MARS ATMOSPHERE SIMULATIONS WITH THE ROCKE-3D GCM:
SENSITIVITY TO INTERACTIVE H2O SNOW AND RADIATIVELY
ACTIVE DUST CYCLE
I. Aleinov1,2,3, 1Center for Climate Systems Research, Columbia University, New York, NY, USA
(igor.aleinov@columbia.edu), 2NASA Goddard Institute for Space Studies, New York, NY, USA, 3Sellers
Exoplanet Environments Collaboration, NASA Goddard Space Flight Center, Greenbelt, MD, USA, J. P.
Perlwitz2,3,4, 4Climate, Aerosol, and Pollution Research, LLC, Bronx, NY, USA, K. Tsigaridis1,2,3, S. D.
Guzewich3.5, 5NASA Goddard Space Flight Center, Greenbelt, MD, USA , M. J. Way2,3,6, 6Theoretical
Astrophysics, Department of Physics & Astronomy, Uppsala University, Uppsala SE-75120, Sweden, E. T.
Wolf3,7, 7University of Colorado, Boulder, USA.

Introduction:
One of the capabilities of the Resolving Orbital
and Climate Keys of Earth and Extraterrestrial
Environments with Dynamics (ROCKE-3D) [1]
planetary General Circulation Model (GCM) is the
ability to model the atmosphere of modern Mars.
Recent developments include implementation of
separate H2O and CO2 snow packs and of a
radiatively active dust cycle. Here we investigate the
effect of their treatment on a simulated Mars
climatology.
The model:
ROCKE-3D is a three-dimensional GCM
developed at NASA Goddard Institute for Space
Studies (GISS) as a generalization of its parent Earth
GCM, GISS ModelE [2,3] for general planetary
applications.
The atmospheric part of ROCKE-3D uses a
Cartesian grid for all quantities. The horizontal
resolution is 4ox5o with the Arakawa B-type
discretization [4] for the velocity. Vertically, the
model has 40 layers and employs a hybrid
sigma/constant pressure coordinate system [4]. In
our Mars simulations, the upper atmospheric
boundary was set at ~0.7 microbar. The advection of
tracers (including aerosols) is performed by a 9moment algorithm [5], which effectively accounts
for their subgrid variability.
The model includes all elements of a complete
hydrological cycle, with the formation of H2O
clouds, precipitation and ground hydrology.
Currently the model does not include CO2 clouds, so
all CO2 condensation happens only at the surface in
the form of CO2 frost. The ground is represented by
6 layers of soil up to a depth of 3.5 meters. The soil
layers can contain frozen and liquid water, with
liquid water being exchanged between the layers
according to gravitational and capillary forces. The
hydraulic and thermal properties of the soil layers
are defined by their textures. The bottom boundary
of the soil is assumed to be impermeable to heat and
water, although it is possible to specify a geothermal
heating flux. On top of the soil the model can
accumulate snow.

The snowpack consists of three layers of snow
which accumulate due to precipitation and
condensation and lose their mass due to sublimation
and melting. The liquid phase can drain to the lower
layers, where it can refreeze or leave the snowpack
as a melt water. The density of the layers is
computed prognostically according to a gravitational
compaction algorithm [6].
The model simulates the aerosols as radiatively
active tracers. Dust aerosols are represented by a
sectional scheme that partitions the simulated dust
into five transport size classes, covering a total size
range from 0.1 to 32 μm particle diameter. The
model simulates the emission from sources,
advection, and turbulent, gravitational, and wet
deposition of dust. The strength of the dust cycle can
be calibrated with a global factor for the dust
emission.
For the radiative transfer we employ the Suite of
Community Radiative Transfer codes based on
Edwards and Slingo (SOCRATES) [7,8], which
provides us the flexibility to simulate a planet with
virtually any atmospheric composition. In this work
we assume a pure CO2 atmosphere with a trace
amount of water (as computed by the model). The
scattering and absorption of aerosols (such as clouds
and dust) is computed according to Mie theory. The
smallest transport size bin of dust, 0.1 to 2 μm
particle diameter, is additionally partitioned into four
sub sizes for the radiative calculations.
For the boundary conditions at the surface we use
MOLA topography, TES dataset for the ground
albedo and an Earth-like sand texture for the soil.
Experiments:
We investigate the effect of surface snow on
Mars' climate. We considered several configurations
with H2O snow in the polar caps. In particular, we
considered a snow-free case and a case of a 4 m
snow water equivalent H2O snow cap ~1000 km in
diameter located at the North pole. Figure 1 shows
the resulting atmospheric surface pressure in such
experiments at the Viking 2 landing site compared to
observations. The experiment with the H2O snow
cap produces lower pressures which better fits the
observations. This is most likely due to the lower

surface temperature caused by the presence of the
H2O snow.
In our dust experiments we investigate the effect
of the interaction of the dust cycle with the radiation.
In dust cycle models, the emission factor is typically
tuned to the conditions on a particular planet. Since
for non-Earth applications it is poorly constrained,
we performed experiments for a range of plausible
emission factors. Figure 2 shows the aerosol optical
depth (AOD) for simulations with radiatively active
and inactive dust, compared to the observed values
averaged over 11 years [9,10]. In general, within the
limits on tuning parameters, the simulated AOD fits
the observations. Compared to inactive dust, the
radiative effect of dust tends to weaken the dust
cycle when the dust AOD is low (negative
feedback). However, the dust cycle responds
nonlinearly to an increase in dust emission with
radiatively active dust, indicating the emergence of a
positive feedback between dust emission and
radiative effect, when radiative heating by dust is
sufficiently large. Figure 3 shows the effect of
atmospheric dust on the surface air temperature. The
radiatively active dust leads to a 2o-3o K warmer
surface temperature, most likely due to increased
greenhouse effect.

Figure 1. Surface pressure (mb) at Viking 2 landing
site. Black line - simulations without the H2O snow
cap. Blue line - simulations with the H2O snow at the
North pole.
Conclusions:
The Mars version of ROCKE-3D was recently
updated with a more flexible treatment of surface
snow and radiatively active dust. Our experiments
show that inclusion of a permanent deposit of H2O
snow around the North pole improves the seasonal
cycle of surface pressure. Radiatively active dust can
cause both negative and positive feedback on the
dust cycle (as compared to a radiatively passive
dust). The dust cycle simulated by ROCKE-3D is in
qualitative agreement with the observations.

Acknowledgments:
We acknowledge support from the GSFC Sellers
Exoplanet Environments Collaboration (SEEC),
which is funded by the NASA Planetary
ScienceDivision's Internal Scientist
Funding
Model. This research was also supported by NASA
Solar
System Workings program award
80NSSC21K0163. Resources supporting this work
were provided by the NASA High-End Computing
(HEC) Program through the NASA Center for
Climate Simulation (NCCS) at Goddard Space
Flight Center.
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Figure 2. Global mean dust aerosol optical depth as a function of the emission factor: radiatively active dust
(Emis-A) vs inactive dust (Emis-I).

Figure 3. Global mean surface temperature as a function of the emission factor: radiatively active dust (Emis-A)
vs inactive dust (Emis-I).