Assimilation of both column- and layer-integrated dust opacity
observations in the Martian atmosphere
Abstract
A new dust data assimilation scheme has been developed for the UK
version of the Laboratoire de Météorologie Dynamique (LMD) Martian
General Circulation Model. The Analysis Correction scheme (adapted from
the UK Met Office) is applied with active dust lifting and transport to
analyze measurements of temperature, and both column-integrated dust
optical depth (CIDO), τref, (rescaled to a reference
level) and layer-integrated dust opacity (LIDO). The results are shown
to converge to the assimilated observations, but assimilating either of
the dust observation types separately does not produce the best
analysis. The most effective dust assimilation is found to require both
CIDO and LIDO observations, especially for Mars Climate Sounder (MCS)
data that does not access levels close to the surface. The resulting
full reanalysis improves the agreement with both in-sample assimilated
CIDO and LIDO data and independent observations from outside the
assimilated dataset. It is thus able to capture previously elusive
details of the dust vertical distribution, including elevated detached
dust layers that have not been captured in previous reanalyses.
Verification of this reanalysis has been carried out under both clear
and dusty atmospheric conditions during Mars Years 28 and 29, using both
in-sample and out of sample observations from orbital remote sensing and
contemporaneous surface measurements of dust opacity from the Spirit and
Opportunity landers. The reanalysis was also compared with a recent
version of the Mars Climate Database (MCD v5), demonstrating generally
good agreement though with some systematic differences in both time mean
fields and day-to-day variability.