ISSN:0149-0419    

DOI:10.1080/15210608809379594

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Sea level measurements have proven to be extremely valuable for investigations of the dynamics of the world's oceans. Although a comprehensive review of studies using sea level is beyond the scope of this article, it can give an idea of the impact that these data have had on the development of our understanding of ocean and ocean‐atmosphere dynamics. The discussion is restricted geographically and temporally to the variability of the Pacific Ocean on time scales longer than several days and is organized into two broad categories. The main section is concerned with the description of a few selected phenomena that are conveniently divided according to their time scale. For example, research studies concerned with the dynamics of the seasonal cycle of the Pacific Ocean are covered. This category also contains a description of the important work on interannual sea level fluctuations and their relationship to global climate disturbances, followed by a short discussion of the use of sea level variability as a tool for monitoring other interesting quantities that are difficult to observe directly. For example, the use of the geostrophic approximation allows sea level differences to be interpreted as an index for surface currents. The article concludes with a brief discussion of several developing technologies that promise further advances in our understanding of Pacific sea level variability.

ISSN:0149-0419    

DOI:10.1080/15210608809379595

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

NOAA has begun work on a pilot absolute sea level network in Hawaii. Tide gauge stations on the islands of Hawaii, Maui, Oahu, and Kauai have been upgraded by installing Next Generation Water Level Measurements Systems (NGWLMS). A regular program of monitoring the stability of each tide gauge in the International Earth Rotation Service (IERS) conventional terrestrial reference frame has begun. Two primary IERS stations are located in Hawaii: the NASA Very Long Baseline Interferometry (VLBI) observatory at Kokee Par, Kauai, and the University of Hawaii lunar and satellite laser ranging station, Haleakala, Maui. During March and April 1987, and again during April 1988, geodetic surveys using the Global Positioning System (GPS) were performed to determine the positions of the tide gauges relative to these observatories. The vectors between the stations range from about 10 to more than 350 kilometers, with height differences as large as 3,050 meters. The RMS scatter of repeated measurements on the longest lines was approximately 1 centimeter in latitude, 2–3 centimeters in longitude (equivalent to better than 1 part in 10 million), and 5–6 centimeters in height, excellent results for the current status of the partially completed GPS satellite constellation and the available satellite ephemerides. A second independent method of monitoring changes in the heights of stations, by measuring changes in absolute gravity, is being tested at stations on Kauai, Oahu, and Maui. The first observations, made during October 1987, have uncertainties equivalent to approximately 2–3 centimeters in height.

ISSN:0149-0419    

DOI:10.1080/15210608809379596

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A method is derived for extracting oceanic dynamic height anomaly from collinear (exact repeat mission) GEOSAT short (∼ 1,000 km long) orbit segments. The procedure requires at least 1 year of simultaneous in situ observations and involves: (1) computing with respect to the ellipsoid, a mean sea surface height (SSH) profile solely from altimetry, (2) linear least‐squares removal of tilt and bias from individual SSH profiles with respect to the mean profile, (3) determining an independent mean dynamic height anomaly profile from hydrographic data along the orbit segment, (4) demeaning the tilt‐and‐bias removed individual SSH profiles and addition of the mean in situ dynamic height anomaly, and (5) correcting for concurrently observed dynamic height anomaly at two or more suborbital points during satellite transit. Analysis of the concept suggests root sum squared errors of ±5 cm, which can be reduced by smoothing and longer term measurements along the same orbit segment. A 1‐year comparison between two orbit segments at an open ocean crossover point shows differences of ±2 cm, and comparison with 6 months of simultaneous in situ data shows corrections of ±3 cm are required. Space‐time plots of demeaned tilt‐and‐bias removed GEOSAT SSH profiles, compared with similarly processed NMC/CAC numerical circulation model calculations, show good agreement with variability in the South Equatorial Current/North Equatorial Counter Current system in the eastern Pacific Ocean, and suggest that further development of the concept is warranted.

ISSN:0149-0419    

DOI:10.1080/15210608809379597

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Oceanic temporal variability is calculated from satellite altimeter data by differencing sea level measurements repeated at the same location. These differences yield variations independent of any permanent undulations of sea level. If satellite groundtracks are collinear (nested), altimeter measurements are repeated in a regular fashion continuously along a repeating groundtrack, and calculation of sea level variation is straightforward. For an orbit that repeats only at intersections (crossovers) of the groundtrack, the problem is more complicated, but results equal in accuracy to those obtainable from a collinear analysis can be achieved. For both collinear and crossover analyses, long wavelength error in the altitude of the satellite must be eliminated by using a model for the orbit error and adjusting each pass of data into a reference pass in its nest for the collinear case or into a reference grid of intersecting passes for nonnested tracks.

ISSN:0149-0419    

DOI:10.1080/15210608809379598

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The essential features in generating altimetric sea level time series from crossover differences (as originally proposed by Fu and Chelton, and followed by several other adaptations) are reviewed here. New results are also presented in an effort to answer questions raised in the review. All procedures involve explicit or implicit spatial and temporal smoothing, which are necessary for error reduction and for ensuring reasonably dense temporal sampling rates. One crucial step in the procedures involves the designation of a spatial sampling box, where a larger box results in better error reduction and denser temporal sampling, but may cause excessive signal attenuation. These and various other issues are discussed here by comparing the island tide gauge data to GEOSAT (first 17 months, the nonrepeat era) sea level time series in the tropical Pacific. It is found that the optimal box size varies from island to island because of the geographical dependence of the error as well as the signal. Furthermore the idea of limiting the crossover adjustment process (an orbit error removal procedure) to crossovers between tracks that are less than certain time apart in order to preserve the long‐term, large‐scale oceanic signal is also tested for the first time against the island tide gauge data. The results show improvements around many island stations, albeit stations showing deterioration outnumber those showing improvement, indicating the worsening of the signal‐to‐noise ratio on average either due to lack of signal at the longest and largest scales or due to too much noise at these scales.

ISSN:0149-0419    

DOI:10.1080/15210608809379599

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Since the apparent sea slope along the Pacific Coast between San Diego, California, and Neah Bay, Washington, was originally reported by Bowie in 1929, numerous points of view, both geodetic and oceanographic, have been expressed concerning this possibility.

ISSN:0149-0419    

DOI:10.1080/15210608809379600

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

ISSN:0149-0419    

DOI:10.1080/15210608809379593

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor