Properties of Plasma Waves Observed Upstream from Mars
Journal Article
Overview
abstract
We describe a new method to analyze the properties of plasma waves, and; apply it to observations made upstream from Mars by the Mars Atmosphere; and Volatile EvolutioN (MAVEN) mission. The slow measurement cadence of; most charged particle instrumentation has limited the application of; analysis techniques based on correlations between particle and magnetic; field measurements. We show that we can extend the frequency range of; applicability for these techniques, for a subset of waves that remain; coherent over multiple wave periods, by sub-sampling velocity; distribution function measurements and binning them by the wave phase.; This technique enables the computation of correlations and transport; ratios for plasma waves previously inaccessible to this technique at; Mars. By computing the cross helicity, we find that most identified; waves propagate upstream in the plasma frame. This supports the; conclusions of previous studies, but enables a clearer determination of; the intrinsic wave mode and characteristics. The intrinsic properties of; observed waves with frequencies close to the proton cyclotron frequency; have little spatial variability, but do have large temporal variations,; likely due to seasonal changes in the hydrogen exosphere. In contrast,; the predominant characteristics of waves at higher frequencies have less; temporal variability, but more spatial variability. We find several; indications of the presence of multiple wave modes in the lower; frequency wave observations, with unusual wave properties observed for; propagation parallel to the magnetic field and for background magnetic; fields nearly perpendicular to the solar wind flow.
