Determination of the response time of the Martian induced magnetosphere from solar wind fluctuations using multi-spacecraft observations

Abstract:

Fluctuations in the solar wind upstream of Mars are frequently measured from orbit by two satellites; the Mars Atmosphere and Volatile EvolutioN (MAVEN) and Mars Express (MEX) orbiters. These fluctuations propagate through the near-Mars space environment and can be identified by observing changes in the plasma properties measured by MAVEN (ions, electrons, and magnetic field) and MEX (ions and electrons). Events that are abrupt, i.e. well-defined in time, can be used to estimate the response time in different parts of the system. We use two approaches: 1. We identify events involving sudden changes in the upstream solar wind above the magnetosheath and corresponding responses inside the induced magnetosphere and ionosphere. With simultaneous measurements in both regions, we can calculate the travel time for any fluctuations we track. 2. We trace test particles in an average velocity map of ion fluxes based on MAVEN measurements near Mars, starting from the solar wind upstream at 3.2 R_M and traced down to the induced magnetosphere. With this method, the flight-time of the test particles determines the cumulative time-delay in the system. The fluctuation events and the travel time map are independent and complementary; combined these provide a robust model of the response time of the Martian induced magnetosphere, and may provide insight as to whether the fluctuations are simply carried by the ion flow or through some other mechanisms.