Evaluating the role of the jet stream in the moisture budget of glacial western North America

Various proxy reconstructions of late Pleistocene paleoclimate have indicated that southwestern North America was significantly more wet at the last glacial maximum (LGM) than in the present: The Great Basin, now an arid region, was covered in pluvial paleolakes, the largest of which, Lakes Boneville and Lahontan, covered areas similar to the modern Great Lakes. A common explanation for the additional moisture is the ``dipping westerlies," where the topographical influence of the Laurentide Ice Sheet caused the jet stream west of North America to shift southward at LGM, channeling the Pacific storm track into the western US. This mechanism was suggested in early climate models, though their low resolution prevented further investigation. We investigate the influence of the shift of the jet stream between LGM and present day on precipitation in several regions of the western and southwestern US, and evaluate whether differences in moisture are attributable to this mechanism, by analyzing the LGM and control simulations currently available from the Paleoclimate Modelling Intercomparison Project phase 3 (PMIP3). We perform an evaluation of each climate model in the suite against paleoclimatic proxies to better understand the range of responses of the jet stream to the topographical forcing, and the resulting effects on the effective moisture in the region. An important consideration is whether said proxies can be used to better understand and constrain past circulation changes by comparison to models.