Environmental Forecasting Program 



The Environmental Forecasting Program focuses on projects 

 designed to explain the large-scale, long-term behavior of the 

 ocean and the ocean's influence on weather and climate. Experi- 

 ments and studies include: Joint U.S.-U.S.S.R. Mid-Ocean Dy- 

 namics Experiment (POLYMODE); North Pacific Experiment 

 (NORPAX); International Southern Ocean Studies (ISOS); and 

 Climate: Long-range Investigation, Mapping, and Prediction 

 study (CLIMAP). 





MODE 



Joint U.S.-U.S.S.R. Mid-Ocean Dynamics 

 Experiment (POLYMODE) 



The purpose of POLYMODE is to establish the dynamics 

 and statistics of mesoscale motions in the ocean, their energy 

 source, and their role in the general circulation of the ocean. 

 POLYMODE is based on: 1) U.S.S.R. Polygon project — a con- 

 tinuing series of experiments investigating mesoscale phenomena 

 in the Atlantic and Pacific Oceans and in the Arabian Sea, 

 and 2) Mid-Ocean Dynamics Experiment (MODE-I) of the 

 United States and the United Kingdom. A Joint U.S.-U.S.S.R. 

 POLYMODE Organizing Committee, established under the 

 Agreement between the Governments of the United States and 

 the U.S.S.R. on Cooperation in Studies of the World Ocean, 

 directs the POLYMODE experiment. The UNESCO/Inter- 

 governmental Oceanographic Commission's Scientific Commit- 

 tee on Oceanographic Research (SCOR) Working Group 34 

 has invited other countries to participate in POLYMODE. 



The WOE Progress Report Volume 5 gives the overall de- 

 scription of the U.S. POLYMODE effort. Figure 14 summarizes 

 the location of North Atlantic measurements that have been 

 made as part of POLYMODE. Figure 15 is a calender for 

 POLYMODE activities. POLYMODE News No. 39 provides 

 an up-to-date description of U.S. activities, and is available 

 from the POLYMODE Office, 54-1417, M.I.T., Cambridge, 

 MA 02139. This report notes the completion of the MODE-I 

 project, describes SOFAR float development and Soviet POLY- 

 MODE activities, and summarizes other international POLY- 

 MODE activities. 



The IDOE Section and the Office of Naval Research jointly 

 sponsor U.S. participation in POLYMODE. Table 5 lists 

 POLYMODE projects. 



Completion of MODE-I 



With the publication of the article, "The Mid-Ocean Dynam- 

 ics Experiment," (Deep-Sea Research, in press) and the Atlas 

 of the Mid-Ocean Dynamics Experiment (MODE-I) (Massa- 

 chusetts Institute of Technology), the MODE-I experiment is 

 completed. All MODE-I data have been sent to NODC and 

 are available on request. The following are scientific conclusions 

 of MODE-I: 



Midocean eddies are part of an energetic and structured vari- 

 ability field, which is superimposed on the weaker gyre-scale 

 mean circulation. Identifiable closed eddies are part of a con- 

 tinuum of scales up to gyre width in length and (days) -1 in fre- 

 quency. This variability is present in one form or another in all 

 the oceans. 



In the western North Atlantic, there is persistent eddy vari- 

 ability with characteristic scales of 50 days and 70 km, in which 

 currents are horizontally nearly isotropic. Vertical scales are on 

 the order of the depth of water and observed to be principally 

 lowest mode over flat bottoms and highest mode over rough 

 topography. Kinetic energy levels are up to several orders of 

 magnitude above the mean and can vary markedly on the eddy 

 (x2), the subgyre (x5), and gyre (xlOO) scale. Kinetic energy 

 levels at 1,500 m over rough terrain appear to be diminished 

 compared to those over nearby flat abyssal plains. 



The intensity of eddy-and mean-flow kinetic energy increases 

 markedly northward of the MODE-I area toward the Gulf 

 Stream, and to a lesser extent southward from the MODE-I 

 area toward the North Equatorial Current. The Gulf Stream 

 possesses several intense varieties of variability on the eddy 

 scale. Because the eddy and current fields are so intense in that 

 region, the Gulf Stream (and possibly other free boundary cur- 

 rents in the gyre) is probably a source region for the variability. 

 Numerical and analytical models support this conjecture and 

 provide instability and radiative mechanisms to generate eddy 

 variability, as well as details of the energy and scale transforma- 

 tion processes. Although all indicators implicate the boundary 

 currents as at least one source of eddy energy, no conclusive 

 field evidence has been shown. Wind has been shown to be a 

 plausible and large potential source of eddy energy. 



Mechanisms of eddy-internal wave interaction have been de- 

 vised as eddy energy sinks. Large-scale numerical models sug- 

 gest that bottom dissipation is responsible for absorbing eddy 

 energy, and process models provide various mechanisms for 

 cascading of eddy energy to smaller scales. The issue of eddy 

 energy dissipation remains equivocal. 



Deep-eddy momentum transports seem to vary directly in 

 absolute magnitude with the mean, large-scale flows north and 

 east of the MODE-I area. The data are insufficient to resolve 

 cause and effect of this mean flow and eddy momentum trans- 

 port relationship. Deep-eddy heat transports appear inadequate 

 to account for the poleward climatological heat flux, but surface 



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