Session: Glacial Climates (LGM, Last deglaciation, Ice sheet uncertainties, Glacial-interglacial cycles)
Author: Juan M. Lora / jlora@ucla.edu / UCLA
Co-author: Jonathan L. Mitchell, Westmont College & UCLA;
                    Camille Risi, LMD;
                    Aradhna E. Tripati, UCLA;

Abstract:
Paleo-precipitation reconstructions indicate that during the Last Glacial Maximum, northwestern and southwestern North America were drier and wetter than present, respectively. These changes have been associated with southward shifts in the positions of the midlatitude jet stream and wintertime North Pacific storm track, observed in LGM simulations from a variety of models. But the source and delivery processes of water at the LGM have been recently debated. Using the ensemble of PMIP3 LGM simulations, supplemented with reanalysis and additional atmospheric simulations, we explore the role of atmospheric rivers—plumes of water vapor transport of critical importance to western North America—in delivering water to the region during the glacial. Deepened Aleutian Low and weakened North Pacific High pressure systems at the LGM concentrated water transport in atmospheric rivers into California relative to the present, enhancing moisture and precipitation in the southwest and shifting it away from the northwest. While the PMIP3 simulations were crucial for this work, uncertainties remain that will be addressable with PMIP4 results, like the effects of uncertainties in ice-sheet topography. Furthermore, the lack of daily model output and certain derived variables in the PMIP3 archives limited the range of possible analyses; PMIP4 offers opportunities to fill these gaps.