Abstract
Wintertime precipitation in China is most pronounced over the southeastern area, and the Kuroshio in the East China Sea anchors a prominent precipitation band over the warm side of the sea surface temperature front. Previous studies have suggested that many factors contribute to the interannual variation of the precipitation over southeastern China (SC), whereas less attention has been paid to precipitation variability over the East China Sea Kuroshio (ECSK) area. This study focuses on the interannual variation of wintertime precipitation over the SC and ECSK areas. Empirical orthogonal function analysis reveals a spatially uniform pattern from SC to the ECSK area. Composite analysis shows that an El Niño event intensifies wintertime precipitation over our target region, and this effect is tripled when an El Niño follows a positive North Pacific Oscillation (NPO) event in the previous winter. The positive NPO event in the previous winter intensifies the El Niño event via the Victoria mode ocean bridge and the subsequent Bjerknes feedback. In comparison with single-factor El Niño events, a much weaker Walker cell induced by the joint event induces a much weaker regional Hadley cell through anomalous descending motion over the western tropical Pacific. The weakened regional Hadley circulation over the western Pacific directly enhances the precipitation over the SC and ECSK area. In this study, the synergistic effect of an El Niño event and a positive NPO event indicates that the influence of the El Niño event can be amplified by the positive NPO event in the previous winter.
Highlights
Wintertime precipitation in China is most prominent over the southeastern area (Gao et al 2020), where it accounts for ~ 15% of total annual precipitation (Li and Ma 2012), and this proportion has an increasing trend (Sui et al 2013)
Previous studies have suggested that many single factors are responsible for interannual variation of the precipitation intensity over Southeastern China (SC), whereas less attention has been paid to the precipitation variability over the East China Sea Kuroshio (ECSK) area at interannual timescale
This study focuses on the interannual variation of precipitation over the SC and ECSK region from the perspective of joint effect
Summary
Wintertime precipitation in China is most prominent over the southeastern area (Gao et al 2020), where it accounts for ~ 15% of total annual precipitation (Li and Ma 2012), and this proportion has an increasing trend (Sui et al 2013). Anomalous sea level pressure over the southern NPO lobe can be used to forecast the Niño 3.4 index 12–15 months in advance (Anderson 2007) These results suggest that a positive NPO event may have an effect on wintertime precipitation over the SC by inducing a positive VM that results in an El Niño event. By analyzing high-resolution precipitation observations, Sun et al (2020) revealed that the variation of wintertime frontal precipitation over the Gulf Stream is related to the North Atlantic Oscillation on interannual timescales. Previous studies found that the interannual variability of wintertime precipitation in SC may be attributed to many factors, such as El Niño, East Asian winter monsoon intensity, SST anomalies over the South China Sea, Siberian High intensity, and the position of the East Asian Trough (Zhang et al 2015).
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