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Vol. 8, No. 1 ● September 1997 EARTH SYSTEM MONITOR NODC Altimetry Lab tracks 1997 El Niño Operational program improves NWS seasonal forecasts A guide to Bob Cheney NOAA's data and Chief, Laboratory for information Satellite Altimetry services National Oceanographic Data Center INSIDE NOAA/NESDIS The TOPEX/POSEIDON 3 (T/P) altimeter satellite, which News briefs was launched in 1992 as a re- search mission of the American 5 and French space agencies, has The NOAA Central recently become an integral part Library and coastal of NOAA’s operational satellite ocean information system for monitoring the 9 oceans. The transformation was achieved through the efforts of The Earth’s changing NODC’s newest division, the magnetic field on Laboratory for Satellite Altim- record at NGDC etry (LSA), working together 11 with the Jet Propulsion Labora- tory (JPL) and the Naval GOIN: The U.S.-Japan Global Observation Oceanographic Office Information Network (NAVOCEANO). Since late 1996, the highly-accurate sea level 13 observations provided by T/P NASA/NOAA have been available with a delay Prototype Long Term of only two days—fast enough Archive Project to be included in the weekly ocean model run of the Na- 14 tional Weather Service—and NODC’s Internet just in time to follow develop- Security System ment of the 1997 El Niño (Fig- ures 1 and 2). 15 NOAA’s experience with satellite altimetry dates back to Data products and services Geos-3 in 1975. At that time altimeter data were viewed largely as a means of determin- NT OF C E OM TM M ing the marine gravity field, and R E A R P C the program was thus sponsored E E D ▲ Figure 1. A sample series of sea level deviation maps from TOPEX/ ★ ★ by the National Ocean Service’s U (NOS) National Geodetic Sur- POSEIDON showing evolution of the 1997 El Niño. The data are pro- N A C IT I vided in near-real time (2-day delay) by the NODC Laboratory for E R vey. But as other altimeter mis- D E ST AM sions were flown (Seasat in Satellite Altimetry. Because of their high accuracy (5 cm), the T/P data ATES OF 1978; Geosat during 1985-89) are being assimilated in the NOAA/NCEP model to improve seasonal and new applications were de- forecasts. Sea heights shown are relative to the 1992-95 mean. This U.S. DEPARTMENT veloped, the work expanded to sequence shows the ocean’s response to changes in tropical winds. OF COMMERCE include aspects of physical Sea level drops in the west and rises in the east, producing changes in National Oceanic oceanography such as the Gulf ocean circulation and sea surface temperature which ultimately alter and Atmospheric Stream, sea level variability, and global patterns of rain and atmospheric temperature. For color maps Administration tropical ocean dynamics. In at 10-day intervals, see http://ibis.grdl.noaa.gov/SAT/near_rt/enso/ – continued on page 2 topex_97.html 2 EARTH SYSTEM MONITOR September 1997 30 Topex/Poseidon Sea Level EARTH SYSTEM MONITOR 0Ê N, 94Ê W The Earth System Monitor (ISSN 1068- 2678) is published quarterly by the NOAA 20 (Eastern Pacific) Environmental Information Services office. Questions, comments, or suggestions for articles, as well as requests for subscrip- tions and changes of address, should be directed to the Editor, Sheri A. Phillips. 10 The mailing address for the Earth System Monitor is: H (cm) National Oceanographic Data Center NOAA/NESDIS E/OC1 0 SSMC3, 4th Floor 1315 East-West Highway Silver Spring, MD 20910-3282 EDITOR -10 Sheri Phillips 1992 1993 1994 1995 1996 1997 Telephone: 301-713-3280 ext.127 ▲ Figure 2. Sea level near the Galapagos Islands in the eastern equatorial Pacific mea- Fax: 301-713-3302 sured by the T/P altimeter. The abrupt, 30-cm rise since the beginning of 1997 indicates E-mail: [email protected] the beginning of a warm, El Niño event. The July 1997 height of 25 cm is as high as DISCLAIMER during the 1982 El Niño, the largest warm event of the century. Mention in the Earth System Monitor of commercial companies or commercial NODC Altimetry Lab, from page 1 ocean eddies and fronts like the Gulf products does not constitute an endorse- 1991 the altimeter program was moved Stream, but they were not sufficiently ment or recommendation by the National to the NOS Office of Ocean and Earth accurate to be used in general circula- Oceanic and Atmospheric Administration Sciences and finally in 1997 to the Na- tion models of the ocean. or the U.S. Department of Commerce. tional Environmental Satellite, Data, This is where the T/P satellite has Use for publicity or advertising purposes of and Information Service’s National provided a breakthrough. In addition to information published in the Earth System Oceanographic Data Center. The LSA is its precision altimeter, T/P carries a Glo- Monitor concerning proprietary products now a leader in many facets of bal Positioning System (GPS) receiver or the tests of such products is not altimetric applications, providing scien- which is capable of quickly determining authorized. tific analyses that range from maps of the position of the T/P satellite to the ocean floor to determination of glo- within a few centimeters. Once the JPL bal sea level rise. team learned how to use the GPS data as Most recently, the Lab’s focus has part of an automated orbit determina- been on improving the operational, tion system, a new era in global ocean near-real time flow of altimetric sea monitoring began. level data. The operational value of al- The present T/P near-real time sys- timetry depends not only on the turn- tem is a model of interagency collabora- around time, but also on the accuracy of tion. JPL receives the raw altimeter data the measurements. from the satellite several times a day ATMOSPH ND ER A IC IC A For example, altimeter data from and forwards them to NAVOCEANO, N D A M E I the European Space Agency’s ERS-1 sat- C N where an interim data set is constructed I O S L T ellite (1991-96) were processed by A R and stored. The next day, JPL uses GPS A N T O I I O NOAA in near-real time throughout the data from a global network of ground T N A N mission, but the quick-look satellite stations plus those from the T/P receiver U .S E . C orbits contained large-scale errors of up to compute a precise satellite orbit. D R E E P M A M to 1 meter. These data were therefore RT O These refined altimeter observations are MENT OF C useful for finding the edges of mid- provided to NOAA’s altimetry lab for further processing. An adjustment is U.S. DEPARTMENT OF COMMERCE Laboratory for Satellite Altimetry first performed to remove large-scale William M. Daley, Secretary National Oceanographic Data Center errors remaining in the data. T/P sea National Oceanic and SSMC3, 3rd Floor, Room 3620 level profiles are then compared to the Atmospheric Administration 1315 East-West Highway previous 4 years of data along the D. James Baker, Silver Spring, MD 20910-3282 same tracks. Finally, 2 days after the Under Secretary and Administrator E-mail: [email protected] – continued on page 4 September 1997 EARTH SYSTEM MONITOR 3 New Lake Erie bathymetry to be NGDC leads successful field displayed in museum News briefs expedition in Greenland A new bathymetric map of Lake Erie Dr. Jonathan Overpeck of the Na- will be displayed in the Great Lakes Sci- tional Geophysical Data Center (NGDC) ence Center in Cleveland, Ohio, during ronmental Assessment Program (OCSEAP) recently returned from southwest the Ohio Lake Erie Conference, September and Processes and Resources of the Bering Greenland, where he led a successful ef- 18 through September 20. The Confer- Sea Shelf (PROBES). What is needed, and fort to survey and sample lakes for use in ence will be hosted by the International what NOAA Environmental Services Data reconstructing past variability in the Joint Commission for the Great Lakes and Information Management has funded circum-Labrador Sea region. This work, the Ohio governor’s Lake Erie Commis- through this project, is a single, stand- carried out in collaboration with the Geo- sion. Focus will be geared toward environ- alone resource that will reference as much logical Society of Denmark and mental organizations, researchers and historical data as can be located. Greenland, focussed on lakes that will Great Lakes representatives, along with Benefits will be immediate and con- yield annually-dated paleoclimate time public officials from local, state, Federal tinuous. Recently the Bering Sea’s eco- series stretching back centuries. These and Canadian governments. The full color nomic and biological significance has series will allow the testing of key hypoth- Lake Erie map will be available from provided impetus for the proliferation of a eses regarding ocean and atmospheric NGDC in October, along with a CD-ROM number of active regional studies includ- variability in the North Atlantic region. containing downloadable imagery and ing: the joint North Pacific Marine Sci- The new time series should also provide data used in the compilation of the ences Organization/GLOBal ocean the first definitive answer to the question bathymetry. ECosystems dynamics Climate Change of whether Norse settlements disappeared and Carrying Capacity (PICES/GLOBEC around AD 1500 in response to climate. NOAA seeks entries for a Bering CCCC) study and the Bering Sea Impacts Sea ecosystem metadatabase Study; national studies (Bering Sea Fisher- NSSDC agrees to participate This inventory of physical and biologi- ies-Oceanography Coordinated Investiga- in GOIN cal data will help researchers, managers, tion, Southeast Bering Sea Carrying Dr.

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