Influence of the Solar Wind Dynamic Pressure on the Ion Precipitation: MAVEN Observations and Simulation Results

Abstract

AbstractWe discuss the influence of the solar wind dynamic pressure on the ion precipitation using observations performed by MAVEN from 4 June 2014 to 20 July 2017. The increase of the dynamic pressure from 0.63 to 1.44 nPa is clearly associated with an increase of the same order of magnitude of the precipitating oxygen ion energy flux measured by MAVEN/STATIC from 9.9 to 20.6 × 106 eV · cm−2 · sr−1 · s−1 at low energy (from 30 to 650 eV). In the same way, from 650 to 25,000 eV, MAVEN/SWIA (all species) observed an increase from 22.4 to 42.8 × 107eV · cm−2 · sr−1 · s−1 of the precipitating ion energy flux. Performing two simulations using the average solar wind conditions for both solar dynamic pressure regimes observed by MAVEN as input of the LatHyS model (LATMOS Hybrid Simulation), we reproduce some of the key characteristics of the observed oxygen ion precipitation. We characterize the oxygen ions simulated by LatHyS by their energy and time of impact, their time of injection in the simulation and initial position, and the mechanism by which these ions were created. The model suggests that the main cause of the increase of the heavy ion precipitation during an increase of the solar dynamic pressure is the increase of the ion production by charge exchange, proportional to the increase of the solar wind flux, which becomes the main contribution to the ion precipitation at high energy.