Observational Study of a Multiple Microburst-Producing Storm Part I: Kinematic, Dynamic and Thermodynamic Structures

  • Author(s): Yeong-Jer Lin, William E.Mcnamee, and John A.Coover, JR.
  • DOI: 10.3319/TAO.1991.2.2.95(A)
  • Keywords:
  • Citation: Lin, Y.-J., W. E. Mcanamee, and J. A. Coover, 1991: Observational Study of a Multiple Microburst-Producing Storm Part I: Kinematic, Dynamic and Thermodynamic Structures. Terr. Atmos. Ocean. Sci., 2, 95-120, doi: 10.3319/TAO.1991.2.2.95(A)
Abstract

Some kinematic, dynamic, and thermodynamic structures of a multiple microburst-producing storm, which occurred on 5 August 1982 Colorado, were studied for three analysis times at 1845, 1847, and 1850 MDT. Dual Doppler data collected during the project of Joint Airport Weather Studies (JAWS) at Den­ver's Stapleton International Airport were objectively analyzed to produce a three­ dimensional wind field. The domain of interest had a horizontal dimensi9n of 15 km by 15 km covering three microbursts. There were five analysis levels the vertical ranging om 0.25 to 1.25 km AGL. The horizontal and vertical grid spacings were 0.5 and 0.25 km, respectively. Vertical velocities were computed by integrating the anelastic continuity equation upward om the surface. Subsequent , elds of devi­ ation perturbation pressure and temperature were recovered om a detailed wind eld using the three momentum equations. These fields were then subjected to internal consistency checks to determine the level of con dence be re interpretation.
Results show that the microbursts being investigated are embedded within the high-reflectivity cores with heavy precipitation. A wet microburst is accompanied by the misocyclone at levels above 0.75 km in the downdraft. It has the slowly descending dow ow forming a cold core at the l est levels due to the evaporation of raindrops. Near the gust front (GF), a mesocyclone-like circulation develops in the ea where the w m, dry environmental interacts with the negatively buoy­ ant microburst out ow. High pressure forms inside the microburst core with low pressure in the strong wind regions. Pronounced horizontal pressure gradients occur om the microburst center outward to balance the strong diverging out ow that region. The retrieved pressure and temperature fields agree well with the storm's kinematic structure. The combined effects of misocyclone circulations, perturbation pressure gradients, buoyancy and precipitation loading e responsible r maintain­ ing the microburst downdrafts in the atmospheric boundary layer (ABL).

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