Geoscience Reference
In-Depth Information
2. Model Description
The Martian GCM used for simulations has been derived from the Cologne
model of the middle atmosphere (COMMA),
6
a terrestrial GCM which
was extensively used for studies of the dynamics and photochemistry of
the middle atmosphere. A detailed description of the Martian model is
given in Hartogh
et al.
5
The model has 32 grid points in the longitude
and 36 grid points in the latitude; 118 vertical levels span the atmosphere
from the deepest point on the Martian surface to approximately 130 km
with a vertical grid step of about 1.14 km. The model employs the realis-
tic topography, surface albedo and thermal inertia. The comprehensive set
of physical parametrizations includes the surface energy balance scheme,
CO
2
and dust radiation codes, gravity wave drag and turbulent diffusion
parameterizations, and the CO
2
condensation/sublimation scheme with
only thermal effects included. Cooling in 15
µ
mCO
2
band is calculated
with the speeded-up version of the exact non-LTE radiative transfer code,
the accelerated lambda iteration for atmospheric radiation and molecu-
lar spectra (ALI-ARMS).
7
,
8
Heating in the CO
2
near-infrared bands is
computed after Forget
et al.
9
The accuracies of these schemes are tested
in Ref. 5.
The absorption, emission and scattering by the atmospheric dust are
calculated for wavelengths between 0.2 and 200
µ
m using the two-stream
discrete-ordinate/adding method.
10
The dust radiation scheme utilizes
19 representative wavelength bands: nine in the visible and 10 in the infrared
spectral range. The corresponding radiative fluxes depend on the dust
parameters, the refractive indices and the particle size distribution. The
refractive indices of the aerosol for the visible wavelengths (shorter than
5
µ
m) are taken from Ref. 11, the montmorillonite 219b data of Toon
et al.
12
are employed for the wavelengths between 5 and 17
µ
m, and constant val-
ues of Forget
13
are utilized for the wavelengths longer than 17
µ
m.
11
-
13
The
dust particle size distribution is borrowed from Ref. 4. The latter uses the
modified gamma function with the effective radius of 1.6
µ
m and the effec-
tive variance of 0.2
µ
m.
4
The dust parameters employed here are essentially
thesameasinCCSR/NIESMartianAGCM.
14
Hence, the further informa-
tion on the dust parameters can be found therein. The spatial dust distribu-
tion in our simulations is prescribed by the functions which depend on the
aerocentric longitude, latitude and pressure (or height). These functions
were introduced to fit the observations by MGS-TES in 2001.
2
,
15
,
16
The
vertical dust distribution is assumed theoretically from the vertical mix-
ing and gravitational settling.
17
This scenario corresponds to the TES3
