Generalized Empirical Formulas of Threshold Distance to C haracterize C yclone–Cyclone Interactions
Abstract: This paper presents a framework of using remote sensing imagery and image processing techniques to analyze the interaction among typhoons or tropical cyclones (TCs) with and without the involvement of mid-tropical depressions (TDs) or tropical storms (TSs). The cyclone-cyclone interaction (named the Fujiwhara effect) could happen when two TCs are located at a distance within 1400 km. However, when there exists a mid-TD between the two TCs even with a distance of more than 1400 km, but usually within a distance of 1500-2700 km, the mid-TD may induce impacts on the two cyclones, defined as a TD-inlaid cyclone-cyclone interaction. The existence of the mid-TD significantly complicates weather forecasting due to difficulty in modeling its influence on the two cyclones. In this paper, we proposed innovative empirical formulas of threshold distance to characterize cyclone-cyclone interactions either with or without the involvement of the TD(s). We generalize empirical formulas for interaction distances between TCs and TD/TS related to current-intensity number, size factor, height difference, and rotation factor. To validate the appropriateness of the generalized empirical formulas, we choose and analyze seven sets of twotyphoon events. It is shown that the generalized formulas successfully predicted the impact of mid inlaid TC/TS quantitatively. The mid-TD's effects on the two cyclones represent a new aspect and a significantly improved understanding for the prediction of more complicated cyclone-cyclone interactions. Note that the
empirical formulas are derived from a very small set of events and that they must be verified with a sufficient data set for future practical use.