Establishment of an Objective Standard for the Definition of Binary Tropical Cyclones in the Western North Pacific
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• Original Paper •
Establishment of an Objective Standard for the Definition of Binary Tropical Cyclones in the Western North Pacific Fumin REN*1,2, Yanjun XIE3, Biwen YIN4, Mingyang WANG2, and Guoping LI2 1State
Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing 100081, China
2School
of Atmospheric Sciences, Chengdu University of Information Technology, Chengdu 610225, China 3Zhuzhou 4Qinhuangdao
Meteorological Observatory, Zhuzhou 412000, China Meteorological Observatory, Qinhuangdao 066000, China
(Received 30 December 2019; revised 3 July 2020; accepted 7 July 2020) ABSTRACT To develop an objective standard for defining binary tropical cyclones (BTCs) in the western North Pacific (WNP), two best-track datasets, from the China Meteorological Administration and the Joint Typhoon Warning Center, were adopted for statistical analyses on two important characteristics of BTCs—two TCs approaching each other, and counterclockwise spinning. Based on the high consistency between the two datasets, we established an objective standard, which includes a main standard for defining BTCs and a secondary standard for identifying typical/atypical BTCs. The main standard includes two requirements: two coexisting TCs are a pair of BTCs if (i) the separation distance is ≤ 1800 km, and (ii) this separation maintains for at least 12 h. Meanwhile, the secondary standard defines a typical BTC as one for which there is at least one observation when the two TCs approach each other and spin counterclockwise simultaneously. Under the standard, the ratio of typical BTCs increases as the BTC duration increases or the minimum distance between the two TCs decreases. Then, using the JTWC dataset, it was found that there are 505 pairs of BTCs during the period 1951−2014, including 328 typical BTCs and 177 atypical BTCs, accounting for 65.0% and 35.0% of the total, respectively. In addition, a study of two extreme phenomena—the maximum approaching speed and the maximum counterclockwise angular velocity in typical BTCs—shows that the configuration of the circulation conditions and the distribution of the BTCs favor the formation of these extreme phenomena. Key words: objective standard, binary tropical cyclones, Western North Pacific Citation: Ren, F. M., Y. J. Xie, B. W. Yin, M. Y. Wang, and G. P. Li, 2020: Establishment of an objective standard for the definition of binary tropical cyclones in the western North Pacific. Adv. Atmos. Sci., 37(11), 1211−1221, https://doi.org/ 10.1007/s00376-020-9287-3. Article Highlights:
• An objective standard for the definition of BTCs in the WNP, which includes a main standard for defining BTCs and a secondary standard for identifying typical/atypical BTCs, has been established.
• The main characteristics of BTCs in the WNP are analyzed using the objective standard. • Two extreme phenomena show that the configuration of the circulation conditions and the distribution of the BTCs favor
the formation of the extreme phenomena.
1. Introduction A binary vort
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