IGOSS Sea Level Program in the Pacific

Integrated Global Ocean Services System (IGOSS)
IGOSS Sea Level Program in the Pacific (ISLP-Pac)

The IGOSS Sea Level Program in the Pacific was established for the
purpose of making monthly mean sea level data available to a wide
circle of users in a timely fashion, and to generate products that
would be valuable for scientific analysis of climate-related
processes. A pilot project started in June, 1984 and a permanent
program was established in 1988. During the pilot project and in the
first year of the permanent program, maps of the sea level deviations
from the mean sea level were produced without fail beginning in June
1984 (ISLPP.DEVIATIONS, see below). In January 1988, maps were
produced of the anomaly of sea level from the 1975 to 1986 mean annual
cycle of sea level (ISLPP.ANOMALIES). This anomaly is also corrected
for the inverted barometer effect using the atmospheric pressure
fields computed at the National Meteorological Center.

Beginning in 1997, the mean sea level and annual cycle are referenced
to the period 1975 - 1995. Data from previous years have been updated
using the new reference means.

In addition to these basic products, additional products were
developed during the pilot project. These products include time series
of the volume of the tropical Pacific Ocean (ISLPP.VOLUME, published
quarterly) and indices of the equatorial current system
(ISLPP.CURRENTS and ISLPP.TOPOGRAPHY, published annually). The volume
time series has received much attention because of its importance for
El Nino prediction and analysis.

The time series at each station is preceded by one header record,
which includes the station name and location, followed by a series of
data records, each containing data for one year. These data records
contain the station name, the year and the 12 monthly values of the
appropriate quantity.

ISLPP.DEVIATIONS

This file contains the time series of the deviations of sea level from
the 1975 to 1995 mean sea level value computed at each station. The
time series cover the period 1975 to 1997. Large linear trends were
found at five stations and are corrected for in this dataset. The five
stations affected are Kushimoto, Aburatsu, and Naha in Japan, Davao in
the Philippines, and Seldovia in Alaska.

ISLPP.PC_DEVIATIONS

This file contains the time series of the pressure-corrected
deviations of sea level from the 1975 through 1995 mean sea level
value computed at each station. The time series cover the period 1975
through 1997. Large linear trends were found at five stations and are
corrected for in this data set. The five stations affected are Davao
in the Philippines, Kushiro in Japan Suva in Fiji and Seldovia,
Yakutat in Alaska. Units for the pressure-corrected sea level
deviations are millimeters, and missing data points are set to a value
of 9999.

ISLPP.ANOMALIES

This file contains the anomalies of sea level corrected for the
atmospheric pressure. Anomalies of sea level are computed by
subtracting the mean annual cycle of the sea level variation that is
estimated using data from 1975 to 1995. Atmospheric pressure
corrections are derived from the fields computed at the National
Meteorological Center. The time series of the pressure-corrected sea
level anomaly cover the period 1975 to 1997. Large linear trends were
found at five stations and are corrected for in this dataset. The five
stations affected are Kushimoto, Aburatsu, and Naha in Japan, Davao in
the Philippines, and Seldovia in Alaska.

ISLPP.CURRENTS and ISLPP.TOPOGRAPHY

These files contain indices of the equatorial Pacific currents and
estimates of the equatorial ridge and trough topography that are used
to derive the current indices. Current indices are provided for the
North Equatorial Countercurrent, the North Equatorial Current, and for
the portions of the South Equatorial Current lying north and south of
the equator. The current indices are computed by perturbing the
meridional profile of mean surface dynamic height with the monthly
mean time series of the sea level variations and calculating the
appropriate ridge to trough difference for each current for each
month. The mean values of the indices have not been removed from the
time series. The calculation of these indices is discussed in greater
detail in Wyrtki (74); see reference section.

ISLPP.VOLUME

This file contains the monthly time series of the variations in the
upper layer volume of the tropical Pacific between 15N and 15S. The
volume is computed from a gridded field of the sea level deviations
via a one and a half layer approximation for the vertical structure of
the tropical Pacific. Further details of the calculation are given by
Wyrtki (87); see reference section. The units for the volume changes
are 10 to the 12th cubic meters, and the variations are relative to a
mean value of about 7000 of these units. The annual cycle has not been
removed from the volume deviation time series.

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Data is distributed by anonymous ftp:
"ftp://ilikai.soest.hawaii.edu"

and cd to the islp directory.

Alternate ftp (users have had some difficulty with alphanumeric version):
"ftp://128.171.153.56"

There are seven files available: README, ISLPP.DEVIATIONS,
ISLPP.PC_DEVIATIONS, ISLPP.ANOMALIES, ISLPP.CURRENTS,
ISLPP.TOPOGRAPHY, and ISLPP.VOLUME. The README file contains a
somewhat more detailed version of the information given in this
summary.

We ask that you help the University of Hawaii monitor the success of
their effort to enhance the access to IGOSS products. To do this,
please let them know what data you have copied, and make comments or
suggestions for improvement. You can send mail messages to Mark
Merrifield ([e-mail]), or to Shikiko Nakahara
([e-mail]).

If you cannot use the anonymous ftp, contact the University of Hawaii
using the information given below in the personnel section.