Guillermo Podestá

Ocean color: Availability of the global data set

The National Aeronautics and Space Administration/ Goddard Space Flight Centers Nimbus Project Office, in collaboration with the NASA/GSFC Space Data and Computing Division, the NASA/GSFC Laboratory for Oceans and the University of Miami/Rosenstiel School of Marine and Atmospheric Science, have undertaken to process all data acquired by the Coastal Zone Color Scanner (CZCS) to Earth-gridded geophysical values and to provide ready access to data products [Esaias et al., 1986]. An end-to-end data system utilizing recent advances in data base management and both digital and analog optical disc storage technologies has been developed to handle the processing, analysis, quality control, archiving and distribution of this data set. A more complete description of this system, which has been fully operational for the past 2 years, is in preparation. The entire Level-1 data set (see Tables 1, 2) has been copied from magnetic tape to digital optical disc, and all data from the first 32 months (50% of the total scenes acquired, and covering the period November 1978 through June 1981) have been processed to Levels 2 and 3 and are now available for distribution. The remainder of the data set should be completed and released by fall 1989.

Research on Coupled Human and Natural Systems (CHANS): Approach, Challenges, and Strategies

William J. McConnell, James D. A. Millington, Nicholas J. Reo, Marina Alberti, Heidi Asbjornsen, Lawrence A. Baker, Nicholas Brozov, Laurie E. Drinkwater, Scott A. Drzyzga, Jose, Fragoso, Daniel S. Holland, Claire A. Jantz, Timothy Kohler, Herbert D. G. Maschner, Michael Monticino, Guillermo Podesta, Robert Gilmore Pontius, Jr., Charles L. Redman, David Sailor, Gerald Urquhart, and Jianguo Liu. (2011). Research on Coupled Human and Natural Systems (CHANS): Approach, Challenges, and Strategies. Bulletin of the Ecological Society of America April: 218-228.

Responding to stakeholder's demands for climate information: from research to applications in Florida

Abstract Previous research shows that Floridas climate and agricultural production are influenced by the El Nino-Southern Oscillation, suggesting that farmers and ranchers might use new methods of climate forecasting to modify management, increase profits and reduce economic risks. The purposes of this paper are to describe the framework used by a Florida Consortium (FC) of researchers to assess the potential use of climate forecasts in agricultural decision-making and to summarize what was learned in the research process. The framework includes components for generation, communication and use of climate information as well as an implementation and evaluation component. Results showed that winter months are affected most by ENSO phase (higher rainfall and lower temperatures in El Nino years and the opposite during La Nina years). Yields of most crops were significantly associated with ENSO phase as were prices of some commodities. Through various mechanisms of interacting with farmers, ranchers, and extension faculty, we learned that interest in climate forecasts varied widely from highly optimistic to skeptical, and that these clients had good ideas of how to vary management if they have good forecasts. Case studies aimed at understanding potential value and risks associated with use of climate forecasts were conducted for winter fresh market tomato, cow-calf operations, and peanut production. Analytical results, confirmed by interactions with clients, showed significant value in using climate forecasts to alter specific decisions. Risks of using climate information varied among commodities, with considerable risk found in tomato due to the strong link between production and price. Perhaps the most important lesson learned was the importance of engaging trusted advisors in research and outreach efforts. A major output of the project was the close cooperation established between the FC and the Florida Cooperative Extension Service. Prospects for sustaining a climate information program in Florida are high due to joint research and extension initiatives.

The Vitória Eddy and Its Relation to the Brazil Current

In late austral summer 1991 a cyclonic thermocline eddy was detected in the subtropical western South Atlantic off the Brazilian shelf near the city of Vitoria. This Vitoria eddy was tracked for 55 days by surface drifters drogued at 100-m depth. The drifters had been deployed in the western boundary current regime by FS Meteor as part of a basinwide surface current study. The analysis of a combined CTD/XBT section across the Vitoria eddy, together with drifter data and satellite images of the thermal surface structure revealed the unexpected complexity of the region. The eddy interacted not only with the local topography and the Brazil Current, located farther offshore, but also with an extended upwelling regime north of Cabo Frio. The hydrographic and kinematic properties and anomalies of the Vitoia eddy are analyzed and compared with similar vortices described elsewhere in literature.

Sea surface velocities from sea surface temperature image sequences: 2. Application to the Brazil‐Malvinas Confluence area

An inverse variational model is applied to four exceptionally cloud-free sea surface temperature image sequences of the Brazil-Malvinas Confluence area for the purpose of estimating sea surface velocity fields. The velocity fields are constructed by minimizing a mixed layer integrated form of the heat balance equation while the horizontal divergence and vorticity of the flow field are controlled. The source terms involved in the heat balance are determined by fitting a polynomial to diurnal temperature variations as a function of temperature and longitude. A sensitivity study of the solution to perturbations of the weights imposed to the constraints on divergence and vorticity as well as of the representation of the source terms yields error fields associated with the velocity. A comparison of the estimated velocity fields with available concomitant in situ velocity measurements shows that the fields are realistic. Errors are of the order of 15–20% in magnitude and 20°–25° in direction. These errors fall within the error bars of 25–30% in magnitude and of 30°–35° in direction, except for the summer image series. Surface velocities of 0.5–0.6 m s−1 are obtained across the Malvinas Current. They are > 1 m s−1 in the frontal region, in the Brazil Current overshoot, and in warm and cold core rings and vary between 0.3 and 0.8 m s−1 in the Brazil Current. With some hypotheses on the vertical shear of the horizontal flow the transport of the Malvinas Current is estimated to be 25±5 Sv between 41° and 40°S.

IMPACT OF CLIMATE INFORMATION ON REDUCING FARM RISK BY OPTIMIZING CROP INSURANCE STRATEGY

Predictability of seasonal climate variability associated with the El Nino Southern Oscillation (ENSO) suggests a potential to reduce farm risk by selecting crop insurance products with the purpose of increasing farm income stability. A hypothetical 50% peanut, 50% cotton, non-irrigated, 40 ha (100 ac) north Florida farm was used to study the interactions of different crop insurance products with ENSO-based climate information and levels of risk aversion under uncertain conditions of climate and prices. Crop yields simulated by the DSSAT suite of crop models using multiyear weather data combined with historical series of prices were used to generate long series of stochastic income distributions in a whole-farm model portfolio. The farm model optimized planting dates and simulated uncertain incomes for 50 alternative crop insurance combinations for different levels of risk aversion under different planning horizons. Results suggested that incomes are greatest and most stable for low risk-averse farmers when catastrophic (CAT) insurance for cotton and 70% or 75% actual production history (APH) for peanut are selected in all ENSO phases. For high risk-averse farmers, the best strategy depends on the ENSO phase: (1) 70% crop revenue coverage (CRC) or CAT for cotton and 65% APH for peanut during EL Nino years; (2) CAT for cotton and 65%, 70%, or 75% APH for peanut during neutral years; and (3) 65% to 70% APH, or CAT for cotton and 70% APH for peanut during La Nina years. Optimal planting dates varied for all ENSO phases, risk aversion levels, and selected crop insurance products.

Error Characteristics of the Atmospheric Correction Algorithms Used in Retrieval of Sea Surface Temperatures from Infrared Satellite Measurements: Global and Regional Aspects

Abstract A database of cotemporal, collocated satellite and in situ observations is used to examine the association between the brightness temperature differences measured by the thermal infrared channels (T45) of the Advanced Very High Resolution Radiometer (AVHRR) and water vapor estimates (ω) derived from the Special Sensor Microwave Imager (SSM/I). This channel difference is used to estimate the atmospheric correction (due mostly to water vapor absorption) in sea surface temperature (SST) algorithms. The association between T45 and ω is found to be greatest for tropical latitudes; for mid- and high latitudes, the association is best during summer. However, the association tends to decrease toward mid- and higher latitudes during other periods. SST residual errors (satellite − buoy) show a negative mean in the Tropics, suggesting undercorrection for water vapor attenuation in the Tropics. This underestimation is explicitly shown for SST residuals in the high-water-vapor regimes of the Arabian Sea. In m...

Intermediate water in the Brazil‐Malvinas Confluence Zone: A Lagrangian view

The subsurface flow within the subantarctic and subtropical regions around the Brazil-Malvinas (Falkland) Confluence Zone is studied, using daily hydrographic and kinematic data from four subsurface floats and a hydrographic section parallel to the South American shelf. The float trajectories are mapped against sea surface flow patterns as visible in concurrent satellite sea surface temperature (SST) images, with focus on the November 1994 and October/November 1995 periods. The unprecedented employment of Lagrangian θ-S diagrams enables us to trace the advection of patches of fresh Antarctic Intermediate Water (AAIW) from the Confluence Zone into the subtropical region. The fresh AAIW consists of a mixture of subtropical AAIW and Malvinas Current core water. Within the subtropical gyre, these patches are discernible for extended periods and drift over long distances, reaching north to 34°S and east to 40°W. The cross-frontal migration of quasi-isobaric floats across the Confluence Zone from the subtropical to the subantarctic environment is observed on three occasions. The reverse process, float migration from a subpolar to a subtropical environment was observed once. These events were located near 40°S, 50°W, the site of a reoccurring cold core feature. Subsurface float and SST data comparison reveals similarities with analogous observations made in the Gulf Stream [Rossby, 1996] where cross-frontal processes were observed close to meander crests. The limited number of floats of this study and the complex structure of the Brazil-Malvinas Confluence Zone, however, restricts the analysis to a description of two events.

Environmental Citizenship in Latin America: Climate, Intermediate Organizations, and Political Subjects

In recent decades, the impacts of climate on society and on human well-being have attracted increasing amounts of attention, and the forecasts that predict such impacts have become more accurate. Forecasts are now distributed and used more widely than they were in the past. This article reviews three cases of such use of forecasts in Latin America. It shows that in all cases, the users are concentrated in particular sectors and regions (agriculture in the Argentine pampas, fisheries on the Peruvian coast, water resources in northeastern Brazil) and that the forecasts are distributed not by government agencies but by intermediate organizations—semistatal organizations or nongovernmental organizations. It draws on the concept of environmental citizenship to discuss these cases and assesses them for such attributes of citizenship as equity, transparency, accountability, and promotion of collective goals. It traces the implications of these cases for the current era of global warming.

Analysis of a general circulation model product: 1. Frontal systems in the Brazil/Malvinas and Kuroshio/Oyashio regions

In the present paper (part 1 of 2), the product of the Semtner and Chervin general circulation model (GCM) is compared with available observations in the frontal areas of the Brazil/Malvinas and the Kuroshio/Oyashio confluences. The dimensionality of the systems studied is reduced by using the empirical orthogonal functions (EOF) and frontal density methods. The two sets of data utilized to validate the model are the sea surface temperature (SST) from the satellite observations and temperature fields product from the GCM at levels 1 (12.5 m), 2 (37.5 m) and 6 (160 m). Comparisons are made between the dominant empirical modes and the locus of maximum probability for observations and model product. The model reproduces intense thermal fronts at the surface and in the upper layers. In the upper layer (level 1) they are induced by the internal dynamics of the model and not by the restoring of the model to climatology alone. The variability of these fronts is less pronounced in the model than in the observations. The dominant period in the observations is annual with contributions of semiannual and high frequency oscillations. In the model, the dominant variability is also annual at all analyzed levels. A semiannual oscillation contributed to a lower degree and is related to eddies that, in the model, have an annual and semiannual periodicity. For the regions examined, the location of the fronts are reproduced in the model within differences of 4° to 5° with observations. In the Brazil/Malvinas region, the Confluence front is reproduced approximately 4° towards the west of the observed front. This appears to be due to the resolution of the model that, in a 0.5° × 0.5° grid, does not resolve the sharp slope at the edge of the Argentine continental shelf. The maximum southward penetration of the warm tongue of Brazil waters occurs in the model approximately 4° towards the north. This is related to the fact that, in the model, the Malvinas transport doubles the one derived from the observations. This might be due to the effect of a large modeled transport for the Circumpolar Current or, again, to a poor resolution of the topography. In the Kuroshio area, the Oyashio front, which in observations is more pronounced at the surface than in the lower layers, is well reproduced in the surface temperature field. On the contrary, the Kuroshio front, more intense in the lower layers but still marked in the satellite observations, is visible in the model only below 160 m. The front is not present in the surface temperature field but, as a consequence of the thermal wind balance, an intense eastward flow at the location of the Kuroshio Extension is observed in the model velocity field. When compared with the observations, the location of the Extension is shifted approximately 5° towards the south. This indicates a shift in latitude between the modeled and observed latitude of separation. The resolution of the model is marginal to reproduce the process of eddy formation, but large scale eddies are observed in the model in both analyzed areas. They are generated as a pinch of the main flow with an annual and semiannual periodicity. We conclude that some of the differences between model and observations, like the differences found in the locations of the fronts, and the diminished variability, will decrease with a higher resolution.