Inactive Period of Western North Pacific Tropical Cyclone Activity in 1998–2011

Abstract

Tropical cyclone (TC) activity over the western North Pacific (WNP) exhibits a significant interdecadal variation during 1960-2011, with two distinct active and inactive periods each. This study examines changes in TC activity and atmospheric conditions in the recent inactive period (1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011). The overall TC activity shows a significant decrease, which is partly related to the decadal variation of TC genesis frequency in the southeastern part of the WNP and the downward trend of TC genesis frequency in the main development region.The investigation on the factors responsible for the low TC activity mainly focuses on the effect of vertical wind shear and subtropical high on multidecadal time scales. A vertical wind shear index, defined as the mean magnitude of the difference of the 200-and 850-hPa horizontal zonal winds (108-17.58N, 1508E-1808) averaged between June and October, is highly correlated with the annual TC number and shows a significant interdecadal variation. Positive anomalies of vertical wind shear are generally found in the eastern part of the tropical WNP during this inactive period. A subtropical high area index, calculated as the area enclosed by the 5880-gpm line of the June-October 500-hPa geopotential height (08-408N, 1008E-1808), shows a significant upward trend. A high correlation is also found between this index and the annual TC number, and a strongerthan-normal subtropical high is generally observed during this inactive period. The strong vertical wind shear and strong subtropical high observed during 1998-2011 together apparently lead to unfavorable atmospheric conditions for TC genesis and hence the low TC activity during the period.

Explaining Extreme Events of 2014 from a Climate Perspective

“…The variations of TC genesis frequency and intensity in the WNP, from intraseasonal to interdecadal time scales, are related to ISO phases (e.g., Gray 1979;Huang et al 2011;Li and Zhou 2013;, monsoon trough variability (e.g., Ritchie and Holland 1995;Chen et al 2004;Wu et al 2012), the El Niño-Southern Oscillation (e.g., Chan 2005;Du et al 2011;Kim et al 2011), and the PDO (e.g., Yang et al 2012;Liu and Chan 2013). WNP TC genesis frequency depends on the ISO phase ) and might also vary with different climate backgrounds of the EASM (Zhou et al 2009;Wang et al 2012) and PDO phase (Liu and Chan 2013).…”

“…WNP TC genesis frequency depends on the ISO phase ) and might also vary with different climate backgrounds of the EASM (Zhou et al 2009;Wang et al 2012) and PDO phase (Liu and Chan 2013). Previous studies suggested that the modulation of TCs by the ISO during July-August of 1979-2008 or 1979-2004 was relatively weak compared to other seasons Kim et al 2008).…”

Multidecadal Variability of Tropical Cyclone Rapid Intensification in the Western North Pacific

“…Yeh et al (2010) showed a decadal relationship between the TC frequency and tropical Pacific SST, with a positive correlation during the period 1990-2000 but a negative correlation during the period 1979-89. Liu and Chan (2013) examined changes in TC activity and atmospheric conditions during 1998-2011. TC activity shows a significant decrease, which is partly related to the decadal variation of the TC genesis frequency in the southeastern part of the WNP.…”

Anomalous Tropical Cyclone Activity in the Western North Pacific in August 2014

“…The variations of TC genesis frequency and intensity in the WNP, from intraseasonal to interdecadal time scales, are related to ISO phases (e.g., Gray 1979;Huang et al 2011;Li and Zhou 2013;Yang et al 2015), monsoon trough variability (e.g., Ritchie and Holland 1995;Chen et al 2004;Wu et al 2012), the El Niño-Southern Oscillation (e.g., Chan 2005;Du et al 2011;Kim et al 2011), and the PDO (e.g., Yang et al 2012;Liu and Chan 2013). WNP TC genesis frequency depends on the ISO phase (Huang et al 2011) and might also vary with different climate backgrounds of the EASM (Zhou et al 2009;Wang et al 2012) and PDO phase (Liu and Chan 2013).…”

“…WNP TC genesis frequency depends on the ISO phase (Huang et al 2011) and might also vary with different climate backgrounds of the EASM (Zhou et al 2009;Wang et al 2012) and PDO phase (Liu and Chan 2013). Previous studies suggested that the modulation of TCs by the ISO during July-August of 1979-2008 or 1979-2004 was relatively weak compared to other seasons (Huang et al 2011;Kim et al 2008).…”