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The effect of mechanical forcing on the formation of a mesoscale vortex
Author(s) -
Wu GuoXiong,
Chen ShouJun
Publication year - 1985
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.49711147009
Subject(s) - orography , mesoscale meteorology , forcing (mathematics) , geology , vortex , climatology , meteorology , atmospheric sciences , precipitation , geography
The influence of mechanical forcing on the formation of a mesoscale vortex which occurred over the eastern flank of the Qinghai‐Tibetan Plateau (QTP) is investigated by running a series of numerical experiments. Different orography schemes are tested. It is shown that there are three branches of air flow converging towards the vortex: the northerlies associated with the middle latitude westerly currents, the southerlies with the lowlevel monsoon jet, and the easterlies with the west Pacific subtropical high. These flows are very sensitive to mechanical forcing and play very important roles in the formation and location of the vortex. The model with either the mean or the envelope orography is shown to be capable of predicting the formation of the vortex and the associated torrential rain. However, its location is not predicted precisely. A modified orography, simulating the ‘step’ structure of the eastern flank of the QTP, is then used in an attempt to improve the prediction. Results from this experiment suggest that the weakening of some of the steep slopes of the large‐scale orography in a numerical model, due to excessive smoothing of mountain height and expanding of mountain area, is responsible for the inaccuracy in the forecast of such synoptic systems. Therefore further improvements in the orography scheme are discussed.