Tropical Cyclone Formation within Strong Northeasterly Environments in the South China Sea

Abstract

In the South China Sea (SCS), 17% of tropical cyclones (TCs) formed in the late season (November−January) were associated with a strong northeasterly monsoon. This study explores the effects of northeasterly strength on TC formation over the SCS. The Weather Research and Forecasting (WRF) model is used to simulate the disturbances that develop into TCs (formation cases) and those that do not (non-formation cases). Two formation (29W on 18 November 2001 and Vamei on 26 December 2001) and two non-formation (30 December 2002 and 9 January 2003) cases are simulated. To address the importance of upstream low-level northeasterly strength to TC formation, two types of sensitivity experiments are performed: formation cases with increased northeasterly flow and non-formation cases with decreased northeasterly flow. If the strength of the northeasterly is increased for the formation case, the stronger cold advection reduces the convective instability around the disturbance center, leading to the weakening of the simulated disturbance. If the strength of the northeasterly is decreased for the non-formation case, the simulated disturbance can develop further into a TC. In summary, strength of the upstream low-level northeasterly flow does affect the environmental conditions around the disturbance center, resulting in the change of TC formation probability over the SCS in the late season.

Corals Reveal Interdecadal Variation of Tropical Cyclones Modulated by Pacific Decadal Oscillation

“…As a whole, the interdecadal variation of TC frequency in the SCS is linked to the phase transitions of the PDO. TC formation and development in the SCS in response to climate change highlights the role of dynamic factors (Lin et al., 2021; Sun et al., 2019). When PDO is in the negative phase, the more negative ZSG could modulate the atmospheric circulations at interannual and interdecadal time scales (Li & Zhou, 2014), which induces the eastward movement of the WPSH (Li et al., 2019; Figures 8d and 8e).…”

“…The SCS, a large semi‐enclosed marginal sea in the WNP (Figure 1a), is influenced by the climatic scale systems such as the East Asian monsoon and ENSO (Haghroosta & Ismail, 2017; Lin et al., 2021; Yan et al., 2011). The summer and winter SST in the northern SCS are influenced by the Western Pacific Warm Pool and the East Asian winter monsoon, respectively (Chen et al., 2018; Yan et al., 2015), while summer rainfall is affected by the East Asian summer monsoon (Ding & Chan, 2005).…”

Unraveling the strong covariability of tropical cyclone activity between the Bay of Bengal and the South China Sea

“…Therefore, TCs over the SCS may have a closer connection with TCs over the BOB after summer. It was suggested that SCS TCs are even more active than those over the western North Pacific (WNP) during the late-season [14][15][16] . Although TC activity in the SCS peaks in the summer months, late-season TCs can still account for 31% of the annual TC frequency in this region (Fig.…”

“…Besides, similar to the BOB, the SCS is also surrounded by land. The geography of bay and sea leads to a short warning period for countries surrounding the bay and the sea 16 , requiring deeper understanding of TC variability there.…”