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It has been noted that in large solar energetic particle (SEP) events, the peak intensities show an East‐West asymmetry with respect to the source flare locations. Using the 2D improved Particle Acceleration and Transport in the Heliosphere (iPATH) model, we investigate the origin of this longitudinal trend. We consider multiple cases with different solar wind speeds and eruption speeds of the coronal mass ejections (CMEs) and fit the longitudinal distributions of time‐averaged fluence by symmetric/asymmetric Gaussian functions with three time intervals of 8, 24 and 48 hr after the flare onset time respectively. The simulation results are compared with a statistical study of three‐spacecraft events. We suggest that the East‐West asymmetry of SEP fluence and peak intensity can be primarily caused the combined effect of an extended shock acceleration process and the evolution of magnetic field connection to the shock front. Our simulations show that the solar wind speed and the CME speed are important factors determining the East‐West fluence asymmetry. Large solar energetic particle (SEP) events are quite common during the solar maximum period when the solar activity is high. In these events, particles can be accelerated to relatively high energies at shock waves driven by coronal mass ejections (CMEs) in large SEP events. These energetic particles are the leading concern of astronaut safety and are a central topic of space weather studies. The intensity and the maximum particle energy, as well as the spectral shape of energetic particles vary significantly from one event to another. In particular, an interesting feature of these events is the so‐called East‐West asymmetry, where the intensity of energetic particles are not symmetric with respect to the source flare location and the peak intensity is shifted to the west of the source location. Using the 2D improved Particle Acceleration and Transport in the Heliosphere model, we examine this East‐West asymmetry. Model results clearly show this asymmetry and suggest that its origin arises from the history of shock acceleration and magnetic connection. We also discuss the role of the background solar wind speed and the CME speed as key parameters organizing this asymmetry. The time‐averaged fluence of solar energetic particles shows an East‐West asymmetry with respect to the source flare locationsUsing the improved Particle Acceleration and Transport in the Heliosphere model, we find the asymmetry is a result of the effects of shock acceleration history and the geometry of the magnetic fieldThe background solar wind speed and the coronal mass ejection speed are key factors affecting this asymmetry The time‐averaged fluence of solar energetic particles shows an East‐West asymmetry with respect to the source flare locations Using the improved Particle Acceleration and Transport in the Heliosphere model, we find the asymmetry is a result of the effects of shock acceleration history and the geometry of the magnetic field The background solar wind speed and the coronal mass ejection speed are key factors affecting this asymmetry

AbstractThe Earth-Moon-Mars Radiation Environment Module (EMMREM) is a numerical model for characterizing the time-dependent radiation environment in the Earth-Moon-Mars and interplanetary space environments. In this work we demonstrate the capabilities of the module for performing analyses of time-dependent exposures from solar energetic particle (SEP) events near Earth and Mars by calculating time-dependent dose rates, dose equivalent rates, and accumulated dose and accumulated dose equivalents for surrogates of the skin and the blood forming organs (BFOs) of crew members shielded by as much as 10 g/cm2of aluminum shielding for the January 15, 2005, SEP event. The motivation for the development of EMMREM is the need to better understand the radiation hazards in deep space and near Earth and other planetary bodies, in near real time in support of possible future space exploration by manned and unmanned spacecraft. Characterizing the radiation environment for different locations on and close to Earth for SEP events is fairly well developed. However, estimating the probable radiation environment near Mars and other locations throughout the solar system is not currently supported for SEP events. Such capability is critical for future human exploration of the Moon and Mars in the upcoming decades. The calculated doses for the skin and BFO surrogates are compared with the National Aeronautics and Space Administration’s short-term permissible exposure limits.

The densities of six neutral species in the Martian upper atmosphere were analyzed before and during the 2018 Martian global dust storm (GDS 2018) using data from the Neutral Gas and Ion Mass Spectrometer of the Mars Atmosphere and Volatile EvolutioN mission. The trends of the dayside densities of the neutral species and their relative abundances were investigated between May 27 and June 17, 2018, at altitudes of 160–210 km. GDS 2018 caused variations in the neutral species abundance of the upper atmosphere at its onset in June 5–8, 2018, with the CO2, Ar, CO, O, N2, and He densities decreasing relative to prestorm conditions. The densities of the examined neutral species increased during the storm, except those of O and He. During the storm, the relative abundances of CO2and Ar increased, while those of CO and O decreased and those of N2and He remained the same. The variation in the neutral species with altitude was consistent with the regular atmospheric conditions and unrelated to the GDS 2018 drivers. The higher thermospheric temperature observed during the storm onset suggested that changes in the composition of the neutral species were caused by storm‐induced thermal enhancements. Global dust storms are important dynamical planetary‐scale events on Mars that have been monitored by several spacecraft in orbit and on the surface over the past few decades. Here, we study the most recent planet‐encircling dust even in 2018 (global dust storm [GDS] 2018). From June through October, this event grew from local to planet encircling dust storm and dust was intense enough to significantly reduce sunlight from reaching the planet's surface. Although dust particles are mostly concentrated in the lower atmosphere, they are expected to have affected the upper atmosphere and ionosphere. In this study, we use Mars Atmosphere and Volatile EvolutioN spacecraft data to investigate how the GDS 2018 affected the abundance of neutral species in the upper atmosphere of Mars. The variability of neutral species in the upper atmosphere pre‐, during, and post‐storm is determined for six chemical species. The densities of the examined neutral species increased during the storm, except those of O and He. The variation in the neutral species with altitude was consistent with the regular atmospheric conditions and unrelated to the GDS 2018 drivers. These observations provide a link between the dynamics of the lower and upper atmospheres during dust events, and advance our understanding of the thermal and dynamical characteristics of the Martian atmosphere. The composition of atmospheric neutral species varied during MY34 global dust storm (GDS)During the GDS onset, CO2, Ar, CO, and N2densities increased and O and He densities decreasedThe mean thermospheric temperature increased by ∼14 K during the GDS onset The composition of atmospheric neutral species varied during MY34 global dust storm (GDS) During the GDS onset, CO2, Ar, CO, and N2densities increased and O and He densities decreased The mean thermospheric temperature increased by ∼14 K during the GDS onset