Experiment Based TerraSAR-X Research Study on internal

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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.