Wavelet analysis of low frequency plasma oscillations in the magnetosheath of Mars

Abstract

Wavelet analysis was employed to identify the major frequencies present in the plasma oscillations in the Martian magnetosheath. We have selected magnetosheath crossings and applied the Morlet wavelet transform to the electron density and temperature data, obtained from the Analyzer of Space Plasmas and Energetic Atoms experiment (ASPERA-3), onboard the Mars Express (MEX). In a study of 9667 magnetosheath crossings observed from 2005 to 2016, we have found 22,912 frequencies with high wave power between 5 and 60 mHz for the electron density data, For about 2/3 of the high wave power periods (63.3%), the most energetic frequencies were identified in the range 5–20 mHz. The analysis of the electron temperature data led to similar results, with 61.9% of the highest power frequencies in the 5–20 mHz range. No significant influence of the solar cycle on the frequencies of ULF waves has been observed in our analysis. The frequencies obtained here are near the O+ gyrofrequency. The main fact that controls the ion gyroradius is the interplanetary magnetic field that is compressed around the planet.