A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

The influence of land surface winds show how fluxes on the onset of Amazon rainyseason and the influence of South American rainfall on the winter climate overNorth Atlantic, Europe and eastern North AmericaRong FuEarth & Atmospheric Sciences, Georgia Institute of Technology221 Bobby Dodd Way, Atlanta, GA 30332-0340Tel: 404-385-0670; Fax: 404-385-1512; Email: fu@eas.gatech.eduAbstract:Our analysis of satellite observations and reanalyses products has suggested thatthe transition from dry to wet season over Amazon is initiated by an increase of landsurface fluxes, whereas the dynamic responses to the increase of the surface flux, such asan increasing moisture transport, accelerate the transition. A delayed onset could eitherby caused by abnormally preseasonal dryness, or by a slower increase of the surfacefluxes, in addition to a weaker large-scale moisture transport.We have also observed that during boreal winter, decreases of South Americanrainfall are correlated with enhanced anticyclonic surface winds over the mid-latitudeNorth Atlantic and cyclonic flow over the Northeastern North Atlantic a few days later.The latter also increases cyclonic weather activity over Western and Northern Europe andeastern United States, and decreases precipitation over the Mediterranean region.Comparison with simulations by a time-dependent barotropic model suggests that theprevailing weak westerly winds in the upper tropospheric tropical Atlantic during borealwinter allow latitudinal propagation of a Rossby wave disturbance that leads to theobserved remote influence of South American rainfall on winds over the North Atlantic.1