Characterization of middle‐atmosphere polar warming at Mars

Abstract

[1] We characterize middle-atmosphere polar warming (PW) using nearly three Martian years of temperature observations by the Mars Climate Sounder. We report the observed structure of PW and share hypotheses as to possible explanations, which have yet to be tested with global dynamical models. In the data, PW manifested between p = 15 Pa and p = 4.8Â10 -3 Pa. The latitude where PW maximized shifted poleward with decreasing pressure. The nightside magnitude was larger than the dayside magnitude. The maximum nightside magnitudes ranged from 22 to 67 K. As expected, the annual maximum magnitude in the north occurred during late-local fall to middle-local winter. In the south it occurred during late-local winter. Also as expected, the maximum magnitude near MY 28's southern winter solstice was smaller than that at that same year's northern winter solstice, when a global dust storm was occurring. Unexpectedly, the maximum magnitude at southern winter solstice was comparable to that at northern winter solstice for both MY 29 and MY 30, years that did not experience global dust storms but certainly experienced greater dust loading during L s = 270 than L s = 90 . Another unexpected result was a hemispheric asymmetry in PW magnitude during most of the observed equinoxes. This paper also provides tables of (1) averaged temperatures as a function of latitude, pressure, and season, and (2) the maximum polar warming features as a function of pressure and season. These tables can be used to validate GCM calculations of middle-atmosphere temperatures and constrain calculations of unobserved winds.

General circulation modeling of the Martian upper atmosphere during global dust storms

“…The difference between the first and second runs is shown in the same figure with color shades, accounting for subgrid‐scale GWs results in spectacular changes. Below the mesopause, GWs enhance the polar temperatures, in particular, around winter seasons (known as the “winter polar warmings”) by up to 15 K. These results are in a good agreement with the recently published characteristics of the middle‐atmosphere polar warmings based on the MCS‐MRO measurements [ McDunn et al , ]. Above the mesopause, GWs induce coolings by up to 45 K. We have already presented similar results from our simulations for the perpetual solstice at L s =270° [ Medvedev and Yiğit , , Figure 1c].…”

Mars Global Ionosphere‐Thermosphere Model: Solar cycle, seasonal, and diurnal variations of the Mars upper atmosphere

“…Such numerical schemes could provide enhanced meridional flows in response to retarded zonal winds in the middle atmosphere. Subsequently, a more realistic lower atmosphere temperature structure may result, consistent with observed polar warming features during MY30 [ McCleese , ; McDunn et al , ].…”

“…However, climatological constraints for this atmospheric region are needed to validate the M‐GITM simulated temperature structure. The MRO Mars Climate Sounder (MCS) instrument has been operating nearly continuously since September 2006, spanning more than four Martian years (MY = 28–31) [e.g., McCleese , ; Kleinböhl et al , ; McDunn et al , ]. Hence, MCS retrieved (version 4.0) temperatures (∼0–90 km) are utilized (as a function of season, latitude, and local time) to provide constraints for validating the basic features of the M‐GITM temperature structure below ∼80–90 km.…”

Martian polar vortices: Comparison of reanalyses

“…The winter “polar jet” tilts toward the pole with height, with maximum winds at each level occurring around 50°N at 5 hPa but occurring poleward of 70°N above 0.01 hPa. In the upper atmosphere (pressure around 0.01 hPa) there is a reversal of the meridional temperature gradient with higher temperatures occurring at the north pole, corresponding to the so‐called “polar warming” [e.g., McDunn et al ., ].…”