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Appendix G Working Group 3: Currents, Ocean Processes, and Ice ALLAN R. ROBINSON, Harvard University, Leader RICHARD B. ALLEN, Atlantic Offshore Fishermen's Association PAUL H. GLAIBER, Great Lakes Dredge and Dock Company WARREN W. HADER, Montauk Fishermen's Association WALTER E. HANSON, International Ice Patrol, U.S. Coast Guard SAUNDERS ~ JONES, Puerto Rico Marine Management, Inc. R. MICHAEL LAURS, National Marine Fisheries Service, National Oceanic and Atmospheric Administration JAMES S. LYNCH, National Ocean Service, National Oceanic and Atmospheric Administration CHRISTOPHER N. K MOOERS, Institute of Naval Oceanography, U.S. Navy DAVID F. PASKAUSKYj Research and Development Center, U.S. Coast Guard WILLIAM C. PATZERT, Jet Propulsion Laboratory, National Aeronautics and Space Administration DAVID J. H. PETERS, Conoco, Inc. ALLEN M. REECE, Shell Development Company GEORGE P. SPARACINO, Sun Transport Company ANDREW M. SULLIVAN, Weather Network, Inc. JOHN A. VERMERSCH, JR., Exxon Production Research Company Working Group 3 was chartered to examine the requirements to im- prove observations and forecasts of oceanic currents and thermal structure, 96
97 sea ice, and related fields (ocean structures, fronts, salinities, nutrients, pollutants, sound speed and propagation, and so on). An excellent cross- section of users (recreational, commercial, safety and enforcement, and military) and providers (academia, private sector, and government) partic- ipated in frank and open discussions. Five specific topics were discussed at length. 1. What is the present status and perceived needs for nowcasts and forecasts of ocean currents, thermal structure, and related fields globally and within the coastal ocean? 2. What is the prospectus and potential impacts of enhanced obser- vations and forecasting capabilities? 3. What is the status of relevant ocean and ice models, observational networks, and forecast schemes. 4. What are the short- and long-term requirements for nowcasts and forecasts accuracies, duration, frequency, and geographic coverage? 5. What are the present capabilities and future prospects for obse~v- ing and forecasting sea ice, and what specific ice-related parameters are required? Processes, such as waves, spray, and ice accretion, were the purview of other working groups. Furthermore, a number of issues were not exam- ined (due primarily to the limited time available during the workshop and the limitations of the experience of the working group). These omissions included offshore mining applications, large-scale a~r-sea interaction and global change processes, planetary environmental management and pollu- tion, and living marine resource issues tie., marine ecosystem modeling). Finally, sea ice was discussed and found to be an important issue, but the group's breadth of expertise was limited here. CAPABILITIES Ocean Observing Network The inherent problem in monitoring and predicting the oceans has been the limitations of the observing network Ocean observations have always been sparse, especially in areas seldom traveled by ships, and without a definable network except along coastlines. In addition, conventional ocean observation systems are very expensive to design, build, deploy, and maintain because of the harsh environment in which they dwell and the requirement of ship support time. Recent technological advances have allowed for a merger of in situ observations with remotely sensed data (land, ocean, and space based) and also for space-based communications systems.
98 TABLE G-1 Status of Operational and Planned Satellites Satellite Sensor Velocity Ice A`railabilityC DMSP SSM/I b + ongoing NOAA AVHRR *** + ongoing GEOSAT Altimeter + + 1985-1990 ERS-1 Scatterometer + b + 1990-1994 JERS-1 Synthetic aperture *** +d 1992-1995 radar TOPEX/POSEID ON 1992-1996 bSSM/I is probably underutilized Indicates velocity derived from flow ~risualiz~ation. CIssues concerning availability 1. Data acquisition will not be real-time without significant upgrades to processing and ground station capabilities. 2. Uncertainties of data distribution. 3. Lacking U.S. commitment to maintain a space-based ocean observing (altimeter/~catterometer) capability beyond GEOSAT. Ace from synthetic aperture radar, 1990-1995 Conventional platforms (such as coastal tide stations, moored buoys, drifting buoys, and ships) are more frequently incorporating sophisticated onboard electronic processing capabilities that permit the platform to pro- vide some internal quality assurance and data storage capabilities, as well as to communicate via satellite to shore facilities and platform operators. Many of these systems are still expensive to deploy and maintain, but mod- ern manufacturing techniques and reduced production costs due to mass production are becoming offsetting considerations. Land- and ocean-based remote sensing capabilities are becoming im- portant tools in monitoring physical properties of the ocean, especially in the coastal zone. Systems, such as the Coastal Ocean Dynamics Application Radar (CODAR) and acoustic Doppler current profilers, are emerging as cose-effective methods to determine ocean currents from shore, from oil and gas-production rig', from ships underway, and from sensors mounted on the seafloor. Microcomputers required to operationally process this information are becoming inexpensive, and can be packaged to be housed within the observing system. Space-based remote sensing systems are becoming an essential com- ponent to the global ocean observing network. To basic types of satellite sensors have been designed: passive systems, which receive but do not emit radiated energies; and active systems, which emit and receive radiated energies. Present status of operational and planned satellites is depicted in Able G-1.
99 Passive satellite systems include visible and infrared radiometers, imag- ing spectrometers, and passive microwave sensors. Ocean color instruments and imaging spectrometers can be used to measure the color of the ocean surface, and from this information they can imply the level of chloro- phyll and primary productivity of the upper ocean, as well as the type of suspended sediments and sea surface temperature (SST) pattern. Pas- sive microwave systems, such as the Special Sensor for Microwave/Imaging (SSM/I), can- be used to delineate SST patterns, ocean heat fluxes, surface geostrophic currents, Gulf Stream shear waves, sea-ice boundary, concen- tration, type, and surface melt. Visible and infrared radiometers are capable of discriminating SST, ocean frontal boundaries, and sea ice boundaries. Active satellite systems include scatterometers, altimeters, and syn- thetic aperture radars (SARs). Scatterometers and altimeters can be used to define wave heights, water levels and topography, ocean currents, surface wind stress, and sea ice location. SARs and other active microwave sensors can be used to characterize the structure of the ocean surface, including current and frontal boundaries, eddy fields and cold water regions, internal waves, bathymetric signatures, ocean wave spectra, and sea-ice extent, type, and motion. . Prediction Capabilities From a predictive standpoint, considerable similarity exists between atmosphere and ocean, with mainly time and space scale differences due to density. The oceanic "internal weather systems" are smaller but slower than comparable atmospheric weather systems. Dynamicists see the ocean as a thin film, with a structure often reflected throughout the entire water column except for some submesoscale features and surface boundary layer effects. From a dynamical view, all of the physical fields are coupled (interre- lated). Even if we want to know a particular field, we may actually measure something else. Moreover, much of the forecast problem is similar to that of meteorology, complicated by turbulence and nonlinear processes, and characterized by a "limit to predictability." The kinds of ocean forecast problems include the following: · Evolution via mesoscale internal dynamical processes, particularly for the energetic oceanic mesoscale that is analogous to the atmospheric synoptic scale. The oceanic mesoscale is generally remotely energized with mismatched coupling of the air and sea, resulting in long-term energy accumulation in the ocean. · Evolution via local atmospheric forcing, fluxes of momentum (via wind stress), and fluxes of heat. These more rapid, forced, oceanic tran- sients primarily occur in the upper ocean with atmospheric time scales.
100 Thus the oceanic forecast will then be ultimately limited by the ability to predict the atmosphere. lithe requirements for observing the ocean for making forecasts are enormous, because of the small size of mesoscale "internal weather" fea- tures. Data requirements are very difficult to meet. Fortunately, most oceanic processes are somewhat slower than the atmosphere such that data can be assimilated over a longer period. As oceanographers build their forecast schemes now, a modern ap- proach to nowcasting and forecasting requires melding all available infor- mation into a total data set (satellite and in situ). Relationships between fields allow integration of temperature and velocity fields into a meaningful overall data set. The SYSTEMATIC APPROACH (four-dimensional data assimilation) molds data sets and observations with dynamical model output. Dynami- cal interpolation allows for a three-dimensional analysis capability from a satellite data set. In situ observations can also be used for the analysis and nowcast. Such melded nowcasts are the most powerful. Continuous data assimilation permits the forecast to be updated and extends the validity of the forecast. The hope for useful nowcasts and forecasts lies with the SYS- TEMATIC APPROACH, which optimizes information thus providing the required resource for feasible and practical prediction. The ocean prediction problem is often broken down into four scales: local scale (i.e., Chesapeake Bay), regional scale (i.ee, the Gulf Stream Meander Region), basin-wide models (i.e., the North Pacific basin), and global models. Currently, the greatest emphasis within the Navy is on regional and basin-wide models, whereas efforts of NOAA have focused on local and global (climate) scales. Global and basin-wide (dynamical) models will require considerable satellite data, and require state-of-the-art and advanced generations of supercomputers. The need definitely exists to maintain at least an altimeter in space until operational satellite systems are launched in the menW-first century. USER COMMUNllY REQUIREMENTS A representative cross-section of the user community participated in identifying user requirements. Working group members represented the recreational and commercial fishing community, oil and gas exploration and production industries, marine transportation industries, the U.S. Coast Guard,- and the U.S. Navy. A summary of user requirements is depicted in Bibles G-2, G-3, and G-4.
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102 TABLE G-3 Summary of User Requirementea for Sea-Ice Information Area Primary Users Resolution Frequency Duration CONUS Oil inductor and aids to navigation Great Lakes Aids to navigation and flood management Polar areas Ship routing and pollution 1 nmi 24 he 0-6 hr 1 nmi 24 hr 48 hr 10 nmi 12 hr 48 hr Note: CONUS--Continguous United States. aConsensus of parameter requirements ice edge (location and movement, including leads and polynas) concentration of ice ice thickness ridging and related pressure fields development stages underice roughness Marine Transportation Industry The marine transportation industries that were represented included commercial shipping, barge owners, and coastal dredging. The user com- munity uniformly requires information on surface velocity, and some cargo and tanker operations require nowcasts and forecasts of surface tempera- ture. Optimum ship routing requires accurate information of surface cur- rents. Ship captains over the centuries have come to rep on sea surface temperature measurements and patterns as the only reliable tool to identify the location of the ems of the currents, but continue to rely on climatolo- gies to estimate the speed. U.S. vessels operate throughout the world, and therefore require accurate current globally. Cargo ships transporting perishable commodities (especially certain food items) and modern tankers carrying-"exotic" fuels are beginning to require nowcasts and forecasts of ocean surface temperatures. Many of the commodities carried by these vessels are susceptible to warm or cold temperatures; in order to maintain thermal stability within the cargo and tanker holds, ship captains and navigators require accurate information. Fisheries Industry The fishing industry (both recreational and commercial) require a considerable variety of oceanic data. Fisheries management needs both physical and biochemical data and forecasts that affect eggs, larvae, and year class strength. Fisheries operations need accurate information to
103 TABLE G-4 User Requirements for Geographic Coverage Shipping Industry Global requirements (predominantly along shipping lanes) Need highest resolution at major fronts and currents South Africa (AGULHAS) Southern Japan (KUROSHIO) Kuril Islands (OYASHIO) U.S. East Coast (Gulf Stream) Equatorial counter currents Selected straits and passages Fisheries Industry Major, large, marine ecosystems Coastal: full water column over continental shelf Pelagic: full water column to base of thermocline Oil Industry U.S. Exclusive Economic Zone Gulf of Mexico (as deep as 3,000 m) Continental shelf of the U.S. East Coast Foreign and international waters Off Japan West of the Shetlands Near Somalia Near the Amazon Delta Off northwestern Australia U.S. Coast Guard Coastal and offshore waters of the contiguous United States Great Lakes Polar regions (Arctic and Antarctic) Other areas of the U.S. Exclusive Economic Zone U.S. Nary Global requirements Regional (300 nmi x 300 nmi) support for mooring battle groups identifier stock distn~ution, catch rates and quality, and other behavioral responses (feeding, depth, and geographic location). The information is needed for a varier of "large marine ecosystems" that the U.S. industry manages or harvests. Many of these geographic areas are within the U.S. Exclusive Economic Zone (EEZ3. Some, like the tropical Pacific tuna region, must be considered in a global context The fisheries community is rapidly becoming sophisticated in the type of information that it uses; such as temperature; salinity, dissolved oxygen; turbidity and light; chlorophyll plankton, and carbon content; nutrients (nitrogen and phosphorus); pollutants; pH; transport and velocity; and color.
104 Oil and Gas Industry The oil and gas industry, especially the "exploration" sector, requires accurate velocity nowcasts and forecasts in support of floating drilling operations to provide station keeping and for riser management. The industry representatives noted that accurately forecasting the size and track of loops, eddies, and meanders was extremely important for minimizing lost production time and platform damage. Accurate climatological data is needed to identify the maximum possible currents within their operating areas as use in risk management for permanent facilities (20- to 30-year life). The U.S. industry operates in many parts of the globe. Within the U.S. EEZ, the industry operates in the Gulf of Mexico (as deep as 3000 m) and along the continental shelf of the U.S. East Coast- representatives noted that the Alaskan North Slope will likely be inactive for an extended period. In addition, the industry operates in foreign and international waters off Japan, west of the Shetlands, near Somalia, near the Amazon Delta, and off northwestern Australia. U.S. Coast Guard The Coast Guard, as a user group, has five missions to which it needs accurate oceanic analyses, nowcasts, and forecasts. These activities include search and rescue, international ice patrol, marine environmental response (pollution), transit operations, and maritime defense. The majority of Coast Guard operations are within the U.S. EEZ, but the agency has a number of international responsibilities requiring global coverage. Observations, nowcasts, and forecasts of surface currents for coastal and offshore areas are required to support search and rescue, marine environmental response, international ice patrol, and transit operations. Surface temperature information is required to support search and rescue, marine environmental response, and international ice patrol operations. Accurate nowcasts and forecasts of temperature, salinity, and turbidity for the entire water column are required to support the USCG's maritime defense mission (i.e., mine countermeasures). U.S. Navy Navy representatives concurred with the requirements outlined by the other users and included the need for accurate nowcasts of three- dimensional sound velocity fields. The oceanic information (0- to 48- hour forecasts) requires a global capability, but in limited areas (operational regions) at various times to support tactical oceanography operations and
105 battlegroups in transit. Specific regional areas, based on maritime strat- egy and tactical requirements, include the North Pacific Ocean, North Atlantic Ocean, North Indian Ocean, Mediterranean Sea, and Norway and Greenland seas. OTHER ISSUES Processes The working group came to a consensus that the understanding, obser- vation, and prediction of a number of oceanic processes were fundamental to the safe and effective use of the ocean, such as · internal ocean weather and related boundary processess, including upwelling, advection, frontal processes, m~xed-layer processes, eddy-shelf interaction, and eddy shedding and meandering; and · sea-ice processes, including ice edge (location and movement, leads, and polynas); sea-ice concentration and thickness; ice ridging, pressure fields, and development stages; and under-ice roughness. COST-BENEFIT ANALYSIS Each user group could identify meaningful and sustainable benefits from improved observations and forecasts of oceanic phenomena. Able G-5 highlights the basic categories of benefits for the user communities. SUMMARY FINDING: There exists a common national interest in, and need for, nowcasting and forecasting oceanic velocity, temperature, sea ice, and related fields. Significant and sustainable benefits to a variety of commercial, military, and recreational oceanic activities are identifiable based on existing national capabilities. Recent progress in understanding oceanic processes, as well as new and innovative observing methods (conventional in situ and remote sensing systems) and forecasting techniques, indicate the nation's technological and scientific readiness to provide operational oceanic nowcasts and forecasts. Short- and long-term; requirements for oceanic observations and forecasts have been identified by user groups, and include specific parameters, geo- graphic location, duration and timeliness, and accuracies. RECOMMENDATION: An increased national effort is needed to improve or establish operational capabilities that should include
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107 · expanded and accelerated efforts to (1) produce fisheries forecasts and (2) develop an observing and forecasting capability to support commer- cial, military, recreational, and research activities within the U.S. Exclusive Economic Zone (EEZ); · coordination and cooperation of ongoing and component efforts of federal and state agencies, academia, and the prorate sector, and · a national policy on the importance of the oceans, especially the EEZ, to the welfare and economic prosperity of the nation.