Role of stationary and transient waves in CO₂ supersaturation during northern winter in the Martian atmosphere revealed by MGS radio occultation measurements

Abstract

The Martian atmosphere, which mainly consists of carbon dioxide (CO2), is characterized by extremely low temperatures that cause CO2 gas to freeze and dry ice to form. To date, temperatures below the CO2 saturation temperature, which can be attributed to the effects of atmospheric waves, have been observed in the polar winter and in the mesosphere. Using data from Mars Global Surveyor (MGS) radio occultation measurements, we investigated the role of large‐scale atmospheric waves including stationary and transient waves at northern high latitudes in winter on CO2 supersaturation. A distinct longitudinal dependence of CO2 supersaturation was observed at altitudes higher than the pressure level of 200–400 Pa, where a stationary wave with a wave number of 2, whose temperature amplitude had minima at 30–100 Pa, lowered the background temperature to a level close to the CO2 saturation temperature. However, the stationary wave alone was not sufficient to cause CO2 supersaturation. Additional temperature disturbances caused by transient waves, namely, superposition of both waves, had a significant role in CO2 supersaturation. The longitudinal dependence of the occurrence of CO2 supersaturation revealed by our study might affect the longitudinal distribution of CO2 snowfall and the formation of the seasonal polar ice cap.

Annual Cycle of Gravity Wave Activity Derived From a High‐Resolution Martian General Circulation Model

“…The lower‐resolution version of the MGCM has been validated against the observed zonal mean climatology (Kuroda et al, ) and applied for studies of baroclinic planetary wave activity (Kuroda et al, ), annular mode variability in the middle and high latitudes (Yamashita et al, ), equatorial semiannual oscillations (Kuroda et al, ), winter polar warmings during dust storms (Kuroda et al, ), and CO 2 snowfalls during northern polar winters (Kuroda et al, ). Recently, this model has been used for validating the temperature retrievals from the MGS radio occultations during the southern polar night (Noguchi et al, ), studying modulation of CO 2 clouds by stationary and transient waves (Noguchi et al, ), and exploring the influence of a global dust storm on the electron densities in the D region of the ionosphere (Haider et al, ).…”

Atmospheric CO2 Depletion Near the Surface in the Martian Polar Regions

“…This similarity is expected because CO 2 ‐depleted atmosphere near the surface is buoyant, statically unstable, and should spread upward within the atmospheric column (Hess, 1979; Weiss & Ingersoll, 2000). Indeed, in the South, the overall agreement between the GRS and the MCS enhancement factors suggests that the light depleted air formed at the surface rises and mixes throughout the atmospheric column, including with supersaturated air, or air depleted by the formation of snow (Noguchi et al., 2014, 2017). In addition, even modest eddies in the Southern winter are capable of significant mixing throughout the atmospheric column (Lian et al., 2012), further confirming the expectation of a well‐mixed column.…”