Microphysical Processes Contributing to Extreme Rainfall in Complex Terrain

Extreme rainfall in complex terrain remains a forecasting challenge with devastating impacts. In the moisture rich environment of Taiwan, steep topography modifies the ingredients and processes leading to extreme rainfall with impacts across an intensity-duration spectrum. NCAR’s S-Pol radar was deployed for nearly 3 months on the northwest coast of Taiwan for the 2022 Prediction of Rainfall Extremes Campaign in the Pacific (PRECIP), capturing nearly continuous dual-polarization measurements including a range of rainfall events from the Mei-Yu season through to late summer tropical cyclone influences. These unique measurements provide an opportunity to investigate microphysical processes leading to heavy rainfall and the role topography plays in these processes. Our hypothesis going into the campaign was that the transition from high intensity to long duration rain events could be viewed similarly to the transition from deep convection to stratiform-dominant MCSs. Previous campaigns in Taiwan showed graupel in deep convective towers and distinct microphysical characteristics for heavy rainfall events with differing precipitation efficiencies. With the S-Pol quality-controlled dataset recently available, this presentation quantifies our initial assessments from in the field in which we observed similar radar signatures across different heavy rain events, including convective cells embedded within widespread stratiform persisting along the mountain slopes. Pathways forward using this exciting dataset will also be presented to address the microphysical aspect of our overarching goal to improve understanding and prediction of heavy rainfall.