Impact of atmospheric and oceanic conditions on the frequency and genesis location of tropical cyclones over the western North Pacific in 2004 and 2010
Impact of Atmospheric and Oceanic Conditions on the Frequency and Genesis Location of Tropical Cyclones over the Western North Pacific in 2004 and 2010
Pan SONG 0 2
Jiang ZHU 1
Zhong ZHONG 2
Linlin QI 0
Xiaodan WANG 0
0 Beijing Institute of Aeronautical Meteorology , Beijing 100085
1 International Center for Climate and Environment Science, Institute of Atmospheric Physics
2 College of Meteorology and Oceanography, PLA University of Science and Technology , Nanjing 211101
This study examines the impact of atmospheric and oceanic conditions during May-August of 2004 and 2010 on the frequency and genesis location of tropical cyclones over the western North Pacific. Using the WRF model, four numerical experiments were carried out based on different atmospheric conditions and SST forcing. The numerical experiments indicated that changes in atmospheric and oceanic conditions greatly affect tropical cyclone activity, and the roles of atmospheric conditions are slightly greater than oceanic conditions. Specifically, the total number of tropical cyclones was found to be mostly affected by atmospheric conditions, while the distribution of tropical cyclone genesis locations was mainly related to oceanic conditions, especially the distribution of SST. In 2010, a warmer SST occurred west of 140◦E, with a colder SST east of 140◦E. On the one hand, the easterly flow was enhanced through the effect of the increase in the zonal SST gradient. The strengthened easterly flow led to an anomalous boundary layer divergence over the region to the east of 140◦E, which suppressed the formation of tropical cyclones over this region. On the other hand, the colder SST over the region to the east of 140◦E led to a colder low-level air temperature, which resulted in decreased CAPE and static instability energy. The decrease in thermodynamic energy restricted the generation of tropical cyclones over the same region.
tropical cyclone; SST; numerical simulation; western North Pacific
1. Introduction
The western North Pacific (WNP) is the world’s most
active tropical cyclone basin (Emanuel, 2005; Peduzzi et al.,
2012; Lin et al., 2013). The interannual variability of
tropical cyclone activities, including the frequency, intensity,
location and landfalling, is complicated and has been found to
be closely related to large-scale circulation, including ENSO
(Chan, 1985, 2000; Lander, 1994; Wang and Chan, 2002;
Camargo and Sobel, 2005; Wada and Chan, 2008), MJO
(Liebmann et al., 1994; Nakazawa, 2006; Nakano et al., 2015),
quasi-biennial oscillation (Chan, 1985; Lau and Chan, 1993),
Asian–Pacific Oscillation (Zhou et al., 2008), North Pacific
oscillation (Wang et al., 2007), Antarctic oscillation (Ho et
al., 2005; Wang and Fan, 2007), North Atlantic oscillation
(Zhou and Cui, 2014), and Hadley circulation (Zhou and Cui,
∗ Corresponding author: Pan SONG
Email:
2008). In addition, many researchers consider global
warming, and related SST change, to be a key driver of changes
in tropical cyclone activity (Webster et al., 2005; Emanuel et
al., 2008; Sugi et al., 2002, 2012; Gleixner et al., 2014;
Scoccimarro et al., 2014; Holland and Bruye`re, 2014). However,
the exact impacts that changes in SST may have on tropical
cyclone activity remain ambiguous, especially when changes
are not uniform.
The effects of climate change on tropical cyclones have
been a prominent issue for a number of years. In recent
decades, SST in major tropical cyclone generation regions
has increased several tenths of a degree Celsius (Santer et
al., 2006). As a result of the recent increase in the
capabilities of climate models, such models have captured some of
the essential physical relationships that govern the links
between the climate and tropical cyclones. Early climate model
simulations, however, suggested some ambiguity in changes
of tropical cyclone characteristics induced by warmer SST.
While many models projected fewer tropical cyclones
globally (Sugi et al., 2002; Bengtsson et al., 2007; Gualdi et and discussed in section 4, followed by a summary in section
al., 2008; Knutson et al., 2010), other climate models sug- 5.
gested some increase in future numbers (Broccoli and
Manabe, 1990; Haarsma et al., 1993; Emanuel, 2013). Yoshimura
and Sugi (2005) investigated impacts of SST warming on 2. Choice of abnormal years for tropical
cythe tropical cyclone climatology using a high-horizontal- clone activity, and the climate background
resolution AGCM. The results of numerical experiments in
which SST was uniformly higher by 2 K demonstrated that 2.1. Analysis of tropical cyclone frequency
the changes in SST had a relatively small influence on the Tropical cyclone numbers were analyzed using the best
tropical cyclone frequency. Similar to Yoshimura and Sugi track dataset of the China Meteorological Administration
(2005), Held and Zhao (2011) carried out an experiment in (CMA) (http://tcdata.typhoon.gov.cn/en/index.html) for the
which SST was uniformly higher by 2 K, (...truncated)