Speaker
Description
Mission design is driven by human and spacecraft safety and accurate space radiation environment models are crucial. For space mission planning, flux predictions in the radiation belts are considered. For this, the AP-8 model for proton fluxes and AE-8 model for electron fluxes are used. They are empirical models of the omnidirectional trapped integral fluxes in Earth’s magnetosphere. The INTEGRAL Radiation Environment Monitor (IREM) is a particle detector that measures high-energy electrons and protons providing particle species and spectral information. It consists of three detectors in two detector head configurations. Here, the IREM is used to investigate the dependency of inner belt flux anisotropies environment (L < 2.5) on equatorial pitch angle distributions (B/B0 < 1.5). In specific, measured countrates are compared to countrates calculated from omnidirectional radiation belt model fluxes which are folded with the 3D instrument response functions and a sin^n pitch angle anisotropy model, where n is determined empirically.
Several satellite passages from December 2019 are investigated. In the comparison we find that AP-8 and AE-8 omnidirectional flux predictions (n=0) underestimate the measured countrates, which are about two times higher for channel C1 (for L>2) and channel S34 (all L). Introducing a sin^n (PA)anisotropy term, the predictions can be improved for both tested channels (S34 and C1). The anisotropy term changes the steepness of the varying countrates and shifts the predicted countrate evolution closer to the measured countrate evolution. The countrate magnitude is better approached for pitch angles closer to 90◦, as this increases the countrates.
In another approach, an anisotropy factor can be found by a fit through the measured countrates. For IREM, two periods of solar minima were explored (P1:2010-2014, P2:2018-2020). IREM fluxes are globally higher past 2018 than before. Equatorial, low L-shell countrates are higher in P1 than in P2. The peak countrates are observed at around 90 degrees for all channels. The anisotropy factor n is larger (n=8-9) for the lower energy channel (S34) for the L-shell 2 - 2.25 and lower (n=2-4) for the higher energy channels (C1-C3). In the higher L-shell region 2.25 < L < 2.5 the anisotropy factors for the lower energy channel (S34) is 6-7 and for the higher energy channel 2-6. Similar behaviour is found for the PROTEL data.
