Towards a general theory of global monsoons (Invited Presentation)

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Tuesday, 4 February 2014: 5:00 PM
Room C106 (The Georgia World Congress Center )
Peter J. Webster, Georgia Institute of Technology, Atlanta, GA

About half of the global population lives under the influence of the Asian monsoon. The Asian monsoon is part of a global family of monsoons that circle the globe some with ascent over the oceans and others associated with Africa, the Americas, Asia and Australia. Each system has its own regional character. Understanding the physical nature of these difference may lead to understanding transients and improved prediction. Here we address the following questions: (1) What drives the oceanic monsoon systems? Maximum precipitation lies in the on the summer hemisphere but equatorward of the warmest sea-surface temperature and lowest surface pressure. (2) What determines the location of maximum precipitation in the African and Australian monsoons located quite close to the coastal margins? Both precipitation maxima lie well equatorward of minimum surface pressure that a collocated with the great deserts of North Africa and Central Australia (3) The great deserts of Africa and Australia are located at the same latitudes as the precipitation maximum of the South Asian monsoon. What physical processes produce this anomalously poleward location of the Asian monsoon? It is argued that there is a common physical basis underlying each of these questions, whereby horizontal pressure gradients associated with SST differences and thermal forcing from elevated terrain results in a simple perpetual instability. These ideas allow an assessment of the predictability of monsoon variability on time scales ranging from intraseasonal to interdecadal and an assessment of projections in a changing climate