Entrainment Rates in Deep Convection using Multi-Doppler Radar Observations

Description

Deep moist convection plays an important role in climate as it influences the chemical, radiative, and energy budgets of the atmosphere and effects the large-scale atmospheric dynamics. One of the most important impacts on deep convection, and hence, on feedbacks to climate forcing is entrainment. The entrainment of cold, dry air into the updraft reduces the buoyancy of air via dilution and effects the depth, magnitude, and evolution of convection. Directly determining the entrainment rate is challenging, as in-situ observations in deep convection are infrequent and dangerous to retrieve; however, remote sensing platforms such as radars can be utilized instead. As part of the Department of Energy’s Science Graduate Student Research (SCGSR) Program, a methodology is developed to retrieve entrainment rates with height for deep convective cells using a mixing parcel approach that is constrained by observations. The mixing parcel utilizes environmental data from soundings and vertical velocity retrievals from multi-Doppler radar observations taken during the Midlatitude Continental Convective Clouds Experiment (MC3E). The mixing parcel accounts for hydrometeor drag, ice processes, and simplistic perturbation pressure gradient forces. Entrainment rates are found to be the highest near cloud base, where air enters the updraft. Entrainment rates in the mid-level of the storms were relatively constant. By accounting for or ignoring each process, the sensitivity of the retrieved entrainment rates is discussed. The mixing parcel method is also compared to a plume method, which uses the observed level of maximum detrainment to identify the dynamic storm top, yielding a bulk entrainment rate. The mixing parcel entrainment rates are up to two times higher than the plume method for analyzed cases.