Tropical Cyclone (TC) Intensity Change Caused by Binary TC Interaction

Binary tropical cyclone interaction not only affects the TC's motion and track, but also influences the intensity change of both TCs in the pair. When the trend of axis connected with centers of both TCs appears southwest to northeast, namely the relative locality of TC B is in the southwest and TC A is in the northeast. TC B would transport vorticity and moisture to the TC A which would be intensified after gain energy from TC B. The energy transportation is via the peripheral southwesterly flow of TC B. Most typhoons will gradually decrease somewhat intensity when they approach the coastal land, but small amount of typhoons will increase its intensity (Yu 2015). Super typhoon Saomai (0608) is the typical one which increases intensity dramatically when it moves approach of the east coast of China. In this special period, Saomai (0608) interact with another severe storm Bopha (0609) in the coastal water that occur a binary typhoon interaction. The research (Yu et al 2014) shows that large amount vorticity lumps from Bopha was engulfed by Saomai that was rapid intensified. On the other hand, Bopha was gradually dissipated in the coastal water after it lost the energy. The another pair of binary TC interaction is occurred between Morakot (0908) and Goni (0907). Morakot maintained its intensity and circulation over land surface for longer time without dissipation and brought about extremely heavy rainfall. Study (Xu et al 2011) shows that the severe storm Goni transport a plenty of water vapor into Morakot to maintain its intensity and produce heavy rainfall. The another study indicates that the dissipation of Goni is caused by Morokot which absorb large amount of moisture from Goni and finally lead to dissipation of the storm in the coastal water of South China Sea. The dissipation of Goni is a result of binary typhoon interaction. We call it as a pumping effect (Zeng 2012). Most of binary TC interaction show that the pair TC would be separated after their interaction. Only a few of them would merge each other. Observational analysis (Chen et al 2012) showed that Ellen (7009) and Fran (7010) is a pair of binary TC. Both of their circulation was merged each other after the interaction. The intensity of the vortex was rapidly intensified after its merging. Apart from the binary typhoon merging, the study (Chen and Luo 2004) showed the tropical cyclone would increase its intensity rapidly if a peripheral mesoscale vortex is engulfed by the original TC.

References Yu Hui 2015. Statistics on tropical cyclone intensity rapid intensification, weakening and dissipation over coastal water. Content in the Chapter 5 of the Book of 973 National Key Program on Tropical Cyclone Rapid Change Phenomena in Coastal Water. (waiting for publication). Yu Yubin 2014. Numerical simulation on rapid intensification of super Typhoon Saomai with a remnant embroiled. Acta Oceanologica Sinica, 36(1) (in Chinese). Xu Xiangde et al 2011. A possible Mechanism responsible for exceptional rainfall over Taiwan from Typhoon Morakot. Atmospheric Science Letter, 2011. Doi. 10. 1002/asl. 338.pp.1-6. Zeng Zhihua 2015. The Content in the Chapter 5 of the Book of 973 National Key Program on Tropical Cyclone Rapid Change Phenomena in Coastal Water (waiting for publication). Chen Lianshou et al, 2012. Typhoon Forecast and Its Disaster. China Meteorological Press (in Chinese). Chen Lianshou, Luo Zhexian 2004. Interaction of typhoon and mesoscale vortex. Advances in Atmospheric Sciences, 12(4).