Interaction of binary tropical cyclones in a coupled tropical cyclone-ocean model

The motion and evolution of binary tropical cyclones was investigated using a coupled tropical cyclone-ocean movable nested grid model. The model cons ists of eight-layer atmospheric and seven-layer ocean primitive equation mo dels. Several regimes of binary storm interaction have been identified, dep ending on the initial separation distance (d) and differences in storm stre ngths. At d less than a few hundred kilometers, interacting storms experien ced complete merger (CM) or partial merger (PM). At larger d (between about 600 km and 1000 km), three regimes of storm interaction have been found: P M, straining out (SO), characterized by complete disintegration of the weak er storm, and mutual straining out (MSO), characterized by weakening and di ssipation of both storms. SO occurred when the interacting storms had subst antially different intensities and strengths. MSO was observed when the int eracting storms were comparable in size and intensity. In the latter case t he storms were unable to approach each other at distances smaller than a ce rtain minimum distance (of about 450-500 km) without being mutually stretch ed out. Moreover, initial attraction of the storms in this regime was repla ced by repulsion, as frequently observed in the western Pacific. At d excee ding about 1000 km, elastic interaction CEI) was found, when the storms int eract without any significant changes in their intensity and structure. In additional experiments with a conditional instability of the second kind (C ISK) type parameterization of convective heating the storm interaction was very different: The storms were nearly axisymmetric and very compact, and t hey continued approaching each other until they merged Thus more realistic simulations of binary storm interaction can be achieved by using a physical ly more reasonable convective parameterization.