Effects of Environmental Wind and Thermodynamic Profiles on the Interaction of Binary Tropical Cyclones

The interactions of idealized binary tropical cyclones (TCs) in a β-plane with different background wind and thermodynamic soundings are investigated through three-dimensional numerical simulations. Relatively high resolution simulations in a wide single domain with a horizontal grid spacing of 10 km are conducted by 288 hours integration to represent realistic dynamic as well as thermodynamic processes of each TC and their interactions. In the control simulations (CTL) conducted with a Jordan thermodynamic sounding without background wind, two TCs merge with a filamentation process when they originally separated by 300 km (CTL-300). When thermodynamic profiles are changed to the soundings from National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) reanalysis data averaged over the western North Pacific (WNP) during the last 34 years (1979-2012), the interaction between two TCs becomes weaker due to weaker intensities of TCs by smaller maximum potential intensity (MPI). In the simulation with background wind profile from the reanalysis data, two TCs merge earlier and stronger TC is formed after merger than those from the CTL-300 simulation. The earlier merger is caused by north-south orientation of two TCs due to the effect of southeasterly background wind, and the combined single TC can more develop without the competition with a counterpart TC. When the background wind and thermodynamic profiles obtained from the reanalysis data are used, no merge takes place for two TCs, because weaker tangential velocity from a counterpart TC with smaller MPI induces weaker interactions between two TCs, regardless of the northwestward background wind that pushes the western TC to the northwestward compared with the CTL-300 simulation.