Relationship of tropical-cyclone-induced remote precipitation with tropical cyclones and the subtropical high

Abstract

This study concerns the precipitation induced by a tropical cyclone (TC) before the TC arrives, which will be referred to as TC remote precipitation (TRP). Based on the distribution characteristics of the non-rotational wind and the divergent-wind vertical circulation related to TC, the subtropical high, and TRP of 45 TRP events during June, July, and August of 2000‒2009, the relationships among these three entities (TC, subtropical high, and TRP) can be categorized into four patterns. The first pattern accounts for the highest proportion of the TRP events (59%), and a conceptual model is then provided for this pattern. The primary characteristics of this model are as follows: TC, the subtropical high, and TRP can interact with each other through the divergent-wind secondary circulation at both sides of the ridge line of the subtropical high (between the subtropical high and TC, and between the subtropical high and TRP). At the upper level (150 or 200 hPa), the northward non-rotational wind from the TC converged toward the subtropical high ridge line and subsided, and at 950 hPa the divergent wind from the ridge line of the subtropical high converged toward TC; these constructed the secondary circulation between TC and the subtropical high. In the meantime, the southward nonrotational wind at the upper level (150 or 200 hPa) from TRP and the divergent wind at 950 hPa from the subtropical high ridge line toward TRP constructed the secondary circulation between TRP and the subtropical high. As TC and TRP interacted with each other, the subtropical high ridge line was usually under the downdraft area of the whole atmosphere. The other three patterns are different from the first pattern mainly in terms of the intensity and position of the non-rotational-wind secondary circulation. The numerical simulation of the Beijing 7•21 rainstorm confirmed the relationship among TC, the subtropical high, and TRP, indicating that when the interaction weakened, the TRP also weakened.