Insight into the Microphysics and Mesoscale Dynamics of Atmospheric Rivers: A Satellite Radar and WRF-Simulated Reflectivity Perspective

Atmospheric rivers (AR) account for more than 90% of the total meridional water vapor flux in mid latitudes and are the primary driver of precipitation in the western United States, among other locations. Despite the importance of ARs to global moisture fluxes and regional water resources, their formation and propagation over the World’s oceans limits their in-situ observation prior to landfall. Here, reflectivity profiles from the Global Precipitation Measurement Mission’s Dual-Frequency Precipitation Radar (GPM DPR) are used to evaluate precipitation and temperature characteristics of ARs over the Western US and Eastern Pacific Ocean. The objectives of this research are to 1) advance observation of AR precipitation processes over the ocean, 2) assess the fidelity of a version of the Weather Research and Forecasting (WRF) model, specifically configured for AR research and forecasts, in representing the observed precipitation and temperature characteristics within ARs prior to landfall, and 3) use satellite radar, alongside model-simulated reflectivity and full volume scans from regional ground-based radars to provide new insight into AR structure, microphysics and mesoscale dynamics in the nearshore environment. Model results are presented for two well-observed case studies of ARs that impacted California during winter 2017, for which extensive sensitivity tests were performed. Output from the best-performing configuration demonstrates that analyzing the 3-dimensional distribution of hydrometeor species within ARs can aid in explaining precipitation variability that is not directly attributable to orographic or quasi geostrophic forcing. Results from this research are potentially insightful to a wide range of questions on the influence of ARs at regional to global scales. Furthermore, assessing the accuracy of model representation of clouds and precipitation features in ARs over the ocean, and diagnosing rectifiable errors, may improve quantitative precipitation forecasts over the Western United States.