Asymmetry of the El Nino-Spring Rainfall Relationship in Taiwan

Abstract

Spring rainfall in Taiwan can be either enhanced or suppressed by an El Niño event, revealing an asymmetric relationship. This observational study aims at examining this asymmetric relationship and associated large-scale dynamic processes. Analysis results disclose four major El Niño/Southern Oscillation (ENSO)-spring rainfall relationship types during 1950-2003: El Niño-anomalous wet (EN-w) type, La Niña-anomalous dry (LN-d) type, El Niño-anomalous dry (EN-d) type, and La Niña-anomalous wet (LN-w) type. The EN-w and LN-d (EN-d and LN-w) types exhibit a positive (negative) correlation between the spring rainfall anomaly and the ENSO-related sea surface temperature anomaly (SSTA). The overall ENSO-spring rainfall relationship is dominated by the positive correlation.The cause of the asymmetric ENSO impacts between the positive-and negative-correlation groups is attributed to a connection between ENSO and the Indian Ocean (IO) SSTA and associated large-scale atmospheric circulation. The positive-correlation types tend to concur with an evident ENSO-IO connection, featuring significant in-phase SSTA centers in the tropical eastern Pacific and eastern IO. During the El Niño (La Niña) event, these SST anomalies force a descending (ascending) branch over the western Pacific and help initiate and maintain a lower-level anticyclone (cyclone) anomaly in the Philippine Sea (southeast of Taiwan). Flows west of this anomalous anticyclone (cyclone) enhance (suppress) moisture transport from the South China Sea into Taiwan, resulting in increased (decreased) spring rainfall. For the negative-correlation types, the ENSO-IO connection tends to be weak or broken. The significant SSTA appears only in the tropical eastern Pacific, which induces a major vertical motion branch over the maritime continent. As a result, an anomalous lower-level anticyclone (cyclone) occurs over the Asian continent (west of Taiwan) during the El Niño (La Niña) event. Flows east of this anomalous anticyclone (cyclone) weaken (strengthen) moisture transport from the South China Sea into Taiwan, leading to suppressed (enhanced) spring rainfall.It is also noted that the variability of the Pacific subtropical high (PSH) over the western Pacific is closely linked to these four relationship types. The EN-d (LN-w) type concurs with a moderate westward expansion (eastward retreat) in the western-Pacific sector, while the EN-w (LN-d) type is concurrent with a southward (great eastward) displacement.

Constructing a 1-km Gridded Multi-Scalar Drought Index Dataset (1960 - 2012) in Taiwan Based on the Standardized Precipitation Evapotranspiration Index-SPEI

“…The interannual variability in spring rainfall in Taiwan is largely associated with El Niño-Southern Oscillation (ENSO) (Wang and Hwu 1994;Chen et al 2003Chen et al , 2008Chen et al , 2013. Analyses conducted in previous studies still relied on the station-level data and often attempted to identify the top-down causal relationship between the large-scale lowfrequency variability as the cause and the regional hydroclimate response.…”

“…In other words, the general notion: the excess (deficient) spring rain in Taiwan can be attributed to the strengthened southwesterly (northeasterly) winds induced by the anomalous Philippine anticyclone (cyclone) which is maintained by the local air-sea interactions during the decaying stage of warm (cold) ENSO phase, needs to be scrutinized (cf. Chen et al 2008).…”

Probabilistic Drought Forecasting in Southern Taiwan Using El Niño-Southern Oscillation Index

“…Jiang et al (2003) examined the effect of interdecadal variation on the relationship between spring rainfall (February and March) and ENSO, elucidating the characteristics of large-scale circulations associated with heavy spring rainfall events in Taiwan in strong ENSO and non-ENSO years. Chen et al (2008) studied the asymmetric relationship between spring rainfall (February, March, and April) in Taiwan and ENSO. This asymmetric relationship shows that spring rainfall in Taiwan can be enhanced or suppressed by an El Niño event because of connections between ENSO and the Indian Ocean SST anomaly and associated large-scale atmospheric circulation.…”

A Spatial-Temporal Projection Method for Seasonal Prediction of Spring Rainfall in Northern Taiwan

“…1c). A number of investigators have studied the factors that may affect the spatial and temporal variations of spring rainfall in Taiwan (e.g., Jiang et al 2003;Hung et al 2004;Chen et al 2008), particularly the relationship between El Niño-Sothern Oscillation (ENSO) and spring rainfall in Taiwan. In general, enhanced Taiwan spring rainfall occurs when an El Niño condition occurs in the equatorial eastern Pacific in the preceding winter .…”

“…This moisture transport favors intensified rainfall activity during spring Jiang et al 2003). In addition, the ENSOinduced mid-latitude frontal system (Wang and Zhang 2002;) and variability of the Pacific subtropical high (Lu 2001;Chen et al 2008) may also modulate the interannual variability of spring rainfall in Taiwan.…”