Eda Tide Gauge & AVISO

background John et al. (2001) Tide gauge ∆SSHA Observed Kuroshio transport fv=g(d ƞ /dx ) Goal: Kuroshio variation east off Taiwan and its dynamics

Time period of data Keelung: Ishigaki: Gangfeng: Suao: Lanyu: Dawu: 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 first Then, 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 Ishigaki Fill in the gap of Ishigaki Ganfeng & Keelung Keelung & Ishigaki

Anomaly of Ishigaki-Keelung Black: monthly mean Red: 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 coefficient Regression Y(i,j)=a(i,j)+b(I,j)*X X:tide gauge, Y:AVISO Plotted 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, VgRegression, 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