Eda20100903

Tide Gauge&

AVISO

background

John et al. (2001)

Tide gauge ∆SSHAObserved Kuroshio transport

fv=g(dƞ/dx)

Goal:Kuroshio variation east off Taiwan and its dynamics

Time period of dataKeelung: 1980-2009Ishigaki: 1969-2008Gangfeng: 1997-2007Suao: 1999-2005Lanyu:1992-2009Dawu:2004-2009

Mean SSH from Rio et al.2009

Black dots are the locations of the tide gauge stations.

Blue contours are the isobaths.

Data: tide gauge

• Keelung & Ishigaki: (from university of Hawaii’s sea level web)

Hourly data• Ganfeng, Suao, Dawu and Lanyu: (from cwb)

High tide and low tide (about every 6 hour)

All data had done 40hr low pass firstThen, save into daily format

Original data after 40 hrs low pass. There are some missing data

The linear regression is done in order to fill in the gap.

1.Ganfeng and Keelung (same side)Fill in the gap of Keelung.2.Keelung and IshigakiFill in the gap of Ishigaki

Ganfeng & Keelung

Keelung & Ishigaki

Anomaly of Ishigaki-Keelung

Black: monthly meanRed: 360days running mean

Nino3.4, West Pacific with Tide Gauge SSHA

Colored bar are Nino3.4 or WP

Contour is tide gauge SSHA

SSHA does not correlate with Nino3.4.

The correlation is better in WP (yellow box)

AVISO & Tide Gauge• Time: 1992/10/14~2008/12/31 (16 years)• Tide Gauge : Ishigaki, Keelung• AVISO: SSH, Ug, Vg (1/5 degree)• Both tide gauge and AVISO data are monthly

averaged Discussion:

What contribute to the variation of the Kuroshio northeast off Taiwan?

In order to answer this, the next part is the regression (correlation) between Tide Gauge SSHA and AVISO SSH, Ug, Vg.

Correlation coefficientRegressionY(i,j)=a(i,j)+b(I,j)*XX:tide gauge, Y:AVISOPlotted here is b

Correlation Coef. Is very similar to regression b. The following plot will only use “b”.

Tide gauge SSHA correlates well with a zonal band region east of Taiwan.

Zonal band=high EKE region

The eddy activity contributes to the variation of Kuroshio transport northeast off Taiwan.

Regression, Vg Regression, Ug

Tide Gauge SSHA has good correlation with Kuroshio upstream and the Mindanao Current

1. Eddy zone (anti-cyclonic eddy)2. Two branches of Kuroshio; East China

Sea; Ryukyu Island

p.s. the regressions are very similar to dSSH/dx, dSSH/dy (fig. not shown).

corr

Tide Gauge SSH (black) & mean eddy zone SSHA (red)

Defined eddy zone

Eddy activity has important influence to the variation of Kuroshio transport east off Taiwan

Regression : AVISO ∆SSH (same locations) & AVISO

Regression : AVISO ∆SSH (East Luzon) & AVISO

High regression also shows in eddy zone.

Further south, at east of Luzon, the Kuroshio transport does not have high regression with eddy zone

East Luzon AVISO ∆SSH & AVISO Vg

Interestingly, the Kuroshio transport east off Luzon does not correlate well with futhur north transport.

Nino3.4

WP

summary

• Kuroshio transport east off Taiwan is affected by eddy activity, therefore, it shows different variation with East Luzon transport where is south of the eddy zone.

• Tide gauge ∆SSH has good regression with two branches of Kuroshio; one enter East China Sea; the other one moves along Ryukyu Island

http://en.wikipedia.org/wiki/Philippine_Sea