Onset of the Rainy Seasons in the Eastern Indochina Peninsula

• DOI: 10.1175/jcli-d-14-00373.1
• Publication Date: 2015-04-20T20:41:14Z
• Authors: Dzung Nguyen-Le; Jun Matsumoto; Thanh Ngo-Duc
• Keywords: Empirical orthogonal functions; Wet season; Westerlies; Subtropical ridge; Peninsula; Madden–Julian oscillation; Trade wind; Atmospheric Circulation

Abstract The onset dates of rainy season over the eastern Indochina Peninsula (8.5°–23.5°N, 100°–110°E) are objectively determined for individual years from 1958 to 2007 using empirical orthogonal function (EOF) analysis. On average, summer (SRS) by EOF1 is 6 May, with a standard deviation 13 days. autumn (ARS) indicated EOF2 has mean and 16 September 12 days, respectively. SRS characterized evolution monsoon westerlies northward propagation strong convection equatorial region. Conversely, withdrawal northeastern in late summer–early favors ARS onset. Both onsets strongly associated intraseasonal oscillation on 30–60- 10–20-day time scales. Examination precursory signals early/late both implies that ENSO significant impact their year-to-year variations. In La Niña years, subsequent tends have early onsets. Simultaneously, western Pacific subtropical high (WPSH) weakens retreats eastward earlier. contrast, advanced generally occurs during an El Niño–developing weakened easterlies suppressed central Indian Ocean preceding summer, as evident Walker circulation. However, robust SST observed only midsummer (July–August). An earlier also development anomalous Philippine Sea anticyclone westward-extended WPSH midsummer. no coherent correlation found between Niña.