The Response of Northern Hemispheric Monsoon Precipitation Patterns to Extra-Tropical Forcing Under Last Glacial Maximum

Understanding the response of monsoon precipitation distributions to different climate states can serve to test climate model simulations, but many challenges remain owing to multiple controlling factors. Here, we quantitatively compare a synthesis of pollen proxies of precipitation during Last Glacial Maximum (LGM, 21ka) precipitation over North America to constrain the Paleoclimate Intercomparison Model Project (PMIP3) ensemble. In model simulations that compare favorably with proxy synthesis, we find a strong correlation between monsoon precipitation and meridional wind anomaly, suggesting the patterns are mainly governed by extra-tropical forcing. The major perturbations of meridional wind anomaly under LGM consist of topographic forcing due to rising elevation from the Laurentide ice sheets and thermodynamic forcing due to alteration of the mean state from albedo change. Weak westerlies are generated by models with favorable comparison to the proxy synthesis. We are testing if the alteration of westerlies contributes to Rossby waves and monsoon precipitation distributions in North America during LGM.