D. Enfield and V. Barros chaired a review of current field programmes relevant to VAMOS, with the notion of looking for ways to build upon these efforts, to establish links between them, and to see how they address VAMOS scientific objectives. Table 1 gives brief summaries of these field programmes.
| Presenter | Program | Countries | Time Frame | Resources | Funding Orgs. | Goals/Objectives |
| Nobre | LBA | Brasil + U.S. + Amazon countries | 1997-2003 | 25M TOTAL | NASA, EEC, BRASIL | (1) how does Amazon function as climate system; (2) how is it likely to change under anthropogenic forcings |
| Lawford | GCIP | U.S. | 1998-2004 | 6M/year | NOAA, NASA | Understand/predict spatial & S-I temporal variability of water resources over Mississippi River Basin |
| Esbensen | PACS | U.S. | 1995-2004 | 2.5-3M/ year | NOAA/OGP | (1) Understand seasonal to interdecadal climate varaitions of Americas; (2) extend scope & improve skill of climate prediction, including tropical storms |
| Weller | EPIC | U.S. | 2000-2001 | 2M/ year | NOAA/OGP | Understand processes of Pacific cold tongue, warm pool and stratus deck |
| Rogers | CORC | U.S. | 1998-2000 | 4M/ year | NOAA/OGP | Understand through observations & modeling the ocean variability on scales of years to centuries & predictability |
| Vianna | PIRATA | U.S., Brasil, France | 1997-2000 | 4M total | NOAA, ORSTOM, Brasil navy, INPE | Monitor the tropical Atlantic, describe seasonal to interannual variability of near-surface processes and fluxes |
| Wilcox | IAI | Americas | 1996 onward | 2-3M/ year | U.S. OGP, NSF | Promote multidisciplinary, cooperative climate research in Americas with emphasis on applications for human dimensions |
| Aceituno | N. CHILE | Chile | 1999-2001 | 100K/ year | FONDECYT, CONICYT | (1) understand climatology of Bolivian altiplano; (2) study causes aridity & PBL variations over western Andes & adjacent coast |
| Matano | SACC | Brasil, U.S., Argentina, Uruguay | 1996-2002 | 200K initial
6M totla |
IAI, NSF FAPESA, CONICET, | Describe & understand the Brasil-Malvinas confluence, its variability & influence on adjacent land climate |
| Douglas | UPPER AIR | U.S., cooperating countries | 1997-1998 | 200K total | NOAA/OGP | Improve the geographical coverage of land-based upper air observations during concurrent with PACS process studies |
| Castro | DPROAS | Brasil | 1997-2000 | 2M/ year | IOUSP, INPE | Understand mechanisms & ecological impacts of seasonal variability of coastal cold water intrusions (southern Brasil) |
| Mooers | IAS | U.S., Brasil, Cuba, Mex,, Pan., Venez., Colom. | 1998 onward | 5M/ year (proposed) | US/ONR, NSF, NASA, NOAA, in kind | Understand the circulation, heat balance & ecological/climate impacts of the Intra-American Seas through observations and modeling |
| Grimm | MONSOONS | Americas | 1998-2002 | not known | WMO/CAS | Help to understand the American monsoon system |
| Picaut | ECLAT | France | 1995-2005 | 3M/ year | ORTSOM, LODYC, CNRS, CNES | Understand ocean-atmosphere interactions and climate varaibility in the tropical Atlantic sector on seasonal to interdecadal time scales |
a) LBA (J. Marengo and C. Nobre)
New knowledge and improved understanding of the functioning of the Amazonian system as an integrated entity and of its interaction with the Earth system will support development of national and regional policies to prevent the exploitation trends from bringing about irreversible changes in the Amazonian ecosystem. Such knowledge, in combination with enhancement of the research capacities and networks between the Amazonian countries will stimulate land managers and decision makers to devise sustainable alternative land use strategies along with forest preservation strategies.
The Land-Biosphere-Atmosphere experiment in the Amazonia (LBA) is designed to create this necessary new knowledge to understand the climatological, ecological, biogeochemical and hydrological functioning of Amazonia (Nobre et. al., 1996). The interactions between land use and the physical climate will be studied over a range of space and time scales. The natural ecosystems will be studied at undisturbed forest and cerrado sites. Conversion of primary tropical forests to agriculture or to secondary vegetation in combination with the inputs from agricultural burning and forest clearing will be studied in relation to altered carbon and biogeochemical cycles in vegetation, soils and atmosphere. The net sources of the key greenhouse gases, oxidants and aerosols, and their transport in the atmosphere will be quantified. Changes in hydrological regimes will be studied in relation to land use change in river catchments. Land use will be studied in both the context of its physical and socioeconomic causes. Models will be parameterised and used to extrapolate experimental results in space and in time, and to predict the future functioning of Amazonia as an entity and its interactions with the Earth system.
LBA will contribute, through measurements and improved models, to make these assessments and to explore scenarios of future change. The fundamental scientific questions addressed by LBA are:
The Physical Climate component of LBA is highly relevant to VAMOS. This LBA component will study the transport of energy and water through the atmospheric part of the energy and water cycles, and how the interactions between the vegetation and the atmosphere influence these cycles.
The tropical land and atmosphere form a highly coupled system. The surface fluxes not only control the inputs of water and energy to the atmosphere, but depend themselves on the dynamical and thermodynamical properties of the planetary boundary layer through a chain of processes involving cloudiness, soil water content, evaporation, sub-surface hydrology and vegetative cover. Observing and modelling these coupled land surface/atmosphere processes is the first task of the Physical Climate component of LBA:
2. What are the meso-scale mechanisms by which differences in surface characteristics translate into large-scale weather and climate anomalies?
3. What is the role of dry and moist convection in transferring energy and how will it change with different land use patterns?
4. How is the rainfall of Amazonia controlled by the large-scale land-surface-atmosphere interaction? Which areas within Amazonia have the most influence on rainfall and how does this vary in time?
5. What is the relative importance of Amazonia in generating its own climate compared to the role of external planetary-scale forcing, and conversely what is the influence of Amazonia on global climate?
6. How will the climate of Amazonia change in response to changes in land use and global climate forcing?
The information and insight derived from diagnostic studies and from model simulations will be applied to evaluate the impact on Amazonia of climate variability and change, both natural and anthropogenic, particularly as it affects the water resources and their critical role in maintaining the ecological balance at regional and global levels. Also the improved understanding of the physical climate processes, as well as the better surface and atmospheric datasets, will serve to improve the predictive capability of current weather forecast models for Amazonia.
The GEWEX Continental-scale International Project (GCIP) is a large observational and modelling climate study being carried out in the Mississippi River Basin under the auspices of the Global Energy and Water Cycle Experiment (GEWEX) and WCRP. The project receives funding from NOAA and NASA and involves more than 35 principal investigators from universities and government laboratories. The overall mission of the project is "to demonstrate the ability to predict changes in water resources on time scales up to seasonal and interannual as an integral part of a climate prediction system".
In order to pursue this overall mission the work has been divided into scientific foci and objectives. The basin scale challenge is to close water budgets for the Mississippi River Basin to within 15% uncertainty. In the southwestern part of the basin the focus has been land surface effects and the control of the LLJ on summer precipitation and hydrology in the semi-arid areas. Research in the North Central part of the basin addresses the hypothesis that the atmosphere is relatively decoupled from the atmosphere in the winter but significant coupling occurs as surface changes (e.g. snowmelt) in response to the onset of spring. In the eastern part of the basin the focus is on assessing the degree to which precipitation and runoff variations and extremes are predictable at climate time scales in complex topography. The project addresses these science issues by pursuing the five following objectives:
2. develop and evaluate coupled hydrologic-atmospheric models at resolutions appropriate to large scale continental basins.
3. develop and evaluate atmospheric, land and coupled data assimilation schemes that incorporate both remote and in-situ observations.
4. improve the utility of hydrologic predictions for water resources management up to seasonal and interannual time scales.
5. provide access to GCIP in-situ, remote sensing and model data sets for use in GCIP and as benchmarks for model evaluation.
GCIP is endeavouring to develop comprehensive data sets to address each of these science issues and objectives by having a two-year focus in each portion of the basin. To date the focus on the southwest is completed; the north central is ending; the eastern focus is underway and on the northwest focus is being planned this fall. The GCIP project is scheduled to complete its field phase in the fall of 2000.
GCIP has made considerable progress on all the above objectives with the exception of objective No.4. Consequently more emphasis has been given to this topic in recent calls for proposals. GCIP is currently developing plans for the period beyond 2000. Priority areas for this time period include working more closely with the Pan-American Climate Studies (PACS) programme on prediction problems, addressing process and prediction issues related to water and energy budgets over all of the continental U.S.A. and participating in the Co-ordinated Enhanced Observing Period (CEOP) being organized by GEWEX.
The Pan American Climate Studies (PACS) programme is a component of the U.S. CLIVAR/GOALS programme in the 1995-2005 time frame, providing a phenomenological context for some of the U.S. CLIVAR/GOALS research. The overall goal of PACS is to extend the scope and improve the skill of operational seasonal-to-interannual climate prediction over the Americas. Particular emphasis is placed on warm season rainfall, for which a predictive capability does not yet exist. In the context of PACS, climate prediction is concerned not only with seasonal mean rainfall and temperature, but also with the frequency of occurrence of significant weather events such as hurricanes or floods over the course of a season or seasons.
The scientific objectives of PACS are to promote a better understanding and more realistic simulation of (1) the boundary forcing of seasonal-to-interannual climate variations over the Americas, (2) the evolution of tropical sea surface temperature anomalies, (3) the seasonally varying mean climate over the Americas and adjacent ocean regions, (4) the time-dependent structure of the cold tongue/Intertropical Convergence Zone (ITCZ) complex (CTIC), and (5) the relevant land surface processes.
PACS scientific objectives map very closely onto VAMOS scientific objectives. PACS will therefore seek to contribute to the VAMOS programme through its activities in field studies, modelling, empirical studies and enhanced ocean-atmosphere monitoring, and will benefit from VAMOS coordination and facilitation of collaborative research in North and South America.
PACS field studies focus on different regions of the Pan-American climate system in sequence. During the 1995-2000 time period, field activities will focus on atmosphere-ocean interaction in the tropical eastern Pacific, in association with the ENSO cycle and the climatological-mean annual march. At the present time, PACS is conducting several pilot field studies and enhanced monitoring activities in the eastern Pacific and adjacent land areas (see Figs. 1 and 2). These activities will culminate in the PACS EPIC field programme, described by Bob Weller in more detail below.
Fig. 1. PACS-funded pilot studies for the period 1995-98 superimposed on annual mean sea surface temperature contours. Also shown are pre- existing TAO Array Automated Temperature Line Aquisition System (ATLAS) and current meter mooring sites, and a wind profiler site in the m Galapagos Islands. The location of pilot study activities is offset from the TAO mooring locations for clarity. Soundings will be made along 95W and 110W; Improved Meteorological Instrument (IMET) and radar measurements will be within 30km of one another, and within 30 km of the ATLAS mooring at 10N, 125W.
During the 2000-2004 time frame, the emphasis will shift toward the tropical Atlantic Ocean where the sea surface temperature anomalies are more subtle and more diverse in terms of horizontal structure than in the Pacific, but no less important in terms of their influence upon precipitation in the adjacent continental regions.
While it is premature to propose specific PACS process studies in the tropical Atlantic or the Inter-American warm pool region at this time, we anticipate that pilot monitoring efforts will be required to establish seasonal-to-interannual variability in upper ocean structure and its relationship to wind stress and the surface heat fluxes. Of particular interest to PACS is the PIRATA array of 14 moored air-sea interaction buoys in the tropical Atlantic, described in more detail below by Joel Picaut. When combined with ocean observations from planned profiling float arrays, tide gauges, and expendable profilers of temperature and salinity, plus observations from satellite and conventional meteorological in situ observations, the PIRATA buoy array can help to provide the context for developing more focused tropical Atlantic field activities.
PACS contributions to field activities over land will be primarily through collaboration with the Global Energy and Water Experiment (GEWEX) and its regional programmes, with PACS supplying atmospheric modelling expertise and GEWEX the hydrological expertise. Much of this research will require the use of meso-scale models, applied in a climatological setting. Direct PACS support of land-based observations is expected to be limited.
Fig. 2. Upper-air sounding stations with enhanced monitoring for PACS.
The Eastern Pacific investigation of Climate processes (EPIC) in the ocean-atmosphere is a five year process study to improve the description and understanding of the CTIC and the stratus deck region. It focuses on investigating the key physical processes that must be parameterised for successful CTIC and stratus deck simulation with dynamical ocean-atmosphere models. The pilot phase of the Pan American Climate Study (PACS) conducted field work in the equatorial Pacific at 125°, where the prevailing September-October surface winds are easterly. EPIC will be located further to the east in the CTIC, principally between 95°W and 110°W, where southerly surface winds prevail at the equator in September-October. EPIC will also work in the stratocumulus deck region off the coasts of Peru and Chile.
The main objective of the Consortium on the Ocean's Role in Climate (CORC) is to "observe, deduce, and model climatically important variations in the global oceans that take place on time scales of a century of less. CORC seeks to understand the causes of both abrupt changes and quasi-periodic changes over periods from years to centuries and to assess their predictability". This document outlines the programme and focuses on the observational part of the programme most directly relevant to VAMOS.
The present phase of CORC, which is supported through 2001, is organized around the two scientific themes: 1) The Southern Ocean and Global Climate and 2) Interannual and Decadal Climate Variability in the Pacific. Each theme has a clear geographical focus for fieldwork and a surrounding area where analysis and modelling studies will be carried out. The focus of Southern Ocean fieldwork is the Weddell Sea where air-sea interaction affects both the deep thermohaline overturning circulation and the shallower intermediate-depth circulation that is involved in overturning circulations in all three subtropical oceans. Fieldwork in the Pacific theme, which is most directly relevant to VAMOS, focuses on the eastern tropics where large interannual variations of sea surface temperature mark the oceanic influence on the El Niño/Southern Oscillation (ENSO) cycle.
The Pacific programme is part of a broad international effort to understand and predict ENSO and its decadal variations of form and predictability. In particular the CORC observations are designed to supplement those TOGA observations now transitioning to an operational NOAA observing system, while CORC data-sensitive modelling addresses, in a research setting, the questions of integrating observations and dynamics that are addressed in an operational framework at NCEP. A team of observationalists, analysts, and ocean and atmospheric modellers from universities and NOAA laboratories are working together to make progress on this complex and important problem.
The objectives of the program are 1) to describe from observations how the tropical and subtropical Pacific are changing over seasonal-to-interannual periods, 2) to construct a dynamically consistent picture of how this happens, which can then be extendedto decadeal time scales, and 3) to study the predictability of these changes and their effect on the atmosphere.
A fundamental hypothesis of the work is that on interannual to decadal time scales, the oceanic advection of mass, heat and salt is crucial to the evolution of patterns of stored heat and freshwater and, through these patterns, to air-sea interactions and climate variability.
The overall scientific objective is to describe, simulate, and understand climate change in the ocean-atmosphere system of the Pacific basin on interannual and decadal time scales. To make significant progress toward achieving this objective, CORC has identified a number of scientific questions to be answered.
2. What are the relative importances of advection of heat by the ocean, surface heat fluxes and ocean mixing in generating and maintaining SST and heat storage anomalies on these time scales?
3. How are the extra-tropical atmosphere and ocean coupled together? What are the relative strengths of mid-latitude coupling and remote forcing of the mid-latitude atmosphere by tropical SST anomalies? Is there a cooperative coupling between the mid-latitude atmosphere and ocean that sustains slowly propagating SST and SLP anomalies? Do coupled mid-latitude modes (if they exist) have the ability to alter climate variability in the tropical Pacific?
4. How do decadal changes in upper ocean heat storage and SST alter the evolution of ENSO? Is the observed decadal variability of ENSO caused by mid-latitude variability, evidence of two-way coupling between the tropical and mid-latitude Pacific, or purely tropical in origin?
What is the atmosphere-ocean feedback responsible for any coupled modes of North Pacific variability? What determines the time scale? Is the time scale of the gyre response critical, or does it revolve around an advective time scale? Alternatively is the time scale set by the time it takes for subducted subtropical waters to upwell and impact equatorial SST?
The programme of new observations is designed to gain maximum advantage both from present in situ observing systems and from the global satellite observations of the sea surface that have recently come on-line. Continuing TOGA and WOCE observations, such as the TAO moorings, broad scale and high resolution XBT networks, surface drifter and ALACE float arrays, provide a substantial base on which to build. In addition to satellite SST, the more recent and dynamically revealing measurements of sea surface height from radar altimeters and wind stress from scatterometers is crucial. A central theme of the observational and analysis frameworks is to develop a statistical relation between sea surface height and subsurface density structure, which can be utilized to propagate information from the altimetric dataset downward through the water column. A primary requirement of broad-scale profiling then becomes the estimation of this correlation, rather than the far more demanding task of mapping the subsurface fields directly. Without such powerful advantages as are accorded by present in situ observations and satellite sensors, any feasible observing system that might be implemented would be too sparse for its objectives. With them, a substantial fraction of the variance in subsurface density and velocity structure can be recovered.
The second part of this programme focuses on the development of data-sensitive modelling. This can be thought of as using ocean dynamics to add to the information content of the datasets by adding constraints that the time evolution should obey known physics. The approach is complementary to corrective data assimilation techniques such as the one applied by NCEP. In the latter scheme, a dynamical model is initialized with data and run in a predictive mode with observed forcing. It is then corrected to match new data (a non-physical form of forcing) and run for a subsequent time interval. The objective is prediction and the internal dynamical inconsistency due to the corrections is not an issue. Our alternative approach will be to determine what initial and boundary conditions and forcing fields are consistent with ocean observations via the dynamical forward problem. It is a form of inverse problem, where the initial guess (with known error variance) of boundary and forcing fields is adjusted so that the model results reproduce the data. Model testing hinges on whether the model can be made to reproduce the observations within their error bars by altering the boundary and forcing fields within their error bars. Clearly, the ability to test the model depends on the amount and quality of constraining data. If the fit is successful, then the resulting dynamically consistent evolution is a 4-D interpolation of the observations, using the dynamical constraints to contribute additional information beyond what is contained in the observations.
The third part of the programme focuses atmospheric modelling and retrospective data analysis on the problem of atmospheric forcing by SST. Atmospheric modelling is used to determine how tropical (via teleconnections) and extra-tropical SST anomalies modulate storm track activity. Global datasets of atmosphere and ocean variables, extending from 500 m in the ocean to 200 mb in the atmosphere, are being constructed for the period 1955 to the present. These are analysed to determine whether ENSO evolved differently during different periods of the modern record and, if so, whether different feedback mechanisms operated at different times or whether the feedbacks were modulated by background decadal change. A further exercise tests various hypotheses of feedback mechanisms for the observed decadal variability. These analyses provide a valuable perspective as well as datasets for eventual extension of the data-sensitive models from their initial annual/interannual focus out to decadal scale.
The research strategy includes five projects:
2. Ocean observations: augment the existing in situ observing system in the eastern and central tropical Pacific to improve diagnosis of climate dynamics. Focus on transport and accumulation of heat and freshwater, and on ways of utilizing altimetry with scattered subsurface observations. The observational programme, as part of an extended Pacific climate observing network focused on tropical/extratropical exchanges, will provide valuable information on oceanic variability. Moreover, successful integration of the observations into the data-sensitive models will increase its effective resolution and its utility.
3. Air-sea fluxes: improve quantitative knowledge of surface fluxes and understand their relation to modelled ocean/atmosphere variability. Provision of the best possible forcing fields is critical to the success of data-sensitive modelling.
4. Analysis of past climate change: analyse historical observations to develop descriptions of phenomena and extend the climate record as a test of models and ideas about the oceanís role in climate.
5. Atmospheric modelling: diagnose atmospheric response to SST on climate scales and develop fast atmospheric models to predict this response. Focus on the crucial problem of this response at middle latitudes as a step toward improving the NCEP atmospheric model.
The CORC programme of ocean observations builds on existing measurements in the eastern and central tropical Pacific to investigate seasonal to decadal variability in that domain. The measurements form the foundation for an extended climate study of the Pacific Ocean, determining the variability in tropical/subtropical exchanges of heat and freshwater. Within the tropics they target the patterns through which advection contributes to the formation and evolution of large-scale anomalies via both surface and subsurface circulations. The concentration in part of the Pacific basin also provides the enhanced dataset which is required to adequately constrain data-sensitive models. Measurements include temperature/salinity profiling autonomous floats, near-surface velocity and temperature from drifters, eddy-resolving XBT/XCTD transects, and the development of a surface layer T/S profiler for deployment from volunteer ships.
There is presently a substantial array of Pacific Ocean observations targeting climate variability. The broad-scale XBT network provides temperature profile data to 760 m depth at approximately 2° (along track) by monthly resolution along a number of commercial shipping routes. These are supplemented by quarterly eddy-resolving transects along a subset of the routes. The total number of XBT profiles averaged about 1,500 per month for the entire Pacific Ocean during 1995. An additional set of temperature profiles comes from the TAO network, with 7 moorings between 8°N and 8°S every 15° of longitude. These moorings, which also measure velocity profiles at the equatorial sites, provide the high temporal resolution, which is required to observe rapid propagating features in the equatorial waveguide. An array of surface drifters is maintained in the Pacific to measure both velocity and sea surface temperature. While the ongoing observing system represents a valuable resource and has provided a wealth of information on climate variability in the upper ocean, it has a number of deficiencies which limit further study. It is these deficiencies, which are addressed by CORC:
ii) Lack of salinity. The eastern Pacific is a region where there is both large forcing and important advection of freshwater. Strong evaporative forcing in the southeast creates a high salinity water mass that is subducted as it flows westward in the South Equatorial Current. This gives rise to a strong meridional gradient in salinity in the equatorial thermocline. Strong hemispheric asymmetry in freshwater forcing results from the large precipitation in the northern ITCZ, about 5 meters per year, with low salinity waters carried mainly eastward by the North Equatorial Countercurrent. Finally, equatorward currents along the coasts of both North and South America carry cool, low salinity waters of subpolar origin into the tropics. Variability in the distribution of freshwater anomalies is likely to be a crucial diagnostic of interannual to decadal E-P and circulation patterns. This signal is unobserved in the present network. Moreover, the salinity anomalies in this region are a significant part of fluctuating density fields and hence important to the accurate calculation of steric height and geostrophic shear. The salinity problem is approached in three ways - with salinity sensors on autonomous profiling floats, with XCTD deployments on high density XBT/XCTD transects, and through the development of a recoverable sensor to profile surface layer salinity from merchant vessels.
iii) Depth limitation. Ocean-atmosphere interaction occurs through air-sea fluxes of heat and water, which are characterized by anomalies of SST. At low frequencies, however, these fluxes would destroy the SST anomaly that causes them unless ocean dynamics, particularly mixing and advection, can maintain the anomaly. Therefore understanding air-sea feedbacks on interannual to decadal time scales depends on knowing the underlying stratification and shear that determine the vertical exchanges and horizontal advection which, together with air-sea fluxes, govern SST evolution. Broadscale XBTs typically sample to 760 m. An extended depth range is required for calculations of geostrophic advection and also for interpreting the altimetric height field in relation to subsurface temperature structure. Autonomous profiling floats collect data to 1750 m, and the high density XBT/XCTD network is being used to test new XBTs with 2000 m range and improved fall rate determination.
iv) Lack of subsurface velocity. Geostrophic calculations of velocity generally provide upper ocean circulation estimates sufficient for climate purposes. Direct observations of velocity are, however, needed near the equator, where geostrophy becomes unreliable, and where the depth extent of frequent sampling does not capture all the shear. Where variability plays an important role in transport, current-following observations can elucidate the mechanism. For example, WOCE sampling at 1000 m revealed an unexpectedly strong field of zonally polarized variable flow. Profiling floats in the CORC array are set to follow flow on the 15° isotherm, providing both patterns of flow on that surface and a reference for geostrophic calculations.
v) Resolution limitations. Even with the observational enhancements that CORC is implementing, the extended array will still have sparse resolution - both spatially with regard to broadscale profiling, and temporally with regard to the quarterly transects along high density XBT/XCTD tracks. These resolution limitations are diminished by combining subsurface profiling data with satellite altimetry.
vi) Ekman layer physics. Directly driven Ekman currents are an important component of the upper ocean meridional cell which advects heat salt and mass from the equator. Equatorward of 15° latitude, under the Trades, the meridional Ekman currents tend to be twice as strong as the meridional geostrophic currents. Yet today, ocean models lack the ability to produce Ekman currents correctly. Comprehensive observations of upper ocean currents in many seasons and in many locations are being made to analyse why this deficiency occurs and to correct it.
The combination of temperature and salinity profile data with satellite altimetry is a major thrust of the CORC observations. If the profile data are used to determine the correlation of surface height with subsurface density structure, then it is possible to exploit the superior spatial and temporal resolution of the altimeter by projecting surface height onto the subsurface density and temperature fields. In this way, a significant fraction of the unresolved subsurface variance can be recovered. Specific sampling plans in the observational programmes are as follows:
1. Profiling floats
The profiling float array is building toward an operating inventory of 75 floats by deploying 25 per year, each float profiling on 15-day cycle and operating for 3 years. Floats profile to 1750 m depth but, between profiles, track flow on the 15° isotherm. Profiling to 1750 m extends the depth of samples for geostrophic shear calculations and provide temperature/salinity samples in a relatively stable water mass with which to correct any drift in the conductivity sensor. While the 15° isotherm does not outcrop in the cold tongue it is likely among the densest waters involved in equatorial upwelling and is a candidate for possible subduction links from the subtropics to the tropics.
Sounding Oceanographic Lagrangian Observer (SOLO) floats, developed with earlier CORC funding, are being used to improve reliability and operational efficiency over the predecessor ALACE float. Specific efforts at both SIO and WHOI are directed at improving longevity of the FSI conductivity. The complete array will deliver 1800 temperature and salinity profiles and velocity measurements per year. These data supplement the existing NOAA broadscale XBT network by filling unsampled areas, extending coverage to greater depth and providing critical salinity profiles and direct velocity observations. The main objectives of broadscale profiling are: (i) to determine patterns of variability in temperature, salinity and velocity, (ii) to determine the correlation statistics between surface height and subsurface density fields for use with satellite altimetry, and (iii) to provide interior data for constraining data-sensitive models.
2. High density XBT/XCTD transects
A Pacific-wide network of high density XBT/XCTD transects has been initiated and continued under the auspices of WOCE, CLIVAR and the first phase of the NOAA/SIO/LDEO Consortium. The present effort is continuing the previously initiated Consortium transects across the South Pacific (Valparaiso to Auckland) and across Drake Passage, and we will begin a new transect between Valparaiso and Honolulu. For the eastern and central tropical Pacific, the total network then includes zonal lines along the northern and southern boundaries of the domain and meridional lines crossing the equator in the central and eastern Pacific. The eddy-resolving XBT measurements, with sparse XCTDs, will target patterns of variability in meridional advection across the northern and southern boundaries and zonal advection in the tropics. Since 3 of these 4 lines already include multi-year time series (10 years for the central Pacific line), it is possible to begin immediately considering seasonal-to-interannual variability in the study domain. Objectives of high density sampling are: (i) to measure patterns of transport variability, (ii) to close oceanic heat and freshwater budgets (together with storage and air-sea fluxes) over large ocean areas, (iii) to provide boundary value information for the data-sensitive modelling, (iv) to determine the adequacy of model resolution through comparison of integral transports in models to those from highly resolved data, and (v) to determine correlation statistics between surface height and subsurface density fields.
An additional project is developing and testing a tethered recoverable T/S profiling instrument, with depth capability of about 100 m at 20 knot speed. Such an instrument would be highly valuable deployed in the high resolution network or on other volunteer ships. Low cost of profiles will enable tight spatial resolution in areas of significant T/S variability.
3. Surface drifters
The objectives of the surface drifter are to gather observations on the scales which resolve the seasonal and interannual evolution of the near surface currents and SST. This objective can be achieved because during the onset of the 1991-92 ENSO sufficient numbers of drifters were deployed in the central and western Pacific to capture the anomalous movement of water parcels to the east during that event. In the eastern tropical Pacific there have been sufficient observations of surface velocity to define the space scales of the seasonal cycle, but not the interannual variations. A concentrated effort is thus being made there, as was done in the western Pacific during TOGA/COARE. Drifters are being deployed on the known scales of seasonal signals in the anticipation that the interannual evolutions will be comparable.
Two sources of drifters are being utilized. The CLIVAR drifter array is being augmented to a total of 170 drifters in the region 30°N to 30°S, east of 150°W. Those deployed in the eastern equator for CLIVAR (about 70 units per year) rapidly diverge from the equator and transit through the regions of our study. Secondly, CORC deployments are being made from the XBT/VOS network and the TAO deployment vessel (100 units per year). Special consideration is given to the regions near the continental boundaries, where with the aid of the Colombian and Peruvian oceanographers, additional drifters can be deployed. An effective conduit of SST and subsurface anomaly dispersion from the equator to higher latitude is through Rossby and Kelvin wave processes, so a concentration of drifter augmentation is initially being done along the eastern boundary of the tropical Pacific. The drifter data make the following contributions:
(ii) Drifter data are used to test hypotheses of upper ocean thermal balances. During the warm phases of the interannual evolution, abnormally weak tropical currents are expected. In that case, local air-sea interaction will tend to be the principal process in the SST evolution. During the cold phases, the three-dimensional circulation in all of the tropical currents will be amplified and significant horizontal SST gradients will be established. It is anticipated that the surface advection of heat will play an increasingly important role in the evolution of SST.
4. IMET sensors
A realistic description of air/sea fluxes is central to understanding how the ocean responds to atmospheric forcing, and to understanding how the ocean feeds back to influence the atmosphere. Previous work has demonstrated that the primary direction of this interaction is atmosphere-forcing-ocean on monthly-interannual time scales in the extratropics, and an ocean model (with mixed layer) forced by monthly fluxes produces quite realistic anomalous upper ocean temperature variability at seasonal-decadal scales over a few decades in the North Pacific. Ocean-forcing atmosphere becomes more important in the tropics. However, the relative weight of ocean feedbacks in the subtropics (equatorward of 20°) is not very well understood, nor is their importance generally well known as time scales increase from seasonal to interdecadal. Modelled ocean currents driven by estimated wind stress have not been validated using observations. The anomalous components of evaporation vs. precipitation over the oceans is not well described and has not been examined in comparison to surface salinity fluctuations. The CORC study provides an opportunity to better test these interactions using a suite of estimated fluxes together with observed and modelled ocean/atmosphere data relating to the heat and fresh water variations.
IMET sensors are being deployed on selected volunteer vessels to provide quality control and research quality ground truth for the marine observations employed above, and as a basis for improved flux formulations. The period of concentration of the historical data is 1992-1997, although earlier years may be included when data are available. Monthly averages will be produced, but shorter intramonthly periods (weekly and perhaps daily) are also be considered. Surface marine weather observations (ships and buoys: wind, temperature, pressure, humidity, etc.) and satellite remote sensed data (wind (ERS and NSCAT), precipitation (microwave from NASA and combination microwave/IR), temperature, short wave radiation are being used. Comparisons between various derived products from the observed data will be conducted.
f) PIRATA (A. J. Busalacchi and C. A. S. Tanajura)
The interaction of the atmosphere and the tropical oceans is a subject of both scientific interest and societal importance, as demonstrated through the accomplishments of the international TOGA programme (1985-1994). The primary focus to date has been in the Pacific sector, owing to the prominence of El Niño and the Southern Oscillation in global climate. At the same time, it is well recognized that atmosphere-ocean interactions throughout the global tropics are potentially important to the earth's climate variability on the time scales of years to decades. Among the regions of particular interest, and the focus of this project, is the tropical Atlantic.
The tropical Atlantic is characterized by a strong seasonal cycle, deriving ultimately from radiative forcing and land-sea contrast, but strongly modified by atmosphere-ocean coupling. Superimposed on this seasonal cycle, there appears to be two modes of interannual and longer-term variability. The so-called dipole mode, which operates primarily at decadal and longer time scales, involves north-south interhemispheric variations in SST. This mode has been linked to severe climate anomalies in Northeast Brazil (Nordeste) and in parts of Africa (Sahel and Sub-Sahel). A second equatorial mode, operating preferentially at seasonal and interannual time scales, has many similarities to the ENSO phenomenon in the Pacific, and involves trade wind variations and the excitation of equatorial Kelvin and Rossby waves. This mode has been associated with rainfall extremes in the Gulf of Guinea and marine ecosystem disruptions in the Benguela current area. It is not presently known whether the two modes are related. Our current understanding of these phenomena is limited, and to a great extent this is because of the lack of routine, quality controlled, oceanic and atmospheric observations in the region. The observation system that exists relies mainly on volunteer observing ships and occasional research vessels that pass through the area. The generally infrequent oceanographic cruises in much of the region are insufficient even for monitoring interannual variability. Recently, a new observational programme known as PIRATA (Pilot Research Moored Array in the Tropical Atlantic) has been initiated by Brazil, U.S., and France in part to remedy this crucial lack of oceanic and atmospheric data in the tropical Atlantic. The scientific goals of PIRATA are:
The technical and capacity building goals are:
These data will be useful for both weather and climate prediction for the region. Among those who will use the data in research or operational mode are: IRI, CPTEC, NCEP, ECMWF and GFDL. During its experimental pilot phase in the years 1997 to 2000, PIRATA will demonstrate the feasibility of solving the engineering, logistical and maintenance problems that might arise in the implementation of such an observational system in South America. The idea of a pilot project is to establish the appropriate technology for a meaningful and cost-effective observational system in the Atlantic in an incremental and efficient manner. After its completion, a careful evaluation of the PIRATA would determine if recommendations for a long-term continuation and/or expansion of the array in the tropical Atlantic are appropriate. It is envisioned this would form a substantial contribution to GOOS and GCOS. The international research effort under the World Climate Research Programme (WCRP), especially the post-TOGA activities (CLIVAR-GOALS, CLIVAR-VAMOS) will greatly benefit from the additional high quality data that will be provided by PIRATA.
In addition to a better understanding of the local coupled dynamics in the tropical Atlantic, it is expected that PIRATA will help in determining the linkages between the Atlantic and ENSO. The data will also help in determining the relationships between regional climate variations and agricultural/fisheries impacts for South America and West Africa. Ultimately, it is expected that better data will aid the development of useful forecast models and forecast capability for the region.
This pilot observing system for the tropical Atlantic Ocean follows on the scientific successes of TOGA and on the proven technology that is operative in the Pacific Ocean, particularly in the in situ observational system of approximately 70 buoys that form the TOGA-TAO array. PIRATA has been funded to install and maintain an array of 12 moored ATLAS buoys during the years 1997 to 2000 for monitoring the surface variables and upper ocean thermal structure at key locations in the tropical via satellite (e.g. CLS-Argos) in real-time (once a day). The data is available to all interested users in the research or operational communities in the Web Site www.ifremer.fr/orstom/pirata/pirataus.html. The total number of moorings is a compromise between the need to put out a large enough array for a long enough period of time to gain fundamentally new insights into coupled ocean-atmosphere interactions in the region, while at the same time recognizing the practical constraints of resource limitations in terms of funding, shiptime, and personnel. The objectives of the PIRATA array then, are to demonstrate scientific success in a limited geographical region for a limited duration of time, as a guide to more serious long range planning.
It is expected that at the end of the pilot phase of PIRATA, other nations will join in the maintenance and possible expansion of PIRATA to constitute a tropical Atlantic Ocean observing system and component of GOOS and GCOS. The programme is appropriately multinational since variations in the tropical Atlantic affect many nations in the Americas and Africa. PIRATA will create a true partnership in the study of tropical oceanography and ocean-atmosphere interactions in the Atlantic by bringing key research institutions in the region to a continuing collaboration. The observations that PIRATA will acquire are in direct response to requests from the international scientific community that these data be obtained in order to investigate the predictability of the coupled climate system in the region. Thereby, PIRATA addresses directly the call from several international working groups dealing with tropical ocean climate studies, including those from TOGA, VAMOS and the OOSDP.
In recognition of the importance of a regional approach to the study of global change, eleven countries of the Americas signed an agreement establishing the Inter American Institute for Global Change Research on May 13th, 1992, at Montevideo, Uruguay: Argentina, Bolivia, Brazil, Chile, Costa Rica, Dominican Republic, Mexico, Panama, Peru, United States, and Uruguay.
The IAI focuses on the 1) increased understanding of global change related phenomena and the societal implications of such phenomena, 2) increased overall scientific capacity of the region, 3) enhanced regional relationships, establishment of new institutional arrangements, and 4) promotion of the open exchange of scientific data and information generated by the Institute's research programmes, implementation of IAI Training and Education Programs.
The following research themes have been identified as initial properties of the IAI: 1) tropical ecosystems and biogeochemical cycles, 2) impact of climate change on biodiversity, 3) ENSO and interannual climate variability, 4) ocean/atmosphere/land interactions in the inter-tropical Americas, 5) comparative studies of oceanic, coastal and estuarine processes in the temperate zones, and 6) comparative studies of temperate terrestrial ecosystems and high latitude processes.
Although they are primarily concerned with the science of climate assessment and prediction on seasonal-to-interannual time scales, the regional programmes organised under the CLIVAR/GOALS contribute to a broader range of human endeavours. The participation of IAI is of special importance to VAMOS in view of the Institute's major thrust on the societal impacts of climate variability over the Americas. VAMOS will provide IAI researchers with opportunities for enhanced co-operation with other science programmes focusing on the American climate system, particularly with the large and regional scale modelling efforts developed in PACS and GCIP. It will also provide enhanced co-ordination of field activities in the American sector.
The South Atlantic Climate Change programme (SACC) effort is an international and multidisciplinary programme to study the effects of climate change in the southwestern South Atlantic. The oceanic conditions in the Western South Atlantic Ocean affect the climate of a region inhabited by approximately 200 million people, whose economic resources are closely tied to agricultural and fisheries activities. The effects of climatic variations on the general well-being of this region have become evident during the last few decades as drought periods produced dramatic changes in Brazil's cattle population while precipitation excess produced significant expansions of Argentina's farming regions. While it is obvious that these issues are most relevant to communities in South America, such climate anomalies are also an inextricable part of variations in the global climate system. This region has a well documented mid-latitude climate anomaly pattern that has been linked to global phenomena such ENSO, while recent results point toward important contributions from the Antarctic Circumpolar Wave. The fairly simple coastal geometry of this region combined with the emerging international scale expertise in Argentina and Brazil make this an ideal region in which to explore the important IAI/CLIVAR goal of understanding meridional climate linkages. The multinational and multidisciplinary studies being developed or planned by the SACC will significantly expand our knowledge of oceanic variations in the region and how they relate to, and coupled with, variations in Earth's climate system on relatively short time scales.
The main goal of the SACC programme is to understand the interactive relationship of the southwestern South Atlantic SST and the larger scale climate behaviour. The specific objectives are to:
SACC resulted from efforts initiated as part of the IAI Start Up Grant programme and is today a well established programme sponsored by IAI and several other agencies in Argentina, Brazil, Uruguay and the U.S
An atmospheric sounding network sponsored by PACS (PACS-SONET) has been operating in Central America and northwestern South America since mid-1997, as part of a research project to investigate rainfall variations over Central America during the warm season. This network has consisted of between 12 and 18 pilot balloon (wind only) stations, and continues to operate with daily soundings being made at most sites. Three stations are operating in southeastern Mexico, one in Nicaragua, two in Costa Rica, one in Panama, one in Colombia, 3 in Ecuador, and up to 5 in Peru. Soundings are made at San Cristobal Island in the Galapagos Islands and have been made on Cocos Island, Costa Rica. The sites are maintained through support of PACS, with contributions by various countries. (The network is designed to end observations on October 31, 1998).
The program in the Dinamica do Ecossistema de Plataforma da Regiño Oeste do Atlantico Sul (DEPROAS; Dynamics of the Ecosystems of the Continental Shelf in the Southwestern Atlantic) has two goals:
DEPROAS is a multi-disciplinary program, involving physical oceanography, biological oceanography, geological oceanography, and meteorology. It is also a multi-institutional (IOUSP, INPE) enterprise, with collaborations with the University of Maryland, SCIO and Centre ORSTOM). Several social benefits are expected. For example, the results will contribute to a better understanding of the cause and effects of fluctuations in fish population, to obtain proper information for adequate coastal management, and to assess the economical relevance of policies (ports, oil, fishing potential and tourism).
PRECURSOR is a proposed, combined meteorological and oceanographic observational and modelling pilot project focused on the Intra American Seas (IAS). IAS comprise the combined Caribbean Sea, Gulf of Mexico, Straits of Florida, plus the adjacent waters of the western North Atlantic between ca. 5° and 30°N and ca. 55°W to the coastline of the Americas. (Bruce Albrecht and Chidong Zhang are responsible for the atmospheric observations, and Kevin Leaman and Doug Wilson for the oceanic observations, while Shuyi Chen is responsible for the atmospheric model, and Chris Mooers for the oceanic model.) It plans to explore the meso-scale and synoptic scale atmospheric plus meso-scale and seasonal oceanic circulation processes, and their interactions, in the largely unexplored southwestern subdomain of the IAS over the course of two years (1999/2000). Here is the Panama-Colombia Gyre, a large cyclonic recirculation cell that overlies the Colombia Basin of the southwestern Caribbean Sea and interacts with the Caribbean Current and the continental margin. A pair of interacting and highly variable upper level cyclones are embedded in the larger cyclonic recirculation cell. They overlie a pair of anticyclones that interact with the bottom topography.
Participants are from U.S. (RSMAS/AOML), Panamá, and Colombia at this stage. PRECURSOR aims to determine the importance of meso-scale resolution and processes in estimating the impact of intense precipitation on the oceanic circulation in the Panama-Colombia Gyre, the air-sea fluxes, and the moisture flux from the region. It will also take other initial steps in examining land-air-sea interaction, including the regional hydrological cycle. Because the Gyre is the locus of strong air-sea fluxes according to climatology and is known to have strong diurnal (meso-scale), easterly wave (synoptic scale), and intraseasonal (TIO) variability, it is suspected to play a significant role in regional climate, which is a perspective that the pilot study should begin to bring into focus. Based on the results of PRECURSOR, it is intended to develop a more expansive programme of research, which is anticipated to contain components treating coastal ocean ecology; for example, the physical transport and dispersal of fish larvae between their spawning and nursery grounds. The initial observing strategy includes two moored current meter arrays, drifters with acoustic rain gauges, repeated CTD/ADCP/GPS rawindsonde transects, and additional VOS tracks. The meteorological strategy also includes diagnostic studies of satellite scatterometer winds, MSU precipitation, OCR data, NCEP/NCAR reanalysis and SST analysis, and the oceanographic strategy also includes use of coastal (over the horizon) radar-derived surface current data. The modelling strategy, for both the atmosphere and ocean, involves meso-scale resolution over the entire IAS (the atmospheric model covers a slightly larger domain; for example, extending inland over northern South America.) Issues of ocean-atmosphere coupling will proceed with the analysis of one-way coupling issues first and of two-way coupling progressively.
From the VAMOS perspective, PRECURSOR's hypotheses are:
It is anticipated that the PRECURSOR pilot project will lead to refinements and extension of the above hypothesis list, including topics regarding the IAS warm pool and compensating subsidences.
l) WMO Tropical Meteorology Research Programme (A. Grimm)
The WMO Commission of Atmospheric Sciences (CAS), in its twelfth session, recommended that the proposed activities in the Tropical Meteorology Research Programme (TMRP) involving the study of the Asian and Australian monsoon should be extended to also include American monsoon studies.
The purpose of TMRP is to promote and co-ordinate research activities by Members in high priority areas of tropical meteorology. The emphasis is on weather system scale, except for monsoons and drought related studies, which emphasize variability and prediction at the regional and seasonal scale.
In the redefinition of the TMRP elements, a new project on American Monsoon Studies was included (M3). This new project aims to enable CAS support of activities developing in the Americas on monsoon studies, in co-ordination with the CLIVAR/GOALS components of the WMO/ICSU World Climate Research Programme on the monsoon, including the Pan American Climate Studies programme.
The programmes ECLAT (Etudes Climatiques de l'Atlantique Tropical and ECOP (Etudes Climatiques de l'Océan Pacifique tropical) are the French contributions to the CLIVAR international programme in the tropical Atlantic and Pacific oceans.
The aim of the ECLAT programme is to improve our understanding of the role of the Tropical Atlantic in the climate variability, focusing on its effects on a regional scale. Among the several issues addressed by CLIVAR, ECLAT intends to contribute answering these two fundamental questions:
ECLAT addresses the relationship sbetween remote forcing and local coupling of the tropical Atlantic Ocean in order to improve the predictability of rainfall in the bordering West African and South American countries. ECLAT was initiated by ORSTOM, and it started in 1997, in partnership with research institutes of West African countries and Brazil. It will include scientific teams from several French research institutes as well as from other countries. Due to the peculiarities of the Atlantic Ocean variability, as revealed by previous studies, ECLAT overlaps the GOALS (Seasonal to Interannual Variability and Predictability of the Global Ocean-Atmosphere-Land System) and DecCen (Decadal to Centennial Climate Variability and Predictability) components of CLIVAR.
ECLAT is a multidisciplinary programme that includes all components of the climatic variability associated with the ocean/atmosphere/continent coupling. It is based on a comprehensive observations programme including in situ and satellite observations and calling on real time data transmission, complemented with oceanographic cruises. Process studies, to a large extent, will use numerical simulations, using a complete hierarchy of models.
Several elements of the observing systems have been handled for years by the ORSTOM Centre in Brest, mostly the Ship of Opportunity network, with measurements of winds, sea surface temperature, sea surface salinity and temperature profile (XBT) along several lines crossing the tropical Atlantic. The master piece in the observational network of ECLAT is PIRATA. Specialized research cruises will be done during the course of this long-term program. In particular, the EQUALANT cruise will study of the ocean circulation variability and the ocean-atmosphere interactions in the equatorial Atlantic. The main objectives of the cruise are to examine the: 1) large scale variability of the thermohaline circulation in the 6°N-6°S equatorial band 6° of the Atlantic, 2) redistribution of mass, heat and tracer, between surface water and deep layers, 3) role of equatorial processes such as upwelling and deep jets in this redistribution and in its high frequency variability, and 4) variability of heat fluxes at the ocean-atmosphere interface in the equatorial upwelling area.
EQUALANT represents a combination of French WOCE cruises and will take place between an American experiment in 1998 and a German experiment in 2000, in the same area, in order to study the large scale variability of the different parameter distributions. Hydrographic, current and tracer measurements will be done along six meridional sections across the equator. During the cruise, the high frequency variability will be studied through repeated stations at the location of PIRATA moorings. In addition to altimetric measurements and modelling work, PIRATA and EQUALANT are complementary ways to study the variability of the ocean, from the surface to the bottom, and the role of the deep ocean - surface ocean - atmosphere interactions in this variability.
ECOP (Etudes Climatiques de l'Océan Pacifique tropical) is a continuation of the French effort in the tropical Pacific during the 1985-94 TOGA (Tropical Ocean and Global Atmosphere) programme and its 1992-93 COARE (Coupled Ocean-Atmosphere Response Experiment) sub-program. As such it is part of the international CLIVAR/GOALS program. ECOP is divided in three components:
Several French research teams are involved in this program, but the lead is taken by the SURTROPAC (Survey of the Tropical Pacific) group at the Centre ORSTOM of Noumea, New Caledonia.
With the continuation of long-term measurements in the tropical Pacific (e.g., Ship of Opportunity network), the strong involvement of several research teams in the TOPEX/Poseidon mission, and the use of different classes of model, data assimilation is an important tool for this programme.
n) GOOS (http://ioc.unesco.org/GOOS)
The Global Ocean Observing System (GOOS) is intended to be a permanent global system for observations, modelling and analysis of marine and ocean variables needed to support operational ocean services worldwide.
GOOS will provide: (i) accurate descriptions of the present state of the oceans, including living resources; (ii) continuous forecasts of the future conditions of the sea for as far ahead as possible; and (iii) the basis for forecasts of climate change. GOOS is being implemented by national and international facilities and services
o) GOOS-BRAZIL (http://www.labmet.io.usp.br/~goos-br/ingles/)
GOOS-BRAZIL, much like its international counterpart, is to (i) use continuous, multidisciplinary monitoring of the oceans aims to predict phenomena and processes that exert direct impact on issues related to the marine environment, such as its preservation, conservation and sustainable use, (ii) identify priorities for operational oceanography based on what will bring the greatest socioeconomical benefits, (iii) assess the current state of systematic ocean monitoring already underway, and (iv) provide services, data products and necessary information for the management of the marine environment.
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