Clustering of large‐scale circulation patterns during tropical cyclone preformation period using self‐organizing maps

Abstract

Based on self‐organizing maps (SOM), clustering analysis is performed on the lower‐level large‐scale flow fields centred at the tropical cyclone (TC) genesis points averaged over the 24‐hr TC preformation period. A total of 461 TCs over the western North Pacific (WNP) from June to November in 2000–2019 are classified into five patterns, that is, convergence (CON) pattern, monsoon trough (MT) pattern, pre‐existing cyclone (PC) pattern, subtropical high (SH) pattern and easterly wave (EW) pattern. The most frequent and southmost pattern, the CON pattern, is characterized by a confluent zone of monsoonal southwesterly flows and easterly flows. The second dominant pattern, the MT pattern, occurs the westmost and has a larger cyclonic vorticity in the strongest monsoon trough among the five patterns. In contrast, cyclogenesis in the SH pattern is featured by both the confluent zone and the cyclonic wind shear largely attributed to the subtropical high. The PC pattern features a pre‐existing cyclone to the northwest. The EW pattern with easterly flows in all four adjacent quadrants has the smallest number of TC formation and relatively northeast genesis location. Statistics also shows that the CON pattern dominates in late season, while the other four mainly appear in summertime. Large‐scale environmental conditions are quantified and comparisons with previous studies are also discussed.

An Approach to Link Climate Model Tropical Cyclogenesis Bias to Large‐Scale Wind Circulation Modes

“…Tropical cyclogenesis (TCG) climatology is fundamental for understanding TC variation and changes in the past and future. Large‐scale wind circulations can provide favorable conditions for TCG (Feng et al., 2022; Lander & Holland, 1993; Ritchie & Holland, 1999; Wang, 2017; Wang et al., 2019, 2022). Through scale interactions with synoptic disturbances, the monsoon trough (MT) and intertropical convergence zone are hypothesized to act a “seeding bed” of WNP TCs (Feng & Wu, 2022; Gu et al., 2022; Wu et al., 2012).…”