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and to use observational data in numerical models. New models must include better representations of the surface and bottom boundary layers, and of frictional descriptive processes generally. Para- metric studies with a coupled eddy-resolving basin model and shelf model, both of which have the necessary resolution pertinent to the dominant scales to be expected, should be attempted. No matter how clever one is with open boundary conditions, nothing new will be learned unless one actually allows for an adjoining basin with realistic dynamics. Such modeling studies coupled with related field experiments will allow an understanding of the interchange of momentum, vorticity, and other properties between the deeperâwater region and the shelf. Some important questions are the following: Does the shelf act only in a passive sense of responding to excita- tion from the open sea, or can the shelf dynamics have a significant feedback on the open ocean dynamics? Does the shelf act as a sink for all oceanic wave phenomena (other than gravity waves) that are incident on it? PREREQUISITES FOR RESEARCH Several classes of prerequisites are essential for the success of the recommended research initiatives, as well as for the continued excellence of the general individual research program in physical oceanography. These prerequisites include new developments and replacement of the existing infrastructure to support research in this discipline. 29
Scientific Manpower If we are to approach seriously the challenging problems of the next decades, we require new young scientists who are creative and farsighted. The number of subdisciplines of physical oceanography must be increased. Special emphasis must be placed on training in the application of mathematics to oceanography, especially in numerical modeling and the application of numerical and statistical techniques to oceanographic data analysis. Manpower is our shortest commodity in physical oceanography; thus, its acquisition should receive our highest priority. Ocean Satellites New technology providing global views of the oceans from space by satellite-borne instruments and new high-speed computers promises to allow major breakthroughs to be made in the description and understanding of the ocean. Research satellites have demonstrated a remarkable ability to measure several critical ocean parameters. Different types of radar measure sea surface topography, from which ocean currents and seabed shape can be deduced; ice shelf elevations, from which we can determine whether polar ice caps are melting; ocean wave heights, which are important for ship routing; sea surface winds, which are important for ocean circulation; and high-resolution sea ice imagery, which is important for supporting commercial operations in ice-infested waters. Detailed measurements of ocean color provide an estimate of biological productivity, which affects fish yield; infrared radiation from the ocean gives sea surface 30
temperatures; and longer-wavelength radiation gives temperature, wind speed, rain rate, and sea ice concentrations under all weather conditions. As an example of what can be achieved using satellite techniques, the global ocean wind field was acquired every three days by an instrument aboard the National Aeronautics and Space Administration's (NASA's) Seasat satellite in 1978. During the entire 100 days of this mission, as many individual measurements of wind speed and direction were collected as during the previous 100 years and more of shipborne observations. To assess future impacts of the new satellite technology and set priorities for its effective use, a report was prepared by the Joint Oceanographic Institutions Inc. (JOI), Satellite Planning Committee (1984), which included representatives from 16 major U.S. ocean research institutions. The report stressed the immediacy of our nation's need for a better understanding of the oceans and showed how a significant part of that need can be met by satellite observing systems. Although existing weather satellites operated by the National Oceanic and Atmospheric Administration and the Department of Defense provide some routine surface observations, measurements of surface winds, ocean currents, biological productivity, and the gravity and magnetic fields of the earth are still needed. The JOI report (1984) presented a plan for acquiring these measurements in phases from space. Four new satellite missions are proposed that will include an overlap of flight missions. The first is the Naval Remote Ocean 31
Sensing System (NROSS), which will carry a NASA scatterometer to measure winds and waves at the ocean surface. NROSS is awaiting approval for a 3-year mission, perhaps beginning in 1991. For the measurement of ocean surface topography (surface currents), the Ocean Topography Experiment (TOPEX/POSEIDON), which is joint with the French, has been approved and will have a 3- to 5-year mission to begin in 1991. NROSS and TOPEX/POSEIDON are crucial to the World Climate Research Programme; their timing must remain as scheduled to ensure their simultaneous performance with other complementary satelite and field activities of this international program. NASA is currently investigating flight opportunities for ocean color measurements. In view of the importance of these measurements, the JO I report (1984) strongly recommended deployment of a satellite-borne Ocean Color Imager. For gravity and magnetic field measurements, the Geopotential Research Mission is proposed for a new start in 1988 and deployment in the 1990s. Academic Fleet Replacement First-class oceanographic research requires the availability of well-equipped research vessels. In large measure because of the quality of our academic research fleet and their associated instru- mentation, the U.S. finished the decade of the 1970s in the forefront of ocean science. The preeminence of our academic research fleet, however, is now being challenged by research vessels from many other countries. Based on a 30-year age criterion, nine of the 20 vessels of our University-National Oceanographic Laboratory System (UNOLS) 32
fleet should be replaced before the year 2000. Though age alone is not a sufficient criterion, replacements are warranted because of changes in the direction of science, technological obsolescence, operational cost escalation of older vessels, and needs for special-purpose vessels. To establish a prudent fiscal expenditure policy and to benefit from the experience gained from the operation of existing vessels, the U.S. should have a continuing program to improve the capability of our research fleet. The UNOLS has commissioned a study leading to a coordinated plan for the replacement of the aging UNOLS fleet and the construction of new ships. This study consists of the following elements: review and verification of requirements for research vessels; status of current ships and the identification of needed capabilities and priorities; report of critical areas of ship replacement and specifications for priority replacements; conceptual design studies of several selected alternative platforms; community-wide review and discussion of the foregoing; development of a replacement plan incorporating desired fleet mix to meet requirements, priorities, time frame, and costs of new construction; and preliminary design of the vessel types needed to implement the early phase(s) of the replacement plan. Multiagency agreement on, and backing of such a plan is essential to the continued health of oceanographic research in the U.S. Support for Existing Technologies Within the U.S. there are presently a number of groups providing specialized oceanographic services that help keep us in the forefront 33
of research. These include capabilities in float and drifter techno- logy, data transmission, analytical techniques, CTD, chemical sampling, and data analysis. The capabilities are essential and very difficult to develop; they require continuing funding adequate for not only ongoing operation, but the incorporation of technological developments as well. Development of Sampling Technology Though undirected and often unsupported, the development of technology for ocean research has provided physical oceanographers with an array of innovative, useful tools. Vector current meters; long-lived acoustic release systems; floats for remote tracking of currents near sound channel depths; expendable profilers of vertical shear of ocean current; systems for profiling salinity, temperature, and density from a conducting cable while obtaining water samples; and satellite-tracked ocean surface drifters are examples. Nevertheless, the technological developments that will be needed to support the new research thrusts of the 1990s and beyond are foreseen, and many either are not under way or are progressing too slowly to make their maximum contributions in terms of cost efficiency or under sampling capability. New systems of subsurface drifters might internally record their positions for very long periods and then surface to report these positions by satellite. Rugged, all-environment communication links are needed between subsurface moored instrument arrays and satellites in order to monitor the status and records of ocean sensors. 34
Semi-intelligent vertical profilers are needed that operate without a connection to a surface vessel, alleviating the need for special winches and rapidly reducing ship time. These are only a few examples to illustrate the capabilities that are presently needed and within reach but that are yet undeveloped. A long-term program of technological development must be fostered. Numerical Modeling and Data Analysis Numerical ocean models presently are limited by the capability of available computers and by the numbers of trained numerical ocean modelers. Basin-wide and global numerical models with eddy-resolving capabilities must be implemented to take full advantage of the global data sets anticipated. Global-scale coupled atmosphere-ocean models must be realistically formulated for climate studies. A national ocean modeling initiative must have three thrusts: the development and availability of class seven computers and their descendants, academic access to present and future supercomputer facilities, and training of additional research scientists to develop and make effective use of vector codes. Oceanographic modelers need to develop the capability of merging real data and dynamic principles into a meaningful tool, perhaps by using the objective analysis techniques that diagnostic meteorologists have employed and refined. One of the important steps in numerical weather prediction on long time scales is proper ini- tialization, particularly if primitive equation models are employed. Oceanographers must be even more clever in initializing their models since the data not only contain gaps, are not simultaneous, and do 35
not have the advantage of absolute pressure measurements, but they also consist of a variety of different types of data, for example, hydrographic data, Lagrangian drifter data, surface sensed temperatures, and chemical tracers. (It is hoped that satellite altimetry data soon will be useful for oceanographic signals of barotropic modes, given an accurate geoid and accurate knowledge of oceanic tides.) In any event, there is a real need for an objective method of blending all sources of data into a meaningful whole. The ocean satellite data expected in the 1990s will require new concepts of data management. Requirements of the Interannual Variability of the Tropical Oceans and Global Atmosphere Experiment (TOGA) and the World Ocean Circulation Experiment (WOCE) for data reduction, dissemination, analysis, and archiving are now being addressed by the working groups planning these experiments. It seems likely that completely new data transmission links and distributed data-processing centers will be the effective solution. Ocean Data Archiving Dissatisfaction with the present system of archiving oceano- graphic data in the U.S. has been expressed by the ocean science community for at least a decade. However, the system capability has improved little, if at all, relative to the increase in volume and diversity of data. The entire archival system of ocean data within the U.S. requires a new look and drastic modification to accommodate even the present types and levels of data collected, much less those anticipated in the next decades. Consideration is needed of how to couple archived data, new 'm situ data, and satellite-derived data to processing and analysis centers. 36
