Using radar observations to evaluate 3-D radar echo structure simulated by the Energy Exascale Earth System Model (E3SM) version 1

摘要

The Energy Exascale Earth System Model (E3SM) developedby the Department of Energy has a goal of addressing challenges inunderstanding the global water cycle. Success depends on correct simulationof cloud and precipitation elements. However, lack of appropriate evaluationmetrics has hindered the accurate representation of these elements ingeneral circulation models. We derive metrics from the three-dimensionaldata of the ground-based Next-Generation Radar (NEXRAD) network over theUS to evaluate both horizontal and vertical structures of precipitationelements. We coarsened the resolution of the radar observations to beconsistent with the model resolution and improved the coupling of the CloudFeedback Model Intercomparison Project Observation Simulator Package (COSP)and E3SM Atmospheric Model Version 1 (EAMv1) to obtain the best possiblemodel output for comparison with the observations. Three warm seasons(2014–2016) of EAMv1 simulations of 3-D radar reflectivity features at anhourly scale are evaluated. A general agreement in domain-mean radarreflectivity intensity is found between EAMv1 and NEXRAD below 4 kmaltitude; however, the model underestimates reflectivity over the centralUS, which suggests that the model does not capture the mesoscaleconvective systems that produce much of the precipitation in that region. Theshape of the model-estimated histogram of subgrid-scale reflectivity isimproved by correcting the microphysical assumptions in COSP. Different fromprevious studies that evaluated modeled cloud top height, we find the modelseverely underestimates radar reflectivity at upper levels – the simulatedecho top height is about 5 km lower than in observations – and this resultis not changed by tuning any single physics parameter. For more accuratemodel evaluation, a higher-order consistency between the COSP and the hostmodel is warranted in future studies.