Airborne Doppler Radar Observations of Mid-Latitude Storms Interacting with Mountainous Terrain During OLYMPEX

The 2015-2016 OLYMPEX field campaign deployed numerous observational platforms around the Olympic Mountains with a goal of better understanding the dynamic and microphysical processes controlling hydrometeor formation near topography. The observational network included rawinsondes, rain gauges, disdrometers, ground radars and aircraft outfitted with radars, passive microwave sensors and microphysical instruments; this dense and diverse network provided comprehensive sampling of mid-latitude cyclones interacting with terrain.

This study focuses on APR-3 data onboard NASA's DC-8 aircraft to examine how microphysical processes are modified by terrain both on the windward and leeside slopes of the Olympic mountains. The APR-3 radar is unique due to the combination of Ku-, Ka- and W-band radars with high vertical resolution that provide detailed snapshots of the vertical precipitation structure. Analysis of three-dimensional radar data highlights the horizontal and vertical location of maximum orographic enhancement on the windward slopes, while also capturing the precipitation structure on the leeside slopes. Surface observations of precipitation and drop size distribution complement the reflectivity and hydrometeor velocity structures on the windward slopes and at Hurricane Ridge. Finally, the patterns derived from the radar data are placed within the context of the larger synoptic pattern.

Of particular focus is data collected during a DC-8 flight on 8 December 2015 through an atmospheric river that ultimately produced 100-300 and 50 mm of precipitation on the windward and leeside slopes, respectively. The DC-8 aircraft made several passes over the terrain, which allows for an examination of the persistence of the precipitation and dynamic features.