Storm-Scale Dynamics of Winter US East Coast Cyclones in a Warmer Climate

Midlatitude cyclones represent the dominant mode of extreme weather to affect the eastern United States during the winter months. Flooding rain, damaging wind and crippling snow are amongst the threats winter cyclone events pose to inhabitants of this region. Given the significant socioeconomic impacts these events can have, it is important to determine how they may change in a warmer world. Previous studies have investigated a wide range of potential climate warming impacts, including shifts in the midlatitude storm tracks, and changes in the frequency and intensity of midlatitude cyclones. Fewer studies have directly investigated the effect of climate warming on the dynamics of individual cyclones. Such analysis is complicated by projected changes in a number of competing processes such as baroclinicity and static stability. Projected increases in atmospheric moisture content also mean moist diabatic processes may play a larger role in future cyclone dynamics. In order to investigate the cumulative effects of these changes, we perform high-resolution simulations of winter US East Coast cyclones in present and future climates using the Weather Research and Forecasting (WRF) model. High resolution allows for the diagnosis of changes in moist diabatic processes that may be unresolved by GCMs. A pseudo-global warming approach is used in which end of century thermodynamic changes are applied to the initial and lateral boundary conditions that drive WRF. These thermodynamic changes are derived from an ensemble of five IPCC AR4 GCMs using the A2 emissions scenario. The same approach is also used with thermodynamic changes derived from an ensemble of CMIP5 GCMs. Possible changes in the evolution and intensity of individual US East Coast cyclone events due to climate warming are investigated. Potential vorticity (PV) analysis is implemented to diagnose these changes. An Ertel PV budget is computed in order to determine whether changes in intensity may be attributable to changes in diabatic PV. A comparison of results using the IPCC AR4 and CMIP5 derived thermodynamic changes is also included.