Relationship between level of neutral buoyancy and dual-Doppler observed mass detrainment levels in deep convection

摘要

Although it is generally accepted that the level of neutral buoyancy (LNB) isonly a coarse estimate of updraft depth, the LNB is still used to understandand predict storm structure in both observations and modeling. This studyuses case studies to quantify the variability associated with usingenvironmental soundings to predict detrainment levels. Nine dual-Dopplerconvective cases were used to determine the observed level of maximumdetrainment (LMD) to compare with the LNB. The LNB for each case wascalculated with a variety of methods and with a variety of sources (includingboth observed and simulated soundings). The most representative LNB waschosen as the proximity sounding from NARR using the most unstable parcel andincluding ice processes.The observed cases were a mix of storm morphologies, including both supercelland multicell storms. As expected, the LMD was generally below the LNB, themean offset for all cases being 2.2 km. However, there was a markeddifference between the supercell and non-supercell cases. The two supercellcases had LMDs of 0.3 km and 0.0 km below the LNB. The remaining cases hadLMDs that ranged from 4.0 km below to 1.6 km below the LNB, with a meanoffset of 2.8 km below. Observations also showed that evolution of the LMDover the lifetime of the storm can be significant (e.g., >2 kmaltitude change in 30 min), and this time evolution is lacking frommodels with coarse time steps, missing significant changes in detrainmentlevels that may strongly impact the amount of boundary layer mass transportedto the upper troposphere and lower stratosphere.