Zonal mean wind, the Indian monsoon, and July drying in the western Atlantic subtropics

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Abstract

[1] A fully closed zonal momentum budget is decomposed to explain the occurrence of zonal mean easterlies at subtropical latitudes in July. Eddy momentum fluxes from stationary eddies, most prominently the western sector of the Indian monsoon Tibetan High, are the primary mechanism governing the negative tendency of zonal mean momentum near 20°N–30°N. This strengthening of the zonal mean easterlies in July is significantly correlated with the concurrent strengthening of the North Atlantic Subtropical High (NASH) and the rainfall deficit in the western North Atlantic (WATL). Interannual variations of the Indian monsoon reflect changes in the strength of these zonal mean easterlies, with downstream teleconnections on the westward displacement of the NASH and precipitation in the WATL. An increase in rainfall in India from June to July corresponds to a decrease in rainfall in the WATL.

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