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PalatinoMars GCM=20
Climate Catalog Description & Content
PalatinoThe
catalog consists of graphs and tables of GCM output that emphasize the
climate of Mars and how it varies with season. The purpose of the
catalog is to provide PSG members a ready reference tool for use during
the mission itself. The intent is to provide a climate context for the
interpretation of MGS mapping data as they are received. Clearly, since
these simulations are based mostly on Viking data, revision will be
necessary as new data are acquired. This is particularly true of global
surface elevation which is not well known at the present time.
Nevertheless, it should be useful to have some estimate of what we
might expect the Martian climate system to be like.
The simulations the catalog is constructed from use the Smith and Zuber
(1996) long wavelength topography, Consortium Data surface thermal
inertia and albedo, and a new boundary layer scheme as described in
Haberle et al. (1999). Two annual simulations were performed: one with
a dust visible optical depth of 0.3, and one with a dust visible
optical depth of 1.0. The optical depth 0.3 simulation is designated
(our nomenclature) "Run 98.04"; the optical one simulation is
designated "Run 98.27".
In both simulations the dust is horizontally uniform and does not
change with time. However, its concentration does fall off
quasi-exponentially with height as shown in Figure 1. Above 50 km,
dust is virtually absent. This assumed vertical distribution also does
not change with time. Clearly, a dust distribution fixed in time and
space is unrealistic and this will no doubt be a major reason for
discrepancies between the GCM and observations. But again, at this
point we are not trying to make accurate predictions. Instead, we want
to provide a starting point for making comparisons, and gain some
experience in interacting with potential users. At the end of the
mission, we plan to redo these simulations using MOLA topography,
TES/MOC dust & water ice distributions, and an updated version of the
model radiation code with improved dust optical properties based on
Viking, Pathfinder, and MGS observations.
The catalog runs were carried out with a horizontal resolution of 7.5=B0
in latitude, 9.0=B0 in longitude, and with 30 vertical layers. The model
top is at the 0.005 Pa level (~12 scale heights). The mean pressure
and height of the midpoint of each model layer is given in Table 1. The
heights are computed assuming a constant scale height of 10 km and are
therefore approximate. The total amount of CO2 in the atmosphere-cap
system is 788 Pa. The polar cap properties (albedo and emissivity) were
taken from Hourdin et al. (1995) and produce a seasonal variation in
daily mean surface pressure in reasonable agreement with Viking Lander
data.
In constructing the catalog, we divide the Mars year into 12 periods
("seasons") beginning with Ls=3D0 and continuing every 30=B0 of Ls
thereafter. For each of these seasons we compute averages of
temperature, wind, surface pressure, and surface stress. The averages
are either time averages, or time and zonal averages (i.e., averages
around a latitude circle). Standard deviations and variance fields are
also included. Time averages for each period are based on 30 sols of
simulated data centered on each of the Ls subdivisions (0=B0, 30=B0, 60=B0,
=2E... ). This was done so as not to wash out features which change
rapidly with time such as the Hadley cells at the equinoxes. Note,
however, that the time averaging does wash out the diurnal cycle. Table
2 lists the output provided for each season in the order they appear in
the catalog.=20
Each of the figures listed in Table 2 can also be accessed on the
enclosed CD. When opening the CD two folders appear: RUN98_04 and
RUN98_27. These correspond to the optical depth 0.3 and 1.0 runs,
respectively. Within each of these folders are twelve subfolders
labeled "XXX_YYY" where XXX can be 0P3 or 1P0 (optical depth 0.3 or
1.0), and YYY is the three-digit Ls seasonal index (e.g., 090 is
Ls=3D90=B0). Within each of these subfolders are the corresponding gif
(GIF), text (TXT), and postscript (PS) file for each of the figures
listed in Table 2. The GIF and PS files are graphical displays (in
color), while the TXT files are provided for digital access to the
numbers making up the figure. This should be useful for comparing the
catalog results with observations.=20
While it is not our intent here to discuss the results in detail there
are some robust features of the catalog that will be worth looking for
in the observations:
(1) The pronounced seasonal variation in the thermal structure of the
atmosphere and associated wind systems. At both solstices a pronounced
polar vortex develops in the winter hemisphere which is characterized
by a strong poleward decrease of temperature. In the summer hemisphere
temperatures actually increase toward the pole. Indeed, the summer pole
is actually the warmest region of the planet at solstice. The equinoxes
tend to be more hemispherically symmetric, though there are some
notable exceptions: at high latitudes where the polar caps have
different latitudinal extents, and at low latitudes where one Hadley
cell still dominates over the other.
(2) The predominance of easterly winds in the tropics at all times of
year. At the solstices they extend well into the summer hemisphere.
Westerly winds characterize the winter polar regions with "jet streams"
well in excess of 100 m/s.=20
(3) The hemispheric asymmetry in midlatitude weather systems. The model
predicts vigorous weather systems in midlatitudes of the northern
hemisphere from late-fall to early spring, but only weak systems by
comparison in the southern hemisphere during the same seasons. (See
surface pressure RMS time deviation maps). In the model, topography is
suppressing the southern systems.
(4) The highest surface stresses on the planet occur in the
midlatitudes of the northern hemisphere during fall and winter. The
region north of Tharsis is particularly breezy. In the southern
hemisphere, the highest surface stresses occur along the western rim of
the Hellas basin during southern fall and winter.
( 5) An upper atmosphere tropical "dipole" in the 2pm-2am temperature
differences. This feature, presumably due to thermal tides, is present
at all seasons and is flanked by weaker dipoles of opposite polarity
during the equinoxes.
REFERENCES:
Haberle, R.M., M.M. Joshi, J.R. Murphy, J.R. Barnes, J.T. Schofield, G.
Wilson, M. Lopez-Valverde, J. L. Hollingsworth, A.F.C. Bridger, and J.
Schaeffer. (1999). General Circulation Model Simulations of the Mars
Pathfinder Atmospheric Structure Investigation/Meteorology
Data, J. Geophys. Res., In press.
Hourdin, F., F. Forget, and O. Talagrand. (1995). The Sensitivity of
the Martian Surface Pressure and Atmospheric Mass Budget to Various
Parameters: A Comparison Between Numerical Simulations and Viking
Observations, J. Geophys. Res., 100,
5501-5524.
Smith, D.E., and M.T. Zuber. (1996). The Shape of Mars and the
Topographic Signature of the Hemispheric Dichotomy,
Science, 271, 184-188.
=20
=46igure 1. The variation of the dust mixing ratio (normalized to the
surface value) as a function of scale height.
=20
Table 1: Mean pressures and heights of the midpoints of
MGCM
layers.Times
PalatinoLayer
Pressure, Pa Height
Palatino1 .007 115
km
2 .011 110 km
3 .019 105 km
4 .034 99 km
5 .060 93 km This region not shown in Figures
6 .101 88 km
7 .177 82 km
8 .305 77 km
9 .522 71 km
10 .895 66
kmTimes
Palatino11 1.54 61 km
12 2.65 55 km
13 4.57 50 km
14 7.67 45 km
15 12.7 40 km =09
16 20.9 35 km
17 34.4 30 km=09
18 56.7 25 km
19 93.4 20 km
20 154 15 km This region shown in Figures
21 242 10 km =09
22 344 6.5 km
23 440 4.0 km
24 524 2.3 km
25 588 1.1 km
26 626 490 m
27 644 192 m
28 652 81 m
29 655 26 m
30 657 5 m=09
=20
Table 2: CD file name (bold) and description of
its contents.Times
Palatino1.
GLOBALS.TXT - Miscellaneous tabulated global &
hemispheric quantities.
2. PS_XY.* - Time mean surface pressure (top) and surface
pressure variance (bottom).
3. T2AM_YZ.* - Time and zonally averaged 2AM temperature
(top), and 2AM temperature standard deviation (bottom).
4. T2PM_YZ.* - Time and zonally averaged 2PM temperature
(top), and 2PM temperature standard deviation (bottom).
5. TDIFF_YZ.* - Time and zonally averaged temperature
(top) and 2PM-2AM temperature difference (bottom).
6. TGEXT_XY.* - Mean minimum ground temperature (top) and
mean maximum ground temperature (bottom).
7. TGLOC_XY.* - Mean 2AM ground temperature (top) and mean
2PM ground temperature
(bottom).Times
Times
Palatino8. TUVAV_XY.* -
Time mean temperature and horizontal wind at 3 mb (top) and at
0.5 mb (bottom).
9. UVLOC_XY.* - Mean 2AM surface wind (top) and 2PM
surface wind (bottom).
10. UVSAV_XY.* - Time mean surface wind (top) and surface
stress magnitude (bottom).
11. UV_YZ.* - Time and zonally averaged zonal (top) and
meridional (bottom) wind.
12. WMS_YZ.* - Time and zonally averaged vertical wind
(top) and mass stream function (bottom).
=20
Notes on the latitude vs height (*_YZ.*) plots:
(1) There is a black filled region near the surface and above it is a
thick black dashed line. The filled region represents the
zonally-averaged topography. The thick dashed line represents that
altitude at which we begin to loose longitude grid points in
constructing zonal (east-west) means because of topography.=20
(2) The zero altitude level is defined to be the 610 Pa level (6.1 mb).
Thus, the topography moves up and down in these plots with season due
to the CO2 cycle.
(3) Only that part of the atmosphere below the 1 Pa level is shown.
This is the region emphasized by TES and RS, and it is also the region
where the MGCM is probably more credible.
=20
********************************************
Robert M. Haberle
Space Science Division, MS 245-3
NASA/Ames Research Center
Moffett Field CA 94035-1000
Phone: 650-604-5491
=46AX: 650-604-6779
E-mail: bhaberle@mail.arc.nasa.gov
haberle@humbabe.arc.nasa.gov
********************************************