MCS and MCV divergence profiles: Observations and model sensitivities

Radar-observed divergence profiles are compared to ensemble simulations of several mesoscale convective systems (MCSs) in southeast Texas, including an extreme rain-producing mesoscale convective vortex (MCV) on 9 June 2010. Eight MM5 simulations are conducted for each case using two single-moment microphysics schemes and four treatments of convection (i.e., two convective parameterizations and explicit vs. parameterized convection at 9 km). Observed and simulated radar reflectivities are also objectively separated into convective, stratiform, and non-precipitating anvil columns, with most simulations producing deficient stratiform and excessive convective and anvil echo relative to observations. Storms whose simulated divergence structures, areal echo coverages, and vertical reflectivity distributions exhibit a large ensemble spread and deviate significantly from observations are highlighted, identifying possible implications for diabatically-maintained midlevel circulations like MCVs.

Research completed suggests that divergence profiles do not reveal large sensitivities to the single-moment microphysics schemes used in this study even though the scheme that prescribes stronger rain evaporation rates and produces greater snow mass aloft generates significantly more anvil than its counterpart. Divergence profiles exhibit larger sensitivities to the convective treatments used in this study associated with changes in convective intensity, likely affecting the level of maximum detrainment of ice to anvil and stratiform regions. As a result, ensemble members that generate stronger convective vertical velocities and associated stratiform updrafts aloft produce more elevated heating structures and stronger midlevel vortices in simulations of the MCV case. Therefore, results from WRF-ARW simulations of the MCV case utilizing two-moment microphysics schemes will also be presented if time permits to investigate whether they curtail excessive anvil and generate less intense convection that results in more accurate diabatic divergence profiles and improved forecasts of MCV circulations.