Interannual Variability of the Western North Pacific Summer Monsoon: Differences between ENSO and Non-ENSO Years

Abstract

The interannual variability of the western North Pacific (WNP) summer monsoon is examined for the non-ENSO, ENSO developing, and ENSO decaying years, respectively. The ENSO developing (decaying) year is defined as the year before (after) the mature phase of ENSO, and the non-ENSO year is defined as the year that is neither the ENSO developing year nor the ENSO decaying year. A strong (weak) WNP summer monsoon tends to occur during the El Niño (La Niña) developing year and a weak (strong) WNP summer monsoon tends to occur during the El Niño (La Niña) decaying year. In all non-ENSO, ENSO developing, and ENSO decaying years, the strong (weak) WNP summer monsoon is associated with the positive (negative) rainfall anomalies, cold (warm) sea surface temperature anomalies, warm (cold) upper-tropospheric temperature anomalies, low (high) surface pressure anomalies, and a low-level cyclonic (anticyclonic) circulation anomaly over the subtropical WNP. The 850-hPa wave train associated with the WNP and east Asian (EA) summer monsoons in the non-ENSO, ENSO developing, and ENSO decaying years extends northward and suggests a possible teleconnection between the WNP summer monsoon and the North American climate. The wave train extended into the Southern Hemisphere in the non-ENSO and ENSO developing years implies a teleconnection between the WNP summer monsoon and the Australian winter climate. The anomalous WNP monsoon in the non-ENSO and ENSO developing years exists only in summer, while the anomalous WNP monsoon in the ENSO decaying year persists from the beginning of the year to the summer season. The anomalous WNP summer monsoon exhibits a strong ocean–atmosphere interaction, especially in the ENSO decaying year. This study suggests that the anomalous WNP summer monsoon in the non-ENSO year is associated with the variation of the meridional temperature gradient in the upper troposphere, while the anomalous WNP summer monsoon in the ENSO developing and decaying years is associated with ENSO-related SST anomalies.

Thermodynamic characteristics and responses to ENSO of dominant intraseasonal modes in the East Asian summer monsoon

“…The post-Changma mode indicated the decaying phase of the La Niña. This was the same result as that obtained by Chou et al (2003), who showed that a strong WNPSM tended to occur in the decaying year of the La Niña. The dry-spell mode was also observed to be related with the La Niña events.…”

“…Lee et al (2013b) indicated that the moisture convergence is simultaneously enhanced by inducing impact of more evaporation through anomalous SST warming over the IO. The moisture supply over East Asia is also related to external forcing such as the ENSO through the modulation of an anomalous WNPSH (Huang and Wu 1989;Wang et al 2000Wang et al , 2013Chou et al 2003;Lee et al 2013a;Yun et al 2013). The anomalous WNPSH is attributed to local air-sea interactions, the influence of the IO, and the combined effect on atmospheric circulation (Ashok et al 2001;Saji and Yamagata 2003;Xie et al 2009;Lee et al 2013b;Yun et al 2013).…”

Impacts of recent El Niño Modoki on dry/wet conditions in the Pacific rim during boreal summer

“…All the three largest El Niño Modoki events during our data period did not occur in the summer ''after'' the mature phase of a cold ENSO. This fact further elucidates that the intensities of the western North Pacific summer monsoon and the East Asian summer monsoon do not have a simple relation with the phase of the warm-cold ENSO cycle (Chou et al 2003). It further shows that El Niño Modoki is not necessarily one stage of the ENSO cycle, so that the influence of El Niño Modoki on these monsoons should not be mixed up with that of El Niño.…”

Seasonal to Interannual Variability of Satellite-Based Precipitation Estimates in the Pacific Ocean Associated with ENSO from 1998 to 2014

“…Advances in remote sensing have provided us with long-term and globally complete satellite-gauge-merged precipitation products and satellite-based estimates, such as the Global Precipitation Climatology Project (GPCP) [8], the Climate Prediction Center Merged Analysis of Precipitation (CMAP) [9], and the Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) [10]. Many studies have investigated the impacts of ENSO on precipitation using these satellite-based precipitation datasets [11][12][13][14][15][16]. For example, Dai and Wigley [11] and Haddad et al [14] derived the global climatology and variability of ENSO-induced precipitation using the CMAP and TRMM datasets, respectively, and found that ENSO is the major driver of the interannual variability of global rainfall.…”