Relative Controls of Asian–Pacific Summer Climate by Asian Land and Tropical–North Pacific Sea Surface Temperature

Abstract

The dominant pattern of summertime tropical and North Pacific sea surface temperature (SST) is characterized by an out-of-phase relationship between the tropics and the extratropics. This pattern, defined as the tropical-North Pacific mode (TNPM) in this study, is closely correlated with the variability of climate over Asia and the Pacific Ocean. A high TNPM index, with positive (negative) SST anomalies over the extratropics (tropics) of the Pacific, is linked to deep negative anomalies of tropospheric temperature over the extratropical Pacific, with shallow positive anomalies in the lower troposphere, and is also linked to deep positive temperature over Asia. It is also found that these anomalies of tropospheric temperature and SST are significantly related to the Asian-Pacific Oscillation (APO), an extratropical zonal-vertical atmospheric pattern connecting Asia and the Pacific. Indeed, when the variability of APO is removed, the above-described climate anomalies weaken significantly. Although the above relationships observed between atmospheric circulation and SST can be captured by general circulation models, sensitivity experiments show that the variations of summertime AsianPacific atmospheric circulation may not be mainly forced by the Pacific SST. Instead, the Asian land elevated heating seems to play a more important role in generating the climate anomalies, as shown by model-sensitivity experiments in which changes in topographic height are included. Moreover, the relative importance of Asian land and Pacific SST for the variations of Asian-Pacific climate in summer and winter is compared in this study. In winter the most dominant mode of Pacific SST exerts a stronger impact on the Asian-Pacific climate.

Boreal summer continental monsoon rainfall and hydroclimate anomalies associated with the Asian-Pacific Oscillation

“…Thus such a poor correlation between the summer APO and the previous winter possibly implies a weaker influence of the previous winter Pacific SST on the boreal summer APO and associated climate anomalies. Moreover, some simulations also showed a weaker forcing of SST anomalies to the APO-like phenomenon (Zhou and Zhang 2009;Zhao et al 2010aZhao et al , 2011b. However, we do not understand the seasonal dependence of the SST-APO relationship.…”

“…The previous study has noted the link of the APO with ENSO and PDO (Zhao et al 2010a(Zhao et al , 2011b. Here, we further examine the relationship between the APO and global SST.…”

Precessional forced extratropical North Pacific mode and associated atmospheric dynamics

“…The studies of the present climate have also argued that the warming of the western‐central extratropical North Pacific may induce significant anomalies of tropospheric temperature and atmospheric circulation over the Asian‐Pacific region during winter [ Kushnir et al ., ; Peng et al ., ; Zhao et al ., ]. The results from full air‐ocean coupled model experiments showed a quasibarotropic warm SST‐ridge response over the North Pacific in early winter [ Liu et al ., ; Liu and Wu , ; Wu and Li , ] and this response is possibly associated with nonlinear feedback of atmospheric transient eddies [ Peng and Whitaker , ; Peng et al ., ].…”

What does the APO mean?

“…(3) There have been many investigations showing the relationship between the APO and other atmospheric phenomena (Zhou et al, 2009;Liu et al, 2011a;Wang et al, 2012;Zhou and Zhao, 2013, etc.). These simultaneous correlations or composite analyses were used to demonstrate that APO phases could be associated with variations in other indexes, for example, the monsoon index (Z07; Zhao et al, 2011aZhao et al, , 2011bZhao et al, , 2011cZhao et al, , 2012aZhao et al, , 2012b. However, these analyses may be unnecessary since the APO cannot replace any other index that specialised in describing a specific phenomenon due to the weak correlations.…”