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GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L17810, doi:10.1029/2006GL026672, 2006

Geographic variability in the export of moist static energy and vertical motion profiles in the tropical Pacific

L. E. Back

Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA


C. S. Bretherton

Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA


Abstract

Column-integrated moist static energy (MSE) budgets were calculated using daily data from three reanalyses (1998–2001) and ISCCP radiative cooling. The MSE export by the circulation was separated into vertical and horizontal MSE advection components in order to examine how observationally-derived vertical motion profiles affect gross moist stability calculations. In a 2000 km-wide region in the central-eastern Pacific ITCZ, vertical motions import MSE, implying a negative gross moist stability. Horizontal MSE advection is negative and of similar magnitude to vertical MSE advection in rainy regions. Geographic differences in export of MSE by the vertical circulation are primarily due to differences in the shape of the vertical motion profile. In the west Pacific warm pool rainy regions, mean horizontal convergence extends up to 300 mb, while in parts of the Pacific ITCZ where meridional SST gradients are strong, the vertical motion profile is bottom-heavy, with convergence below 800 mb and divergence above. On daily timescales, the mode of vertical motion variability has little dependence on precipitation rate and is consistent with observed regional differences in the vertical structure of TRMM PR reflectivities.

Received 22 April 2006; accepted 31 July 2006; published 9 September 2006.

Index Terms: 3399 Atmospheric Processes: General or miscellaneous; 3374 Atmospheric Processes: Tropical meteorology; 3367 Atmospheric Processes: Theoretical modeling.

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Citation: Back, L. E., and C. S. Bretherton (2006), Geographic variability in the export of moist static energy and vertical motion profiles in the tropical Pacific, Geophys. Res. Lett., 33, L17810, doi:10.1029/2006GL026672.