First Assimilation of Atmospheric Temperatures from the Emirates Mars Infrared Spectrometer

With its 20,000 x 43,000 km altitude orbit, the Emirates Mars Mission (EMM) is unprecedented among Mars orbiters as it observes Mars' full range of local times, latitudes, and longitudes over a 10-sol period, and makes fully-hemispherical observations of the planet. EMM entered orbit around Mars on 9 February 2021 and its science phase began on 23 May 2021. As it can observe extended weather systems in one snapshot, EMM observations are uniquely suited for analysis using data assimilation. This technique combines observations with a numerical forecast model such that the resulting analysis is consistent with the uncertainties in both. This fills in unobserved regions and retrieves unobserved quantities using the internal consistency of the forecast model. We present the first assimilation of atmospheric temperatures from the Emirates Mars Infrared Spectrometer (EMIRS) instrument. These observations are assimilated into the LMD Mars Global Climate Model, using the Local Ensemble Transform Kalman Filter method. EMIRS measures thermal infrared spectra across the entire Martian disk 20 times in each 55-hour orbit, from which atmospheric temperatures between 10-50 km altitude with a typical vertical resolution of about 10 km are retrieved (alongside other quantities which we will not address at this time). We focus on observations from the early part of the science phase and on how EMM's unique observation platform captures hitherto unobserved phenomena such as coherent weather systems and the complete diurnal cycle. We will also describe the method used to compare the forecast model with observations, as well as any challenges associated with assimilating observations from a platform whose sub-spacecraft point moves slowly across the planet compared with spacecraft that have been used for Mars data assimilation before.