Determining Best Method for Estimating Observed Level of Maximum Convective Detrainment based on Radar Reflectivity

Convective mass transport is the transport of mass from near the surface up to the upper troposphere and lower stratosphere (UTLS) by a deep convective updraft. This transport can alter the chemical makeup and water vapor balance of the UTLS, which can affect cloud formation and the radiative properties of the atmosphere. It is therefore important to understand the exact altitudes at which mass is detrained from convection. These detrainment altitudes are also important for constraining deep convective transport in chemical transport models and climate models. Previous studies have used radar reflectivity as a direct observer of vertical transport for a squall line from the Tropical Rainfall Measuring Mission Large-Scale Biosphere-Atmosphere field campaign. This study builds upon that using a variety of storm types from the Severe Thunderstorm Electrification and Precipitation Study (STEPS).

The purpose of this study is to improve the methodology for estimating the level of maximum detrainment (LMD) within convection using data from individual radars. Such an approach would maximize the spatial and temporal coverage of convective mass-detrainment estimates compared to current methods such as chemical tracers from satellite retrievals or updraft velocities from dual-Doppler radar retrievals. Since hydrometeors are advected by the storm motions, the level of maximum detrainment should be co-located with the level of maximum ice mass. To test this hypothesis, three methods were used to identify convective cores and anvil reflectivity locations. An empirical relationship relating ice mass to reflectivity was used to calculate total anvil mass, and vertical mass distribution plots were validated against dual-Doppler derived divergence fields to identify the best method. Based upon this comparison, the best method for locating the LMD was determined to be the method that uses a horizontal reflectivity texture-based technique to determine convective cores and a multi-layer echo identification to determine anvil locations.

This methodology is then applied to archived National Mosaic & Multi-Sensor Quantitative Precipitation Estimate (NMQ) gridded 3D radar mosaic data. The regions of analysis were chosen to coincide with the observation regions for the Deep Convective Clouds and Chemistry Experiment (DC3): the Colorado Foothills, Southern Plains (OK/TX), and Southeast US (AL). These three regions provide a wide variety of convection. The dates analyzed were from May and June of 2012 so the results can be compared to future DC3 studies. The variability of detrainment heights for the early convective season for these different geographical regions will be presented.