Winter storms, namely snowstorms and ice storms, are a major hazard and forecasting challenge across central North Carolina. This dissertation employs a trajectory approach to analyze the ingredients (i.e. temperature, moisture, and lift) associated with heavy snowstorms and ice storms that occurred within the Raleigh, NC National Weather Service forecast region from 2000 to 2010. The Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) tool is used to a calculate 72-hour backward (i.e. upstream) air parcel trajectories from three critical vertical pressure levels at the time and location of heaviest precipitation for each storm. Analysis of composite trajectories reveals the source regions and meteorological properties of air parcels associated with heavy winter storms. Adiabatic and diabatic contributions to air parcel temperature and moisture content are also calculated along each trajectory to assess the physical processes connected with heavy winter precipitation in the region. Comparative and ensemble trajectories are calculated to determine the physical processes that distinguish between precipitation type and intensity and assess the sensitivity of the trajectory calculations to the meteorological input data. A synoptic analysis of geopotential height fields is undertaken to determine those aspects of the large-scale circulation responsible for the back trajectory motions. Results indicate that diabatic warming and cooling contribute significantly to the vertical temperature profile during heavy winter storms and therefore dictate the resulting precipitation type. The main source of diabatic warming is fluxes of sensible and latent heat within the marine atmospheric boundary layer over the Gulf Stream. These fluxes contribute to a warming and moistening of air parcels associated with heavy ice storms. In contrast, heavy snowstorms are characterized by diabatic cooling in the lower troposphere above the marine atmospheric boundary layer. The most significant moisture source for heavy snowfall is the Caribbean Sea, while heavy ice storms entrain moisture from the Gulf of Mexico and Gulf Stream region near the Carolina coast. The details of the trajectory motions and air parcel characteristics have a significant influence on precipitation type and intensity and in many cases these details can be tied to subtle differences in the evolution of the synoptic-scale circulation.
|Advisor:||Konrad, Charles E., II|
|Commitee:||Bane, Jone, Curtis, Scott, Robinson, Peter, Shepherd, Marshall, Whitmore, Thomas|
|School:||The University of North Carolina at Chapel Hill|
|School Location:||United States -- North Carolina|
|Source:||DAI-B 73/06, Dissertation Abstracts International|
|Subjects:||Physical geography, Climate Change, Meteorology|
|Keywords:||Climatology, North Carolina, Precipitation, Storms, Trajectory, Winter, Winter weather|
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