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Published July 2003 | Published
Journal Article Open

Principal modes of variability of Martian atmospheric surface pressure


An analysis of daily-to-interannual variability in the surface pressure field of the Martian northern hemisphere as given by a Martian climate model is presented. In an empirical orthogonal function (EOF) decomposition, the dominant first two modes of variability comprise a zonal wavenumber 1 feature centered at 70 N latitude moving eastward with a period of 6 to 8 sols. This feature is a baroclinic wave and accounts for 53% of the northern hemisphere non-stationary surface pressure variability, and, when active, has an amplitude of up to 2% of local surface pressure. The third mode of the EOF decomposition is annular about the Martian north pole, is null southward of 70 N, and accounts for 7% of the northern hemisphere non-stationary surface pressure variability. The baroclinic wave (EOFs 1 & 2) is active during northern hemisphere winter and spring, consistent with models of the Martian atmospheric circulation, and the annular mode (EOF 3) is active only at the onset and demise of the baroclinic feature. When active, it is not uncommon for the annular mode to reside in either its positive or negative state stably for 20 to 30 sols. It is postulated that baroclinic waves with longitudinal wavenumber 2, 3, and 4 act as a pump for the annular mode. The annular mode should not be present in MGS TES data.

Additional Information

© 2003 American Geophysical Union. Received 18 July 2002; revised 30 December 2002; accepted 7 January 2003; published 11 July 2003. S. S. Leroy was supported by a grant from the program Living with a Star of NASA's Office of Space Science. Y. L. Yung was supported by NASA's Mars Data Analysis Program. The work benefitted from discussions with C. David Camp. It was done in part at the Jet Propulsion Laboratory of the California Institute of Technology.

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