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Free keywords:
Heat convection; Lakes; Weather forecasting, Cold pool; Land atmosphere interaction; Mesoscale circulation; Numerical weather prediction; Precipitating phase; Propagation speed; Sensitivity studies; Surface discontinuities, Large eddy simulation
Abstract:
A basic understanding of the mechanisms controlling the characteristics of thermally induced mesoscale circulations rests primarily on observations and model studies of dry convection, whereas the influence of moist convection on these characteristics is not well understood. Large-eddy simulations are used to investigate the effect of moist convection on an idealized mesoscale circulation. Sensitivity studies show that moist convection has a significant influence on the characteristics of the mesoscale circulation. We identify three distinct convective phases that influence the mesoscale circulation within the diurnal cycle: firstly, dry convective onset, with a weak circulation and a breeze front that propagates slowly from the cold region into the warmer fluid as a result of the surface discontinuity; secondly, a deep convective phase, where the circulation intensifies and the breeze front propagates faster; and finally a precipitating phase, where strong cold pools develop at the breeze front and accelerate the propagation speed further. Classical density-current theory fails to represent the second phase and is extended using the cloud-base mass flux to account for the observed effects of moist non-precipitating convection on the propagation speed. We demonstrate the applicability of this theory to the results from large-eddy simulations, identify the subtle role of cold pools on density-current propagation and highlight implications for numerical weather prediction. © 2015 Royal Meteorological Society.
