Report to the GLOSS Group of Experts VI, Laboratoire d'Etudes en Geophysique et Oceanographie Spatiales, Toulouse, France 10-14 May 1999 The Research Data of the UH Sea Level Center (UHSLC) Report prepared by Mark Merrifield and Bernard Kilonsky The UHSLC collects and distributes two basic sea level data sets: the Joint Archive for Sea Level (JASL) research quality data set and the WOCE "fast delivery" data set. The UHSLC is also the Specialized Oceanographic Center (SOC) for Mean Sea Level in the Pacific and, as such, distributes products based on data collected and processed under the Integrated Global Ocean Services Systems (IGOSS) Sea Level Program in the Pacific (ISLP-Pac). The JASL data set is designed as a user friendly, scientifically valid, well-documented, standardized set of hourly, daily, and monthly sea level values, suitable for archiving at international data banks. It is an extension of the TOGA sea level data set, first created in 1985, and thus, currently emphasizes the tropical and subtropical regions, with data from 395 stations. The effort under the TOGA project was the first international attempt to acquire, review, assess, manage, and distribute sea level for hourly and daily values, which allow a higher level of quality control and a wider range of applications. Though the TOGA project has ended, this program continues as a cooperative arrangement between the U.S. National Oceanographic Data Center (NODC), the World Data Center-A (WDC-A) for Oceanography, and the UHSLC. Over the years, its development and format have been guided by the needs of scientists--first at the University of Hawaii, and later by investigators in ephemeral programs, such as NORPAX, TOGA, WOCE, as well as the needs of GLOSS. Data used in the JASL data set are provided internally by the JIMAR Sea Level Network and additionally by collaboration with over 60 agencies representing over 70 countries. An important element of the JASL is the active scientific use of the data and the guidance provided by the UHSLC specialists, who help ensure a data set of high scientific integrity. The JASL is charged with collecting sea level information, processing and quality controlling these data, and distributing them within 18 months where possible. The data set is distributed directly from the UHSLC via the internet and on CDROM, and is also provided to the World Data Center system and the U.S. NODC for additional distribution. The demand for the JASL research quality data has risen steadily since the inception of the program. In 1985 we answered approximately 25 data requests per year. By 1990 the number of requests was close to 100, in 1995 data requests surpassed the 500 mark, and in 1998 the requests numbered 1230. These numbers are even more impressive considering that U.S. NODC and the World Data Centers also distribute these data. In the past year, the UHSLC increased its JASL holdings to 6480 station-years of hourly quality assured data. Most of the data are still in the Pacific (219 stations, 4224 station-years), but the Atlantic (105 stations, 1686 station-years) and Indian (71 stations, 570 station- years) data sets have become substantial. The JASL set now includes 4597 station years of data at 218 GLOSS sites. Of the 101 GLOSS stations that are presently operating on islands, data for 93 of them have been obtained by the UHSLC. Though the typical time lag from collection to public dissemination is typically on the order of a few years, the August 1998 submission of the JASL data to the world Data Center-A for Oceanography, included 117 series that contained data through the year 1997. The next update of the data set is due at the World Data Center in July 1999. Both of the basic data sets produced by the UHSLC remain in high demand. In its role as a WOCE Data Assembly Center (DAC), the center has processed data from a globally distributed set of stations and makes it available to users within one to three months of data collection. The WOCE "fast delivery" sea level data set now includes data from 109 stations, 89 of which are located at GLOSS sites. In 1998, 960 users accessed the WOCE internet site and 6,800 station files were copied. These statistics only include sea level data files distributed, not WWW page accesses. A major user of the "fast delivery" data has been the altimetry community. For 73 "fast delivery" stations, the existing time series has been extended backward to 1985 in order to link Geosat altimetric data with the present TOPEX/Poseidon data. In 1984 the UHSLC began the ISLP-Pac. This activity is an early and very successful example of operational oceanography that provides monthly maps of the Pacific sea level fields. We also produce quarterly updates of an index of the tropical Pacific upper layer volume and annual updates of indices of the ridge-trough system and equatorial currents for the Pacific Ocean. The UHSLC presently distribute these products through the internet and by mail to users, including several national agencies that reproduce them and further distribute them. In addition, we also submit the products and a text description to the IGOSS Products Bulletin. The net result is that approximately five weeks after the end of a month, hundreds of users throughout the world receive an analysis of the state of the Pacific Ocean sea surface topography for that month. We also use our World Wide Web site and anonymous ftp account on the internet to allow users to access one of our computers at the University of Hawaii and obtain copies of files containing the most up to date versions of all of our products. By the time our maps are seen by a potential user, the digital data are available to be transferred for any desired additional calculations. Also, note that it is not only last month's data that are available, but the entire time series. All of the data sets and products discussed above are available by this method. The UHSLC in collaboration with the Pacific GPS Facility is implementing co-located continuous GPS (CGPS) receivers at a select set of global tide gauges in support of altimeter drift monitoring. These CGPS-tide gauge stations will constitute a portion of the proposed altimeter calibration network.. The co-location of GPS receivers at the tide gauge stations will provide local estimates of absolute sea level. Emphasis is therefore being placed on selecting tide gauges with relatively long records. All University of Hawaii CGPS stations are scheduled to be in place prior to the Jason launch. We will provide network links to data from the CGPS sites. We also expect to provide links to real-time (one hour delay from sampling) sea level data from selected stations for use in forecast models and for satellite altimeter calibration., and will be providing new analysis based on in-situ sea level for monitoring interannual variations.