Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001dps....33.2701h&link_type=abstract
American Astronomical Society, DPS Meeting #33, #27.01; Bulletin of the American Astronomical Society, Vol. 33, p.1087
Astronomy and Astrophysics
Astronomy
Scientific paper
For Mars' annual and solstitial mean climate, an assessment of the principal modes of transfer of global atmospheric angular momentum is performed using the NASA Ames Research Center Mars global circulation model (MGCM). In the climate simulations, the assumed dust loading is moderate, corresponding to a globally-averaged visible optical depth of τ = 0.3. The dominant modes of transfer are surface pressure (i.e., mountain) and frictional (i.e., stress) torques. For both a present orbital configuration and one with the longitude of perihelion, Λ 0, advanced by 180o, the mean longitudinally averaged (or zonally symmetric) overturning circulations in the annual and solstitial mean are fundamentally different in the northern and southern hemispheres. This difference arises from asymmetries between the two torque components in each hemisphere wherein zonally asymmetric orography provides during northern mean winter conditions a primary positive (eastward) surface pressure torque in the northern subtropics and a secondary negative (westward) pressure torque in the southern subtropics. Frictional torques are predominantly negative (westward) in the southern summer subtropics and northern winter midlatitudes associated with near-surface westerly winds, and positive (eastward) in the winter subtropics associated with near-surface easterly winds. In the annual mean, the vertically integrated relative angular momentum shows an asymmetry between the two hemispheres, with northern winter angular momentum exceeding southern winter angular momentum on the order of 20--30 percent. Furthermore, the surface pressure torque in the northern hemisphere significantly suppresses the intensity and extent of the mean solstitial Hadley circulation, resulting in near gradient-balanced zonal wind and temperature fields that are shifted 10-20o equatorward from corresponding fields in the absence of orography.
Haberle Robert M.
Hollingsworth Jeffery L.
Schaeffer Jack
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