Momentum and eddy kinetic energy transports by a multiple microburst‐producing storm

Abstract

A comprehensive study of the structure and internal dynamics was made for a multiple microburst‐producing storm for August 5, 1982, in Colorado during the Joint Airport Weather Studies (JAWS) Project at Denver's Stapleton International Airport. The analysis levels were contained between 0.25 and 2 km. The horizontal and vertical grid spacings were 0.5 and 0.25 km, respectively. These fields were subjected to internal consistency checks to determine the level of confidence before interpretation. Results show that the combined effects of misocyclone circulations, perturbation‐pressure gradients, melting, buoyancy, and precipitation loading contribute to the maintenance of the microburst downdrafts in the atmospheric boundary layer (ABL). At low levels where the microbursts dominate, the presence of microburst gust fronts and diverging outflow enhances the vertical transport of horizontal momentum and eddy kinetic energy. The misocyclones located above the microbursts largely determine the transport of horizontal momentum and eddy kinetic energy there. In the microburst subdomain, a net transport of horizontal momentum and eddy kinetic energy is downward from the misocyclone to the surface. Its magnitude is directly proportional to the strength of a microburst at low levels and the misocyclone aloft. Budget studies of horizontal momentum flux and eddy kinetic energy within the storm domain and the microburst subdomain have added to a further understanding of the storm's structure and internal dynamics. The pressure and buoyancy effects are two main contributors to the generation/decay of horizontal momentum fluxes and eddy kinetic energy at the microburst levels.