Abstract
A test particle simulation code was developed to simulate the inner proton belt response during the intense geomagnetic storm of 15 May 2005. The guiding center model was implemented to compute the proton trajectories with an energy range of 70–180 MeV. The time-varying magnetic field model implemented in the simulations was computed by the Tsyganenko model TS05 with the associated inductive electric field. One of the most important features of the low-earth orbit (LEO) environment is the South Atlantic Anomaly, which imposes a dangerous radiation load on most LEO missions. This research aims to investigate the proton flux variations in the anomaly region with respect to space weather conditions. The results showed that during the main phase of the geomagnetic storm, the proton flux in the SAA decreased, whereas, throughout the initial and recovery phases, the proton flux was increased at most of the altitudes. Satellite measurements confirmed numerical results.
Highlights
The South Atlantic Anomaly (SAA) is considered a dangerous radiation source for low-earth orbit (LEO) missions
The right panels demonstrate that the proton density at lower L-shells gradually increased along with the storm, while it decreased at higher L-shells, which is consistent with the simulations performed by Engel et al (2015) and the satellite observations by Selesnick et al (2010) and Zou et al (2011)
According to the interpretation of Kim & Chan (1997) and Engel et al (2015), by assuming the conservation of the three adiabatic invariants throughout the storm, the drift shells were expanded radially during the main phase, where the field line curvature was greatest, and the maximum losses should occur near the minimum Dst index, and this was the reason of the SAA proton flux reduction during the main storm phase in our simulations; afterwards, the drift shells were moved inward during the recovery phase by returning to the initial configuration, and this led to the enhancement of the proton density in the high L-shells, the increase of the proton flux in the SAA southern cell
Summary
The South Atlantic Anomaly (SAA) is considered a dangerous radiation source for low-earth orbit (LEO) missions. Energetic particles populating the inner trapped radiation belt fully immerse the anomaly region due to a significant decrease in the magnetic field intensity located at the South of the Atlantic Ocean, under which reversed geomagnetic fluxes at the coremantle boundary are prominent, which in turn, reduce the field strength locally. This interpretation was discussed in detail recently by the following authors Tarduno et al (2015), Aubert (2015), Cottaar & Lekic (2016), and Terra-Nova et al (2017). The inner proton belt dynamics have been studied by various authors such as Selesnick et al (2010), Zou et al (2011), and Engel et al (2015)
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