Using models of mesoscale flows over orography and urban areas to examine effects of climatic and environmental trends
Julian HuntUniversity College London
Monday October 8th, CNRM Conference Room - 11h
Recent research has shown how the patterns of atmospheric flows over and around mountain ranges and areas of large changes in surface roughness vary considerably and quite sensitively depending on their dimensions the characteristics of the approach flow,(wind speed, stratification, and the Coriolis frequency ). 'Slope-flows' driven by local buoyancy forces on mountain/valley slopes may in certain conditions be larger than the synoptically driven winds.
Using linearised theoretical models (Hunt, Olaffson and Bougeault 2001, Hunt, Orr, Rottman and Capon, 2004) for perturbed mesoscale and synoptic scale flows the critical dimensionless parameters and the characteristic flow effects, and their sensitivity to climatic change, can be estimated.
Recent studies comparing these models with lab and field experiments are described, particularly those around the Antarctic peninsula where large rises in temperature have been observed over the past 30 years.
The main effect of global warming on the structure of the atmosphere is (following Mitchell) to reduce the stable stratification in the troposphere, which leads to stronger westerly winds at temperate latitudes and slowly raises the tropopause height. These changes significantly affect orographic flows with profound consequences for the regional climates.
Similar linearised models show how air flow and inversion height vary along coasts and over urban areas as a result of sharp changes in surface roughness and surface temperature/heat flux. Wind jets , which can vary rapidly in strength over a few kilometers along coasts, are exploited for their contribution to wind energy and winning sailing races ! . The effects of Coriolis appear to be significant in reducing the depth of the inversion height over large urban areas , which is of real concern as the heat island and levels of pollution rise in these areas. Both these coastal and urban effects are sensitive to the likely changes in the atmospheric structure caused by future climate change.
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