Oceanologia (2019) 61, 265—275
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ORIGINAL RESEARCH ARTICLE
The response of cyclonic eddies to typhoons based
on satellite remote sensing data for 2001—2014
from the South China Sea
a,b a a,b, a
Fangjie Yu , Qiongqiong Yang , Ge Chen *, Qiuxiang Li
a
College of Information Science and Engineering, Ocean University of China, Qingdao, China
b
Laboratory for Regional Oceanography and Numerical Modeling, Qingdao National Laboratory for Marine Science and Technology,
Qingdao, China
Received 19 August 2018; accepted 26 November 2018
Available online 11 December 2018
KEYWORDS Summary Eddies are known to be affected by typhoons, and in recent years, the general three-
dimensional structure, as well as features of the spatial and temporal distributions of eddies have
Tropical cyclones;
been determined. However, the type of eddy that is most likely to be affected by a typhoon
Mesoscale eddy;
remains unclear. In this paper, quantitative and qualitative methods were used to study the eddies
Eddy kinetic energy
that are most sensitive to upper-ocean tropical cyclones (TCs) from the perspective of eddy
characteristics, and the quantitative results showed that not all eddies were enhanced under the
influence of typhoons. Enhancement of the eddy amplitude (Amp), radius (Rad), area (A), or eddy
kinetic energy (EKE) accounted for 92.3% of the total eddy within the radius of the typhoon.
Qualitative analyses showed the following: First, eddies located on different sides of the typhoon
tracks were differently affected, as eddies on the left side were more intensely affected by the
typhoon than eddies on the right side, and second, eddies with short lifespans or small radii were
more susceptible to the TCs.
© 2018 Institute of Oceanology of the Polish Academy of Sciences. Production and hosting by
Elsevier Sp. z o.o. This is an open access article under the CC BY-NC-ND license (http://
creativecommons.org/licenses/by-nc-nd/4.0/).
* Corresponding author at: College of Information Science and Engineering, Ocean University of China, Qingdao, China.
Tel.: +86 053266781265.
E-mail address: [email protected] (G. Chen).
Peer review under the responsibility of Institute of Oceanology of the Polish Academy of Sciences.
https://doi.org/10.1016/j.oceano.2018.11.005
0078-3234/© 2018 Institute of Oceanology of the Polish Academy of Sciences. Production and hosting by Elsevier Sp. z o.o. This is an open
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266 F. Yu et al./Oceanologia 61 (2019) 265—275
The interaction between eddies and TCs is an important
1. Introduction
branch of air—sea interactions, and the study of this inter-
action improves our understanding of ocean circulation
The South China Sea (SCS) is the largest semi-enclosed
dynamics (Hisaki, 2003; Wang et al., 2009; Zheng et al.,
marginal water body in the Northwest Pacific. Its average
2010). In the past few decades, scholars have suggested that
depth is 1800 m, and its maximum depth is up to 5400 m.
typhoons promote eddy generation. Hu and Kawamura (2004)
Each year, many TCs pass through the SCS (Liu and Xie, 1999)
found that for each case of a looping tropical cyclone, a
(Fig. 1), and many studies have shown that their strong winds
cyclonic eddy with an obvious sea-level depression appears in
stir and vertically mix the upper ocean (Guan et al., 2014;
the sea area where the cyclone takes a loop form, and a cold
Knaff et al., 2013; Price, 1981; Wang et al., 2012), and Mixing
core forms with a difference in SST greater than 28C com-
of the upper and subsurface water causes the sea surface
pared to the surrounding areas (Chen et al., 2012; Chow
temperature (SST) to cool (Chiang et al., 2011; Guan et al.,
et al., 2008; Gordon et al., 2017; Hu and Kawamura, 2004;
2014; Lin et al., 2017; Liu and Xie, 1999; Potter et al., 2017;
Mahadevan et al., 2008; Zhang et al., 2016). Furthermore,
Sun et al., 2015).
the responses of the cyclonic eddies (CEs) to typhoon forcing
Due to the influence of seabed topography and kuroshio
in the Western North Pacific Ocean (WNPO) were analyzed
invasion, many mesoscale eddies occur in the SCS (Chelton
using Argo profiles, and the results indicated that the inflow
et al., 2011b; Du et al., 2016; Wang, 2003; Xiu et al., 2010)
of warm and fresh water, heats and freshens the subsurface in
that have far-reaching impacts on the mixing of sea water,
the CEs to compensate for the cooling. Eddies primarily cool
the transport of deep-sea sediment, and the distributions of
at the surface (0—10 m depth) but deep upwelling occurs
marine organisms, energy, heat, and nutrients. As one of the
from the top of the thermocline (200 m in depth) to greater
characteristics of oceans, mesoscale eddies can also regulate
ocean depths shortly after typhoon forcing (Liu et al., 2017).
air—sea interactions (Chelton et al., 2011a; Lin et al., 2005;
By using satellite and altimeter data to research the response
Patnaik et al., 2014; Shay et al., 2000; Zheng et al., 2010).
of eddies to typhoons, the eddy core has found to have an
obvious sea-level depression after a typhoon, resulting in
both mixed layers and SSTcooling (Jaimes et al., 2011; Shang
et al., 2008); Cyclonic eddies have been found to be
enhanced by typhoons, and one noticeable feature was a
change in the three-dimensional structure accompanied by
reaxisymmetrization and elliptical deformation processes in
the horizontal plane (Lu et al., 2016; Wang et al., 2009).
Additionally, by comparing the EKE and available gravita-
tional potential energy of COEs before and after typhoons,
Sun et al. (2014) found that the energy of a COE can be
increased by a slow-moving typhoon, and the EKE can change
14 15
on order of O (10 —10 J) (Shang et al., 2015; Sun et al.,
2014). Finally, among maximum wind speed, typhoon trans-
lation speed and the typhoon forcing time (Tf), changes in the
geometric and physical parameters of eddies have been
found to mostly be related to the Tf, which is determined
by typhoon translation speed and size and typhoon intensity
(Sun et al., 2014).
In summary, many breakthroughs have occurred in the
response of eddies to TCs over the last ten years, but
important questions remain unanswered. For example, will
the properties of the eddy constrain how it is affected by a
typhoon and if so, which kind of eddy responds more strongly?
In this paper, the data used for eddy identification and
tracking are introduced in Section 2, which is followed by
results of the qualitative analysis based on specific eddy and
typhoon cases (Section 3). Finally, conclusions are offered
that include suggestions for future research (Section 4).
2. Material and methods
2.1. Typhoon data
In this paper, typhoon “best-track data sets” (BTDS) were
obtained from the U.S Joint Typhoon Warning Center (JTWC),
and each contained typhoon maximum sustained wind (MSW)
speeds in knots (i.e., the 1-min mean maximum sustained
Figure 1 Tracks of typhoons and spatial distributions of eddies. wind speed at a height of 10 m), the latitude and longitude of
F. Yu et al./Oceanologia 61 (2019) 265—275 267
the typhoon center, and the typhoon radius in sea miles. this study, and they were generated from a combination of
According to the TC classification standard of the JTWC, a TC data from TOPEX/Poseidon, Jason-1 and Jason-2, and Envir-
is defined as a typhoon when its MSW exceeds 63 knots, and as onmental Satellite. AVISO delayed-time altimeter data from
the MSW surpasses 113 knots, a TC is defined as super January 1993 to December 2015 are daily, two-satellite
typhoons. Only TCs in the Northwest Pacific with MSW 64 merged global seal-level anomalies (SLA) with a spatial
knots from 2001 to 2014 were used in this study. The duration resolution 0.25 0.258. Sea surface temperature (SST) data
of the TCs in the SCS was counted with an accuracy of 0.5 days were acquired from remote sensing systems with a resolution
because the time interval of the BTDS was 6 h (Table 1). of 25 km. The altimeter data were used to identify, detect
and track mesoscale eddies, while SST data were adopted to
2.2. Satellite data and eddy parameters validate the tracking results. The algorithm used to identify,
detect and track mesoscale eddies used in this study was
Altimeter data from Archiving, Validation, and Interpretation provided by Liu et al. (2016) and Sun et al. (2017). The
of Satellite Oceanographic Data (AVISO 2014) were used in meridional component, ug, and the zonal component, vg,
of the geostrophic velocity of the ocean current as well as A
and EKE (e.g., Xu et al., 2011) were calculated as follows:
Table 1 Information of typhoons.
A ¼ N 0:25 0:25 111 111 jcosðlatÞj; (1)
Typhoon name Time/day V_max/knots Number of
(stay in (Typhoon the eddies
the SCS) encountered g @SLA g @SLA
u ¼ ; v ¼ ; (2)
eddy) g f @y g f @x
PABUK(2001) 2.00 90 2
WUTIP(2001) 5.75 115 3
Xn
IMBUDO(2003) 2.25 90 1 1 2 2
¼ ð þ Þr :
EKE 2 ug vg AiHi (3)
MORAKOT(2003) 3.75 120 1
i¼1
MAEMI(2003) 2.00 65 1
In those formulas, N is the number of pixel occupied by the
NEPARTAK(2003) 5.75 115 1
eddy, and 0.25 111 transforms the angle into a distance (in
CONSON(2004) 2.00 125 1
kilometer). The variables ug and vg are the vertical and
HAITANG(2005) 4.00 95 1
horizontal velocity of geostrophic flow, respectively; r is a
TALIM(2005) 1.25 115 1
constant value of the density of the seawater equal to
CHANCHU(2006) 6.25 65 4