An empirical seasonal prediction model of the east Asian summer monsoon using ENSO and NAO

Abstract

[1] How to predict the year-to-year variation of the east Asian summer monsoon (EASM) is one of the most challenging and important tasks in climate prediction. It has been recognized that the EASM variations are intimately but not exclusively linked to the development and decay of El Niño or La Niña. Here we present observed evidence and numerical experiment results to show that anomalous North Atlantic Oscillation (NAO) in spring (April-May) can induce a tripole sea surface temperature pattern in the North Atlantic that persists into ensuing summer and excite downstream development of subpolar teleconnections across the northern Eurasia, which raises (or lowers) the pressure over the Ural Mountain and the Okhotsk Sea. The latter strengthens (or weakens) the east Asian subtropical front (Meiyu-Baiu-Changma), leading to a strong (or weak) EASM. An empirical model is established to predict the EASM strength by combination of the El Niño-Southern Oscillation (ENSO) and spring NAO. Hindcast is performed for the 1979-2006 period, which shows a hindcast prediction skill that is comparable to the 14 state-of-the-art multimodel ensemble hindcast. Since all these predictors can be readily monitored in real time, this empirical model provides a real time forecast tool.

The Asian–Bering–North American teleconnection: seasonality, maintenance, and climate impact on North America

“…Thus North American winter temperature is mostly controlled by these three atmospheric teleconnection patterns. It is noted that stationary Rossby waves, which play an important role in interannual variability of the teleconnections spanning from Eurasia to North America, are observed not only in winter but also in summer (e.g., Schubert et al 2011;Ding et al 2011;Wu et al 2009. Therefore, this study extends our previous analysis by characterizing the seasonality of the ABNA pattern.…”

Decadal-scale teleconnection between South Atlantic SST and southeast Australia surface air temperature in austral summer

“…Previous studies have pointed out that SST anomalies in the North Atlantic can exert remote influences on climate in downstream areas through the eastward propagating Rossby wave train emanating from the North Atlantic (Li and Bates 2007;Wu et al 2009;Cui et al 2015;Sun et al 2015cSun et al , 2016Zhou and Wu 2016). It is hypothesized here that SST anomalies in southwest South Atlantic can also excite a decadal-scale teleconnection wave train similar to that presented in Fig.…”

A delayed oscillator model for the quasi-periodic multidecadal variability of the NAO

“…A simple North Atlantic tripole (NAT) index is therefore defined as the difference between the sum of averaged SST in two negative-value boxes (55°-65°N, 60°-20°W and 15°-30°N, 45°-15°W) and averaged SST in the positive-value box (30°-50°N, 80°-50°W). This definition is similar to Wu et al (2009) but the locations of the three boxes are slightly shifted northward in the simulations. As expected, the 21-year running mean NAT index is highly correlated with the POP1 imaginary PC (r = −0.81, significant at the 95 % confidence level), indicating the POP1 imaginary part corresponds closely to the NAT pattern over multidecadal timescales.…”

“…There is some consensus in observational studies that the NAO leads to the NAT nearly instantaneously through surface heat flux changes (Wu et al 2009;Deser et al 2010) and that the AMO follows the NAO with a 15-20 year delay through AMOC changes (Latif et al 2006a, b;Latif and Keenlyside 2011;Li et al 2013). These two mechanisms may provide an alternative interpretation for the oscillatory sequence and could partly explain the lead-lag relationships found in the present study.…”