Inferring source properties of monoenergetic electron precipitation from kappa and Maxwellian moment-voltage relationships
arXiv:1904.02869 · doi:10.1029/2018JA026158
Abstract
We present two case studies of FAST electrostatic analyzer measurements of both highly nonthermal (~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 \citet{Gershman2015} moment uncertainty framework, are used in Monte Carlo simulations to infer ranges of magnetospheric source population densities, temperatures, values, and altitudes. We identify the most likely ranges of source parameters by requiring that the range of values inferred from fitting experimental moment-voltage relationships correspond to the range of 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 ~0.7--0.8~cm, source temperature ~70~eV, source altitude ~6.4--7.7~, and ~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 ~0.07--0.09~cm, source temperature ~95~eV, source altitude ~6~, and ~2--6.