A Frontal Dust Storm in the Northern Hemisphere at Solar Longitude 97-An Unusual Observation by the Emirates Mars Mission

The Emirates Mars Mission (EMM) science phase began in Martian Year 36, solar longitude 49, which is outside of the classical Mars dust storm season. EMM observed a distinct dust cloud at northern mid-to-high latitudes on 10 September 2021 (Martian Year 36, solar longitude 97). The dust cloud is an arc-shaped dust storm, typically observed at the northern polar cap edge. This type of non-season dust storm is a well-known phenomenon, but this particular case is interesting because the dust cloud has frontal structure. A large atmospheric front is unusual in this location and season. Moreover, EMM's unique observational coverage adds value to this observation. EMM provided a sequence of four camera images, which are separated by just 2-3 hr. The dust cloud showed very little motion over 7-8 hr, that is, it is quasi-stationary. We discuss relevant dynamical processes, supported by a consistency check with the Mars Climate Database.