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

Abstract

Abstract. The motion and evolution of binary tropical cyclones was investigated using a coupled tropical cyclone-ocean movable nested grid model. The model consists of eight-layer atmospheric and seven-layer ocean primitive equation models. Several regimes of binary storm interaction have been identified, depending on the initial separation distance (a) and differences in storm strengths. At d less than a few hundred kilometers, interacting storms experienced 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: PM, straining out (SO), characterized by complete disintegration of the weaker storm, and mutual straining out (MSO), characterized by weakening and dissipation of both storms. SO occurred when the interacting storms had substantially different intensities and strengths. MSO was observed when the interacting storms were comparable in size and intensity. In the latter case the storms were unable to approach each other at distances smaller than a certain minimum distance (of about 450-500 km) without being mutually stretched out. Moreover, initial attraction of the storms in this regime was replaced by repulsion, as frequently observed in the western Pacific. At d exceeding about 1000 km, elastic interaction (EI) was found, when the storms interact without any significant changes in their intensity and structure. In additional experiments with a conditional instability of the second kind (CISK) type parameterization of convective heating the storm interaction was very different: The storms were nearly axisymmetric and very compact, and they continued approaching each other until they merged. Thus more realistic simulations of binary storm interaction can be achieved by using a physically more reasonable convective parameterization.

Satellite radiance data assimilation for binary tropical cyclone cases over the western North Pacific

“…Previous studies with nondivergent barotropic models primarily focused on the critical separation distance for mutual interaction, attraction, or repulsion, and the factors that determined the degree of binary interaction [ Chang , ; DeMaria and Chan , ; Ritchie and Holland , ; Prieto et al ., ]. The interaction between binary TCs is more complicated, and it is significantly affected by baroclinicity in a three‐dimensional framework [ Wang and Holland , ; Khain et al ., ; Wu et al ., ; Jang and Chun , ]. Wang and Holland [] utilized a three‐dimensional primitive‐equation model to investigate the binary interaction of TCs, and they found two critical separation distances: mutual approach separation (MAS) and mutual merger separation (MMS).…”

Effects of thermodynamic profiles on the interaction of binary tropical cyclones

“…In that sense, we used the three observed climatological soundings, and this approach is generally similar to use a control sounding and two additional soundings with positive and negative changes from the control sounding in pure idealized systematic simulations. Similar to the present study, Falkovich et al [] and Khain et al [] investigated the interaction of binary TCs by using observed thermodynamic sounding from Jordan [].…”

“…Khain et al [] showed that two vortices on the β plane move northwestward with cyclonic looping motion when the initial separation distance is 640 km, based on the numerical simulation of the coupled tropical cyclone‐ocean model with the finest horizontal grid spacing of 40 km and 8 sigma levels. The results of Khain et al [] are more similar to those of the CTL‐B300 simulation in this study than those of the CTL‐B640 simulation. These differences are likely due to the use of different numerical models with different horizontal and vertical resolutions.…”

“…These differences are likely due to the use of different numerical models with different horizontal and vertical resolutions. The sensitivity of the model resolution is examined based on a few additional experiments on the β plane with a 40 km horizontal resolution, which is the same as that in the study by Khain et al []. It is found (not shown) that the two TCs rotate cyclonically with attraction when the initial separation distance is 640 km, and the two TCs probably merge in a similar manner to the results of Khain et al [] with a longer integration time.…”

A computational study on the nature of meso‐β scale vortex coalescence in a tropical atmosphere

“…As one might expect, similar conclusions on moist convection assisting merger can be found in earlier studies addressing the behavior of binary tropical cyclones [e.g., Chang , ; Wang and Holland , ]. Be that as it may, the generality of the principle that diabatic processes play a positive role in vortex coalescence has not gone unquestioned [ Falkovich et al ., ; Khain et al ., ]. The principle just stated will be further challenged by several of the numerical experiments at hand.…”