On the Solar Wind Proton Temperature Anisotropy at Mars' Orbital Location

Abstract

The Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft can act as an intermittent upstream solar wind monitor at (Formula presented.) 1.5 AU. To inspect the evolution of solar wind turbulence in the Martian exosphere, we have gathered proton (i.e., ionized hydrogen) temperature measurements taken by the Solar Wind Ion Analyzer (SWIA) onboard the MAVEN spacecraft. Here we investigate instabilities driven by the proton temperature anisotropy at Mars during southern hemisphere fall, winter, spring, and summer seasons. We look at the relationship between the temperature anisotropy, (Formula presented.) (i.e., the ratio of the perpendicular proton temperature component to the parallel proton temperature component), and the parallel plasma beta, (Formula presented.), to determine any constraints imposed by kinetic instabilities. Furthermore, we report on the properties of turbulence near Mars' orbital location during upstream solar wind intervals from January 2015 to December 2016 ((Formula presented.) 1 Martian year). We find that the probability distributions of ((Formula presented.))-values become limited when (Formula presented.) deviates greatly from unity. We also find evidence of intermittency implying nonlinear, non-homogeneous energy transfer. Additionally, spectral indices obtained from basic fittings of power spectral densities of magnetic field fluctuations demonstrate a power law decay for inertial ranges ((Formula presented.) Hz to 0.1 Hz).