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Annual cycle and spatial structure of zonal momentum fluxes in the deep tropics
  • Abu Bakar Siddiqui Thakur,
  • Jai Sukhatme
Abu Bakar Siddiqui Thakur
Indian Institute of Science

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Jai Sukhatme
Indian Institute of Science, Bangalore
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The longitudinal structure and annual cycle of mean meridional and eddy momentum fluxes in the upper troposphere of the deep tropics are studied using ERA-Interim reanalysis over a 40 year period. In a zonal mean sense, these two terms oppose each other and peak during the Indian summer monsoon. This zonal mean character arises from a rich longitudinal structure revealed by splitting the globe into three zones, namely, the Asia-West Pacific, central Pacific-West Atlantic, and African sectors. The mean meridional convergence term is cohesive across these three regions; it has a single peak in the boreal summer and always acts to decelerate the zonal flow. On the other hand, eddy fluxes are much more varied and go from being small and seasonally invariant in the African sector to having large seasonal peaks of acceleration (deceleration) in the Asia-West Pacific (central Pacific-West Atlantic) sector. This longitudinal variation in eddy momentum fluxes presents interesting insights into the overturning circulation in these zonally limited sectors, which previously remained hidden in the zonal mean.