Abstract
The Asian monsoon region is highly dependent on boreal summer rainfall, which directly impacts the socio-economic stability and welfare of billions of people each year. Precipitation variability over East China has been extensively studied and is known to be characterized by meridional tripole and dipole precipitation structures. In contrast, few studies have focused on precipitation variability over Mainland Southeast Asia (MSEA) and the possible relationship with the variability over East China. Here we focus on how interannual precipitation variability across MSEA during 1983–2017 may be associated with the tripole or dipole patterns using an empirical orthogonal function (EOF) analysis. The first EOF shows a meridional tripole pattern in East China summer precipitation and an in-phase relationship between MSEA and South China precipitation. In contrast, the second EOF shows a meridional dipole pattern in East China precipitation and an out-of-phase relationship between MSEA and South China precipitation. We show that the first EOF mode is a delayed precipitation response to the El Nino-Southern Oscillation (ENSO), while the second EOF mode is a simultaneous precipitation response to the remote influence of the North Atlantic Oscillation (NAO). Therefore, the in-phase or out-of-phase variations in precipitation between MSEA and South China may be used to gauge the relative importance of local Pacific and remote Atlantic influences on Asian monsoon climate.
Highlights
We conduct statistical analyses with observational data, numerical experiments with a forced atmospheric general circulation model (AGCM), and case studies with major El Niño events since 1950 to show that the impacts produced by the Central Pacific (CP) and EP types of El Niño on United States (US) winter temperatures are different from the classical view and that the El Niño impacts are changing
The sea surface temperature (SST) anomalies regressed with the Niño1+2 (0–10S, 80W–90W) SST index were removed before the Empirical Orthogonal Function (EOF) analysis was applied to obtain the YU ET AL.: IMPACT OF EL NINO ON US TEMPERATURES
[6] By separately regressing winter (January–February– March; JFM) surface air temperature anomalies to the EP and CP El Niño indices, we show in Figures 1a and 1b that the El Niño impacts on US winter temperatures are different between these two types
Summary
[2] The increasing recognition that there are two different flavors or types of El Niño events [e.g., Wang and Weisberg, 2000; Trenberth and Stepaniak, 2001; Larkin and Harrison, 2005a, 2005b; Yu and Kao, 2007; Ashok et al, 2007; Kao and Yu, 2009; Kug et al, 2009] offers the research community a new way to consider interannual sea surface temperature (SST) variability in the tropical Pacific and to rethink how the type of El Niño and its impacts may change as the climate changes. While El Niño is traditionally recognized as a warming of the sea surface in the eastern-to-central equatorial Pacific, it has been noticed that El Niño events with warming confined to the international dateline region can occur This flavor or type of El Niño has been referred to as the Central Pacific (CP) El Niño [Yu and Kao, 2007; Kao and Yu, 2009], Date Line El Niño [Larkin and Harrison, 2005a], El Niño Modoki [Ashok et al, 2007], or warm pool El Niño [Kug et al, 2009], while the conventional El Niño is referred to as the Eastern-Pacific (EP) type [Yu and Kao, 2007; Kao and Yu, 2009]. We conduct statistical analyses with observational data, numerical experiments with a forced atmospheric general circulation model (AGCM), and case studies with major El Niño events since 1950 to show that the impacts produced by the CP and EP types of El Niño on US winter temperatures are different from the classical view and that the El Niño impacts are changing
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