Estimation of Wind Drift Current in the Soya Strait Wei Zhang, - PowerPoint PPT Presentation

Estimation of Wind Drift Current in the Soya Strait Wei Zhang, Naoto Ebuchi, Yasushi Fukamachi Institute of Low Temperature Science Hokkaido University zhangwei@lowtem.hokudai.ac.jp 1

The Soya Strait Russia Sea of Okhotsk China Japan Connection of Sea of Japan Sea and Sea of Okhotsk Soya warm current Fishery 2

Example of HF Radar Snapshot 17h20m (JST) 3 Aug 2003 3 http://wwwoc.lowtem.hokudai.ac.jp/hf-radar/index.html

Wind Drift Current u u u Wind s i wd Surface current u wd : Wind Drift Current Interior Current 4 Cushuman-Roisin (1994)

Drift Parameter u A ( , ) W wd cos sin A ( , ) sin cos α: speed factor θ: deflection angle W : wind vector 5 Cushuman-Roisin (1994)

How to calculate wind drift parameter min( u ) ( u u ) A ( , ) W err s i Surface current (HF radar data) Interior current (ADCP data) Wind (JMA GPV/MSM) 6

Observation • HF radars • ADCP (Bottom mounted) • Tide gauges • Wind (JMA GPV/MSM) 7

Example of ADCP vertical profiles Monthly-mean of alongshore velocity observed by ADCP. 8 Fukamachi et al .(2010)

Interior Current Correlation Coefficient between sea level difference and alongshore velocities of different ADCP bins. Surface 25 20 ~28m ADCP bins Number 15 ~51m 10 Bin10 5 Bottom 0 0.77 0.77 0.78 0.78 0.79 0.79 0.8 0.8 0.81 0.81 0.82 0.82 0.83 0.83 0.84 0.84 9 Correlation Coeffiicent

Bin10 VS. Sea Level Difference Alongshore Current 1.5 HF Bin10 Alongshore Velocity (m/s) 1 0.5 0 -0.5 Nov/06 Feb/07 Jun/07 Sep/07 Dec/07 Apr/08 Jul/08 Sea Level Difference Sea lever difference 0.2 height (m) 0.1 0 -0.1 Nov/06 Feb/07 Jun/07 Sep/07 Dec/07 Apr/08 Jul/08 Alongshore velocities correspond well with sea level difference. 10

Process Steps 11

Monthly Drift Parameters deflection angle speed factor 0.04 250 200 0.03 150 0.02 100 deflection angle speed factor 0.01 50 0 0 -50 -0.01 -100 -150 -0.02 -200 Nov/06 Feb/07 Jun/07 Sep/07 Dec/07 Apr/08 Jul/08 Nov/06 Feb/07 Jun/07 Sep/07 Dec/07 Apr/08 Jul/08 time (month) time (month) 700 Root-Mean-Square 600 500 error of monthly and number of data 400 daily drift parameters 300 200 100 12 0 Nov/06 Feb/07 Jun/07 Sep/07 Dec/07 Apr/08 Jul/08 month

Average Drift Parameter value RMSE Deflection angle 34 deg. 83 deg. Speed factor 0.0078 0.0156 Root-Mean-Square error of average and daily drift parameters 13

Seasonal variation in drift parameters deflection angle speed factor 250 0.04 200 0.03 150 0.02 deflection angle (deg.) speed factor 100 0.01 50 0 0 -0.01 -50 -0.02 -100 -0.03 2 4 6 8 10 12 2 4 6 8 10 12 calendar month calendar month 1600 Root-Mean-Square 1400 error of calendar 1200 number of data 1000 monthly and daily 800 600 drift parameters 400 200 14 0 1 2 3 4 5 6 7 8 9 10 11 12 calendar month

Seasonal variation comparison Yoshikawa and Masuda (2009) speed factor deflection angle 0.025 100 90 0.02 80 70 deflection angle (deg.) 0.015 60 speed factor 50 0.01 40 30 0.005 20 10 0 0 0 2 4 6 8 10 12 0 2 4 6 8 10 12 calendar month calendar month Seasonal variation in drift parameters are not significant. 15

Comparison1 for alongshore component RMS of Alongshore Interior Current 0.4 Monthly drift parameter Average drift parameter 0.35 Correlation Seasonly drift parameter Coefficient 0.3 +: 90.35% 0.25 RMS error (m/s) 0.2 +: 90.23% 0.15 +: 90.34% 0.1 0.05 0 Nov/06 Feb/07 Jun/07 Sep/07 Dec/07 Apr/08 Jul/08 time (month) High Error: Aug. Sept. Oct. Low Error: Dec. Jan. Feb. Mar. Apr. 16

Relationship between sea level difference and Bin10 1.5 1.5 Estimated Current Alongshore Current 1 1 bin10 alongshore current (m/s) Alongshore Current (m/s) 0.5 0.5 0 0 -0.5 -0.5 -1 -1 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0 2000 4000 6000 8000 10000 12000 14000 16000 18000 sea level difference (m) Time Serial (/hour) Correlation coefficient: 81.26% a 2.52 u a b b 0.13 iSL 17

Comparison2 for alongshore component RMS of Alongshore Interior Current Driven from Sea Level Difference 0.5 Monthly drift parameter Average drift parameter 0.45 Seasonly drift parameter Correlation 0.4 Coefficient +: 74.69% 0.35 RMS error (m/s) 0.3 +: 75.44% 0.25 +: 71.77% 0.2 0.15 0.1 Nov/06 Feb/07 Jun/07 Sep/07 Dec/07 Apr/08 Jul/08 time (month) High Error: Aug. Sept. Oct. 18

Wind in Summer Aug. 07 Sept. 07 Oct. 06 Oct. 07 19 The wind is weak, and its direction is unstable.

Wind in Winter Dec. 07 Jan. 07 Feb. 07 Feb. 08 Jan. 08 Dec. 06 The wind is strong, and its direction is stable. 20

Affection of bottom on drift parameter Surface The bottom boundary layer depth * : Bottom boundary U ~28m * 0.4 40 m ~51m E f 2 1 4 1 U 10 ms , f 1 10 s Bin10 40m * The bottom boundary layer affects on the wind drift current. Bottom 21 * Yoshikawa and Masuda (2009); Cushuman-Roisin (1994)

Affection of coastline on drift parameter The horizontal boundary layer width * : 1/2 2 A D H 2.2 km H f E 2 1 A 200 m s , D 50 m H + ADCP The horizontal boundary layer effect on the wind drift current can be neglected. 22 * Yoshikawa and Masuda (2009); Pedlosky (1987)

conclusion Average drift parameter is a simple and effective way to estimate wind drift current. Wind drift current estimation is more accurate in winter and spring, but worse in summer and autumn. Seasonal variation in drift parameters are not significant. The bottom boundary layer affects wind drift current. 23

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. • Pedlosky, J. (1987), Geophysical Fluid Dynamics, 2nd ed., 710 pp., Springer, New York. 24

Thank you for your attention!!! 25

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Monthly drift parameter in seasonal variation speed factor 0.02 0.015 speed factor 0.01 0.005 0 0 2 4 6 8 10 12 deflection angle 200 deflection angle 100 0 -100 0 2 4 6 8 10 12 month 28

Seasonal variation comparison Yoshikawa and Masuda (2009) speed factor deflection angle 0.025 100 90 0.02 80 70 deflection angle (deg.) 0.015 60 speed factor 50 0.01 40 30 0.005 20 10 0 0 0 2 4 6 8 10 12 0 2 4 6 8 10 12 calendar month calendar month Seasonal variation in deflection angles are obvious. 29

Wind direction in each month Nov. 06 Dec. 06 Oct. 06 Feb. 07 Mar. 07 Jan. 07 Jun. 07 Apr. 07 May 07 30

Wind direction in each month Aug. 07 Sept. 07 Jul. 07 Nov. 07 Dec. 07 Oct. 07 Oct. 07 Feb. 08 Mar. 08 Jan. 08 31

Wind direction in each month Apr. 08 May 08 Jun. 08 Jul. 08 32