Vertical Structure and Microphysical Characteristics of Frontal Systems Passing over a Three-Dimensional Coastal Mountain Range

Abstract

As midlatitude cyclones pass over a coastal mountain range, the processes producing their clouds and precipitation are modified, leading to considerable spatial variability in precipitation amount and composition. Statistical diagrams of airborne precipitation radar transects, surface precipitation measurements, and particle size distributions are examined from nine cases observed during the Olympic Mountains Experiment (OLYMPEX). Although the pattern of windward enhancement and leeside diminishment of precipitation was omnipresent, the degree of modulation was largely controlled by the synoptic environment associated with the prefrontal, warm, and postfrontal sectors of midlatitude cyclones. Prefrontal sectors contained homogeneous stratiform precipitation with a slightly enhanced ice layer on the windward slopes and rapid diminishment to a near-complete rain shadow in the lee. Warm sectors contained deep, intense enhancement over both the windward slopes and high terrain and less prominent rain shadows owing to downstream spillover of ice particles generated over terrain. Surface particle size distributions in the warm sector contained a broad spectrum of sizes and concentrations of raindrops on the lower windward side where high precipitation rates were achieved from varying degrees of both liquid and ice precipitation-generating processes. Spillover precipitation was rather homogeneous in nature and lacked the undulations in particle size and concentration that occurred at the windward sites. Postfrontal precipitation transitioned from isolated convective cells over ocean to a shallow, mixed convective–stratiform composition with broader coverage and greater precipitation rates over the sloping terrain.

Atmospheric Rivers Contribution to the Snow Accumulation Over the Southern Andes (26.5° S–37.5° S)

“…feature is further demonstrated in transects of Figure 3C, and could be a response of greater orographic enhancement of precipitation on the first rise of the strong, cross-barrier moisture flux from ARs as has been suggested by other studies on the coastal western mountains of North America (Neiman et al, 2017;Zagrodnik et al, 2018Zagrodnik et al, , 2019. Figure 3 illustrates the strong orographic effects of the Andes on the snow accumulation and the ARs contribution to this accumulation in along-and cross-barrier directions.…”

Linkage Between the Vertical Evolution of Clouds and Droplet Growth Modes as Seen From FY‐4A AGRI and GPM DPR

“…Each CFAD was normalized by its overall maximum at a horizontal interval of 1 dBZ and a vertical interval of 0.25 km. Compared with normalization by level maximums (McMurdie et al, 2018), this method is more suitable for comparing results at different heights (Zagrodnik et al, 2019; Zhang et al, 2018).…”

Statistical characteristics of raindrop size distribution over the Western Ghats of India: wet versus dry spells of the Indian summer monsoon

“…The broader distribution and relatively higher median value of D m represent the continental convection on the mountain's leeward side. Zagrodnik et al (2019) also observed the narrow D m distribution during the Olympic Mountains Experiment (OLYM-PEX) on the Olympic peninsula's windward side.…”