Keppenne, Christian L. and Ingersoll, Andrew P. (1995) High-Frequency Orographically Forced Variability in a Single-Layer Model of the Martian Atmosphere. Journal of the Atmospheric Sciences, 52 (1). pp. 1949-1959. ISSN 0022-4928 http://resolver.caltech.edu/CaltechAUTHORS:KEPjas95
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A shallow water model with realistic topography and idealized zonal wind forcing is used to investigate orographically forced modes in the Martian atmosphere. Locally, the model produces barotropic modes with periods within the broad range of periods observed at the sites of Viking Lander I and II (VILI and VL2) during the fall and spring seasons. Its variability at those sites is dominated by an oscillation of 3 Martian solar days (sols) in the region of VL1 and by a 6-sol oscillation in that of VL2. These oscillations are forced by the zonal asymmetries of the Martian mountain field. Their robustness with respect to changes of the fundamental model parameters is examined. Since the exhibited periods occur for a barotropic forcing field that is highly idealized, it is difficult to say whether they have much to do with the real Mars, but their resemblance to some of the periodicities present in the observed Martian climatology deserves further investigation. The spatial variability associated with the orographically forced oscillations is studied by means of extended empirical orthogonal function (EEOF) analysis. The 3-sol VL1 oscillation corresponds to a tropical, eastward traveling, zonal wavenumber one pattern. The 6-sol VL2 oscillation is characterized by two midlatitude, eastward traveling, mixed zonal wavenumber one and two and zonal wavenumber three and four patterns, with respective periods near 6.1 and 5.5 sols. The corresponding phase speeds are in agreement with some of the conclusions drawn from the lander observations. A linear stability analysis of the zonally asymmetric climatology reveals that the two most unstable modes are associated with periods near 3 and 6 sols; with the corresponding eigen-vectors showing patterns consistent with the results of the EEOF analyses.
|Additional Information:||© 1995 American Meteorological Society. (Manuscript received August 25, 1993, in final form November 7, 1994) The authors acknowledge conversations with D.J. Banfield, D.H. Boggs, J.O. Dickey, M. Ghil, and S.L. Marcus. They also thank Jim Pollack for providing the Martian GCM topography and three anonymous referees for their constructive criticisms and suggestions. The research described in this publication was carried out in part by the Jet Propulsion Laboratory (JPL), California Institute of Technology (CIT), under a contract with the National Aeronautics and Space Administration, and in part by the Climate Dynamics Center, University of California, Los Angeles. It was funded through the JPL/CIT Director's Discretionary Fund for 1992. The model development and simulations took place on JPL's and the NASA Ames Research Center's CRAY Y-MP computers.|
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