DPS 2001 meeting, November 2001
Session 27. Mars Atmosphere I: Circulation
Oral, Chairs: J. Hollingsworth, A. Toigo, Thursday, November 29, 2001, 10:30am-12:30pm, Regency E

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[27.01] Hemispheric Asymmetry in Mars' Mean Meridional Circulation

J.L. Hollingsworth (NASA Ames/SJSU Foundation), R.M. Haberle (NASA Ames), J. Schaeffer (Raytheon STX Corp)

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 \tau = 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, \Lambda0, advanced by 180\circ, 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 10-20\circ equatorward from corresponding fields in the absence of orography.


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The author(s) of this abstract have provided an email address for comments about the abstract: jeffh@humbabe.arc.nasa.gov

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