The Changing Annual Cycle of Climate in the Northeast United States

To understand the ongoing transition in the climate of the Northeast United States, this research begins by examining the largest mode of variability - the annual cycle. Analysis emphasizes temperature and rainfall, as well as changes projected through the 21st century. Gridded observations and experiments from the World Climate Research Program's (WCRP) fifth Climate Model Intercomparison Project (CMIP5) are used to verify the present day simulated annual cycle in the multi-model dataset, and to evaluate spatial and temporal changes in seasonality projected in the RCP8.5 scenario. As expected, the suite of models performs well in simulating the annual cycle of temperature and cold season precipitation, but overestimates summertime rainfall. The multi-model projections indicate a decrease in amplitude of the temperature annual cycle due to greater warming in winter. The precipitation annual cycle also shows a decrease in amplitude but with a change of sign meridionally across the region. This transition highlights the uncertainty in precipitation changes across mid-latitude regions, particularly during warm season, which will be discussed in some detail.