Ultra‐Fast Kelvin Wave Packets in Mars' Atmosphere and Their Interactions With Tides as Viewed by MAVEN/NGIMS and MRO/MCS

Abstract

AbstractA key element of successful aerobraking operations at Mars is accurate thermospheric density predictions. Evidence suggests that much of the longitude variability in Mars' aerobraking region is associated with atmospheric tides, and the day‐to‐day variability is connected with tidal modulation by longer‐period global‐scale waves. Specifically, ultra‐fast Kelvin waves (UFKWs) and their modulation of the tidal spectrum play a key role in coupling Mars' lower (<∼80 km) and middle (∼80–100 km) atmosphere with the aerobraking region above. In this study, over 5 years of Mars Atmosphere and Volatile Evolution Neutral Gas and Ion Mass Spectrometer CO2 density observations are employed to reveal prominent, frequent, and persistent 2.5‐ to 4.5‐day UFKW packets in the whole Martian middle and upper thermosphere (ca. 150–200 km), and large secondary waves arising from their nonlinear interactions with the tidal spectrum. Detailed analyses focusing on a prominent ∼2.5‐day UFKW event in late 2015 demonstrate primary and secondary wave amplitudes growing twofold with altitude from ∼7%–14% near 150 km to ∼12%–25% near 200 km and their combined effects to account for ∼60%–80% of the altitude‐longitudinal variability of Mars' thermospheric density. Concurrent temperature measurements from Mars Reconnaissance Orbiter Mars Climate Sounder reveal consistent wave signatures near 80 km altitude suggesting propagation of both primary and secondary waves from the lower atmosphere. This study demonstrates that UFKWs and secondary waves from UFKW‐tide interactions are sources of significant altitude‐longitude variability in the Mars' aerobraking region that should be accounted for when analyzing satellite observations and nonlinear models.