Session 3.4 Comparison of the level of neutral buoyancy observed from soundings and radar

Monday, 17 August 2009: 2:15 PM
The Canyons (Sheraton Salt Lake City Hotel)
Amanda J. Homann, University of North Dakota, Grand Forks, ND; and G. Mullendore, J. S. Tilley, and S. T. Jorgenson

Presentation PDF (432.1 kB)

Determining the level of detrainment, or storm depth, in deep convection is important operationally for aviation forecasts and also important for constraining mass transport calculations. Using the level of neutral buoyancy (LNB) determined from environmental soundings as a proxy for the detrainment height is widely believed to be unrepresentative in many convective situations. One reason for this is the high spatial and temporal variability between sounding stations which provides an incomplete picture of many convective environments. There are many situations in which convection forms and propagates across an area where environmental soundings are not available at that specific time or location. Therefore, using parcel theory to find the LNB may not always be the most accurate method to finding actual storm deposition heights.

Sounding data and dual-Doppler radar data (vertical velocity and divergence fields) were utilized to calculate parcel theory LNBs and observed detrainment heights, respectively. Dual-Doppler data from a squall line during the Tropical Rainfall Measuring Mission Large Scale Biosphere-Atmosphere (TRMM-LBA) campaign in Brazil was analyzed along with a supercell case from the Severe Thunderstorm Electrification and Precipitation Study (STEPS) campaign, which took place in the central United States. The parcel theory LNB for each case was determined from the environmental sounding chosen as most representative of each convective environment. Actual storm deposition heights were determined by examining where the maximum detrainment is taking place from the total divergence profiles from the dual-Doppler data. The use of radio occultation (RO) soundings for upper troposphere and lower stratosphere measurements will also be investigated. The significantly greater spatial and temporal resolution of RO measurements as compared to surface based environmental soundings should prove beneficial to more accurate parcel theory LNB estimations.

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