Terrain-influenced Microphysical Processes Observed by Dual-polarization Radar during OLYMPEX

During the 2015-2016 OLYMPEX field campaign, two dual-polarization, Doppler scanning precipitation radars were deployed on the windward side of the Olympic Peninsula to document the evolution of frontal systems as they encountered terrain. NASA's S-band, NPOL, radar operated near the coast, collecting high-resolution vertical cross sections through systems over the ocean and inland toward the Quinault Valley. An X-band Doppler on Wheels (DOW) radar was located further up the valley beneath the NPOL beam to document details over the lower elevations. By operating nearly continuously for about 6 weeks during an active, wet season, the role of terrain on influencing precipitation across a range of frontal systems can be explored.

Low-level, down-valley flow was often observed by the DOW radar, underlying strong ascent toward the terrain. At times, Kelvin-Helmholtz instability manifested as billows within this shear zone, with an apparent influence on the microphysical processes in their vicinity. The role of shear-induced turbulence in precipitation enhancement along the windward slopes will be explored in this context through a description of the polarimetric variables. The relative roles of warm-rain and ice-based microphysical processes in precipitation enhancement is also explored within the context of storm sector and type, with a focus on hydrometeor vertical profiles and characteristics of the melting level relative to terrain. Coincident in-situ aircraft observations along NPOL and DOW radials provide a means to evaluate radar-inferred microphysical processes in select cases.