Process Evaluation of Warm Season Precipitation Variability in the Northeast United States: NARCCAP driving AOGCMs and Timeslice Experiments

This research evaluates simulations of processes important to Northeast U.S. warm season precipitation variability in the global AOGCMs (~140 km) and the high-resolution (~50 km) timeslice experiments (GFDL-CM2.1 & CCSM3) performed for the NARCCAP dataset (Mearns et al., 2007). Future warm season moisture deficits are likely to impact water resources and water quality in this highly populated region, especially as mean summer temperatures increase. Regression analysis of 500 hPa geopotential height (20th Century Reanalysis, 20CR) and Northeast precipitation anomalies (CMAP) show that wet/dry summers in the Northeast are associated with 1) a reduced/increased center in the height field located over the Great Lakes, and 2) a region of positive/negative height anomalies located over the Atlantic Ocean east of the Mid-Atlantic States. These features work together to increase/decrease the poleward flow of moisture into the Northeast. Observed (20CR and CMAP) and simulated characteristics of large-scale circulation anomalies and moisture transport in dry and wet summers in the Northeast are examined using a composite analysis. In addition to evaluation of the NARCCAP driving AOGCMS, the high-resolution NARCCAP timeslice experiments are compared to results from several CMIP5 models. Projected changes are also examined for the mid-21st century time period.