Proton Telescope measurements onboard Van Allen Probes, the evolution of electron pitch angle distributions (PADs) during the different phases of magnetic storms is studied. Electron fluxes are sorted in terms of storm phase, urn:xwiley:jgra:media:jgra55457:jgra55457math0001 value, energy, and magnetic local time (MLT) sectors for 55 magnetic storms from October 2012 through May 2017. To understand the potential mechanisms for the evolution of electron PADs, we fit PADs to a sinusoidal function urn:xwiley:jgra:media:jgra55457:jgra55457math0002, where urn:xwiley:jgra:media:jgra55457:jgra55457math0003 is the equatorial pitch angle and n is a real number. The major inferences from our study are (i) at L urn:xwiley:jgra:media:jgra55457:jgra55457math00045, the prestorm electron PADs are nearly isotropic (n urn:xwiley:jgra:media:jgra55457:jgra55457math00050), which evolves differently in different MLT sectors during the main phase subsequently recovering back to nearly isotropic distribution type during the storm recovery phase; (ii) for urn:xwiley:jgra:media:jgra55457:jgra55457math0006 urn:xwiley:jgra:media:jgra55457:jgra55457math0007 3.4 MeV, the main phase electron PADs become more pancake like on the dayside with high n values (>3), while it becomes more flattop to butterfly like on the nightside, (iii) at L = 5, magnetic field strength during the storm main phase enhances during the daytime and decreases during the nighttime. (iv) Conversely, at L urn:xwiley:jgra:media:jgra55457:jgra55457math00083, the electron PADs neither respond significantly to the different phase of the magnetic storm nor reflect any MLT dependence. (v) Main phase, electron fluxes with urn:xwiley:jgra:media:jgra55457:jgra55457math0009 <4.2 MeV shows a persistent 90\textdegree maximum PAD with n ranging between 0 and 2, while for urn:xwiley:jgra:media:jgra55457:jgra55457math0010 urn:xwiley:jgra:media:jgra55457:jgra55457math0011 4.2 MeV the distribution appears flattop and butterfly like. Our study shows that the relativistic electron PADs depend upon the geomagnetic storm phase and possible underlying mechanisms are discussed in this paper. Pandya, Megha; Bhaskara, Veenadhari; Ebihara, Yusuke; Kanekal, Shrikanth; Baker, Daniel; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2019 YEAR: 2019 DOI: 10.1029/2019JA027086 electron flux; inner magnetosphere; Pitch angle distribution; Radiation belts; Van Allen Probes 
Relativistic electron flux responses in the inner magnetosphere are investigated for 28 magnetic storms driven by Corotating Interaction Region (CIR) and 27 magnetic storms driven by Coronal Mass Ejection (CME), using data from the Relativistic ElectronProton Telescope (REPT) instrument on board VanAllen Probes from Oct2012 to May2017. In this present study we analyze the role of CIRs and CMEs in electron dynamics by sorting the electron fluxes in terms of averaged solar wind parameters, Lvalues, and energies. The major outcomes from our study are: (i) At L = 3 and E = 3.4 MeV, for >70\% cases the electron flux remains stable, while at L = 5, for ~82\% cases it changes with the geomagnetic conditions. (ii) At L = 5, ~53\% of the CIR storms and 30\% of the CME storms show electron flux increase. (iii) At a given Lvalue, the tendency for the electron flux variation diminishes with the increasing energies for both categories of storms. (iv) In case of CIR driven storms, the electron flux changes are associated with changes in Vsw and SymH. (v) At L ~ 3, CME storms show increased electron flux, while at L ~ 5, CIR storms are responsible for the electron flux enhancements. (vi) During CME and CIR driven storms, distinct electron flux variations are observed at L = 3 and L = 5. Pandya, Megha; Veenadhari, B.; Ebihara, Y.; Kanekal, S.G.; Baker, D.N.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2019 YEAR: 2019 DOI: 10.1029/2019JA026771 electron flux; innermagnetosphere; Magnetic Storms; Radiation belt; solar wind driver; Van Allen Probes 
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