Observational Study of a Multiple Microburst-Producing Storm Part II: A Comparision Between the Simple Case and the Complex Case

Abstract

A cross-comparison in structure and internal dynamics was made between a single microburst-producing storm (the simple case) and a multiple microburst­ producing storm (the complex c e) in Colorado. Emphasis was placed on the observed features m the atmospheric boundary layer (ABL} where the microburst activities dominated. In each case, the dual-Doppler derived winds and retrieved thermodynamic v iables at two analysis times were employed to conduct the study.
Results show that there are similarities and differences in structural features between the two c es. Similar features found include: (1) the microbursts being investigated were embedded within the high-reflectivity regions with precipitation occurrence; (2) a wet microburst is accompanied by the bow echo with the out ow in the direction parallel to the maximum reflectivity gradient; (3) high pressure forms inside the microburst core with low pressure in the strongest out ow regions; (4.) a rotor forms near the microburst gust front due to the out ow colliding with the environmental flow; (5) a net eddy transfer of horizontal momentum and kinetic energy in the microburst area is predominantly downw d; and (6) 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. On the other hand, different features between the cases are (1) each c e h unique en­vironmental ingredients, such the wind, vertical shear, stability, and moisture; (2) the environmental mean flow in the ABL is opposite in direction {southeast versus northwest); (3) a strong (weak) down ow occurs in the main downdraft for the simple (complex) case; (4) only one microburst occurs in the simple c e, while at least two microbursts occur in the complex case at each analysis time; (5) no apparent circulation center is found in the simple case, while the complex case h the mesocyclone-like vortex and misocyclones; and (6) a wet microburst has a warm (cold) core for the simple (complex) case.

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