GEM-Mars database for interpolated atmopsheres
J. Erwin (justin.erwin@aeronomie.be), F. Daerden, L. Neary, L. Trompet, A. C. Vandaele, S. Viscardy,
Royal Belgian Institute for Space Aeronomy, Brussels, Belgium.

Introduction:
We present a summary of the GEM-Mars database and tools developed for interpolating vertical
profiles to any local geometry. We also introduce a
publicly data service on VESPA for easy access.
GEM-Mars:
GEM-Mars is a General Circulation Model for
the atmosphere of Mars with online atmospheric
chemistry. The model is operated on a grid with a
horizontal resolution of 4°x4° and with 103 vertical
levels reaching from the surface to ~150 km. It calculates atmospheric heating and cooling rates by
solar and IR radiation through atmospheric CO and
dust and ice particles and solves the primitive equations of atmospheric dynamics. Geophysical boundary conditions are taken from observations. Physical
parameterizations in the model include an interactive
condensation/surface pressure cycle, a fully interactive water cycle including cloud radiative feedbacks,
a thermal soil model including subsurface ice, interactive dust lifting schemes for saltation and dust devils, turbulent transport in the atmospheric surface
layer and convective transport inside the planetary
boundary layer (PBL), subgrid scale vertical mixing
in the free troposphere, a low level blocking scheme,
gravity wave drag, molecular diffusion, noncondensable gas enrichment, and atmospheric chemistry. A detailed description of the model, its formulation, grid, dynamical core and physical parameterizations, together with extensive validation against
multiple datasets, was given in [1], and further details can be found in [2, 3, 4].
Database and interpolation:
A database is available for Mars year 34 and 35,
and is occasionally updated as improvements are
made in the GEM-Mars model. Each year of the database is comprised of 48 time steps per day, 36 days
per year (every 10° Ls). Each year is approximately
50GB, and is captures well the annual and diurnal
cycles.
A bi-linear spherical interpolation is performed to
interpolate the Latitude and Longitude GCM grid
points to the particular value. Then, 4 surrounding
timesteps in solar longitude (Ls) and local solar time
(LST) are used to make a bi-linear interpolation to
the desired values.
The interpolation from GEM produces a linear
variation in surface height between GEM-Mars grid
points. The MOLA data set [5] is used to get an im-

proved value for the surface height. A pressure scaling similar to the one discussed with in the MCD
User’s Guide [6] is made to adapt the interpolated
atmosphere to the high-resolution topography.
The interpolated atmospheric profiles from
GEM-Mars have been used as inputs for retrievals
for many within the NOMAD team. Please contact F
Daeden or L. Neary if you’re interested in using or
comparing to GEM-Mars. Refer to our website
(https://gem-mars.aeronomie.be) for up to date information.
VESPA interface:
A public data service is set up with DaCHS software [7] and is accessible through the VESPA portal
(http://vespa.obspm.fr/) [8] and other TAP interfaces
including, e.g., Jupyter notebooks. Coverages are
provided by the EPN-TAP parameters which allow
searches on specific conditions (Ls, local time, location, etc). The “granule uid” parameter is of the form
“GEM-Mars_myearA_latB_lonC_lsD_lstE” where A
is the Martian year (34 or 35), B is the latitude (degree), C is the longitude (degree), D is the solar longitude (degree) and E is the local solar time (0-24).
The data can be provided for any combination of
those coordinates and time. The “access_url” launches a python WSGI API that reads the user-supplied
geometry (Mars Year, solar longitude, latitude, longitude, and local solar time) in the URL, processes
the interpolation among the GEM-Mars data and
returns a VOTABLE (XML document). Fields included in the VOTABLE are profiles of temperature,
pressure, air density, mixing ratios of CO2, H2O
(vapor and ice) and O3. Surface values of temperature, CO2, and H2O ice are also given with the local
time and solar zenith angle. An example of “access_url” is:
https://gem-mars.aeronomie.be/vespagem?myear=34&lat=-88&lon=328&ls=0&lst=2
and follows the same nomenclature as the “granule_uid” described previously. The VOTABLE is
generated “on the fly” at user request and can be read
with VO tools like TOPCAT [9].

References:
[1] Neary, L., and F. Daerden (2018), The GEMMars General Circulation Model for Mars: Description and Evaluation, Icarus, 300, 458-476,
https://doi.org/10.1016/j.icarus.2017.09.028
[2] Daerden, F., J. A. Whiteway, L. Neary, L.
Komguem, M. T. Lemmon, N. G. Heavens, B. A.

Cantor, E. Hébrard, and M. D. Smith (2015), A solar
escalator on Mars: Self-lifting of dust layers by
radiative heating. Geophys. Res. Lett., 42,
73197326.doi:10.1002/2015GL064892
[3] Smith, M., F. Daerden, L. Neary and S.
Khayat (2018), The climatology of carbon monoxide
and water vapor on Mars as observed by CRISM and
modeled by the GEM-Mars general circulation model,
Icarus,
301,
117-131,
https://doi.org/10.1016/j.icarus.2017.09.027
[4] Daeden, F., et al. (2022), Explaining
NOMAD D/H Observations by Cloud-Induced Fractionation of Water Vapors on Mars, JGR Planets,
https://doi.org/10.1029/2021JE007079.

[5] Smith, D. E., et al. (1999). The Global Topography of Mars and Implications for Surface Evolution,
Science,
284
(5419),
1495–503,
doi:10.1126/science.284.5419.1495.
[6] Millour, E., Forget, F., Lewis, S. R. (2015),
Mars Climate Database v5.2 User Manual,
http://wwwmars.lmd.jussieu.fr/mars/info_web/user_manual_5.2.
pdf.
[7] Demleitner, M. et al. Astronomy and
Computing, 7-8, 27-36, 2014,
[8] Erard, S. et al., Planetary and Space Science,
150, 65-85, 2018,
[9] Taylor M., Astronomical Society of the
Pacific Conference Series, 347, 2005.