Guillermo P. Podestá

Overview of the NOAA/NASA advanced very high resolution radiometer Pathfinder algorithm for sea surface temperature and associated matchup database

The National Oceanic and Atmospheric Administration (NOAA)/NASA Oceans Pathfinder sea surface temperature (SST) data are derived from measurements made by the advanced very high resolution radiometers (AVHRRs) on board the NOAA 7, 9, 11, and 14 polar orbiting satellites. All versions of the Pathfinder SST algorithm are based on the NOAA/National Environmental Satellite Data and Information Service nonlinear SST operational algorithm (NLSST). Improvements to the NLSST operational algorithm developed by the Pathfinder program include the use of monthly calibration coefficients selected on the basis of channel brightness temperature difference (T4–T5). This channel difference is used as a proxy for water vapor regime. The latest version (version 4.2) of the Pathfinder processing includes the use of decision trees to determine objectively pixel cloud contamination and quality level (0–7) of the SST retrieval. The 1985–1998 series of AVHRR global measurements has been reprocessed using the Pathfinder version 4.2 processing protocol and is available at various temporal and spatial resolutions from NASAs Jet Propulsion Laboratory Distributed Active Archive Center. One of the highlights of the Pathfinder program is that in addition to the daily global area coverage fields, a matchup database of coincident in situ buoy and satellite SST observations also is made available for independent algorithm development and validation.

Use of ENSO-related climate information in agricultural decision making in Argentina: a pilot experience

Abstract The availability of long-lead ENSO-related climate forecasts has led many to speculate that such forecasts may benefit decision making in agriculture. To explore the conditions required for the effective use of climate forecasts, we conducted a pilot study focused on central-eastern Argentina. Historical records showed higher (lower) average precipitation during warm (cold) ENSO events in November–December. However, variability of the precipitation signal within ENSO phases was high. National-level yields of maize, soybeans and sorghum tended to be higher (lower) during warm (cold) events. A field survey was conducted to identify impediments for forecast adoption and learn how to communicate climate information. Most farmers surveyed know about ENSO, with the 1997–1998 event marking a “turning point” in their awareness of the phenomenon. Finally, various modeling approaches were used to explore outcomes of alternative management options (changes in crop management and land allocation) tailored to climate scenarios associated with each ENSO phase. Simulation exercises identified differences in optimal management between ENSO phases.

Exploring the association between swordfish catch rates and thermal fronts on U.S. longline grounds in the western North Atlantic

Abstract Associations between ocean surface thermal fronts and the swordfish catch rates of U.S. longline vessels were explored. The study area was the western North Atlantic off the United States, extending from 32°N to 45°N and from 76°W to 63°W. To locate and describe fronts, we used three variables computed from satellite-derived sea surface temperature (SST): horizontal gradient, distance to nearest thermal surface front, and frontal density. Most of the fishing effort analysed occurred along the edge of the continental shelf, where there was a high frequency of frontal presence. Very high catch per unit effort (CPUE) occurred more frequently in the vicinity of fronts than would be expected by chance. The high variability of CPUE that could not be explained by our frontal parameters suggested other, unmeasured, factors also influenced catch rates.

The influence of Loop Current perturbations on the formation and evolution of Tortugas eddies in the southern Straits of Florida

Large cyclonic eddies on the northern edge of the Florida Current are the dominant mesoscale features within the southern Straits of Florida. The most prominent of these features is a quasi-stationary eddy that forms near the Dry Tortugas. Our observations, compiled from 3 years of advanced very high resolution radiometer measurements in the Straits of Florida and Gulf of Mexico, demonstrate a strong relationship between the generation of anticyclonic rings from the Gulf of Mexico Loop Current and the evolution of Tortugas eddies within the southern Straits of Florida. In six cases, Tortugas eddies evolve from cyclonic frontal eddies which form along the boundary of the Loop Current. The eddies remain stationary near the Dry Tortugas until they are impacted by an approaching Loop Current frontal eddy. The length of time an eddy spends near the Dry Tortugas is increased when the Loop Current sheds an anticyclonic ring. The involvement of a Loop Current frontal eddy in the ring-shedding process results in a delay in its, and hence the Tortugas eddys, downstream propagation. Results suggest that the lifetime of a Tortugas eddy can be as long as 140 days when a ring-shedding event occurs, or as short as 50 days in the absence of any ring-shedding events. Upon entering the Straits of Florida, the Tortugas eddies are deformed by the narrowing topography and shrink to approximately 55% of their original size as they propagated downstream. The shrinking of these eddies is accompanied by an accelerated translation from 5 km/d in the western Straits of Florida to 16 km/d in the east.

Associations between Grain Crop Yields in Central-Eastern Argentina and El Niño–Southern Oscillation

Abstract Associations are investigated between yields of major crops in the Argentine Pampas (central-eastern Argentina) and El Nino–Southern Oscillation (ENSO) phase. For maize and sorghum, higher (lower) yield anomalies occur more frequently than expected by chance alone during warm (cold) ENSO events. For both crops, the depression of yields during cold events is, on average, larger and less variable than yield increases are during warm events. A yield decrease during cold events also is observed in soybean yields, although the effect of warm events is not statistically significant. There is a marginally significant tendency for low sunflower yields to occur less frequently than expected during cold events. Wheat, the only winter crop considered, did not show an association with ENSO. Precipitation anomalies during October–February (the period with strongest ENSO signal in the Pampas) are summarized through principal component analysis. Precipitation anomalies during November–January are significantly ...

Mississippi River flood waters that reached the Gulf Stream

Distributions of physical, biological, and chemical parameters in florida Keys coastal waters seaward of the reef track were surveyed on September 9 to 13, 1993, as part of a coordinated multidisciplinary study of surface transport processes. A band of low-salinity water was observed along the shoreward side of the florida Current over the downstream extent of the survey from Miami to Key West. Biological and chemical indicators within the band, together with its large volume, satellite imagery, and a surface drifter trajectory suggested the recent Mississippi River flood as the source.

The Annual Cycle of Satellite-derived Sea Surface Temperature in the Southwestern Atlantic Ocean

Abstract The annual cycle of sea surface temperature (SST) in the southwestern Atlantic Ocean was estimated using four years (July 1984-July 1988) of NOAA Advanced Very High Resolution Radiometer observations. High resolution satellite observations at 1-km space and daily time resolution were grided at 100-km space and 5- day time intervals to develop an analysis dataset for determination of low fluency SST variability. The integral time scale, a measure of serial correlation, was found to vary from 40 to 60 days in the domain of interest. The existence of superannual trends in the SST data was investigated, but conclusive results could not be obtained. The annual cycle (and, in particular, the annual harmonic) explains a large proportion of the SST variability. The estimated amplitude of the cycle ranges between 5° and 13°C throughout the study area, with minima in August-September and maxima in February. The resultant climatology is compared with an arbitrary 5-day satellite SST field, and with the COAD...

A linked-modeling framework to estimate maize production risk associated with ENSO-related climate variability in Argentina

Abstract A risk assessment framework is presented to characterize the vulnerability of agricultural production systems to El Nino-southern oscillation (ENSO)-related climate variability. The framework was applied to current maize production systems in two locations (Pergamino and Pilar) in the Pampas of central-eastern Argentina. Climatic, agronomic, and economic models were linked to produce probability distributions of farm-level yields and net returns by ENSO phase. Generally, an enhanced chance of higher (lower) simulated maize yields existed during warm (cold) ENSO events. However, regional differences existed: the effect of warm events on yields was more marked in Pilar, but Pergamino showed a proportionally stronger response to cold events. The modeling framework allowed the exploration of outcomes of high and low scenarios of soil water availability at planting time and ENSO phase. High initial soil water availability in Pilar offset increased yield risks from dry conditions associated with cold ENSO events. Fluctuations of output prices were shown to have considerable influence on the risk associated with ENSO-related climate variability. Despite these general results, there was considerable overlap in yields and net returns for the various ENSO phases. This overlap has significant implications for the adoption of ENSO forecasts in agriculture. The risk assessment framework developed here is a necessary precursor to risk management studies that prescribe or describe possible responses to expected climate scenarios.

Sea surface temperature variability in Panamá and Galápagos: Extreme temperatures causing coral bleaching

We examined associations between warm sea surface temperature (SST) anomalies and coral bleaching in the Galapagos Islands and the Gulf of Panama, in the tropical eastern Pacific Ocean. Interannual SST variability is dominated by the El Nino-Southern Oscillation phenomenon at Galapagos, whereas only strong events have an SST signature in Panama. We explored various SST-related metrics potentially associated with bleaching occurrence: maximum absolute SST, SST anomaly, and the combined effect of intensity and duration of both SST anomalies (described via a “degree days” index) and high SST events. In Galapagos, three Nino years (1983, 1987, and 1992) coincided with bleaching. These were the top three years in both maximum annual SSTs and degree days values. In Panama, bleaching in 1983 coincided with high maximum SSTs and high degree days. In contrast, no bleaching was detected in 1972 despite high values of both quantities. We found all temperature-related metrics to be highly correlated, and it was impossible to isolate their effects.

A Stochastic Precipitation Generator Conditioned on ENSO Phase: A Case Study in Southeastern South America

Abstract Stochastic precipitation generators can produce synthetic daily rainfall series with statistical characteristics similar to those of historical data. Typically, parameters of precipitation generators have been fit using all historical data for a given period. This approach, however, fails to capture differences in the precipitation process associated with an El Nino–Southern Oscillation (ENSO) signal. Stochastic precipitation generators conditioned on the ENSO phase were developed to address this problem. Precipitation models with a range of parameterization schemes were tested in six locations in central-eastern Argentina and western Uruguay (southeastern South America), an important agricultural region with a clear ENSO precipitation signal in October–March. Conditional precipitation models (occurrence, intensity, or both) were superior to simple models in 24 of the 36 locations/months analyzed. Graphic diagnostics showed that conditional occurrence models successfully captured differences in t...