Interannual Variation in the Tropical Cyclone Formation over the Western North Pacific

Abstract

The interannual variation in tropical cyclone genesis frequency over the western North Pacific was examined for the active tropical cyclone (including summer and fall) during 1979-94. An emphasis was put on the possible effect of the interannual variation of atmospheric circulation and monsoon trough on tropical cyclone occurrence. The major findings of this study are the following. 1) A distinct increase (decrease) of tropical cyclone genesis frequency occurs north of the climatological location of the monsoon trough in the Philippine Sea during summers (June-August) with anomalous cold (warm) sea surface temperature (SST) over the NINO3 region. The interannual variation of tropical cyclone genesis in this region results from the appearance of an anomalous cyclonic (anticyclonic) cell situated in a summer teleconnection wave train emanating from the western tropical Pacific and progressing along the rim of the North Pacific. In addition to the north-south interannual variation, there is also a longitudinal interannual variation in the summer tropical cyclone genesis frequency over this region. The contrast of tropical cyclone genesis between the regions west and east of 150ЊE is reduced (enhanced) when the monsoon trough extends (retreats) eastward (westward) across this longitude during warm (cold) summers. 2) For fall (September-November), there is no clear relationship between the north-south interannual variation in the tropical cyclone genesis over the western North Pacific and SST (NINO3). However, there is a perceptible tendency of the longitudinal interannual variation in tropical cyclone genesis frequency to follow the eastward extension/westward retreat of the monsoon trough in a way such as it does during the summer season.

Interannual and interdecadal variations of tropical cyclone activity in the South China Sea

“…This north-south discrepancy is not seen in the WNP in the late season, and is opposite to the situation in the early season, where TCs in LN are found to form preferably to the north, while those in EN to the south (Chen et al, 1998). Various studies have pointed out the relationship between the location of TC formation and the monsoon trough in the WNP (e.g.…”

Contrasting Various Metrics for Measuring Tropical Cyclone Activity

“…5a), positive anomalies dominate the southeastern part of the WNP; while negative anomalies dictate the northwestern part. This implies that the major birthplace of TC would be shifted southeastward during an El Niño year (Chen et al 1998;Chia and Ropelewski 2002;Chen et al 2006). For TCD, ACE, RACE, PDI and RPDI anomalies (see Figs.…”

“…In climate studies, selections of El Niño (La Niña) years are often defined according to the Nino 3.4 index over the period of interest (Chen et al 1998;Chan 2000). In this study, an El Niño (La Niña) year is referred to one in which the Nino 3.4 index is greater (smaller) than 0.5 (-0.5) during the JASON period.…”

“…Among various metrics commonly used for measuring the total TC activity, the "number of tropical cyclones" (hereafter NTC) is perhaps the most popular due to its easyto-interpret nature (Landsea et al 1996;Chen et al 1998;Goldenberg et al 2001;Emanuel 2006). Since NTC only considers the total number of TC formations in an ocean basin, the contribution from intensity and duration of a TC is by no means included.…”

Relationship between the Meiyu over the Yangtze-Huaihe River Basins and the Frequencies of Tropical Cyclone Genesis in the Western North Pacific

“…4c). Based on the above analysis, on one hand the number of TC genesis is closely related to the intensity of the tropical largescale monsoonal circulation, and on the other hand the precipitation and regional circulation patterns over the YHRB are also influenced by the tropical large-scale monsoonal circulation (Ding et al 1981;Ritchie and Holland 1999;Cheng et al 1998). Figure 6 shows the 500 hPa geopotential fields.…”