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Eda 20100903 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. Mean SSH from Rio et al.2009 Black dots are the locations of the tide gauge stations.
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Eda 20100903 Tide Gauge & AVISO
background John et al. (2001) Tide gauge ∆SSHA Observed Kuroshio transport fv=g(dƞ/dx) Goal: Kuroshio variation east off Taiwan and its dynamics
Mean SSH from Rio et al.2009 Black dots are the locations of the tide gauge stations. Blue contours are the isobaths. Time period of data Keelung: 1980-2009 Ishigaki: 1969-2008 Gangfeng: 1997-2007 Suao: 1999-2005 Lanyu:1992-2009 Dawu:2004-2009
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.
Regression Y(i,j)=a(i,j)+b(I,j)*X X:tide gauge, Y:AVISO Plotted here is b Correlation coefficient 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 Eddy zone (anti-cyclonic eddy) 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 Defined eddy zone Tide Gauge SSH (black) & mean eddy zone SSHA (red) 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
