Modulations of El Niño-Southern oscillation on tropical cyclone activity affecting Taiwan

This study demonstrates asymmetric relationships between El Niño–Southern Oscillation (ENSO) and tropical cyclones (TCs) affecting the Philippines during October–December. In El Niño or La Niña years, the number of TCs impacting the Philippines may increase or decrease. These variations result in four ENSO–TC variability types all of which exhibit strong sea surface temperature (SST) anomalies across the equatorial eastern Pacific. The major difference between the active and inactive types in terms of El Niño or La Niña years is related to the magnitude of SST anomalies in the tropical western Pacific (TWP) over the 120°–150°E region. During El Niño years, moderate cold SST anomalies in this TWP region cause an anomalous divergent centre around the 120°–130°E zone to evoke an anomalous cyclone east of the Philippines. In the western North Pacific (WNP), this anomalous cyclone causes more TCs to form and move toward the Philippines, resulting in active TC activity. For the inactive TC type during El Niño years, very weak cold SST anomalies in the aforementioned TWP region correspond with a northeastward‐extended anomalous divergent centre over the 120°–140°E, 10°S–20°N zone and an anomalous anticyclone across the Philippines and its eastern side. Decreases in the formation of the WNP TC and movement toward the Philippines lead to inactive TC activity. The large‐scale anomalies and regulating processes are mainly opposite between the active TC type during El Niño years and the inactive TC type during La Niña years. These two types are influenced by interdecadal variability of the Pacific decadal oscillation. Opposite anomalies and regulating processes also occur between the inactive TC type during El Niño years and the active TC type during La Niña years. The former type is jointly modulated by the positive Indian Ocean Dipole mode and central‐Pacific El Niño.

Section: Introductionmentioning

confidence: 87%

Asymmetric El Niño–Southern Oscillation and tropical cyclone relationships in the Philippines during October–December

Lai,

Chen

2024

“…The MT migrates northward during summer and displaces southward during fall (Chen et al, 2017). TC activity is normally investigated for its salient feature in the peak JAS season (Lai et al, 2022(Lai et al, , 2023Shan & Yu, 2023) or its gross feature in the broader JJASO period (Chu et al, 2010;Tu et al, 2009). In the former approach, variability features of TC activity may be further compared between the peak JAS and post-peak October-December (OND) seasons (Feng et al, 2021;Shan & Yu, 2021).…”

Section: Interdecadal Variability Of Meridional Tc Genesis In the Wnpmentioning

confidence: 99%

Interdecadal variability of meridional tropical cyclone genesis over the western North Pacific and associated modulating processes

Tu,

Chen,

Tan

et al. 2023

During the period 1970–2020, evident interdecadal variability of meridional tropical cyclone (TC) genesis occurs in the western North Pacific (WNP) from September through October (SO). From the periods 1970–1996 (IP1) to 1998–2020 (IP2), TC genesis during SO is enhanced (suppressed) in the region north (south) of 20°N. The large‐scale modulating processes feature a general warming of sea surface temperature (SST) over the WNP and systematic northward displacement in atmospheric circulations. The northward‐shifted Pacific subtropical high and monsoon trough result in an anomalous anticyclone across the subtropical region and an anomalous cyclone across the South China Sea and the northern WNP east of Taiwan. This anomalous cyclone facilitates TC genesis to increase in the northern WNP. Meanwhile, the southeastward‐extending monsoon trough retreats northwestward, leading to an anomalous anticyclone over the tropical eastern WNP and a decrease in TC genesis over the southern region. Correlation analyses indicate that the Pacific Decadal Oscillation (PDO) is more effective than global warming in modulating interdecadal increases of TC genesis in the northern region due to inclusions of both trend and oscillation features. Interdecadal decreases of TC genesis in the southern region exhibit a major oscillation feature and are thus mainly affected by interdecadal oscillation components of PDO. More TCs forming in the oceans east of Taiwan are steered by the overlying anomalous cyclone to recurve northward toward oceans to the northeast and north of Taiwan. TC‐induced rainfall over Taiwan thus increases by 25% from IP1 to IP2, which accounts for about 82% of increased total rainfall in Taiwan, showing the notable impact of interdecadal TC genesis on local climate in the WNP.

“…The appearance of a westward‐extended anomalous cyclone over the WNP reflects a weakened and eastward‐shrunk WPSH. TCs thus tend to move northwestward/northward in the western WNP driven by southeasterly/southerly flows in the western sector of a weakened and eastward‐retreated WPSH (Lai et al, 2022; Zhao et al, 2011). Steering flow analyses in the previous section substantiate that this zonally elongated anomalous cyclone is responsible for steering TCs from the tropical eastern WNP northwestward to strengthen TC activity around Taiwan.…”

Section: Large‐scale Processes Affecting Tc Activity Around Taiwanmentioning

confidence: 99%

“…Most TCs in the WNP have their genesis assisted by the monsoon trough (MT) over a region 10°–20°N and later follow flows in the southern periphery of the western Pacific subtropical high (WPSH) to move westward, northwestward or northward (Chu et al, 2010; Kim et al, 2012; Tu & Chen, 2019). During July–September (JAS), TCs with a northwestward or recurving northward track normally approach or make landfall on Taiwan resulting in its peak TC season (Chen & Shih, 2012; Lai et al, 2022). Although TCs have a very high chance of causing significant losses in property and lives during their landfall, rainfall brought by TCs is a major water resource for Taiwan (Chen & Chen, 2011; Tsou et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

“…During El Niño years, the MT tends to intensify eastward in company with an eastward shift in TC genesis to the southeastern sector of the WNP (Bell et al, 2014; Lai et al, 2021; Lander, 1994; Zhan et al, 2011). The WPSH tends to weaken and yields an anomalous cyclone which guides more TCs northward toward the northern North Pacific (Lai et al, 2022; Zhao et al, 2011), as well as inducing longer lifetimes and stronger accumulated convective energy (Camargo & Sobel, 2005). Accordingly, more TCs move toward Japan and Korea during the TC season of El Niño years (Fudeyasu et al, 2006) with fewer TCs moving toward the Philippines (Kubota & Chen, 2009).…”

Section: Introductionmentioning

confidence: 99%

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Tropical cyclone activity around Taiwan modulated by El Niño during 1900–1945 and 1970–2015

Tan,

Chen,

et al. 2023

Tropical cyclone (TC) activity around Taiwan is analysed via typhoon datasets compiled by the Central Weather Administration (CWA) for the pre‐satellite era of 1900–1945 (IE1) and the satellite era of 1970–2015 (IE2). Modulating processes imposed by El Niño years on active and inactive TC activity around Taiwan in the July–September season are examined and compared between IE1 and IE2. Analyses reveal coherent dynamic relationships between TC variability in Taiwan and large‐scale modulating processes; furthermore, modulating processes exhibit similar features between IE1 and IE2. El Niño years tend to have more (less) TC formation in the eastern (western) sector of the western North Pacific (WNP). In both IE1 and IE2, intensified TC activity around Taiwan is associated with northwestward TC tracks from the eastern WNP toward Taiwan assisted by a westward‐elongating cyclonic anomaly across the WNP and South China Sea. When a WNP cyclonic anomaly stretches northwestward toward oceans north of Taiwan, TCs from the tropical eastern WNP generally move northward toward oceans east of Taiwan to result in suppressed TC activity around Taiwan. The westward‐elongating anomalous cyclone is associated with an anomalous divergent centre over the Indian Ocean and an anomalous convergent centre in the tropical eastern Pacific over the 150°–130°W region. The northwestward‐extending anomalous cyclone connects with an anomalous divergent centre over the Maritime Continent and an anomalous convergent centre over the 130°–110°W region. Anomalous divergent and convergent centres displace westward (eastward) for active (inactive) TC types that are related to a more westward (eastward) maximum centre of anomalous warm waters in the tropical eastern Pacific. The above coherent dynamic relationships justify the reliability of TC records compiled by the CWA during IE1 and IE2.