Season-dependent variability and influential environmental factors of super-typhoons in the Northwest Pacific basin during 2013–2017

Abstract

This paper investigates season-dependent variability and environment-dependent distributions of all 30 super-typhoons (STYs) that occurred in the Northwest Pacific (NWP) basin over 2013–2017. The increasing strength of typhoons (TYs) in the basin in recent years, especially in the winter season, is a big matter of concern for meteorological scientists as the basin already possesses a maximum frequency of TYs every year on the globe. The paper aims to mitigate the impacts of STYs in the study region by enhancing the understanding of their seasonal nature. The incorporation of remote sensing imaginary and wind vector images created using U and V wind component data, successfully identify a dominant and crucial role of southwest air flow and northwest cold air mass in intensifying STYs in summer and winter seasons, respectively. The majority of winter STYs are also partially assisted by southwest air flows and, thus, exhibit higher intensities than summer STYs in general. For the season-dependent variability approach, both lower latitude westward tracks and higher latitude recurvature tracks are depicted within the certain zones for summer and winter STYs, respectively. Meanwhile, both turning points and super-typhoon stage points of both kinds of tracks are of crucial importance to help us understand the environmental zonal components responsible in changing the STYs’ direction and strength. The latitudinal and longitudinal borderline depicted the positions of turning points and super-typhoon stage points from where a TY is prone to take a turn or become a STY. The summer-season super-typhoons have a normal distribution of the higher latitude recurvature tracks. The winter-season super-typhoons have a normal distribution of the lower latitude westward tracks. The summer-season super-typhoons exhibit a higher degree of coincidence than winter-season super-typhoons. For environment-dependent distribution approach, super-typhoons accompanied by southwestern air flows, TC/TS and southwestern air flows, southwestern air flow and cooler air mass, TC, southwestern air flow and cooler air mass, and cooler air masses, are discussed and analyzed respectively. When super-typhoons, accompanied by southwestern air flows or both southwestern air flow and cooler air mass, exhibit a higher degree of coincidence than the other three situations of the accompanied effects. When the TC and TS exist in the environment of super-typhoons, and only accompanied by cooler air masses, the degree of coincidence shall be lower down. A systematic typhoon forecasting procedure with five steps is applied for effective prediction. It is observed that the Siberian-Mongolian High (SMH) originated cold air masses push the genesis positions of winter STYs more down in latitude than summer STYs, which cause not only a big genesis angle, but also a big turning angle on average in winter STYs in the NWP. These results are of crucial importance to investigate the relationship between STYs and their season-dependent environmental factors to mitigate their risk in the region.