Nocturnal Turbulence at Jezero Crater as Determined From MEDA Measurements and Modeling.

Mars 2020 Mars Environmental Dynamics Analyzer (MEDA) instrument data acquired during half of a Martian year (Ls 13°–180°), and modeling efforts with the Mars Regional Atmospheric Modeling System (MRAMS) and the Mars Climate Database (MCD) enable the study of the seasonal evolution and variability of nocturnal atmospheric turbulence at Jezero crater. Nighttime conditions in Mars's Planetary Boundary Layer are highly stable because of strong radiative cooling that efficiently inhibits convection. However, MEDA nighttime observations of simultaneous rapid fluctuations in horizontal wind speed and air temperatures suggest the development of nighttime turbulence in Jezero crater. Mesoscale modeling with MRAMS also shows a similar pattern and enables us to investigate the origins of this turbulence and the mechanisms at play. As opposed to Gale crater, less evidence of turbulence from breaking mountain wave activity was found in Jezero during the period studied with MRAMS. On the contrary, the model suggests that nighttime turbulence at Jezero crater is explained by increasingly strong wind shear produced by the development of an atmospheric bore‐like disturbance at the nocturnal inversion interface. These atmospheric bores are produced by downslope winds from the west rim undercutting a strong low‐level jet aloft from ∼19:00 to 01:00 LTST and from ∼01:00 LTST to dawn when undercutting weak winds aloft. The enhanced wind shear leads to a reduction in the Richardson number and an onset of mechanical turbulence. Once the critical Richardson Number is reached (Ri ∼ <0.25), shear instabilities can mix warmer air aloft down to the surface. Plain Language Summary: Mars is highly susceptible to atmospheric turbulence, which refers to the chaotic and instantaneous variation in the thermodynamic magnitudes of the atmosphere. While the Martian nighttime conditions near the surface are typically stable due to strong radiative cooling that efficiently inhibits convection, turbulence can still occur due to wind shear. Wind shear is defined as a change in wind speed and/or direction over a relatively short distance in the atmosphere. This phenomenon can mechanically force turbulence as described in this study using both Mars 2020 rover observations at Jezero crater and numerical modeling efforts. Both observations and modeling show turbulence during the first part of the night and around midnight during most of the times of the year with a clear hiatus in turbulence centered prior to summer solstice. We provide evidence that points toward the wind shear turbulence being caused by atmospheric bore waves inside the crater. Key Points: Nocturnal turbulence at Jezero crater peaks at Ls ∼ 37, Ls ∼ 56, and Ls ∼ 123 with a clear hiatus lasting tens of sols centered at Ls ∼ 83Both observations and modeling show turbulence during the first part of the night and around midnightTurbulence is produced by wind shear originating from the passage of an atmospheric bore wave related to downslope winds from the west rim [ABSTRACT FROM AUTHOR]