Please wait a minute...

Frontiers of Earth Science

Front Earth Sci    2013, Vol. 7 Issue (4) : 447-455     DOI: 10.1007/s11707-013-0380-0
RESEARCH ARTICLE |
Geostrophic current estimation using altimeter data at ground track crossovers in the northwest Pacific Ocean
Yang YU1,2(), Longfei WANG1, Ziwei LI1,2, Xuan ZHOU3
1. Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, Beijing 100101, China; 2. State Key Laboratory of Remote Sensing Science, Beijing 100101, China; 3. P. O. Box 5111, Beijing 100094, China
Download: PDF(578 KB)   HTML
Export: BibTeX | EndNote | Reference Manager | ProCite | RefWorks
Abstract

Geostrophic current comprises a large portion of the ocean current, which plays an important role in global climate change. Based on classic oceanography, geostrophic current can be derived from pressure gradient. Assuming water density to be constant, we can estimate geostrophic current from Absolute Dynamic Topography (ADT). In this paper, we use ADT data obtained from multi-satellite altimeters to extract sea surface tilts along-track at crossover points. The calculated tilts along these two tracks can be converted into orthogonal directions and are used to estimate geostrophic current. In northwest Pacific, computed geostrophic current velocities are evaluated with Argos data. In total, 771 pairs of temporally and spatially consistent Argos measurements along with estimated geostrophic velocity datasets are used for validation. In this study, the effect of different cut-off wavelengths of the low pass filter applied to ADT is discussed. Our results show that a cut-off wavelength of 75 km is the most suitable choice for the study area. The estimated geostrophic velocity and the Argos measurement are in good agreement with each other, with a correlation coefficient of 0.867 for zonal component, and 0.734 for meridional one. Furthermore, an empirical relationship between the estimated geostrophic velocity and Argos measurement is derived, providing us a favorable and convenient approach to estimate sea surface flow velocity from the geostrophic velocity derived from altimeter data. The experimental application of the derived method on Kuroshio reveals reasonable results compared with previous studies.

Keywords geostrophic velocity      altimeter      northwest Pacific Ocean      crossover method     
Corresponding Authors: YU Yang,Email:yuyang@irsa.ac.cn   
Issue Date: 05 December 2013
 Cite this article:   
Yang YU,Longfei WANG,Ziwei LI, et al. Geostrophic current estimation using altimeter data at ground track crossovers in the northwest Pacific Ocean[J]. Front Earth Sci, 2013, 7(4): 447-455.
 URL:  
http://journal.hep.com.cn/fesci/EN/10.1007/s11707-013-0380-0
http://journal.hep.com.cn/fesci/EN/Y2013/V7/I4/447
Service
E-mail this article
E-mail Alert
RSS
Articles by authors
Yang YU
Longfei WANG
Ziwei LI
Xuan ZHOU
Ground track categoryRepeat period /dayTime span of data used(month/day/year)
TPJ1009/25/1992-12/31/2011
TPJN1009/16/2002-10/08/2005 & 02/14/2009-12/31/2011
EN3510/09/2002-10/22/2010
ENN3010/23/2010-12/31/2011
GFO1701/07/2000-09/07/2008
Tab.1  Time span of various ground track categories.
Fig.1  Argos drifter trace in the study area from September to November (1992-2011). The flow represented by the dense drifter trace at the west boundary of Pacific is the Kuroshio current.
Fig.2  Illustration of altimeter satellite ground tracks at crossover. and are sea surface tilt along Track 1 and Track 2 respectively, positive in northward direction. and are orthogonal component of sea surface tilt along meridional and zonal components respectively. and are angles between ground tracks and north meridian.
Fig.3  Variation of coefficient for possible track pair configuration with respect to latitude. An upper limit of of 10 is required to properly estimate the geostrophic velocity. The limitation corresponds to the latitudinal region between 15o and 60o.
Cut-off wavelength/kmR for zonal componentR for meridional component
No filter applied0.650.24
250.830.54
500.870.72
750.870.73
1000.840.68
1250.820.62
1500.820.59
1750.800.56
2000.780.55
Tab.2  Correlation coefficient () between estimated geostrophic velocity and Argos measurement.
Fig.4  Scatter diagram of estimated geostrophic velocity and Argos measurement (low pass filter cut-off wavelength is 75 km). The -axis for each scatter plot is velocity from the Argos, and -axis is velocity estimated from altimeter data. The solid lines in both plots are the linearly fitted line of the comparison. Correlation coefficient is higher for the zonal component than for the meridional component.
Fig.5  Temporally averaged flow field of Kuroshio (1992-2011) derived from altimeter crossover method. The grey part on the map are regions where water depth is less than 100 m or offshore distance is less than 20 km. Surface flow velocities are not estimated in this part. Triangles denote six crossovers located on the main stream of Kuroshio.
Fig.6  Velocity variation of six crossovers at some typical locations (labeled with triangles in Fig. 5) on the main stream of Kuroshio.
CrossoverIntersected tracksLongitude/oELatitude/oNAveraged flow speed /(cm·s-1)Averaged flow direction (clockwise from north)
AGFO&GFO122.3623.7791±5518o±24o
BTPJ&TPJI124.0225.4058±1979o±36o
CTPJ&TPJI126.8428.32104±3233o±11o
DTPJ&TPJ128.9829.7384±2859o±23o
ETPJ&TPJ131.8029.7267±2941o±38o
FTPJ&TPJ136.0832.3672±3286o±59o
Tab.3  Surface velocity at six typical crossovers.
1 Akitomo K, Masuda S, Awaji T (1997). Kuroshio path variation south of Japan: stability of the paths in a multiple equilibrium regime. Journal of Oceanography , 53(2): 129–142
2 Bouffard J, Vignudelli S, Cipollini P, Menard Y (2008). Exploiting the potential of an improved multimission altimetric data set over the coastal ocean. Geophys Res Lett , 35(10): L10601
doi: 10.1029/2008GL033488
3 Chao S Y (1984). Bimodality of the Kuroshio. J Phys Oceanogr , 14(1): 92–103
doi: 10.1175/1520-0485(1984)014<0092:BOTK>2.0.CO;2
4 Chen C T (2010). Using multi-sensor satellite data to study the variability of Kuroshio. Dissertation for Ph.D degree . Qingdao: Ocean University of China (in Chinese)
5 Chen H X, Qiao F L, Ezer T, Yuan Y L, Hua F (2009). Multi-core structure of the Kuroshio in the East China Sea from long-term transect observations. Ocean Dyn , 59(3): 477–488
doi: 10.1007/s10236-009-0182-9
6 Douglas B C, Agreen R W, Sandwell D T (1984). Observing global ocean circulation with Seasat altimeter data. Mar Geod , 8(1-4): 67–83
doi: 10.1080/15210608409379498
7 Ducet N, Le Traon P Y, Reverdin G (2000). Global high-resolution mapping of ocean circulation from TOPEX/Poseidon and ERS-1 and-2. J Geophys Res , 105(C8): 19477–19498
doi: 10.1029/2000JC900063
8 Feng Y, Chen H X, Yuan Y L (2010). Analysis of Argos drifter data for Kuroshio characteristics in East China Sea. Advances in Marine Science , 28(03): 275–284 (in Chinese)
9 Fu L L, Chelton D B (1985). Observing large-scale temporal variablity of ocean currents by satellite altimetry: with application to the Antarctic circumpolar current. J Geophys Res , 90(C3): 4721–4739
doi: 10.1029/JC090iC03p04721
10 Guo J Y, Chang X T, Hwang C W, Sun J L, Han Y B (2010). Oceanic surface geostrophic velocities determined with satellite altimetric crossover method. Chin J Geophys , 53(11): 2582–2589 (in Chinese)
11 Lagerloef G S E, Mitchum G T, Lukas R B, Niiler P P (1999). Tropical Pacific near-surface currents estimated from altimeter, wind, and drifter data. J Geophys Res , 104(C10): 23313
doi: 10.1029/1999JC900197
12 Le Traon P Y, Nadal F, Ducet N (1998). An improved mapping method of multisatellite altimeter data. J Atmos Ocean Technol , 15(2): 522–534
doi: 10.1175/1520-0426(1998)015<0522:AIMMOM>2.0.CO;2
13 Leeuwenburgh O, Stammer D (2002). Uncertainties in altimetry-based velocity estimates. J Geophys Res , 107(C10): 3175
doi: 10.1029/2001JC000937
14 Morrow R, Churcht J, Coleman R, Chelton D, White N (1992). Eddy momentum flux and its contribution to the Southern Ocean momentum balance. Nature , 357(6378): 482–484
doi: 10.1038/357482a0
15 Morrow R, Coleman R, Church J, Chelton D (1994). Surface eddy momentum flux and velocity variances in the Southern Ocean from Geosat altimetry. J Phys Oceanogr , 24(10): 2050–2071
doi: 10.1175/1520-0485(1994)024<2050:SEMFAV>2.0.CO;2
16 Niiler P P, Sybrandy A S, Bi K, Poulain P M, Bitterman D (1995). Measurements of the water-following capability of holey-sock and TRISTAR drifters. Deep Sea Res Part I Oceanogr Res Pap , 42(11): 1951–1964
doi: 10.1016/0967-0637(95)00076-3
17 Parke M E, Stewart R H, Farless D L, Cartwright D E (1987). On the choice of orbits for an altimetric satellite to study ocean circulation and tides. J Geophys Res , 92(C11): 11693–11707
doi: 10.1029/JC092iC11p11693
18 Pascual A, Faugère Y, Larnicol G, Le Traon P Y (2006). Improved description of the ocean mesoscale variability by combining four satellite altimeters. Geophys Res Lett , 33(2): L02611
doi: 10.1029/2005GL024633
19 Picaut J, Camusat B, Busalacchi A, Mcphaden M (1990). Validation of the geostrophic method for estimating zonal currents at the equator from Geosat altimeter data. J Geophys Res , 95(C3): 3015–3024
doi: 10.1029/JC095iC03p03015
20 Schlax M G, Chelton D B (2003). The accuracies of crossover and parallel-track estimates of geostrophic velocity from TOPEX/Poseidon and Jason altimeter data. J Atmos Ocean Technol , 20(8): 1196–1211
doi: 10.1175/1520-0426(2003)020<1196:TAOCAP>2.0.CO;2
21 Stammer D, Dieterich C (1999). Space-borne measurements of the time-dependent geostrophic ocean flow field. J Atmos Ocean Technol , 16(9): 1198–1207
doi: 10.1175/1520-0426(1999)016<1198:SBMOTT>2.0.CO;2
22 Strub P T, Chereskin T K, Niiler P P, James C, Levine M D (1997). Altimeter-derived variability of surface velocities in the California Current System: 1. Evaluation of TOPEX altimeter velocity resolution. J Geophys Res , 102(C6): 12727–12748
doi: 10.1029/97JC00448
23 Tang T Y, Tai J H, Yang Y J (2000). The flow pattern north of Taiwan and the migration of the Kuroshio. Cont Shelf Res , 20(4–5): 349–371
doi: 10.1016/S0278-4343(99)00076-X
24 Tomczak M, Godfrey J S (2003). Regional Oceanography: An Introduction (2nd ed.). Delhi: Daya Publishing House
25 Yuan Y C, Kaneko A, Su J L, Zhu X H, Liu Y G, Gohda N, Chen H (2000). The Kuroshio east of Taiwan Island and in the East China Sea and the current southeast of Okinawa-jima during early summer of 1996. In: Oceanography in China . Beijing: China Ocean Press (in Chinese)
26 Zhou H, Guo P F, Xu J P, Liu Q Y (2007). The characteristics of the eddies east of Taiwan Island and the Kuroshio in East China Sea. Periodical of Ocean University of China , 37(2), 181–190 (in Chinese)
Viewed
Full text


Abstract

Cited

  Shared   
  Discussed