J6.2
Low Latitude Zonally Symmetric Circulations in the NCEP Reanalyses
Ioana M. Dima, JISAO/Univ. of Washington, Seattle, WA; and J. M. Wallace
The interplay between eddy fluxes and the mean meridional circulations (MMCs) gives rise to significant seasonal and non-seasonal variability in the low latitude zonally symmetric flow, much of which is equatorially symmetric as well as zonally symmetric. In contrast to the situation in the stratosphere, the eddy fluxes are primarily meridional and they are dominated by the stationary waves. For both seasonal and non-seasonal variations, the upper troposphere transport of momentum by the MMC and the eddies is concentrated in the same region and has opposing signs. In the annual mean, the convergence of the eddy flux over the equator is balanced by the advection of easterly momentum by the cross - equatorial flow from the summer hemisphere into the winter hemisphere. Perturbations in the climatological - mean balance give rise to zonal wind anomalies at upper tropospheric levels. These anomalies originate over the equator, widen, and break into poleward propagating bands in the two hemispheres, with a characteristic time scale of weeks. These variations project strongly on the Madden - Julian Oscillation and on the northern and southern hemisphere annular modes. .
Joint Session 6, Observed Climate Variability (JOINT with THE 15TH SYMPOSIUM ON GLOBAL CHANGE AND CLIMATE VARIATIONS AND THE 14TH CONFERENCE ON APPLIED CLIMATOLOGY (Room 609/610)
Thursday, 15 January 2004, 3:30 PM-5:30 PM, Room 609/610
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