Premium
Temperature and moist‐stability effects on midlatitude orographic precipitation
Author(s) -
Kirshbaum Daniel J.,
Smith Ronald B.
Publication year - 2008
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.274
Subject(s) - orographic lift , orography , precipitation , convection , atmospheric sciences , moisture , environmental science , precipitation types , climatology , meteorology , geology , physics
Idealized, convection‐resolving simulations of moist orographic flows are conducted to investigate the influence of temperature and moist stability on the drying ratio ( DR ), defined as the fraction of the impinging water mass removed as orographic precipitation. In flow past a long ridge, where most of the air rises over the barrier rather than detouring around it, DR decreases as the surface temperature ( T s ) increases, even as the orographic cap cloud becomes statically unstable at higher T s and develops embedded convection. This behaviour is explained by a few physical principles: (1) the Clausius–Clapeyron equation dictates that the normalized condensation rate decreases as the flow gets warmer, (2) the replacement of ice‐phase precipitation growth with warm‐rain processes decreases the efficiency by which condensate is converted to precipitation, thereby lowering precipitation efficiency, and (3) embedded convection acts more to vertically redistribute moisture than to enhance precipitation. Over an isolated mountain, the effects of (1) and (2) are counteracted by moisture deflection around the barrier, which is stronger in the colder, more stable flows. Copyright © 2008 Royal Meteorological Society