Transient Eddy Kinetic Energetics on Mars in Three Reanalysis Datasets

Abstract

Abstract The ability of Martian reanalysis datasets to represent the growth and decay of short-period (1.5 < P < 8 sol) transient eddies is compared across the Mars Analysis Correction Data Assimilation (MACDA), Open access to Mars Assimilated Remote Soundings (OpenMARS), and Ensemble Mars Atmosphere Reanalysis System (EMARS). Short-period eddies are predominantly surface based, have the largest amplitudes in the Northern Hemisphere, and are found, in order of decreasing eddy kinetic energy amplitude, in Utopia, Acidalia, and Arcadia Planitae in the Northern Hemisphere, and south of the Tharsis Plateau and between Argyre and Hellas basins in the Southern Hemisphere. Short-period eddies grow on the upstream (western) sides of basins via baroclinic energy conversion and by extracting energy from the mean flow and long-period (P > 8 sol) eddies when interacting with high relief. Overall, the combined impact of barotropic energy conversion is a net loss of eddy kinetic energy, which rectifies previous conflicting results. When Thermal Emission Spectrometer observations are assimilated (Mars years 24–27), all three reanalyses agree on eddy amplitude and timing, but during the Mars Climate Sounder (MCS) observational era (Mars years 28–33), eddies are less constrained. The EMARS ensemble member has considerably higher eddy generation than the ensemble mean, and bulk eddy amplitudes in the deterministic OpenMARS reanalysis agree with the EMARS ensemble rather than the EMARS member. Thus, analysis of individual eddies during the MCS era should only be performed when eddy amplitudes are large and when there is agreement across reanalyses. Significance Statement Dust storms on Mars are initiated by traveling atmospheric waves, so understanding the relationships between waves and dust is critical to surface spacecraft safety. The growth and decay of waves are compared in three datasets to evaluate whether waves behave consistently across datasets and are represented similarly across different eras of instrumentation. Waves grow by instabilities caused by horizontal and vertical temperature gradients and lose energy to slower-traveling waves at higher altitudes, but agreement across datasets declines using more recent observations because of problems measuring temperatures near the surface. Regardless, combining dust storm observations and descriptions of traveling waves provides a new avenue for explaining dust storm variability on Mars.