QUESTION:
What are the general atmospheric circulation patterns on Mars as compared
with the Earth?  Do fronts occur?  Does the relatively warm equatorial and
cooler polar air cause easterlies and westerlies as on Earth?

ANSWER from Mary Urquhart on August 11, 1997:
The atmospheric circulation patterns on Mars and the Earth are similar in
many ways.  Both Mars and the Earth have a similar tilt of the rotational
axis and rotation rate (with counter-clockwise rotation as viewed from the
north pole).  As a result, the seasonal circulation effects are similar and
the Hadley circulation (the large scale equator to pole motion of warm air
and pole to equator motion of cold air in an atmosphere) is deflected in a
similar manner by each planets' rotation.  Air masses moving away from the
poles are not moving as quickly as equatorial air and lag behind producing
an apparent westward motion, while air moving away from the equator and
toward the poles pulls ahead to the east.  Easterlies and westerlies do
therefore exist on Mars.  The patterns are not identical, however.  For
example, Mars has a single Hadley cell going from the the tropics of the
summer hemisphere to the subtropics of the winter hemisphere compared with
the Earth which has a single cell in each hemisphere that goes from equator
to pole at a given altitude.

The general circulation patterns in the atmosphere of Mars differ from those
of the Earth for several reasons.  The atmosphere of Mars has a short
radiative response time. The thermal inertia (the ability to retain heat) of
the surface is low. Condensation and sublimation of a large fraction of the
total mass of the atmosphere (and the resulting motion of the atmosphere)
occurs on Mars but not on the Earth.  The orbit of Mars is less circular
then the Earth's orbit causing the planet as a whole to receive different
amounts of the Sun's energy as its distance from the Sun changes. Large
scale dust storms occur on Mars.  All of these factors cause the circulation
patterns of the martian atmosphere to vary on daily, monthly, seasonal, and
interannual timescales.  The changes are greater than those observed in the
troposphere of our ocean-buffered Earth.

Mars does have fronts but I've never heard them referred to that way.

For more information on the circulation patterns in the atmosphere of Mars
and how they compare to the Earth, try the following sources:

undergraduate/general public level: "Atmospheres of the Terrestrial Planets"
by Jim Pollack in The New Solar System. edited by Betty and Chaikin, Sky
Publishing Corporation.  The edition I have is 1983, but there is probably a
newer edition.

graduate/research level: "Mars Atmospheric Dynamics" by Zurek et al. in
Mars, edited by Keiffer, Jakosky, Snyder, and Matthews, and published by the
University of Arizona Press in 1992.

Mary Urquhart                                    
Laboratory for Atmospheric and Space Physics  
University of Colorado at Boulder