SENSITIVITY OF ASIAN AND AFRICAN CLIMATE TO VARIATIONS IN SEASONAL INSOLATION, GLACIAL ICE COVER, SEA-SURFACE TEMPERATURE, AND ASIAN OROGRAPHY

The sensitivity of Asian and African climate to prescribed changes in specific high-latitude boundary conditions is examined using the GISS general circulation model (GCM) (8-degrees x 10-degrees). In agreement with previous GCM simulations, summer Asian monsoon winds and rainfall were considerably enhanced by the approximately 8% increase in 11 kyr B.P. insolation; the African monsoon was less responsive to insolation forcing in this model. Increased high-latitude glacial ice cover strengthened winter Asian trade winds and imposed cooler and drier conditions over Arabia and northeastern Africa; summer monsoon winds and associated precipitation were diminished over parts of south Asia. Increased high-latitude ice cover alone had little effect on African climate. Cooler North Atlantic sea surface temperatures (SSTs) enhanced winter trade wind circulation over North Africa, promoted cooler and drier conditions, and reduced the summer monsoon circulation; southern Asian climate was relatively unaffected. Reducing Himalayan and Tibetan elevation to 500 m produced dramatic increases in winter Asian trade wind circulation; the summer monsoon circulation persisted but was weakened considerably. African climate was relatively insensitive to the reduced Asian orography. Many of the model results agree qualitatively with available paleoclimate data. These model results suggest that African and southern Asian climate respond to separate elements of high-latitude climate variability. Specifically, Arabian and northeastern African climate is most sensitive to changes in Fennoscandian ice elevation and albedo, whereas northwestern African climate is most sensitive to changes in the North Atlantic SST field.