Accession Number : ADA182097

Title :   Oklahoma Downbursts and Their Asymmetry.

Descriptive Note : Final rept.,

Corporate Author : NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION NORMAN OK NATIONAL SEVERE STORMS LAB

Personal Author(s) : Eilts,Michael D ; Doviak,Richard J

PDF Url : ADA182097

Report Date : Nov 1986

Pagination or Media Count : 50

Abstract : Doppler radar data, collected each spring in 1979-1984, wit h the two Doppler radars operated by the National Severe Storms Laboratory (NSSL), are used to investigate the asymmetry of low-altitude divergent outflows of convective storm downbursts in central Oklahoma. Outflows in Oklahoma storms can be highly asymmetric with horizontal shear along the axis of maximum divergence as much as 5.5 times the shear alon the axis of minimum divergence. The downbursts observed in central Oklahoma, all large-scale (4-10 km) events, were superposed with the maximum reflectivity core of the storms. However, scanning strategies may have precluded detection of smaller scale ( 4 km) microbursts. Typical downbursts observed during the Joint Airport Weather Studies (JAWS) Project were of smaller scale ( 4 km) and were often associated with little or no rain at the surface. The mechanisms for the initiation of the majority of JAWS microbursts was most likely evaporative cooling, which occurred when precipitation fell into a dry, deep and nearly adiabatic boundary layer; it appears that, because of a lower cloud base and a moister and slightly more stable boundary layer, the mechanisms for the initiation of the observed Oklahoma downbursts include low-level melting, as well as evaporation of precipitation, low-level precipitation loading, and evaporational cooling at middle levels due to entrainment of dry hair.

Descriptors :   *THUNDERSTORMS, *WIND SHEAR, ADIABATIC CONDITIONS, BOUNDARY LAYER, ASYMMETRY, LOW ALTITUDE, CONVECTION(ATMOSPHERIC), STORMS, DETECTION, SCALE, EVAPORATION, ATMOSPHERIC PRECIPITATION, HORIZONTAL ORIENTATION, SHEAR PROPERTIES, OKLAHOMA, COOLING, DOPPLER RADAR, AIR ENTRAINMENT, METEOROLOGICAL DATA, SPRING SEASON, RADAR REFLECTIONS, AIRPORTS, WEATHER, MELTING, CORES, REFLECTIVITY, RADAR SCANNING, STRATEGY, STABILITY, CLOUDS, HIGH RATE, RAIN, SURFACES, SCALE

Subject Categories : Meteorology
      Atmospheric Physics

Distribution Statement : APPROVED FOR PUBLIC RELEASE