Surface Layer Turbulence Scaling Parameters at Jezero Crater, Mars

At Jezero crater, Mars, the MEDA instrument on the Perseverance rover provides meteorological measurements of unprecedented quality and cadence [1-2]. Here, we present an investigation of the atmospheric turbulence in the Martian surface layer (SL), which is the lower portion of the planetary boundary layer [3]. Turbulence parameterization schemes aim to reduce the study of near-surface turbulence to a few variables related to the transport of heat and momentum [4]. We use MEDA temperature and wind data to calculate the scaling parameters for shear-stress at the surface (friction velocity), near-surface buoyancy (temperature scale), and typical SL depths (Obukhov Length). Friction velocities, temperature scales, and Obukhov Length are calculated in 5-minute windows when MEDA data of ground temperature, air temperature, and wind speed are available. We present these values up to sol 313 of the Mars 2020 mission (L_S 22.5-153º).

We estimate these SL scaling parameters by following turbulence parameterization schemes previously used on Mars [5-7], which build on the Monin-Obukhov Similarity Theory (MOST) [8]. MOST assumes flat and homogeneous terrain, and hypothesizes that several atmospheric magnitudes, such as gradients and variances of some atmospheric properties, can be expressed in terms of universal functions that only depend on the atmospheric stability. This procedure is useful for estimating surface layer turbulence parameters, while direct measurements of turbulent fluxes are not yet available for Mars. The latter would require vertical wind data, simultaneous horizontal wind measurements at different heights and a sampling frequency greater than 1 Hz capturing the whole spectral range of turbulence [9]. We run atmospheric simulations centered at Jezero crater [10-11] to further evaluate the order of magnitude of SL turbulence scaling parameters in wider spatial scales.

The friction velocity, important for dust lifting thresholds and aeolian activity, is on the order of 0.6-0.9 m/s. The scale of thermal fluctuations can be as high as 6 K, resulting in shallow surface layers with daily maximum depths of 10-55 m. The deepest surface layers develop over high thermal inertia terrains, which highlights the local nature of the SL and the importance of accounting for horizontal heterogeneity. The order of magnitude of these parameters is in line with values found from atmospheric simulations and previous studies at other locations on Mars. We discuss necessary improvements to the current turbulence parameterizations on Mars. Constraining the SL depth at Jezero is relevant to contextualize different atmospheric studies, quantify surface-atmosphere interactions, and to inform the design and operation of future Martian aerial vehicles.

 

References

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Acknowledgements

We acknowledge the operations and hardware teams from the Mars 2020 project. This project is carried out as part of the NASA Mars exploration program in the US. A.M. is a postdoctoral researcher funded by Programa Posdoctoral de Perfeccionamiento de Personal Doctor del Gobierno Vasco. A.M., R.H., A.S.L. and A.S. are supported by grant PID2023-149055NB-C31 funded by MICIU/AEI/10.13039/501100011033/ and FEDER, UE. GM acknowledges funding from grant PID2024-161247OB-C31 funded by MICIU/AEI/ 10.13039/501100011033 and by ERDF/EU.