The Importance of Parcel Choice and the Measure of Vertical Wind Shear in Evaluating the Convective Environment
Matthew J. Bunkers, NOAA/NWSFO, Rapid City, SD; and B. A. Klimowski and J. W. Zeitler
Convective parameters from both observed and model-derived soundings weigh heavily in the thunderstorm forecasting process. There is a multitude of options one can chose from to compute many of these parameters, which further complicates the already difficult problem of forecasting convective initiation and thunderstorm evolution. For example, in the computation of convective available potential energy (CAPE), one may chose the surface parcel, the most unstable parcel in the lower atmosphere, or a mixed parcel of some fixed depth; the virtual temperature correction may or may not be applied. Furthermore, CAPE is used in derived parameters such as the bulk Richardson number (BRN), energy helicity index (EHI), and vorticity generation parameter (VGP), allowing for a wide array of results depending upon parcel choice.
In addition to the parcel choices for these thermodynamic parameters, there are also several measures of vertical wind shear one can use, including the bulk, total, positive, and negative shear. The differences among these measures of vertical wind shear are not trivial, and they can lead to different forecaster interpretations of the potential for supercells and bow echoes, for example. In light of these observations, the present investigation attempts to better document these differences through a climatology of soundings in the central United States. Some of the literature that has applied variants of these parameters is also discussed.
Extended Abstract (176K)
Poster Session 8, Climatological Studies of Severe Local Storms
Wednesday, 14 August 2002, 3:00 PM-4:30 PM
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