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Characteristics of pitch angle distributions of hundreds of keV electrons in the slot region and inner radiation belt
Journal article   Open access   Peer reviewed

Characteristics of pitch angle distributions of hundreds of keV electrons in the slot region and inner radiation belt

H Zhao, A. N Jaynes, X Li, J. B Blake, J. F Fennell, S. G Claudepierre, D. N Baker and D. M Malaspina
Journal of geophysical research. Space physics, Vol.119(12), pp.9543-9557
12/2014
DOI: 10.1002/2014JA020386
url
https://doi.org/10.1002/2014JA020386View
Published (Version of record) Open Access

Abstract

The pitch angle distribution (PAD) of energetic electrons in the slot region and inner radiation belt received little attention in the past decades due to the lack of quality measurements. Using the state‐of‐the‐art pitch angle‐resolved data from the Magnetic Electron Ion Spectrometer instrument onboard the Van Allen Probes, a detailed analysis of hundreds of keV electron PADs below L = 4 is performed, in which the PADs are categorized into three types: normal (flux peaking at 90°), cap (exceedingly peaking narrowly around 90°), and 90° minimum (lower flux at 90°) PADs. By examining the characteristics of the PADs of ∼460 keV electrons for over a year, we find that the 90° minimum PADs are generally present in the inner belt (L<2), while normal PADs dominate at L∼3.5–4. In the region between, 90° minimum PADs dominate during injection times and normal PADs dominate during quiet times. Cap PADs appear mostly at the decay phase of storms in the slot region and are likely caused by the pitch angle scattering of hiss waves. Fitting the normal PADs into sinnα form, the parameter n is much higher below L = 3 than that in the outer belt and relatively constant in the inner belt but changes significantly in the slot region (2 < L < 3) during injection times. As for the 90° minimum PADs, by performing a detailed case study, we find in the slot region this type of PAD is likely caused by chorus wave heating, but this mechanism can hardly explain the formation of 90° minimum PADs at the center of inner belt. Key Points Pitch angle distribution (PAD) of hundreds of keV electrons in low L region is studied The formation of three PAD types in low L region is investigated Ninety degrees minimum PAD is the most prevalent PAD type in low L region
 energetic electrons inner radiation belt pitch angle distribution plasmasphere slot region wave‐particle interaction

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