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Ocean Surface Current Monitoring from Space: Methodology and Progress

Fabrice Bonjean(1) , Gary Lagerloef(1) , Eric Johnson(1) , John Gunn(1) , Laury Miller(2) , Richard Legeckis(2) , Gary Mitchum(3) , Nancy Soreide(4) , and Mark Bourassa(5)

(1) Earth & Space Research, 1910 Fairview Avenue East, Suite 210, Seattle, WA 98102, United States
(2) NOAA/NESDIS, 1335 East-West Highway, Silver Spring, MD 20910, United States
(3) University of South Florida, 140 Seventh Avenue South, St. Petersburg, Florida 33701, United States
(4) NOAA/PMEL, 7600 Sand Point Way NE, Seattle, WA 98115, United States
(5) Florida State University, 2035 E. Dirac Dr., Suite-200 Johnson Bldg , Tallahassee, FL 32310, United States

Abstract

Monitoring the ocean surface currents is a primary application of the highly successful satellite altimetry missions that started 15 years ago. This symposium coincides with the implementation of a significant achievement of the NOAA Ocean Surface Current Analyses Real-time project (OSCAR, http://www.oscar.noaa.gov), namely the extension of satellite-derived surface current processing, and its associated datacenter, to the global ocean. We present a synthesis of the efforts resulting in the estimation of surface currents from satellite and their subsequent application to some climate studies, within the framework of OSCAR. In the first part, we summarize the methodology associated with OSCAR, particularly emphasizing the respective contributions of satellite altimeter data (TOPEX/Poseidon and Jason-1) and scatterometer data (QuikScat) to the diagnostic calculations of surface currents. Additionally, we show how the methodology has been extended from the tropics, where it was initially developed, to the mid and high latitudes. An overview of the comparison between the OSCAR currents and in situ data for each ocean basin and with respect to latitude is presented. Notably, we discuss the accuracy of the calculated velocities when applied to seasonal-to-interannual surface current variations, at present a major application of the OSCAR currents. In the second part, we review the most prevalent types of low-frequency and large-scale variability of the surface currents that are identified in the 13-year OSCAR database. We especially focus on the most important short-term climate disruptions that occurred throughout this time period and that involved large-scale surface current changes. In this regard, the 1997-98 El Nino in the tropical Indo-Pacific, the “El Nino of the 20th century”, remains the most dominant event of this longer-than-a-decade period. We briefly recount the co-evolution of the surface currents (SC) and the sea surface temperature (SST) up to the present, and show how the principal SC mode leads the SST mode by about 3 months on interannual timescales. Substantial surface current anomalies also appeared in the tropical Atlantic, associated with the tropical Atlantic variability (TAV). In the third part, we present an overview of climate events in ocean areas where the ocean surface currents have the largest impact on SST, a crucial variable for ocean-atmosphere interactions. In this regard too, the El Nino/La Nina events in the equatorial Pacific, which account for the 2nd highest mode of global climate variability after the seasonal cycle, are preponderant. The most intense large-scale, surface heat advection transport observed in the world ocean occurs at the frontal region between the warm-pool and cold tongue of the tropical Pacific. We show that surface currents also have a large influence on the SST in specific regions of the tropical Indian and Atlantic oceans. Finally, we underline the near real-time characteristic of these global climate analyses associated with the space-based monitoring of the ocean currents. This would not be possible without the continuous and on-going satellite coverage of the ocean surface height. Concomitant with the present and future altimetry missions, the OSCAR web site and data server will continue to be updated and will provide an account of any extreme surface current change occurring in the global ocean.

 

Workshop presentation

Full paper

 

                 Last modified: 07.10.03