Variations of the Mid-Pacific Trough and Their Relations to the Asian–Pacific–North American Climate: Roles of Tropical Sea Surface Temperature and Arctic Sea Ice

Abstract

The mid-Pacific trough (MPT), occurring in the upper troposphere during boreal summer, acts as an atmospheric bridge connecting the climate variations over Asia, the Pacific, and North America. The first (second) mode of empirical orthogonal function analysis of the MPT, which accounts for 20.3% (13.4%) of the total variance, reflects a change in its intensity on the southwestern (northeastern) portion of the trough. Both modes are significantly correlated with the variability of tropical Pacific sea surface temperature (SST). Moreover, the first mode is affected by Atlantic SST via planetary waves that originate from the North Atlantic and propagate eastward across the Eurasian continent, and the second mode is influenced by the Arctic sea ice near the Bering Strait by triggering an equatorward wave train over the northeast Pacific. A stronger MPT shown in the first mode is significantly linked to drier and warmer conditions in the Yangtze River basin, southern Japan, and the northern United States and wetter conditions in South Asia and northern China, while a stronger MPT shown in the second mode is associated with a drier and warmer southwestern United States. In addition, an intensified MPT (no matter whether in the southwestern or the northeastern portion) corresponds to more tropical cyclones (TCs) over the western North Pacific (WNP) and fewer TCs over the eastern Pacific (EP) in summer, which is associated with the MPT-induced ascending and descending motions over the WNP and the EP, respectively.

Perspective on the northwestward shift of autumn tropical cyclogenesis locations over the western North Pacific from shifting ENSO

“…As the black dashed lines shown in Fig. 2a-d, the climatological TUTT, also known as the mid-oceanic trough (e.g., Ferreira and Schubert 1999) or the mid-Pacific trough (Deng et al 2017), often elongates from east-northeast to west-southwest over the tropical oceans. According to Wang and Wu (2016), the WNP TCs often occur to the west of TUTT, mostly over the region of 115°E-160°E, 0°-20°N, due to the strong vertical wind shear to the southeast of the trough (e.g., Kelley and Mock 1982;Fitzpatrick et al 1995).…”

“…Existing theories also suggest that the east-west shifts of tropical upper-tropospheric trough (TUTT) and MT may induce changes in WNP TCLs (e.g., Lander 1994;Wu et al , 2015Zhao et al 2014b;Huang et al 2016;Wang and Wu 2016;Deng et al 2017;Huangfu et al 2017) on both interannual and interdecadal timescales. It was ever pointed out that the mean TCL showed a westward shift over the WNP mainly due to (1) the pronounced westward shift of TUTT (Wu et al 2015) and/or (2) the interdecadal change of the WNP MT (Huangfu et al 2017).…”

Weakening of Indian Summer Monsoon Synoptic Activity in Response to Polar Sea Ice Melt Induced by Albedo Reduction in a Climate Model

“…Deng et al. (2018) argued that the variability in the Arctic sea ice might influence the mid‐Pacific trough, which in turn can affect the TC genesis over the northwest Pacific. The response of ocean dynamics to the sea ice melt can induce a global oceanic response (Deser et al., 2010; Liu & Fedorov, 2019).…”

“…Aquaplanet simulations suggest that a poleward shift in the ITCZ would result in an increased frequency of TC-like synoptic scale weather systems (Ballinger et al, 2015). Deng et al (2018) argued that the variability in the Arctic sea ice might influence the mid-Pacific trough, which in turn can affect the TC genesis over the northwest Pacific. The response of ocean dynamics to the sea ice melt can induce a global oceanic response (Deser et al, 2010;Liu & Fedorov, 2019).…”

Promoting seasonal prediction capability of the early autumn tropical cyclone formation frequency over the western North Pacific: effect of Arctic sea ice

“…A previous study has noticed an intimate relationship between the spring North Pacific sea ice and the WNP TCF during the ensuing TC season (Fan 2007). More recently, Deng et al (2017) found a statistical connection between the late summer (JA) sea-ice variability from the East Siberian to Beaufort Seas and the variation of the simultaneous TC activity through the middle Pacific trough acting as an 'atmospheric bridge' . Fu et al (2021) proposed that the SST anomaly in the Japan Sea acts as a 'recharger' , prolonging the spring Bering sea ice signal to the TC season to modulate the variability of the TC activity.…”