Abstract
Early spring (March - April) rainfall in Taiwan exhibits evident and distinct inter-annual and inter-decadal variability. The inter-annual varibility has a positive correlation with the El Nino/Southern Oscillation while the inter-decadal variability features a phase change beginning in the late 1970s, coherent with the major phase change in the Pacific decadal oscillation. Rainfall variability in both timescales is regulated by large-scale processes showing consistent dynamic features. Rainfall increases are associated with positive sea surface temperature (SST) anomalies in the tropical eastern Pacific and negative SST anomalies in the tropical central Pacific. An anomalous lower-level divergent center appears in the tropical central Pacific. Via a Rossby-wave-like response, an anomalous lower-level anticyclone appears to the southeast of Taiwan over the Philippine Sea-tropical western Pacific region, which is accompanied by an anomalous cyclone to the north-northeast of Taiwan. Both circulation anomalies induce anomalous southwesterly flows to enhance moisture flux from the South China Sea onto Taiwan, resulting in significant moisture convergence nearby Taiwan. With enhanced moisture supplied by anomalous southwesterly flows, significant rainfall increases occur in both inter-annual and inter-decadal timescales in early spring rainfall on Taiwan.
Highlights
In spring (March - May) Taiwan is affected by two types of large-scale circulation patterns
The simultaneous correlation coefficients between the C1 time series and PL time series in Fig. 3a is 0.98. These results demonstrate that the first Eigen mode is representative of inter-decadal variability for early spring rainfall in Taiwan
The simultaneous correlation coefficient between the Pacific decadal oscillation (PDO) index time series and inter-decadal rainfall variability in Taiwan (Fig. 3a) is 0.61, with effective degrees of freedom around 11. This correlation is statistically significant at the 0.05 level. This suggests that inter-decadal variability in early spring rainfall in Taiwan has occurred in relation to the PDO evolution
Summary
In spring (March - May) Taiwan is affected by two types of large-scale circulation patterns. Hung et al (2004) found that SST anomalies in the central-eastern tropical Pacific and accompanying lowertropospheric circulation anomalies in the Philippine Sea are effective in modulating a 20 - 30 years oscillation of spring rainfall in northern Taiwan. The main purpose of this study is to analyze early spring (March - April) rainfall in Taiwan with a focus on portraying and comparing its inter-decadal and inter-annual variability and associated large-scale regulatory processes. The ERSST and reanalysis data are jointly used to examine large-scale regulatory ocean-atmospheric processes for local rainfall variability in Taiwan. The analysis period in this study spans from 1950 - 2011
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