Publication Date:
2019
Description:
Abstract
We present two case studies of FAST electrostatic analyzer measurements of both highly nonthermal (κlsim; 2.5) and weakly nonthermal/thermal monoenergetic electron precipitation at ∼4000 km, from which we infer the properties of the magnetospheric source distributions via comparison of experimentally determined number density–, current density–, and energy flux–voltage relationships with corresponding theoretical relationships. We also discuss the properties of the two new theoretical number density–voltage relationships that we employ. Moment uncertainties, which are calculated analytically via application of the Gershman et al. [2015] moment uncertainty framework, are used in Monte Carlo simulations to infer ranges of magnetospheric source population densities, temperatures, κ values, and altitudes. We identify the most likely ranges of source parameters by requiring that the range of κ values inferred from fitting experimental moment‐voltage relationships correspond to the range of κ values inferred from directly fitting observed electron distributions with two‐dimensional kappa distribution functions. Observations in the first case study, which are made over ∼78–79° invariant latitude (ILAT) in the Northern Hemisphere and 4.5–5.5 magnetic local time (MLT), are consistent with a magnetospheric source population density nm= 0.7–0.8 cm−3, source temperature Tm≈ 70 eV, source altitude h= 6.4–7.7 RE, and κ= 2.2–2.8. Observations in the second case study, which are made over 76–79° ILAT in the Southern Hemisphere and ∼21 MLT, are consistent with a magnetospheric source population density nm= 0.07–0.09 cm−3, source temperature Tm≈ 95 eV, source altitude ≳ 6 RE, and κ= 2–6.
Print ISSN:
2169-9380
Electronic ISSN:
2169-9402
Topics:
Geosciences
,
Physics
