UCLA

A highly debated research topic has been understanding the magnitude of tropical cooling in the western Pacic warm pool (WPWP) from the Last Glacial Maximum (LGM) to present-day. Paleoclimate data indicates a range of LGM cooling from 1-5°C. Using a radiative-convective model with an entraining plume calculation, the present-day and LGM snowlines can be explained with a 3.5°C surface cooling in the WPWP during the LGM. NCAR's CCSM 3 and 4 simulate LGM cooling of 2°C. By comparing the results of CCSM3 and CCSM4, the higher resolution CCSM4 replicated LGM boundary conditions more accurately, increased LGM precipitation rates 0.4 mm/day, and reduced the transport of drier subtropical air from the Northern Hemisphere into the WPWP. One of the major issues in the CCSM identied in this thesis is the propagation of a temperature signal associated with the boundary layer over mountains to the upper-levels of the troposphere.