On the variation of divergent flow: an eddy-flux form equation based on the quasi-geostrophic balance and its application

Abstract

Based on basic equations in isobaric coordinates and the quasi-geostrophic balance, an eddy-flux form budget equation of the divergent wind has been derived. This newly derived budget equation has evident physical significance. It can show the intensity of a weather system, the variation of its flow pattern, and the feedback effects from smaller-scale systems (eddy flows). The usefulness of this new budget equation is examined by calculating budgets for the strong divergent-wind centers associated with the South Asian high, and the strong divergence centers over the Tibetan Plateau, during summer (June–August) 2010. The results indicate that the South Asian high significantly interacts with eddy flows. Compared with effects from the mean flow (background circulation), the eddy flows’ feedback influences are of greater importance in determining the flow pattern of the South Asian high. Although the positive divergence centers over the Tibetan Plateau intensify through different mechanisms, certain similarities are also obvious. First, the effects from mean flow are dominant in the rapid intensification process of the positive divergence center. Second, an intense offsetting mechanism exists between the effects associated with the eddy flows’ horizontal component and the effects related to the eddy flows’ convection activities, which weakens the total effects of the eddy flows significantly. Finally, compared with the effects associated with the convection activities of the mean flow, the accumulated effects of the eddy flows’ convection activities may be more favorable for the enhancement of the positive-divergence centers.