Modeling the tropical climate and the impact of the western Pacific sea surface temperature at the Last Glacial Maximum

Changes in tropical atmospheric heat and circulation patterns, as well as the effects of sea surface temperature (SST) of the western Pacific during the Last Glacial Maximum (LGM), have been investigated using a climate model and the LGM SST compiled by Wang [1999]. The annual mean LGM SST was 2degrees-4degreesC lower than the present day in the tropical western Pacific west of 140degreesE. Simulations show that the largest decrease of atmospheric heat occurs in the tropics in a region stretching from the Bay of Bengal to the central Pacific Ocean, while there are no significant changes in atmospheric heat at higher latitudes. This indicates that the atmospheric heat in the tropics shows a stronger response to boundary changes between the LGM and the present day than it does at higher latitudes, since the tropical convection amplifies the response of the atmosphere in the former case. Because of this tropical heat change, the Walker circulation, the transverse monsoon, and the east Asian summer monsoon at the LGM were weaker than they are at present. The model with the Wang [1999] LGM SST simulated large changes in atmospheric circulation in the tropics and high northern latitudes compared to the Climate, Long-Range Investigation, Mapping and Prediction (CLIMAP) [CLIMAP Project Members, 1981] project's reconstruction. The Wang [1999] LGM SST was also associated with a lower surface air temperature (SAT) at high northern latitudes and the Arctic and with a cooler temperature of the coldest month in Europe. The annual mean SAT decreased by 2degreesC in the Arctic, and the winter mean SAT decreased by 4degreesC in Europe.