NOAA Topex/Poseidon Analysis

Topex/Poseidon Global Sea Level

The joint NASA/CNES satellite altimeter, Topex/Poseidon, has been collecting sea level observations since October 1992. Analyses based on these data are available from NOAA in three different forms: along-track deviations, gridded deviations, and gridded anomalies. See below for definitions and access to these data sets.

In December 2001, the NASA/CNES altimeter Jason-1 was launched to replace T/P. From January to August 2002, the two satellites followed the same ground tracks for the purpose of cross-calibration. T/P was then moved to a new track halfway between the original ones. Because our analyses depend on having a historical record along each ground track, it will not be possible to process these "new" T/P data into sea level deviations until at least one year of observations are collected along the new T/P tracks. In the meantime, Jason-1 is extending the 10-year record along the original T/P tracks. For links to near-real time Jason-1 sea level analyses, click here.

1. Topex/Poseidon Along-track Deviations

Global Topex/Poseidon sea level deviations (relative to the 3-year mean 1993-95) are computed at 1-degree latitude intervals along the satellite track as shown in the sample map above. These data are available via anonymous ftp in one file for the entire T/P mission. Data files and graphical displays are also available for individual 10-day cycles .

2. Topex/Poseidon Gridded Deviations

Sea level deviations, computed along the Topex/Poseidon track as described above, are averaged in 4x1-degree (longitude x latitude) cells to construct regular grids of sea level deviation with respect to the 3-year period, 1993-1995. The data are averaged over monthly and seasonal periods, where:

Spring = Mar-May, Summer = Jun-Aug, Fall = Sep-Nov, and Winter = Dec-Feb

The seasonal deviations can be viewed in map form:

1992: Fall, Winter 92-93
1993: Spring, Summer, Fall, Winter 93-94
1994: Spring, Summer, Fall, Winter 94-95
1995: Spring, Summer, Fall, Winter 95-96
1996: Spring, Summer, Fall, Winter 96-97
1997: Spring, Summer, Fall, Winter 97-98
1998: Spring, Summer, Fall, Winter 98-99
1999: Spring, Summer, Fall, Winter 99-00
2000: Spring, Summer, Fall, Winter 00-01
2001: Spring, Summer, Fall, Winter 01-02
2002: Spring, Summer

The gridded data are also available via anonymous ftp for monthly and seasonal periods.

Comparisons with Pacific island tide gauge data show that the monthly mean deviations are accurate at the level of 2 cm.

3. Topex/Poseidon Gridded Anomalies

The gridded deviations described above are converted to anomalies by removing the annual and semiannual harmonics. These maps show interannual changes relative to 1993-95 for monthly, seasonal, and annual time periods:

The annual and seasonal anomalies can be viewed in map form:

Annual averages: 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001
1992: Fall, Winter 92-93
1993: Spring, Summer, Fall, Winter 93-94
1994: Spring, Summer, Fall, Winter 94-95
1995: Spring, Summer, Fall, Winter 95-96
1996: Spring, Summer, Fall, Winter 96-97
1997: Spring, Summer, Fall, Winter 97-98
1998: Spring, Summer, Fall, Winter 98-99
1999: Spring, Summer, Fall, Winter 99-00
2000: Spring, Summer, Fall, Winter 00-01
2001: Spring, Summer, Fall, Winter 01-02
2002: Spring, Summer

The gridded data are also available via anonymous ftp for monthly, seasonal, and annual periods.

Many other research groups, both in the U.S. and abroad, are analyzing the Topex/Poseidon altimeter data. See Links

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