Microphysical Enhancement Processes within Stratiform Precipitation on the Barrier and Sub-Barrier Scale of the Olympic Mountains

High-resolution numerical model simulations of six different cases during the 2015/16 Olympic Mountains Experiment (OLYMPEX) are used to examine dynamic and microphysical precipitation processes on both the full barrier-scale and smaller sub-barrier-scale ridges and valleys. The degree to which stra...

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Bibliographic Details
Published in:Monthly weather review 2021-02, Vol.149 (2), p.503-520
Main Authors: Zagrodnik, Joseph P., McMurdie, Lynn, Conrick, Robert
Format: Article
Language:English
Subjects:
Ascent
Barrier winds
Cloud water
Clouds
Coastal waters
Coasts
Cyclones
Foothills
Hydrometeors
Ice
Ice particles
Lee waves
Mathematical models
Mountain waves
Mountains
Numerical models
Numerical simulations
Precipitation
Precipitation processes
Rain
Ridges
Simulation
Slopes
Stratified flow
Upstream
Valleys
Winds
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Summary:High-resolution numerical model simulations of six different cases during the 2015/16 Olympic Mountains Experiment (OLYMPEX) are used to examine dynamic and microphysical precipitation processes on both the full barrier-scale and smaller sub-barrier-scale ridges and valleys. The degree to which stratiform precipitation within midlatitude cyclones is modified over the coastal Olympic Mountains range was found to be strongly dependent on the synoptic environment within a cyclone’s prefrontal and warm sectors. In prefrontal sectors, barrier-scale ascent over stably stratified flow resulted in enhanced ice production aloft at the coast and generally upstream of higher terrain. At low levels, stable flow orientated transverse to sub-barrier-scale windward ridges generated small-scale mountain waves, which failed to produce enough cloud water to appreciably enhance precipitation on the scale of the windward ridges. In moist-neutral warm sectors, the upstream side of the barrier exhibited broad ascent oriented along the windward ridges with lesser regions of adjacent downward motion. Significant quantities of cloud water were produced over coastal foothills with further production of cloud water on the lower-windward slopes. Ice production above the melting layer occurred directly over the barrier where the ice particles were further advected downstream by cross-barrier winds and spilled over into the lee. The coastal foothills were found to be essential for the production and maintenance of cloud water upstream of the primary topographic barrier, allowing additional time for hydrometeors to grow to precipitation size by autoconversion and collection before falling out on the lower-windward slopes.
ISSN:0027-0644
1520-0493
DOI:10.1175/MWR-D-20-0164.1