Current in the Soya Strait Wei Zhang 1 , Naoto Ebuchi 1 , Yasushi - - PowerPoint PPT Presentation

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Estimation of Wind Drift Current in the Soya Strait

Wei Zhang1, Naoto Ebuchi1, Yasushi Fukamachi1, and Yutaka Yoshikawa2

1Institute of Low Temperature Science,

Hokkaido University

2Graduate School of Science, Kyoto

University

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The Soya Strait

• Connection of Sea
• f Japan Sea and Sea
• f Okhotsk
• Soya warm current
• Fishery

Sea of Okhotsk

Japan Russia China

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Geostrophic Current Surface current

uwd: Wind Drift Current

Wind Drift Current

Wind

Cushuman-Roisin (1994)

g s wd

  u u u

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Drift Parameter

Cushuman-Roisin (1994)

c

• s

s i n ( , ) s i n c

• s

               A α: speed factor θ: deflection angle W: wind vector us: surface current ug: geostrophic current

= ( , )

wd s g

    A u u u W

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How to calculate wind drift parameter

• Surface current (HF radar data)
• Geostrophic current

(ADCP data / Tide gauges data)

• Wind (JMA GPV/MSM)

( , )

min[( ) ( , ) ]

s g  

    A u W u

LSM *Complex PCA/EOF

1 1

( , )

wd st st s g

CEOF                          u W u u W

* Kundu and Allen (1976)

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CEOF Brief Introduction

1 1

( ) ( ) ( )

st st

CEOF EOF W U Vi U V i    

Kundu and Allen (1976)

( , ) U V W U Vi  

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Observation

Long Term:

• HF Radars
• Tide Gauges
• Wind

(JMA GPV/MSM)

Short Term: (22 months)

• ADCP

(Bottom mounted)

Example of HF Radar Snapshot

17h20m (JST) 3 Aug 2003

http://wwwoc.lowtem.hokudai.ac.jp/hf-radar/index.html

Example of ADCP vertical profiles

Monthly-mean of alongshore velocity observed by ADCP.

Fukamachi et al.(2010)

0.2 0.4 5 10 15 20 25 Velocity (m/s) Bin Number Along-shore Component

• 0.2

0.2 5 10 15 20 25 Velocity (m/s) Bin number Cross-shore Component

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Geostrophic Current Estimation (Method 1)

5-day geostrophic current estimation from ADCP

• Dec. 23 2007 ~ Dec. 27 2007

Extrapolation

LSM 1 Complex PCA/EOF

0.77 0.78 0.79 0.8 0.81 0.82 0.83 0.84 Correlation Coeffiicent 0.77 0.78 0.79 0.8 0.81 0.82 0.83 0.84 5 10 15 20 25 ADCP bins Number

Correlation Coefficient between Sea Level Difference (SLD) and alongshore velocities of ADCP bins.

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Sea Level Difference vs. Along-shore Current

Alongshore velocities correspond well with sea level difference. Bottom Surface ~51m

Bin15 Bin10 Bin5 Bin22 Bin1 Bin24

5 5 10 15 20 25 Coefficient Bins Coefficient aiBin 0.5 1 5 10 15 20 25 Coefficient Bins Coefficient biBin

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Geostrophic Current Estimation (Method 2)

24 24 Bin g Bin

u b a    

1 5 5 1 15 B n B in Bi in

u b a    

1 8 8 1 18 B n B in Bi in

u b a    

2 2 2 2 22 B n B in Bi in

u b a    

Geostrophic current estimated from Sea Level Difference Coefficient

iBin iBi iB n in

a u b    

• Aug. 2007

LSM 2 Complex PCA/EOF

Nov/06 Feb/07 Jun/07 Sep/07 Dec/07 Apr/08 Jul/08

• 50

50 100

Turning Angle (deg.)

LSM 1 LSM 2 CEOF

Nov/06 Feb/07 Jun/07 Sep/07 Dec/07 Apr/08 Jul/08 100 200 300 400 500 600 700 time (month) number of data

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Monthly-Mean Drift Parameters

The drift parameters are roughly similar.

Nov/06 Feb/07 Jun/07 Sep/07 Dec/07 Apr/08 Jul/08 0.005 0.01 0.015 0.02 0.025 0.03

Speed Factor

LSM 1 LSM 2 CEOF

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Annual-Mean Drift Parameter

Root-Mean-Square error with daily drift parameters

α (×10-2) θ (deg.) Value LSM1 0.87 18 LSM2 1.39 34 CEOF 1.10 21 RMSE LSM1 1.64 78 LSM2 2.60 77 CEOF 1.93 98

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Wind Drift Current Estimation

The wind drift current is strong in winter, but weak in summer.

Nov/06 Feb/07 Jun/07 Sep/07 Dec/07 Apr/08 Jul/08

• 0.1
• 0.05

0.05 0.1

Velocity (m/s) (a) By monthly-mean wind drift parameters

LSM 1 LSM 2 CEOF Nov/06 Feb/07 Jun/07 Sep/07 Dec/07 Apr/08 Jul/08

• 0.1
• 0.05

0.05 0.1

Velocity (m/s) (b) By annual-mean wind drift parameters

LSM 1 LSM 2 CEOF

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Affection of coastline on drift parameter

1/2 2 1

2 2.2 200 , 50

H H E H

A D km f A m s D m  



         

The horizontal boundary layer effect on the wind drift current can be neglected. The horizontal boundary layer width*:

+ ADCP

* Yoshikawa and Masuda (2009); Pedlosky (1987)

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Affection of bottom on drift parameter

* 2 1 4 1 *

0.4 40 10 , 1 10

E

U m f U ms f s 

   

    

The bottom boundary layer affects on the wind drift current. The bottom boundary layer depth*:

Bottom boundary * Yoshikawa and Masuda (2009); Cushuman-Roisin (1994)

Surface Bottom ~51m 40m

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Wind in Summer

The wind is weak, and its direction is unstable.

• Oct. 07
• Oct. 06
• Aug. 07
• Sept. 07
• Jul. 07
• Jul. 08

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Wind in Winter

• Dec. 07
• Jan. 08
• Feb. 08
• Dec. 06
• Jan. 07
• Feb. 07

The wind is strong, and its direction is stable.

Nov/06 Feb/07 Jun/07 Sep/07 Dec/07 Apr/08 Jul/08 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Velocity (m/s) Along-shore Current

Surface Current Estimated Geocurrent

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Evaluation

ˆ ˆ ( ˆ , )

g s

A     u u W

Along-shore current vs. sea level difference

HF LSM 1 LSM 2 CEOF

Corre lation

us Monthly Mean Monthly Mean Monthly Mean 0.710 0.757 0.759 0.785 0.774 0.763 0.768

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Summary

• Wind drift parameters calculated from 3

methods are roughly similar.

• Annual-mean wind drift parameters are a

simple and effective way to estimate wind drift current.

• Wind drift current estimation is more
• bvious in winter, but weak in summer.

Main reference

• Yoshikawa, Y. and A. Masuda (2009): Seasonal variations in the

speed factor and deflection angle of the wind-driven surface flow in the Tsushima Strait. J. Geophys. Res. Oceans, 114, C12022, doi:10.1029/2009JC005632.

• Cushuman-Roisin, B. (1994), Introduction to Geophysical Fluid

Dynamics, 320 pp., Prentice-Hall, Englewood Cliffs, N. J.

• Fukamachi, Y., K. I. Ohshima, N. Ebuchi, T. Bando, K. Ono, and
• M. Sano (2010): Volume Transport in the Soya Strait during 2006-

2008, Journal of Oceanography, 66, 685-696.

• Kundu, P. K., and J. S. Allen (1976), Some three-dimensional

characteristics of low-frequency current fluctuations near the Oregon coast, J. Phys. Oceanogr., 6, 181– 199.

• Pedlosky, J. (1987), Geophysical Fluid Dynamics, 2nd ed., 710 pp.,

Springer, New York.

• Yoshikawa, Y., et al. A surface velocity spiral observed with ADCP

and HF radar in the Tsushima Strait. Journal of Geophysical Research: Oceans (1978–2012) 112.C6 (2007).

Thank you for your Attention

Back Up

Nov/06 Feb/07 Jun/07 Sep/07 Dec/07 Apr/08 Jul/08 100 200 300 400 500 600 700 time (month) number of data

Nov/06 Feb/07 Jun/07 Sep/07 Dec/07 Apr/08 Jul/08

• 60
• 40
• 20

20 40 60 80 100 120 time (month) deflection angle (deg.) LSM 1 LSM 2 CEOF

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Monthly Drift Parameters

Nov/06 Feb/07 Jun/07 Sep/07 Dec/07 Apr/08 Jul/08 0.005 0.01 0.015 0.02 0.025 0.03 time (month) speed factor LSM 1 LSM 2 CEOF

CEOF is a better way to estimate wind drift parameter.

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Annual-Mean Drift Parameter

Root-Mean-Square error with daily drift parameters

α (×10-2) θ (deg.)

Value LSM1 0.87 18 LSM2 1.39 34 CEOF 1.10 21 RMSE LSM1 1.64 78 LSM2 2.60 77 CEOF 1.93 98

Nov/06 Feb/07 Jun/07 Sep/07 Dec/07 Apr/08 Jul/08

• 0.1
• 0.05

0.05 0.1

Velocity (m/s) (b) By annual-mean wind drift parameters

LSM 1 LSM 2 CEOF

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LSM 2 ( , ) ( ) ( , )

err err s g

u v      u A u W

( , ) ( , )

( , ) min( ) min(( ) ( cos(

g err s

u u u

   

          

LSM1

* Kundu and Allen (1976)

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LSM 2 ( , ) ( ) ( , )

err err s g

u v      u A u W

( , )

( , ) min( )

err

u

 

  

* Kundu and Allen (1976)

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LSM1 & CEOF

( , ) ( ) ( , )

err err s g

u v      u A u W

( , )

( , ) min[( , ] )

err err

u v

 

  

LSM1 *CEOF

1 1

( , )

wd st st s g

CEOF                          u W u u W

* Kundu and Allen (1976)

* W U V i  