Seasonal variation in he Yellow Sea derived from satellite a

时间：2025-04-19

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Se~tsonal variation in surface circulation of the East China Sea and the Yellow Sea derived from satellite altimetric dataT E T S U O Y A N A G I, * A K I H I K O M O R I M O T O * and KAORU ICHIKAWA*(Received 8 March 1996;accepted 30 August 1996)

Abstract--Seasonal variation in the surface circulation of the East China Sea and the YellowSea is investigated using altimetric data of TOPEX/POSEIDON and numerical model output. In the Yellow Sea an anticlockwise circulation develops during summer and a clockwise one during winter In the East China Sea an anticlockwise circulation occurs during winter. Such results coincide well with those obtained by the numerical experiment and drifter buoys experiment.© 199"7Elsevier Science Ltd. All rights reserved

1. I N T R O D U C T I O N Satellite altimetry has been very useful for studies of open ocean dynamics (e.g. Ichikawa and Imawaki, 1994) but has not been used for the study of coastal ocean dynamics. This is due to the fact that the tidal signals cannot be correctly eliminated from altimetric data in the coastal sea where the tidal signal and its spatial gradient are very large and where the existing global tidal models do not have sufficient accuracy. We have developed a new procedure:for correctly estimating tidal signals in the coastal sea from the altimetric data of T O P E X/ P O S E I D O N (Yanagi et al., 1997). In this paper, we try to determine the seasonal variation in the sea surface circulation of the East China Sea and the Yellow Sea by use of the altimetric data of T O P E X/ P O S E I D O N after correctly eliminating tidal signals. 2. A L T I M E T R I C D A T A PROCESSING

The satellite T O P E X/ P O S E I D O N was launched in August 1992 and has continued to obtain the altimetric data about every 10 days along seven observation lines in the East China Sea and the Yellow Sea as shown in Fig. l(b). The data are provided as Merged Geophysical Data Record ( M G D R ) by the Physical Oceanography Distributed Active Archive Center at Jet Propulsion Laboratory, U.S.A. We used the data taken by only T O P E X altimeter from Cycle 1 (September 1992) until Cycle 108 (August 1995) in this analysis. Since the P O S E I D O N altimeter had an unknown bias of the order of 20 cm to T O P E X one, we did not use the data taken by P O S E I D O N altimeter in this study (this *Department of Civil and Ocean Engineering, Ehime University, Matsuyama790, Japan. 655

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Satellite altimetric data

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problem was solved by NASA in July 1996 and we can also use POSEIDON data now). Standard data correction including electromagnetic bias correction, ionospheric correction, dry and wet trospheric correction

and solid earth tide correction were made using the values provided in the MGDR. After these corrections, tidal signals of M2,$2, K2, N1, O1 and P~ constituents, which have more than 10 cm amplitude in the East China Sea and the Yellow Sea, are eliminated on the basis of the results of Yanagi et al. (1997). As an example, the sea surface height anomaly from the mean sea surface during the whole observed period derived from the altimetry data (SSHA), estimated tidal signal (TIDE) and the sea surface height anomaly after the elimination of tidal signals (Corrected SSHA) at Sta A in the central part of the Yellow Sea[see Fig. l(b)] are shown in Fig. 2. Temporal variation with the period of about 60 days is dominant in SSHA and this is due to the aliasing of Me constituent. The tidal signal is well eliminated from SSHA and the seasonal variation is dominant in Corrected SSHA as seen in Fig. 2, that is, Corrected SSHA is hi[gh in summer and low in winter. The altimetric data are originally obtained about every 1 s (corresponding to about every 6.2 km along the subsatellite track, which is the projection of satellite track on the sea surface) but the data points differ every cycle. Therefore, we linearly interpolated every data point in a cycle at the fixed points within a 6.2 km interval along the subsatellite track and nine data points are further averaged for the following procedure in order to reduce small-scale phenomena observed along tracks. The distribution of basic data points are shown in Fig. l(b). The estimated sea surface height after the tidal correction at the point r at time t, S(r,t), is expressed by the following formula:

S(r,t)=~ (r,t)+ (N(r)+ en(r)}+{es(r)+ 6r(O) -~-~rn(t)

(1)

where~(r,t) denotes the sea surface dynamic topography, N(r) the geoid, e,,(r) the error of geoid, e~(r)+ e~(t) the spatial and temporal components of orbit error and em(t) the measurement error. The sea surface dynamic topography~(r,t) is divided into the temporal averaged height~m(r) and the anomaly~'(r,t):

~(r,t)= Cm(r)+~'(r,t)

(2)

Altimetric data S(r,t) has to be divided into the temporal averaged value S,~(r) and the anomaly S'(r,t) due to that the accuracy of geoid data is not sufficient:

S(r,t)= Sm(r)+ S'(r,t)From equations (1) to (3), we get

(3)

S'(r,t)=~'(r,t)+ l?r(0 q- Sm( 0

(4)

We ignore the temporal average of er(t ) and em(t) because they are small.~'(r,t) is divided into the temporal mean during the period of q,~'mq(r), and the anomaly~"(r,t):

¢'(r,t)=¢~nq(r)+~"(r,t)Substituting equation (5) into equation (4), we get

(5)

S'(r,t)

~'mq(r)+~"(r,t)= H'q(r)+ E'(r,tq)=

e~(t)

gm(t)(6)

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