Low-level jets and the convergence of Mars data assimilation algorithms

TL;DR

This study compares two Mars data assimilation algorithms using different models, revealing how they influence atmospheric features like low-level jets and temperature fields, and assessing their biases and robustness.

Contribution

It provides a comparative analysis of two Mars data assimilation systems, highlighting their effects on atmospheric jet behavior and model biases, which was previously underexplored.

Findings

Low-level jets shift equatorward and weaken in MACDA reanalysis.

EMARS shows less jet shifting and is less biased than MACDA.

Temperature and wind fields are more consistent across reanalyses than control simulations.

Abstract

Data assimilation is an increasingly popular technique in Mars atmospheric science, but its effect on the mean states of the underlying atmosphere models has not been thoroughly examined. The robustness of results to the choice of model and assimilation algorithm also warrants further study. We investigate these issues using two Mars general circulation models (MGCMs), with particular emphasis on zonal wind and temperature fields. When temperature retrievals from the Mars Global Surveyor Thermal Emission Spectrometer (TES) are assimilated into the U.K.-Laboratoire de M\'et\'eorologie Dynamique (UK-LMD) MGCM to create the Mars Analysis Correction Data Assimilation (MACDA) reanalysis, low-level zonal jets in the winter northern hemisphere shift equatorward and weaken relative to a free-running control simulation from the same MGCM. The Ensemble Mars Atmosphere Reanalysis System (EMARS) reanalysis, which is also based on TES temperature retrievals, also shows jet weakening (but less if any shifting) relative to a control simulation performed with the underlying Geophysical Fluid Dynamics Laboratory (GFDL) MGCM. Examining higher levels of the atmosphere, monthly mean three-dimensional temperature and zonal wind fields are in generally better agreement between the two reanalyses than between the two control simulations. In conjunction with information about the MGCMs' physical parametrizations, intercomparisons between the various reanalyses and control simulations suggest that overall the EMARS control run is plausibly less biased (relative to the true state of the Martian atmosphere) than the MACDA control run. Implications for future observational studies are discussed.