85th AMS Annual Meeting

Tuesday, 11 January 2005: 9:30 AM
Stationary wave configuration associated with principal modes of variability of the tropical upper tropospheric flow
Ioana M. Dima, JISAO/Univ. of Washington, Seattle, WA; and J. M. Wallace
The observed annual-mean climatology of the tropics is dominated by an equatorially symmetric stationary-wave configuration centered over the Indo-Pacific warm pool. This feature is driven by cumulus convection, which typically penetrates to higher levels over this region than anywhere else in the tropics, owing to the extraordinary warmth of the underlying ocean waters.

We show that the principal modes of variability of the near equatorial upper tropospheric flow, i.e. the annual march, ENSO and the MJO, all involve fluctuations back and forth between two states: a "perturbed state" characterized by heavy rainfall over the marine continent and an associated equatorially symmetric juxtaposition of equatorially trapped Kelvin and Rossby-waves, and a "relaxed state" characterized by relatively light rainfall over this region and relatively uniform geopotential height and weak winds over the entire tropics.

We examine the three-dimensional structure of the perturbed state and make reference to the solution to a steady state flow in a nonlinear shallow water wave equation on an equatorial beta-plane, forced by an idealized near equatorial heat source.

The Indo-Pacific region is also of special interest with respect to troposphere-stratosphere exchanges. The tropical pattern in its perturbed state seems to be playing an important role in this process.

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