Tropical Cyclone tracks in present and future climates

The overall objective is to use diagnostic and modeling methods to decipher and understand physical processes/causal links that connect tropical and North Atlantic sea surface temperature (SST) variations associated with the Atlantic Multidecadal Oscillation (AMO) to changes in atmospheric circulation and warm season precipitation regimes for North America. The ultimate goal is to include representations of these processes in forecast models, and thereby improve predictions of summer rainfall variations at intraseasonal, interannual, and decadal timescales for North America, particularly the monsoon region and the central U.S. Scientific questions that will be addressed are: How do the heat and momentum flux anomalies arising from AMO forcing act to develop anomalous regional circulation and rainfall in North America during different phases of AMO? Are atmospheric eddy heat and momentum fluxes and circulation anomalies during different phases of AMO sufficient to account for observed summer rainfall regime changes in North America, and if so, how? How have Pacific Decadal Oscillation (PDO) and ENSO interacted with AMO effects on circulation/rainfall regimes for North America? How have spring soil moisture anomalies interacted with the specific warm season eddy heat and momentum flux anomalies for North America during different phases of AMO to modulate rainfall development and variation? How can the AMO forcing be included in forecasting models and improve summer rainfall predictions? Methods used include the Eliassen-Palm diagnostics, which will be used to quantify eddy heat, momentum, and energy fluxes driven by SST anomalies related to AMO and effects of these eddy fluxes on circulation and summer rainfall regimes for North American during different phases of AMO. Both general circulation model (GCM) and regional climate model will be used to determine AMO forcing and its modification by PDO and ENSO. Specifically, the atmospheric GCM will be integrated with observed SST forcing in the central and North Atlantic Ocean, and climatological SST elsewhere. Additional GCM runs with SST forcing from the Pacific Ocean will be made in order to identify their effects on the AMO induced circulation and rainfall patterns in North America. Regional model will be integrated with initial condition and lateral forcing from observations and GCM output in order to examine in detail changes in moisture and energy transports, precipitation development, and their intraseasonal and interannual variations during the different circulation regimes associated with AMO. Regional model also will be used to examine feedbacks of land surface processes (e.g., soil moisture) to the circulation anomalies and rainfall development during different phases of AMO. The expected key outcome is improved understanding of how summer rainfall variations on intraseasonal and interannual timescales are associated with the forcing from AMO and how these variations have changed during different phases of AMO (thus explaining also decadal timescale variations in summer rainfall in North America). This understanding will be communicated to forecasting modeling groups, with the ultimate goal of improving predictions of intraseasonal and interannual rainfall variations (including likelihood of floods) for North America.