Weakening Relationship between East Asian Summer Monsoon and Asian-Pacific Oscillation after 1990s

Abstract

e East Asian summer monsoon (EASM), which is an important influencing summer climate of East Asia, is associated with large-scale change of the land-sea thermal contrast. e Asian-Pacific Oscillation (APO) can modulate the EASM because it not only represents the upper-tropospheric zonal land-sea thermal contrast over Asia and the Pacific region, but it also affects the sea surface temperature (SST) over the North Pacific, which can tune the land-sea thermal contrast for the EASM. is study revealed weakening of the APO-EASM relationship since the 1990s. It was found that the relationship between the APO and the EASM during 1948-1990 (1991-2016) was statistically significant (insignificant). Further study indicated that the APO was concurrent with significant positive SST in the central North Pacific and subtropical central-western Pacific during , which contributed to the shift of the Pacific Decadal Oscillation (PDO) from its cold to warm phase and led to a weakened EASM. e APO-related SST and atmospheric circulation anomalies were found statistically to be insignificant during 1991-2016, which indicates a weakening of influence of the APO on shift of the PDO, and even a weaker link to the EASM.

Interdecadal Variability in the Interface Between the Indian Summer Monsoon and the East Asian Summer Monsoon

“…The major controls of the IIE‐IDV (i.e., the APO‐like mode and the NAT‐like mode) are also among the climate modes identified as the primary causes of the ISM‐IDV and the EASM‐IDV (Ping et al., 2008; Zhang et al., 2018; Zhao et al., 2007; Zuo et al., 2013). The weakening of the IIE–APO relationship also agrees with previous findings of a weakened relationship between the APO and the EASM (Hua et al., 2019). However, other climate modes significantly associated with the EASM‐IDV or the ISM‐IDV, such as the Pacific decadal oscillation (PDO), Atlantic multidecadal oscillation (AMO), and the Indian Ocean Basin mode (IOBM), are absent in the correlation map of the IIE‐IDV.…”

“…From the perspective of water vapor transport, the meridional mode of the ISM–EASM interaction is associated mainly with the El Niño–Southern Oscillation (ENSO) phase transition and the Indian Ocean basin mode, whereas the zonal mode of the ISM–EASM interaction is related to the developing phase of ENSO (Liu & Huang, 2019). The ISM–EASM interaction is also linked to SSTAs over the tropical and North Atlantic (Chen et al., 2018; Jin & Huo, 2018; Svendsen, 2021; Zuo et al., 2013), tropical and North Pacific (Cha et al., 2011; Hua et al., 2019; Joshi et al., 2021; Karami et al., 2015; Wu, Chen, & Chen, 2012), and tropical and North Indian Ocean (Boschat et al., 2011; Prodhomme et al., 2015; Ratna et al., 2021; Terray et al., 2012; Weldeab et al., 2022).…”

“…The SST modes described above couple with their corresponding atmospheric modes to affect either the ISM or the EASM. These air-sea coupled modes constitute the circumglobal teleconnection (CGT) (Huang et al, 2021;Wang et al, 2012) and the Arctic Oscillation (AO) (Chen et al, 2015(Chen et al, , 2020Dai et al, 2018;Gao et al, 2014;Gong et al, 2011;Sakashita et al, 2018), together with their close relatives the North Pacific Oscillation (NPO) (Sakashita et al, 2017;Yu et al, 2019), the North Atlantic Oscillation (NAO) (Sun & Wang, 2019;Wu, Li, et al, 2012;Zheng et al, 2016;Zuo et al, 2012), and the Asian-Pacific Oscillation (APO) (Hua et al, 2019;Liu et al, 2011;Zhao et al, 2007Zhao et al, , 2010Zhao et al, , 2012Zhou et al, 2010). Specifically, the APO represents the seesaw mode of eddy air temperature over the extratropical Asian-Pacific region, associated with warm (cold) SSTAs over the North Pacific during its positive (negative) phase.…”

Linkage Between Preceding August Asian–Pacific Oscillation and September Precipitation Over Southeast China

“…During summer, when the mid-upper troposphere is warmer over Asia, the troposphere above the North Pacific will be colder, and vice versa. The APO can exert substantial impacts on regional-global climatic change via the monsoon circulations and precipitation (Zhao et al, 2007(Zhao et al, , 2012aZhou et al, 2009;Liu et al, 2011;Zou et al, 2015;Hua et al, 2019;Lin et al, 2019Lin et al, , 2021, tropical cyclone activity (Zhou et al, 2008;Zou and Zhao, 2010), and variations in SST (Zhao et al, 2010(Zhao et al, , 2011(Zhao et al, , 2012b. Furthermore, the APO occurs throughout the year, not just in the summertime Lin et al, 2019).…”