Precipitation And Energization Of Relativistic Radiation Belt Electrons Induced By Ulf Oscillations In The Magnetosphere

Author : Sapna Shekhar
Publisher :
ISBN 13 :
Total Pages : 270 pages
Book Rating : 4.:/5 (11 download)

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Download or read book Spatial Extent of Relativistic Electron Precipitation from the Radiation Belts written by Sapna Shekhar and published by . This book was released on 2017 with total page 270 pages. Available in PDF, EPUB and Kindle. Book excerpt: Relativistic Electron Precipitation (REP) in the atmosphere can contribute significantly to electron loss from the outer radiation belts. In order to estimate the contribution to this loss, it is important to estimate the spatial extent of the precipitation region. We observed REP with the 0° Medium Energy Proton Electron Detector (MEPED) on board Polar Orbiting Environmental Satellites (POES), for 15 years (2000-2014) and used both single and multi satellite measurements to estimate an average extent of the region of precipitation in L shell and Magnetic Local Time. In the duration of 15 years (2000-2014), 31035 REPs were found in this study. Events were found to split into two classes; one class of events coincided with proton precipitation in the P1 channel (30-80 keV), were located in the dusk and early morning sector, and were more localized in L shell and magnetic local time (dMLT ~ 0-3 hrs, dL ~ 0.25-0.5), whereas the other class of events did not include proton precipitation, and were located mostly in the midnight sector and were wider in L shell (dL ~ 1-2.5) but localized in MLT (dMLT ~ 0-3 hrs); both classes occurred mostly during the declining phase of the solar cycle and geomagnetically active times. The events located in the midnight sector for both classes were found to be associated with tail magnetic field stretching which could be due to the fact that they tend to occur mostly during geomagnetically active times, or could imply that precipitation is caused by current sheet scattering. Use of POES to infer information about the precipitation energy spectrum was also investigated, despite the coarse energy channels and contamination issues. In order to study the energy specificity of the REP events, a method to fit exponential spectra to the REP events, wherever possible, was formulated and validated through comparisons with SAMPEX observed spectra. 18 events on POES were found to be in conjunction with SAMPEX in the years 2000-04. The exponentially fitted spectra for these events obtained by Comess et al. [2013] were folded through NOAA POES geometric factors obtained by Yando et al. [2011] and the predicted count rates in E3 (>300 keV) were found to be in agreement with the actual data in the MEPED 0°particle telescopes on board NOAA POES. After comparison and validation with SAMPEX an inversion method was developed and applied to the same POES events. Assuming exponential spectra, E3 (>300 keV)/P6 (>700 keV) electron count rate ratios along with P3 , P4 and P5 proton count rates of the POES MEPED 0° telescope were used to determine an e-folding energy for the electron spectra and compared with SAMPEX. The e-folding energies obtained from POES were found to be systematically lower but followed a similar trend as SAMPEX, and it was concluded that E3/P6 ratio could be used as a parameter to define spectral hardness of POES REP events irrespective of spectral shape. Using this parameter, spatial variation of spectral hardness of REP events was investigated. It was found that very soft events were mostly found in the dusk midnight early morning MLT sectors and L~5-7 whereas the hardest events were located in the post noon sectors peaking at L~4-5. The hardest events peaked at lower L shells and less than 10% were coincident with low energy (30-80 keV) proton precipitation which has been previously used as a proxy for EMIC wave particle scattering (e.g. Carson et al. [2012], Sandanger et al. [2007]). The softer midnight events coinciding with proton precipitation were found to be associated with magnetic field stretching. Finally, three case study events on 1st February and 17-18th January 2013, were investigated combining POES with BARREL, CSSWE, GOES and Van Allen Probes data. EMIC wave activity was observed on 17-18 Jan 2013 on GOES and Van Allen Probes and REP was observed in several POES satellites. On 1st February 2013, no evidence of EMIC waves were found but 4 POES satellites observed the REP event along with BARREL. The spatial scales were in agreement with statistical estimates and the exponential fits to REP energy spectra agreed with BARREL data. It was also found that REPs were accompanied by proton precipitation when the satellite was at the edge of the plasmasphere drainage plume irrespective of the presence of EMIC waves.