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The refraction and reconnection of internal solitary waves (ISWs)
around the Dongsha Atoll (DSA) in the northern South China Sea
(SCS) are investigated based on SAR observations and numerical
simulations. In general, a long ISW front refracts and splits into
northern and southern branches when it passes the DSA. In this
study, the statistics of Envisat ASAR images show that the two
wave branches can reconnect behind the DSA (Figure 1), but the
reconnection location varies.
Methods
Conclusions
Study on internal waves at Dongsha Atoll
Tong Jia, Xiao-Ming Li, Jiangjun Liang, Jin ShaInstitute of Remote Sensing and Digital Earth,
Chinese Academy of Sciences
Abstract
Relative to the extension line of Dongsha Island, the reconnection of ISW
branches can be categorized into the west (Figure 2a), northwest (Figure
2b), southwest (Figure 2c) of Dongsha Island. Besides, there are other
ISWs which still separate from each other behind the DSA (Figure 2d).
The results of E1 prove the validity of the NRM model around the DSA.
Experiments E2-E9 show that ocean stratification, background currents,
and initial wave amplitude all affect the phase speeds of ISW branches and
therefore shift their reconnection locations while initial wave fronts
profoundly influence the subsequent propagation paths.
Envisat ASAR
TerraSAR-X
SAR Observations
of ISW
Reconnection
Behind the DSA
Reference
Experiment Based
on the TSX
Observations by
NRM
Sensitivity
Experiments of
Changing Model
parameters
NRM
HYCOM/NCODA
Ocean
Stratification
Background
Current
Results and
analyses
Variations of
reconnection location
Reference Experiment(E1)
Reference
experiemntInitial Wave
Amplitude
Initial Wave
fronts
NRMComparisons
and analyses
Sensitivity Experiments(E2-E9)
SAR Statistics
Statistical
classification
change
Research
Method
Figure 1. The propagation of ISWs
near the DSA (Hsu and Liu,2000)
ReferencesHsu, M. K., & Liu, A. K. (2000). Nonlinear internal waves in the South
China Sea. Canadian Journal of Remote Sensing, 26(2), 72–81.
Xie, J., He, Y., Lü, H., Chen, Z., Xu, J., & Cai, S. (2016). Distortion and
broadening of internal solitary wavefront in the northeastern South China Sea
deep basin. Geophysical Research Letters, 43(14).
ObjectiveWith the help of SAR data and a nonlinear refraction model (NRM)
which is developed by Xie et al. (2016), this study aims to clarify
the variation in reconnection locations of ISWs downstream of the
DSA and reveals the mechanisms governing the reconnection
process of ISWs near the DSA.
Figure 4. Results of a reference experiment and other eight sensitivity experiments
E1:reference experiment E2:using seasonal summer stratification E3:eastward current velocity
+0.2m/s
E4:eastward current velocity
-0.1m/s E5:initial amplitude +10% E6:initial amplitude +20%
E7:initial wave fronts observed
on 03/27/2005 ASAR image
E8:initial wave fronts observed
on 08/27/2008 ASAR image
E9:initial wave fronts observed
on 06/20/2004 ASAR image
Figure 2. The spatial variations of
reconnection or separation of ISWs behind the DSA
Figure 3. Two consecutive TSX images
within 12 h used in E1
Based on the first realistic simulation
whose results agree well with the
consecutive TerraSAR-X (TSX)
images captured within 12 h of each
other, eight sensitivity simulations
are conducted and show that ocean
stratification, background currents,
and initial wave amplitudes all affect
the phase speeds of wave branches
and therefore shift their reconnection
locations while shapes and locations
of incoming wave branches upstream
of the DSA profoundly influence the
subsequent propagation paths.
ResultsThe results of this study are shown in Figure 2 and Figure 4.
Figure 3 presents the SAR images used in E1.