Robert E. Cheney

The Tropical Ocean‐Global Atmosphere observing system: A decade of progress

A major accomplishment of the recently completed Tropical Ocean-Global Atmosphere (TOGA) Program was the development of an ocean observing system to support seasonal-to-interannual climate studies. This paper reviews the scientific motivations for the development of that observing system, the technological advances that made it possible, and the scientific advances that resulted from the availability of a significantly expanded observational database. A primary phenomenological focus of TOGA was interannual variability of the coupled ocean-atmosphere system associated with El Nino and the Southern Oscillation (ENSO).Prior to the start of TOGA, our understanding of the physical processes responsible for the ENSO cycle was limited, our ability to monitor variability in the tropical oceans was primitive, and the capability to predict ENSO was nonexistent. TOGA therefore initiated and/or supported efforts to provide real-time measurements of the following key oceanographic variables: surface winds, sea surface temperature, subsurface temperature, sea level and ocean velocity. Specific in situ observational programs developed to provide these data sets included the Tropical Atmosphere-Ocean (TAO) array of moored buoys in the Pacific, a surface drifting buoy program, an island and coastal tide gauge network, and a volunteer observing ship network of expendable bathythermograph measurements. Complementing these in situ efforts were satellite missions which provided near-global coverage of surface winds, sea surface temperature, and sea level. These new TOGA data sets led to fundamental progress in our understanding of the physical processes responsible for ENSO and to the development of coupled ocean-atmosphere models for ENSO prediction.

Tracking a Kuroshio cold ring with a free-drifting surface buoy

Abstract A cyclonic ring formed by the Kuroshio Extension southeast of Japan was observed over a 50-day period in 1976 by XBT (expendable bathythermograph), STD (salinity-temperature-depth recorder), and a free-drifting surface buoy. The ring, estimated to be 4 months old, was 240 km in diameter and extended to a depth of at least 3000 m. The satellite-tracked buoy completed 6.5 revolutions around the ring during 37 days as the ring moved 150 m to the north. At the end of this period, the ring coalesced with the kuroshio and the buoy was carried downstream, ultimately drifting 3500 km eastward during the next 7 months. As the buoy passed over the Emperor Seamount chain, it began moving in a series of anticyclonic loops which persisted for nearly one month. An analysis of winds along the buoy trajectory revealed two month-long periods when the buoy velocity was significantly correlated with the wind velocity.

Southern Ocean Waves and Winds Derived from SEASAT Altimeter Measurements

SEASAT altimeter measurements of significant wave height in the Southern Ocean during August and September 1978 have been examined. Significant wave heights of greater than 10 m were observed. Background levels of 2–4 m indicate generally rougher seas than occur in the North Atlantic during a comparable season. The altimeter data set is examined statistically and the spectrum of the worst case situations is determined parametrically based upon a JONSWAP form of the spectrum. Results of a statistical analysis of the altimeter data are presented together with an evaluation of the probable spectral characteristics based upon a parametric derivation of the spectrum.

Oceanographic evaluation of geoid surfaces in the western North Atlantic

An accurate gravimetric model is required for altimetric determination of surface current velocities. Three models of varying resolution and accuracy are evaluated in the western North Atlantic on the basis of oceanographic information.

Ocean eddy structure by satellite radar altimetry required for iceberg towing

Abstract Models for the towing of large tabular icebergs give towing speeds of 0.5 knots to 1.0 knots relative to the ambient near surface current. Recent oceanographic research indicates that the world oceans are not principally composed of large steady-state current systems, like the Gulf Stream, but that most of the ocean momentum is probably involved in intense rings, formed by meanders of the large streams, and in mid-ocean eddies. These rings and eddies have typical dimensions on the order of 200 km with dynamic height anomalies across them of tens-of-centimeters to a meter. They migrate at speeds on the order of a few cm/sec. Current velocities as great as 3 knots have been observed in rings, and currents of 1 knot are common. Thus, the successful towing of icebergs is dependent on the ability to locate, measure, and track ocean rings and eddies. To accomplish this systematically on synoptic scales appears to be possible only by using satelliteborne radar altimeters. Ocean current and eddy structures as observed by the radar altimeters on the GEOS-3 and Seasat-1 satellites are presented and compared. Several satellite programs presently being planned call for flying radar altimeters in polar or near-polar orbits in the mid-1980 time frame. Thus, by the time tows of large icebergs will probably be attempted, it is possible synoptic observations of ocean rings and eddies which can be used to ascertain their location, size, intensity, and translation velocity will be a reality.