Causes of the active typhoon season in 2016 following a strong El Niño with a comparison to 1998

Abstract

This article analysed two typhoon seasons (1998 and 2016) over the western North Pacific (WNP) with similar preceding background conditions of the tropical Pacific sea surface temperature (SST). Following the strong El Niño event in the preceding winter, the typhoon season was inactive in 1998 while active in 2016. Compared with 1998, the monsoon trough (MT) in 2016 shifted more eastwards, leading to an increase of the mid‐level water vapour, lower‐tropospheric relative vorticity and upper‐tropospheric divergence, and a decrease of the vertical wind shear. Additionally, the eastwards extension of the MT in 2016 induced more active tropical depression (TD)‐type waves than those in 1998. The analysis of the energy budget suggested that the eastwards shift of the MT during the 2016 typhoon season provided increased eddy kinetic energy for typhoon genesis, due to the joint contributions of the meridional shear of the mean zonal winds and the zonal wind convergence over the WNP. Moreover, the WNP entered a La Niña‐like SST pattern after July 2016. The relatively slower developing process of this pattern sustained the warmer SST anomalies and the anomalous cyclonic circulation, which the eastwards extension of the MT can be attributed. Hence, compared to 1998, the active typhoon season in 2016 is attributed to the eastwards extension of the MT, more active TD‐type wave activities, and slow developing process of a La Niña‐like SST pattern in 2016 typhoon season.

Why Was the August Rainfall Pattern in the East Asia–Pacific Ocean Region in 2016 Different from That in 1998 under a Similar Preceding El Niño Background?

“…The El Niño events in the winters of 1997/98 and 2015/16 as two strongest events since observational records, their intensities were higher than twice the standard deviation of the Niño-3.4 index, which attracted wide attention from the academic community (C. Gao et al 2018;Huangfu et al 2018). Using NOAA and Hadley sea surface temperature data, we analyzed the Niño-3.4 (58S-58N, 1708-1208W) and Niño-3 (58S-58N, 1508-908W) indices and found that the two El Niño events had similar intensities and decaying processes (figure not shown), which was consistent with the results of previous studies (C. Huangfu et al 2018). Gao et al (2018) analyzed the early summer (May-July) precipitation anomaly pattern in the pan-Asian monsoon region and its physical mechanism during a strong El Niño decaying year.…”

“…In this paper, during the El Niño decaying summer of August 2016, the number of TCs increased and they generated in the east, which is not consistent with the findings of previous research. Huangfu et al (2018) compared the differences of TC activities between 1998 and 2016 during two super-El Niño decaying summers. They found that the active typhoon in 2016 was attributed to the eastward extension of the monsoon trough (MT), more active tropical depression wave activities, and the slow developing process of La Niña-like SST during this year.…”

Differences in the destructiveness of tropical cyclones over the western North Pacific between slow- and rapid-transforming El Niño years

“…The evolutionary characteristics of the El Niño events are also an issue worthy of study. In previous studies, the phase in which the sea surface temperature anomalies (SSTA) gradually weakens after the maturity of El Niño is usually defined as the decaying phase of the El Niño event (Lin and Li 2008, Jiang et al 2017, Huangfu et al 2018. Different rates at which El Niño events decay modulate the atmospheric circulation and oceanic environment differently in the surrounding areas (Pillai and Chowdary 2016).…”

South China Sea summer monsoon withdrawal and the synoptic‐scale wave train over the western North Pacific

“…The synoptic‐scale wave train is characterized by northwest–southeast‐oriented alternating cyclonic and anticyclonic disturbances, with a typical wavelength of 2,500–3,000 km and a period of less than 10 days (Chang, Chen, Harr, & Carr, 1996; Feng et al, 2016; Fu, Li, Peng, & Weng, 2007; Fukutomi et al, 2016; Huang & Huang, 2011; Lau & Lau, 1990, 1992; Li, 2006; Tam & Li, 2006; Yuan, Li, & Wang, 2015; Zhao, Jiang, & Wu, 2016a). The synoptic‐scale wave train has been extensively studied for its role in extremely heavy rainfall events (Wu, Fukutomi, & Matsumoto, 2011; Yokoi & Matsumoto, 2008), seeding tropical cyclone (TC) genesis (Cao, Chen, & Chen, 2013; Dickinson & Molinari, 2002; Fu et al, 2007; Huangfu, Chen, Wang, & Huang, 2018c; Huangfu, Huang, Chen, & Feng, 2018d; Huangfu, Chen, Huang, & Feng, 2019; Li, Fu, Ge, Wang, & Peng, 2003; Xu, Li, & Peng, 2014; Yuan et al, 2015; Zhao et al, 2019; Zhou & Wang, 2007), and interactions with low‐frequency activities, for example, intra‐seasonal oscillations (ISOs; Sobel & Maloney, 2000; Aiyyer & Molinari, 2003; Maloney & Dickinson, 2003; Straub & Kiladis, 2003; Zhou & Li, 2010; Hsu, Li, & Tsou, 2011; Li, 2014; Zhao et al, 2016a; Zhao et al, 2019).…”