Estimation of a Geoid Section across the Kuroshio*

W. J. Teague Naval Research Laboratory, Stennis Space Center, Mississippi

Search for other papers by W. J. Teague in
Current site
Google Scholar
PubMed
Close
,
Z. R. Hallock Naval Research Laboratory, Stennis Space Center, Mississippi

Search for other papers by Z. R. Hallock in
Current site
Google Scholar
PubMed
Close
, and
G. A. Jacobs Naval Research Laboratory, Stennis Space Center, Mississippi

Search for other papers by G. A. Jacobs in
Current site
Google Scholar
PubMed
Close
Full access

Abstract

An estimate of the geoid across the Kuroshio Extension at its separation point from Japan is calculated through an analysis of coincident sea surface measurements from inverted echo sounders (IESs) and Topex/Poseidon (T/P). The IESs were positioned along a T/P descending ground track in the vicinity of 35°N, 143°E. This geoid section can be used in conjunction with altimeter data to estimate total sea surface height. Thus, Kuroshio position, surface geostrophic velocity, and transport along the section can be continuously monitored.

Corresponding author address: Mr. William J. Teague, Naval Research Laboratory, Stennis Space Center, MS 39529-5004.

Abstract

An estimate of the geoid across the Kuroshio Extension at its separation point from Japan is calculated through an analysis of coincident sea surface measurements from inverted echo sounders (IESs) and Topex/Poseidon (T/P). The IESs were positioned along a T/P descending ground track in the vicinity of 35°N, 143°E. This geoid section can be used in conjunction with altimeter data to estimate total sea surface height. Thus, Kuroshio position, surface geostrophic velocity, and transport along the section can be continuously monitored.

Corresponding author address: Mr. William J. Teague, Naval Research Laboratory, Stennis Space Center, MS 39529-5004.

1. Introduction

The satellite altimeter measures the distance between the satellite and the ocean surface. When combined with precise orbit determination, this provides a measurement of sea level (SL), the height of the ocean surface above the earth’s reference ellipsoid. In the absence of currents and external forcing, SL coincides with the geopotential surface known as the geoid. The altimeter SL measurement is the sum of the geoid, which is constant in time, plus sea surface height departures (SSH) due to oceanographic features such as currents and tides. However, the spatial variations of the geoid are one to two orders of magnitude larger than SSH spatial variations. Thus, separation of the geoid from the mean SL is not possible from altimeter data alone. Without an accurate geoid from independent measurements, only temporal variations of SSH about mean SL are observable. Thus, the main focus of altimetry has traditionally been SSH variability.

A method used previously for estimation of the geoid consists of subtracting a mean SSH based on climatological in situ data, such as from the Levitus climatology (Levitus 1982) or the Generalized Digital Environmental Model (GDEM) (Teague et al. 1990), from the mean SL measured by the altimeter. However, the climatological mean SSH is not expected to be an accurate mean during the altimeter sampling time due to variations in ocean currents, which have longer periods than the altimeter sampling record. Thus, errors are expected to exist in the geoid derived through this method. Geoid errors produce a bias (not just random white noise errors) in the mean SSH and, therefore, fictitious geostrophic currents are inferred.

In situ sampling of the ocean dynamic height simultaneous with the altimeter sampling of SL can produce more realistic representations of the geoid for oceanographic purposes. Through airborne expendable bathythermograph surveys made simultaneously with altimeter measurements (Mitchell et al. 1990; Carnes et al. 1990), geoid accuracies are about 10 to 20 cm rms. However, very few samplings are available through these methods to reduce data noise. Thus, long time series of both in situ and altimeter sampling are necessary.

Here, we calculate the geoid beneath a section of one Topex/Poseidon (T/P) ground track with T/P altimeter and in situ inverted echo sounder (IES) data. The twodatasets are concurrent so that the mean observed by each is evaluated over the same time period. Both datasets cover about 2 years and the T/P satellite has a repeat period of about 10 days. Thus, about 70 measurements of the geoid are made to reduce data noise to an error generally better than 3 cm rms. The rms error of the SSH from this geoid using T/P altimetry is about 8 cm. It is essential that long time period in situ measurements be combined with altimeter data where possible so that SSH may be directly observed from the altimeter system.

2. Measurements

The IES measurements are part of the Kuroshio Extension Regional Experiment (KERE) (Mitchell 1990). This program was initiated in 1991 and consisted of T/P altimetry (Benada 1993), extensive basin-scale numerical modeling (Mitchell et al. 1996; Jacobs et al. 1996; Hurlburt et al. 1996), and a regional in situ observational program. A main objective of the latter was to monitor the Kuroshio Extension near the separation point to determine variability levels and relation to the deep flows. The KERE field program consisted of intensive measurements along a section of a T/P groundtrack (henceforth referred to as the KERE section) across the Kuroshio Extension near 35°N, 143°E (Fig. 1). The data include currents measured by moored current meters at various depths, thermocline depths and pressures measured by inverted echo sounders with pressure gauges (Teague and Hallock 1995), and detailed hydrographic measurements. KERE hydrography is reported on in detail in Teague et al. (1993, 1994) and in Shiller et al. (1996), current measurements by Hallock and Teague (1995, 1996), and IES observations compared with T/P altimetry by Teague et al. (1995).

The in situ dataset spans July 1992 to June 1994 and extends from about 37°N, 142°E to 33°N, 144°E along a T/P descending groundtrack (Fig. 1). The KERE section begins near the shelf break just east of Honshu, Japan, extending southeastward across the southern part of the Japan trench. The water depth at the northern end of the KERE section is about 1000 m. Near its center, the KERE section crosses the Japan trench with depths greater than 7000 m. Within the Japan trench beneath the KERE section is the Kashima 1 seamount, which rises to about 4000-m depth.

Six IES/PGs were positioned along the section. IES/PG spacing ranged from 40 to 60 km. The position of the Kashima 1 seamount was advantageous for placement of one of the IES/PGs. A conductivity–temperature–depth (CTD) survey also was made along this T/P groundtrack in July 1992 (Teague et al. 1993). The CTD spacing along the section telescoped from about 15 km at the northern end of the section to about 50 km on the southern end. The north wall of the Kuroshio was located near 35.8°N in the vicinity of the Kashima 1 seamount at the time of the CTD section.

A Neil Brown Mark III CTD was used to collect 18 closely spaced CTD/hydrographic stations from 8 to 23 July 1992 (Teague et al. 1993, 1994). The Kuroshio north wall, indicated from the temperature section by a sharp downward slope in the isotherms, was at approximately 35.9°N. The dynamic height cross-stream profile computed with respect to a 2000-m zero-velocity reference level is shown in Fig. 2 and corresponds to a maximum speed in the Kuroshio in excess of 170 cm s−1. Dynamicheight changes by about 1.3 m across the Kuroshio and has a maximum gradient of approximately 1.5 cm km−1.

Topex/Poseidon was launched 10 August 1992 as a joint effort by National Aeronautics and Space Administration (NASA) and the French Space Agency, Centre National d’Etudes Spatiales (CNES), for studying global ocean circulation (Fu et al. 1994). The T/P mission is also coordinated with the World Ocean Circulation Experiment (WOCE) and the Tropical Ocean and Global Atmosphere program (TOGA). T/P data utilized in this study begin in late September 1992. The T/P data are obtained from the Geophysical Data Records (GDRs) processed at the Physical Oceanography Distributed Active Archive Center (PODAAC) at the Jet Propulsion Laboratory. T/P has a repeat period of 9.92 days and an equatorial cross-track separation of 315 km. T/P data are corrected for the effects of wet troposphere from an onboard water vapor radiometer, dry troposphere, ionosphere from the dual-frequency altimeter, inverse barometer, and electromagnetic bias. The ionospheric correction is smoothed using a Gaussian filter with a rolloff of about 100 km along track. Tidal contamination is removed using the Cartwright and Ray (1991) tide model. The height data are interpolated along track to a reference ground track produced at the Colorado Center for Astrodynamics Research, resulting in about 7-km spacing.

IES/PG records are processed as described by Hallock et al. (1989). Briefly, hourly data series are low-pass filtered (half-amplitude at 40 h). Acoustic travel time and bottom pressure anomaly are converted to baroclinic (Hbcl) and barotropic (Hbtr) components of sea surface height anomaly:
HbclDg,
i1520-0426-14-2-326-e2
and dynamic height anomaly (temporal) is given by
D
where g is the gravitational constant, Pb is the bottom pressure anomaly, ρb is the density near the bottom, B is a regression coefficient based on hydrography in the region (Hallock 1987), and τ′ is the acoustic travel time anomaly between the sea surface and bottom. The regression coefficient B, calculated with travel times inferred from the CTD observations and historical temperature and salinity data (Levitus 1982), is −4.35 ± 0.05 dynamic centimeters per millisecond. The error in B is primarily affected by near-surface temperature–salinity variability. In addition, there is a seasonal bias in B that is related to seasonal heating and cooling of near-surface waters. This effect is discussed by Teague et al. (1994). Statistical uncertainties dominate measurement error. Similar error statistics were found for the Gulf Stream and are fully discussed by Hallock et al. (1989). The total anomaly of SSH is given by
i1520-0426-14-2-326-e4

Some of the pressure-gauge data contain unmodeled long-period drifts, a ubiquitous problem with this type of pressure sensor (Fields and Watts 1991), which can result in errors in the calculation of HIES. Pressure records were acceptable at sites 3 and 5 after removing drifts modeled by exponential trends. Their rms variabilities were calculated using the 1-h resolution data. Average rms valuesusing IES/PG data at sites 3 and 5 were, respectively, 〈Hbtr〉 = 0.041 m, 〈Hbcl〉 = 0.257 m, and 〈HIES〉 = 0.262 m. Here 〈HIES〉 is clearly dominated by Hbcl. The ratio 〈Hbtr〉 / 〈HIES〉 is 0.16 and compares well with estimates by Hall (1989) which indicate that the barotropic component of mean SSH of the Kuroshio Extension represents about 19% of the total SSH variability. This ratio is about half the ratio (0.33) found for the Gulf Stream region by Hallock et al. (1989). Total amplitudes of Hbcl range over 1 m in the Kuroshio region. Thus, it is reasonable to estimate HIES from Hbcl in this region. Calculations of HIES made in this paper are based on Hbcl since the pressure records were problematic.

Expendable bathythermograph (XBT) observations were made at IES sites during deployment and are used to estimate total baroclinic SSH at those times, which we denote as Hbcl(0). We then calculate time series of Hbcl from Hbcl as follows:
HbclHbclHbcl,
where
HbclHbclHbcl
Total Hbcl (rather then the temporal anomaly Hbcl) is needed to combine with T/P derived SL for geoid estimation.

3. Geoid estimation

In the present paper, HIES at each IES site is calculated for almost coincident SL from T/P. Distances from the IES sites to the T/P ground points ranged from 1.5 to 3.7 km (Table 1), while the time differences between the measurements were always less than one-half hour.

The primary source of error in HIES is in the conversion of IES acoustic travel times to dynamic heights. This error is about 7 cm rms for the Gulf Stream region (Hallock 1987) and is similar, 5 cm, for the Kuroshio region. Error variance is caused mainly by temperature and salinity variations in the upper 200 m of the water column. Analysis of the pressure records reveals that an error of up to 4 cm rms can occur by not including the barotropic contribution Hbtr in HIES calculations. Thus, the total rms error in IES SSH is about 6.4 cm. The error of altimeter measurements is estimated to be 4.8 cm rms (Fu et al. 1994). Errors due to the small (1–3 km, see Table 1) mismatch in the T/P and IES geographical positions can be about 2 cm rms due to the high spatial gradient in SSH in the vicinity of the Kuroshio or eddies. Errors caused by a maximum time offset of one-half hour are negligible for the calculations since the T/P and IES data have been detided. Maximum error estimated by the root sum square of the above errors is 8.2 cm.

A geoid section can be estimated along the T/P track for each repeat pass, i. The sea level SL measured by the altimeter is the sum of the geoid and the SSH:
iGi
where G is the geoid height and SSHi isdue to ocean currents. The SSH height approximated from the IES data, described in section 2, is
HIESHbclHbcl
A single geoid estimate, Gi is thus
GiiHIESi
The best geoid estimate, G* at the IES position is
i1520-0426-14-2-326-e10
where N is the number of T/P repeat passes (70 were used), SL is the mean sea level derived from N passes, and HIES is the corresponding mean height from the IES data. The standard error E in the geoid estimate is
i1520-0426-14-2-326-e11
where σ is the standard deviation. Here HIES can be approximated along track by interpolation thereby forming G estimates at each T/P ground point between IES sites.

The estimated geoid along the KERE section is shown in Fig. 3 and numerical values of the geoid with positions are given in Table 2. The geoid reflects the local topography of the Japan trench, and the bump near 35.75°N corresponds to Kashima 1 seamount. The gravimetric geoid supplied on the T/P GDR (Callahan 1993) misses the seamount entirely but has a somewhat similar shape to our estimated geoid. However, geostrophic velocities calculated with our estimated geoid are reasonable (from about 0 to 1 m s−1), while velocities calculated with the GDR geoid are not realistic (from about −4 to 5 m s−1).

An SSH profile can be calculated using T/P data along this geoid section. This profile can be used to provide a time series of Kuroshio along-track location and cross-track geostrophic speed. A times series of SSH along the KERE section is shown for the time period of October 1992 through the end of 1995 in Fig. 4. The north wall of the Kuroshio is approximately tracked by the 2.2-m contour line. Large southward excursions of the Kuroshio are found to occur near days 470 and 1180 (Julian days 105 and 85, respectively).

4. Conclusions

The geoid provided in Table 2 for the T/P track along the KERE section has been estimated to an accuracy generally better than 8 cm rms. The maximum standard error in the geoid estimate is 3 cm. SSH can be estimated for all T/P passes along the KERE section by subtracting G* from T/P-derived SL. Hence, T/P data, along this geoid arc segment, can provide good estimates of Kuroshio position and geostrophic speed. Observations such as these provide boundary conditions for numerical modeling and nowcasts of the Kuroshio.

Acknowledgments

The leadership of Jimmy Mitchell to the KERE project was invaluable. Thanks are extended to Steve Sova of NRL who prepared the IES/PGs and played a major role in their deployment and recovery and to Mark Hulburt of NRL who assisted. We appreciate the assistance given by the officers and the crew of the Moana Wave during the field operations. This work was supported by the Office of Naval Research as part of the Basic Research Project “Kuroshio Extension Regional Experiment” under Program Element 601135N.

REFERENCES

  • Benada, R., 1993: Merged GDR (TOPEX/POSEIDON) Users Handbook. Rep. JPL D-11007. Jet Propulsion Laboratory, 133 pp.

  • Callahan, P. S., 1994: TOPEX/POSEIDON Project GDR Users Handbook. Rep. JPL D-8944. Jet Propulsion Laboratory, 84 pp.

  • Carnes, M. R., J. L. Mitchell, and P. W. deWitt, 1990: Synthetic temperature profiles derived from Geosat altimetry: Comparisons with air-dropped expendable bathythermograph profiles. J. Geophys. Res.,95, 17 979–17 992.

    • Crossref
    • Export Citation
  • Cartwright, D. E., and R. D. Ray, 1991: Energetics of global ocean tides from Geosat altimetry. J. Geophys. Res.,96, 16 897–16 912.

    • Crossref
    • Export Citation
  • Fields, E., and D. R. Watts, 1991: The SYNOP Experiment: Inverted echo sounder data report for June 1989 to September 1990. GSOTech. Rep. 91-2, 255 pp. [Available from Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882-1197.].

  • Fu, L.-L., E. J. Christensen, C. A. Yamarone Jr., M. Lefebvre, Y. Menard, M. Dorrer, and P. Escudier, 1994: TOPEX/POSEIDON mission overview. J. Geophys. Res.,99, 24 369–24 381.

    • Crossref
    • Export Citation
  • Hall, M. M., 1989: Velocity and transport structure of the Kuroshio extension at 35°N, 152°E. J. Geophys. Res.,94, 14 445–14 459.

    • Crossref
    • Export Citation
  • Hallock, Z. R., 1987: Regional characteristics for interpreting inverted echo sounder observations. J. Atmos. Oceanic Technol.,4, 298–304.

    • Crossref
    • Export Citation
  • ——, and W. J. Teague, 1995: Current meter observations during the Kuroshio Extension Regional Experiment. NRL Rep. MR/7332-95-7592, 119 pp. [Available from Naval Research Laboratory, Stennis Space Center, MS 39529-5004.].

  • ——, and ——, 1996: Evidence for a North Pacific deep western boundary current. J. Geophys. Res.,101, 6617–6624.

    • Crossref
    • Export Citation
  • ——, J. L. Mitchell, and J. D. Thompson, 1989: Sea surface topographic variability near the New England seamounts: An intercomparison among in situ observations, numerical simulations, and Geosat altimetry from the Regional Energetics Experiment. J. Geophys. Res.,94, 8021–8028.

    • Crossref
    • Export Citation
  • Hurlburt, H. E., A. J. Wallcraft, W. J. Schmitz Jr., P. J. Hogan, and E. J. Metzger, 1996: Dynamics of the Kuroshio/Oyashio current system using eddy-resolving models of the North Pacific Ocean. J. Geophys. Res.,101, 941–976.

    • Crossref
    • Export Citation
  • Jacobs, G. A., W. J. Teague, J. L. Mitchell, and H. E. Hurlburt, 1996: An examination of the North Pacific Ocean in the spectral domain using Geosat altimeter data and a numerical ocean model. J. Geophys. Res.,101, 1025–1044.

    • Crossref
    • Export Citation
  • Levitus, S., 1982: Climatological Atlas of the World Ocean. NOAA Prof. Paper 13, U.S. Govt. Printing Office, 173 pp.

  • Mitchell, J. L., 1990: Plans for the Kuroshio Extension regional experiment. NOARL Tech. Note 016:321:90, 34 pp. [Available from Naval Research Laboratory, Stennis Space Center, MS 39529-5004.].

  • ——, W. J. Teague, G. A. Jacobs, and H. E. Hurlburt, 1996: Kuroshio extension dynamics from satellite altimetry and a model simulation. J. Geophys. Res.,101, 1045–1058.

    • Crossref
    • Export Citation
  • NOAA, 1986: ETOPO 5 digital relief of the surface of the earth. Data Announcement 86-MGG-07, 2 pp. [Available from National Geophysical Data Center, Washington, DC 20233.].

  • Shiller, A. M., W. J. Teague, and Z. R. Hallock, 1996: Deep water properties near 35°N, 143°E observed during the Kuroshio Extension Regional Experiment. J. Geophys. Res.,101, 16 695–16 702.

    • Crossref
    • Export Citation
  • Teague, W. J., and Z. R. Hallock, 1995: Inverted echo sounder observations during the Kuroshio Extension Regional Experiment. NRL Rep. MR/7332-95-7591, 61 pp. [Available from Naval Research Laboratory, Stennis Space Center, MS 39529-5004.].

  • ——, M. J. Carron, and P. J. Hogan, 1990: A comparison between the generalized digital environmental model and Levitus climatologies. J. Geophys. Res.,95, 7167–7183.

    • Crossref
    • Export Citation
  • ——, Z. R. Hallock, J. M. Dastugue, and A. M. Shiller, 1993: Kuroshio Extension Regional Experiment hydrographic data: Summer 1992. NRL Rep. MR/7332-93-7050, 68 pp. [Available from Naval Research Laboratory, Stennis Space Center, MS 39529-5004.].

  • ——, A. M. Shiller, and Z. R. Hallock, 1994: Hydrographic section across the Kuroshio near 35°N, 143°E. J. Geophys. Res.,99, 7639–7650.

    • Crossref
    • Export Citation
  • ——, ——, G. A. Jacobs, and J. L. Mitchell, 1995: Kuroshio Sea surface height fluctuations observed simultaneously with inverted echo sounders and TOPEX/POSEIDON. J. Geophys. Res.,100, 24 987–24 994.

    • Crossref
    • Export Citation

Fig. 1.
Fig. 1.

IES/PG sites are indicated by triangles, Topex/Poseidon measurements by asterisks, and CTD stations by plus signs along the KERE section. The 6000-m depth contours (bold) indicate the boundaries of the Japan trench. The Kashima 1 seamount is located beneath the section at about 35.7°N. Bathymetry is from ETOPO 5 (NOAA 1986), a 5′ latitude by 5′ longitude worldwide gridded database, and generally reflects the actual depths measured when collecting these data.

Citation: Journal of Atmospheric and Oceanic Technology 14, 2; 10.1175/1520-0426(1997)014<0326:EOAGSA>2.0.CO;2

Fig. 2.
Fig. 2.

Dynamic height referenced to 2000 m for the KERE section. CTD station locations are indicated by plus signs.

Citation: Journal of Atmospheric and Oceanic Technology 14, 2; 10.1175/1520-0426(1997)014<0326:EOAGSA>2.0.CO;2

Fig. 3.
Fig. 3.

Geoid estimation at Topex/Poseidon ground points (asterisks) and IES/PG sites (triangles).

Citation: Journal of Atmospheric and Oceanic Technology 14, 2; 10.1175/1520-0426(1997)014<0326:EOAGSA>2.0.CO;2

Fig. 4.
Fig. 4.

A time series of sea surface height contours (m) along the KERE section computed from Topex/Poseidon data and the IES-derived geoid. The 2.2 contour line indicates the approximate location of the Kuroshio surface current axis.

Citation: Journal of Atmospheric and Oceanic Technology 14, 2; 10.1175/1520-0426(1997)014<0326:EOAGSA>2.0.CO;2

Table 1.

Geographical positions of the IES/PGs and their distances to the closest Topex/Poseidon data.

Table 1.
Table 2.

Estimated geoid G* and error E derived from Topex/Poseidon height data (SL) and IES height data (HIES) over a 2-yr period. Note, for IES 6 (at 34.252°N) data were available only for the first year.

Table 2.

Naval Research Laboratory–Stennis Space Center Contribution Number JA/7332-96-0009.

Save
  • Benada, R., 1993: Merged GDR (TOPEX/POSEIDON) Users Handbook. Rep. JPL D-11007. Jet Propulsion Laboratory, 133 pp.

  • Callahan, P. S., 1994: TOPEX/POSEIDON Project GDR Users Handbook. Rep. JPL D-8944. Jet Propulsion Laboratory, 84 pp.

  • Carnes, M. R., J. L. Mitchell, and P. W. deWitt, 1990: Synthetic temperature profiles derived from Geosat altimetry: Comparisons with air-dropped expendable bathythermograph profiles. J. Geophys. Res.,95, 17 979–17 992.

    • Crossref
    • Export Citation
  • Cartwright, D. E., and R. D. Ray, 1991: Energetics of global ocean tides from Geosat altimetry. J. Geophys. Res.,96, 16 897–16 912.

    • Crossref
    • Export Citation
  • Fields, E., and D. R. Watts, 1991: The SYNOP Experiment: Inverted echo sounder data report for June 1989 to September 1990. GSOTech. Rep. 91-2, 255 pp. [Available from Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882-1197.].

  • Fu, L.-L., E. J. Christensen, C. A. Yamarone Jr., M. Lefebvre, Y. Menard, M. Dorrer, and P. Escudier, 1994: TOPEX/POSEIDON mission overview. J. Geophys. Res.,99, 24 369–24 381.

    • Crossref
    • Export Citation
  • Hall, M. M., 1989: Velocity and transport structure of the Kuroshio extension at 35°N, 152°E. J. Geophys. Res.,94, 14 445–14 459.

    • Crossref
    • Export Citation
  • Hallock, Z. R., 1987: Regional characteristics for interpreting inverted echo sounder observations. J. Atmos. Oceanic Technol.,4, 298–304.

    • Crossref
    • Export Citation
  • ——, and W. J. Teague, 1995: Current meter observations during the Kuroshio Extension Regional Experiment. NRL Rep. MR/7332-95-7592, 119 pp. [Available from Naval Research Laboratory, Stennis Space Center, MS 39529-5004.].

  • ——, and ——, 1996: Evidence for a North Pacific deep western boundary current. J. Geophys. Res.,101, 6617–6624.

    • Crossref
    • Export Citation
  • ——, J. L. Mitchell, and J. D. Thompson, 1989: Sea surface topographic variability near the New England seamounts: An intercomparison among in situ observations, numerical simulations, and Geosat altimetry from the Regional Energetics Experiment. J. Geophys. Res.,94, 8021–8028.

    • Crossref
    • Export Citation
  • Hurlburt, H. E., A. J. Wallcraft, W. J. Schmitz Jr., P. J. Hogan, and E. J. Metzger, 1996: Dynamics of the Kuroshio/Oyashio current system using eddy-resolving models of the North Pacific Ocean. J. Geophys. Res.,101, 941–976.

    • Crossref
    • Export Citation
  • Jacobs, G. A., W. J. Teague, J. L. Mitchell, and H. E. Hurlburt, 1996: An examination of the North Pacific Ocean in the spectral domain using Geosat altimeter data and a numerical ocean model. J. Geophys. Res.,101, 1025–1044.

    • Crossref
    • Export Citation
  • Levitus, S., 1982: Climatological Atlas of the World Ocean. NOAA Prof. Paper 13, U.S. Govt. Printing Office, 173 pp.

  • Mitchell, J. L., 1990: Plans for the Kuroshio Extension regional experiment. NOARL Tech. Note 016:321:90, 34 pp. [Available from Naval Research Laboratory, Stennis Space Center, MS 39529-5004.].

  • ——, W. J. Teague, G. A. Jacobs, and H. E. Hurlburt, 1996: Kuroshio extension dynamics from satellite altimetry and a model simulation. J. Geophys. Res.,101, 1045–1058.

    • Crossref
    • Export Citation
  • NOAA, 1986: ETOPO 5 digital relief of the surface of the earth. Data Announcement 86-MGG-07, 2 pp. [Available from National Geophysical Data Center, Washington, DC 20233.].

  • Shiller, A. M., W. J. Teague, and Z. R. Hallock, 1996: Deep water properties near 35°N, 143°E observed during the Kuroshio Extension Regional Experiment. J. Geophys. Res.,101, 16 695–16 702.

    • Crossref
    • Export Citation
  • Teague, W. J., and Z. R. Hallock, 1995: Inverted echo sounder observations during the Kuroshio Extension Regional Experiment. NRL Rep. MR/7332-95-7591, 61 pp. [Available from Naval Research Laboratory, Stennis Space Center, MS 39529-5004.].

  • ——, M. J. Carron, and P. J. Hogan, 1990: A comparison between the generalized digital environmental model and Levitus climatologies. J. Geophys. Res.,95, 7167–7183.

    • Crossref
    • Export Citation
  • ——, Z. R. Hallock, J. M. Dastugue, and A. M. Shiller, 1993: Kuroshio Extension Regional Experiment hydrographic data: Summer 1992. NRL Rep. MR/7332-93-7050, 68 pp. [Available from Naval Research Laboratory, Stennis Space Center, MS 39529-5004.].

  • ——, A. M. Shiller, and Z. R. Hallock, 1994: Hydrographic section across the Kuroshio near 35°N, 143°E. J. Geophys. Res.,99, 7639–7650.

    • Crossref
    • Export Citation
  • ——, ——, G. A. Jacobs, and J. L. Mitchell, 1995: Kuroshio Sea surface height fluctuations observed simultaneously with inverted echo sounders and TOPEX/POSEIDON. J. Geophys. Res.,100, 24 987–24 994.

    • Crossref
    • Export Citation
  • Fig. 1.

    IES/PG sites are indicated by triangles, Topex/Poseidon measurements by asterisks, and CTD stations by plus signs along the KERE section. The 6000-m depth contours (bold) indicate the boundaries of the Japan trench. The Kashima 1 seamount is located beneath the section at about 35.7°N. Bathymetry is from ETOPO 5 (NOAA 1986), a 5′ latitude by 5′ longitude worldwide gridded database, and generally reflects the actual depths measured when collecting these data.

  • Fig. 2.

    Dynamic height referenced to 2000 m for the KERE section. CTD station locations are indicated by plus signs.

  • Fig. 3.

    Geoid estimation at Topex/Poseidon ground points (asterisks) and IES/PG sites (triangles).

  • Fig. 4.

    A time series of sea surface height contours (m) along the KERE section computed from Topex/Poseidon data and the IES-derived geoid. The 2.2 contour line indicates the approximate location of the Kuroshio surface current axis.

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 172 32 6
PDF Downloads 60 11 4