Relationship between the Interannual Variations of Summer Convective Afternoon Rainfall Activity in Taiwan and SSTA(Ni\xf1o3.4) during 1961\u20132012: Characteristics and Mechanisms

Wan-Ru Huang,Ya-Hui Chang,Po-Han Huang

doi:10.1038/s41598-019-45901-w

Abstract

This study examines the interannual variation of the Convective Afternoon Rainfall (CAR) activity (including frequency and intensity) in Taiwan during the summers (JJA) of 1961–2012 with a focus on identifying its relationship with the changes in sea surface temperature anomalies over the Niño3.4 region [SSTA(Niño3.4)] and the underlying physical mechanisms. Our analyses show that during the colder (warmer) phase of SSTA(Niño3.4), the subtropical high system over the region east of Taiwan is enhanced (weakened), the local surface wind convergence is enhanced (weakened), and the local thermal instability is enhanced (weakened), which facilitates (suppresses) the formation of CAR in Taiwan. This consistent negative relationship between the interannual variation of CAR frequency in Taiwan and SSTA(Niño3.4) occurs throughout 1961–2012. In contrast, the relationship between the interannual variation of CAR intensity in Taiwan and SSTA(Niño3.4) changed from positively correlated to negatively correlated in the late 1980s. This change is attributed to the change in the moisture supply for maintaining the CAR intensity in Taiwan from an increase (decrease) in the warmer (colder) phase of SSTA(Niño3.4) before the mid-1980s to the opposite after the late 1980s. These findings highlight how the rainfall characteristics in East Asia may change in response to changes in SSTA(Niño3.4).

Highlights

This study examines the interannual variation of the Convective Afternoon Rainfall (CAR) activity in Taiwan during the summers (JJA) of 1961–2012 with a focus on identifying its relationship with the changes in sea surface temperature anomalies over the Niño3.4 region [sea surface temperature anomaly (SSTA)(Niño3.4)] and the underlying physical mechanisms
Unlike Huang et al.[5], who focus on the longer timescale variations, this study aims to determine whether SSTA over the tropical Pacific region has played a role in modulating the 4-to-8-year variations of CAR activity in Taiwan during JJA of 1961–2012
Because the changes in the East Asia summer monsoon (EASM) circulation, moisture transport and western North Pacific subtropical high (WNPSH) are the most important factors that affect the CAR formation in Taiwan[10,27,28], we hypothesize based on these documented studies that (1) there might be a close relationship between the interannual variation of CAR activity in Taiwan and SSTA over the tropical Pacific regions, and (2) this relationship might have changed after the 1990s

Summary

Introduction

This study examines the interannual variation of the Convective Afternoon Rainfall (CAR) activity (including frequency and intensity) in Taiwan during the summers (JJA) of 1961–2012 with a focus on identifying its relationship with the changes in sea surface temperature anomalies over the Niño3.4 region [SSTA(Niño3.4)] and the underlying physical mechanisms. Because the changes in the EASM circulation, moisture transport and WNPSH are the most important factors that affect the CAR formation in Taiwan[10,27,28], we hypothesize based on these documented studies that (1) there might be a close relationship between the interannual variation of CAR activity in Taiwan and SSTA over the tropical Pacific regions, and (2) this relationship might have changed after the 1990s These two hypotheses will be examined . In contrast to Chen et al.[6], who only focus on the Taipei basin after 1993, the main objective of this study is to investigate the possible relationship between SSTA(Niño3.4) and the CAR activity (including frequency and intensity) estimated for all of Taiwan over a longer time period (i.e., 1961–2012 JJAs) and to understand its underlying physical explanations Examinations of these issues can lead to a better understanding of the characteristics and maintenance mechanisms of the interannual variation of CAR activity in Taiwan under long-term climate change

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Conclusion