The Climatology of Mars Thermospheric Polar Warming at Aphelion

Thermospheric polar warming (TPW) is observed conclusively for the first time at Mars during the aphelion/Northern Summer season using solar occultation (SO) measurements made by the Extreme Ultraviolet Monitor (EUVM) onboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) orbiter. Aphelion data from Mars Year (MY) 33-36 are analyzed revealing TPW to be present at dawn but not dusk. This is consistent with an earlier analysis of accelerometer data from the Mars Global Surveyor that showed aphelion TPW is also not evident at 15 hr local time. Separating the data into individual MYs reveals TPW is observed during each year except MY 35. TPW is markedly intensified during MY 34, which is attributed to enhanced circulation caused by a northern-hemisphere dust storm coinciding with the observations. Simulations from the Mars Climate Database predict the large TPW enhancement in MY 34 relative to MY 33 observed by EUVM SO, but predicts approximately 20K less overall TPW for both years than that observed by EUVM SO. Warming in the winter upper atmosphere has been observed for the first time in the Southern hemisphere at Mars during aphelion, when Mars is furthest from the Sun, using the Extreme Ultraviolet Monitor onboard the Mars Atmosphere and Volatile EvolutioN orbiter. These observations show the warming trend is typically found at dawn but is not observed at dusk. This warming is believed to be caused by large-scale atmospheric circulation that transports air from the warmer summer hemisphere toward the winter pole. These observations show that the winter upper atmospheric warming is most pronounced when a dust storm is active in the summer hemisphere, which can be explained by the dust storm strengthening the circulation pattern responsible for the warming. These measurements are compared to simulations from an atmospheric model (called the Mars Climate Database) that show reasonably good agreement. Thermospheric polar warming is observed at Mars during aphelion at dawn A significant enhancement of thermospheric polar warming coincides with a dust storm in the summer hemisphere (MY 34) Thermospheric polar warming is evident at dawn local times in two independent solar occultation data sets from two spacecraft, Mars Atmosphere and Volatile EvolutioN and Trace Gas Orbiter