Asymmetry of the El Nino-Spring Rainfall Relationship in Taiwan

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概要

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• Spring rainfall in Taiwan can be either enhanced or suppressed by an El Nino 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 Nino/Southern Oscillation (ENSO)-spring rainfall relationship types during 1950-2003: El Nino-anomalous wet (EN-w) type, La Nina-anomalous dry (LN-d) type, El Nino-anomalous dry (EN-d) type, and La Nina-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 Nino (La Nina) 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 Nino (La Nina) 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.

• 2008-04-25

著者

• CHEN Jau-Ming

  Institute of Navigation Science and Technology, National Kaohsiung Marine University

• LI Tim

  International Pacific Research Center, University of Hawaii

• SHIH Ching-Feng

  Research and Development Center, Central Weather Bureau

• Chen Jau-ming

  Institute Of Navigation Science And Technology National Kaohsiung Marine University

• Shih Ching-feng

  Research And Development Center Central Weather Bureau

• Li Tim

  International Pacific Res. Center Univ. Of Hawaii

関連論文

• Asymmetry of the El Nino-Spring Rainfall Relationship in Taiwan
• Potential Predictability of Tropical Low-level Circulation in CWB GFS Ensemble Hindcast
• Annual Cycle of the South China Sea Surface Temperature Using the NCEP/NCAR Reanalysis
• Processes that Determine the Quasi-Biennial and Lower-Frequency Variability of the South Asian Monsoon

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