Form 3

Annual Report
LaMer, Ehime University

Date (16 , 11 , 2017)
To Director of LaMer

Principle Investigator:
Affiliation Second Institute of Oceanography, SOA
Position

Research AssistantName in print

Ruixiang Zhao

Include the report on the result of the project/meeting in a separate sheet.
1. Project / Meeting title
Applications of pressure-recording inverted echo sounders
2. Members of project / meeting
NamePI
Ruixiang Zhao
Members
Xiao-Hua Zhu

Xinyu Guo

Affiliation

Position

Second Institute of Research
Oceanography, SOAAssistantContribution part

Data processing; Paperwriting

Second Institute of Senior Research Beneficial discussion
Oceanography, SOA
Scientist
Ehime University

Professor

Beneficial discussion

3. Contents (please write in separate sheet, A4-size, within 5 pages

TitleApplications of pressure-recording inverted echo sounders

Members’ names and affiliations
NameInstitution
Department

Zhu Xiao-Hua

Second Institute of Senior
Oceanography,and Employment position

E-mailxhzhu@sio.org.cn

Research Scientist

SOA
Xinyu Guo

Faculty member of Professor

guoxinyu@sci.ehime-u.ac.jp

LaMer

Aim
This project aims to carry out cooperative research with Prof. Guo Xinyu of Ehime
University on the application of pressure-recording inverted echo sounders (PIESs)
deployed in the South China Sea (SCS), Kuroshio and other regions.

Procedure
The principal investigator (PI) has first made an oral presentation “Observations
from pressure-recording inverted echo sounders in the South China Sea” and showed
the recent studies of PI including: 1. The variability of 22-year-long volume transport of
the South China Sea western boundary current based on PIES and satellite altimetermeasurements. 2. The impact of monsoon winds and mesoscale eddies on thermohaline
structures and circulation patterns in the northern South China Sea. 3. Weakest winterSouth China Sea western boundary current caused by 2015/2016 El Niño event.
The PI will carry out further research with Prof. Guo Xinyu on the following
subjects: 1. The variability of internal tide observed by PIESs in the SCS and Kuroshio.
2. The near-5-day nonisostatic response to atmospheric pressure from globallydistributed PIESs. 3. The response of Kuroshio to ENSO from PIES observations. Athorough discussion on the simulation of PIES observations or some numericalexperiments will be carried out if enough time is available.

Results
Our joint research of this year (2016) is focused on the study of internal tides in theSouth China Sea from the PIES observations. During October 2012 to July 2014, 5
pressure-recording inverted echo sounders (PIESs) were deployed in the northern South
China Sea. The PIESs mainly measure vertical acoustic travel time (τ), i.e., the time forsound pulses transmitted from the seafloor to the sea surface and back, and measure thenear-bottom pressure (Pbot), all with a time interval of 1 hour. The Pbot is appropriate
to capture the tides of the barotropic components, and the measured τ is good at
detecting signals of the internal tides, for it is sensitive to the variation of thethermocline depths (Watts and Rossby, 1977; Park and Watts, 2006).
Though the wavelet analysis (Fig.2) of the band-pass filtered τ (with cutoff periodsof 0.2 days and 2 days), the following conclusions are drawn: 1. The internal tide ismore energetic in shallower waters near the continental slope, indicating the effects oftopography. 2. The diurnal internal tide is stronger than the semidiurnal internal tides. 3.
The internal tides are strongly impacted by the barotropic tides. 4. Both the semidiurnal
and the diurnal internal tide show significant variability which may be strongly related
to the occupation of mesoscale eddies. However, their behaviors to eddies are quite
different (Fig.3): the semidiurnal tide strengthened (weakened) when cyclonic(anticyclonic) eddies were present, while the diurnal tides were extensively weakened
with the arrival of cyclonic eddies. The reason why semidiurnal and diurnal internal

tides responded differently to meso-scale eddies are still under investigation, but weguess that variation of internal tides may be due to the fact that mesoscale eddies cancause changes of water properties, which may alter the path of the internal tides
propagation (Park and Watts, 2006).

References:
1. Watts, D.R., and H. T. Rossby (1977), Measuring Dynamic Heights with
Inverted Echo Sounders: results from MODE, Journal of Physical
Oceanography, 7(3): 345- 358.
2. Park, J.-H., and D. R. Watts (2006), Internal Tides in the SouthwesternJapan/East Sea, Journal of Physical Oceanography, 36(1): 22- 34.

Figure 1. Location map of the PIES stations. Red triangles indicate the individual
PIES instruments and blue dots indicate the TOPEX/POSEIDON and Jason-1/2 satellite
altimeter track (track 114). Bathymetry is contoured in meters.

Figure 2. Wavelet analysis results of vertical acoustic travel time (τ) detected by 5pressure-recording inverted echo sounders (PIESs) at the semidiurnal and diurnal bands.

Figure 3. The Hovmöller diagram of the normalized (a) sea level anomaly (b)semidiurnal internal tide signals (c) diurnal internal tide signals (d) semidiurnalbarotropic tide signals (e) diurnal barotropic tide signals.

Publication/conference presentation
Publications:
1. Zhu, X.-H., R. Zhao, X. Guo, Y. Long, Y.-L. Ma ,and X. Fan (2015), A
long-term volume transport time series estimated by combining in situ observation andsatellite altimeter data in the northern South China Sea, Journal of Oceanography, 71(3),doi:10.1007/s10872-015-0305-5.
2. Zhao, R., X.-H. Zhu, and X. Guo (2016), The impact of monsoon winds andmesoscale eddies on thermohaline structures and circulation patterns in the northern
South China Sea, Continental Shelf Research, doi: 10.1016/j.csr.2016.06.009.
Oral presentation:
Title: Applications of inverted echo sounder in the South China Sea.
Lecturer: Ruixiang Zhao.
Time: September 7, 2016.
Location: Ehime University.

Perspectives in future
We expect great progresses on the applications of PIES and our understanding of thecirculation in the South China Sea, Kuroshio and other regions. We wish to publish ourjoint research on famous journals if possible.