Browsing by Author "Alfaro, E"
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Item A method for prediction of California air surface temperature(EOS, Transactions, American Geophysical Union, 2004) Alfaro, E; Gershunov, A; Cayan, D; Steinemann, A; Pierce, D; Barnett, TItem Ajuste de un modelo VAR como predictor de los campos de anomalías de precipitación en Centroamérica(Revista de Matemática: Teoría y Aplicaciones, 2001) Alfaro, E; Soley, FCon el fin de identificar en la región las estaciones pluviométricas con curvas de anomalías similares entre sí, 15 puntos de precipitación de la región fueron sometidos a un proceso de agrupación identificándose cinco conglomerados. Posteriormente se ajustó un modelo Vectorial Autorregresivo VAR, con el objetivo de cuantificar la interacción océano-atmósfera entre distintos índices oceanográficos en el Pacífico y Atlántico Tropical y los regímenes de precipitación en Centroamérica, representados por las primeras funciones ortogonales empíricas de los distintos conglomerados. Este modelo mostró que la principal influencia sobre la región la ejerce el Atlántico Tropical Norte con correlaciones positivas. Por su parte los índices del Atlántico Tropical Sur y del Niño 3 no mostraron una influencia significativa sobre el istmo. Se concluye que al ajustar un modelo estacionario, las anomalías de la temperatura superficial del mar en el Atlántico Tropical Norte influyen más fuertemente sobre la precipitación que aquellas del Niño 3 o del Atlántico Tropical Sur influyendo sobre el grado de formación de la Vaguada Tropical Troposférica Alta.Item Ajuste de un modelo VARMA para los campos de anomalías de precipitación en Centroamérica y los índices de los océanos Pacífico y Atlántico Tropical(Atmósfera, 1999) Alfaro, E; Cid, LDiversos estudios han mostrado que condiciones anómalas de la temperatura superficial del mar (ATSM) de los océanos Pacífico y Atlántico Tropical, afectan la intensidad y duración de la estación lluviosa sobre Centroamérica. Con el fin de identificar en la región las estaciones pluviométricas con curvas de anomalías similares entre sí, 72 estaciones de precipitación de la región fueron sometidas a un proceso de agrupación, identificándose cinco conglomerados. Posteriormente se ajustó un modelo Vectorial Autorregresivo-Medias Móviles (VARMA), con el objetivo de cuantificar la interacción océano atmósfera entre distintos índices oceanográficos en el Pacífico y Atlántico Tropical y los regímenes de precipitación en Centroamérica, representados por las primeras EOF´S de los distintos conglomerados. Este modelo mostró que la principal influencia sobre la región la ejerce el Atlántico Tropical Norte (ATN) con correlaciones positivas. Por su parte, el índice Niño 3 mostró una influencia más débil, con correlaciones negativas sobre aquellas regiones situadas principalmente en la Vertiente Pacífica de Centroamérica. Se concluye que as TASM en el Atlántico Tropical Norte influyen más fuertemente sobre la precipitación que aquellas del Pacífico Tropical este. El primero influye sobre el grado de formación de la Vaguada Tropical troposférica Alta (VTTA) y el segundo sobre la posición de la Zona de Convergencia Intertropical (ZCIT).Item Algunas características de la estratosfera sobre Mesoamérica(Tópicos Meteorológicos y Oceanográficos, 2001) Alfaro, E; Amador, JStatistical values of the Quasi Biennial Oscillation (QBO) were estimated in four latitudinal bands over Meso-America, using the wind and temperature variables of 94 aerological stations from the Comprenhensive Aerological Reference Data Set (CARDS). The period used spans from 01/1958 to 12/1991 and the bands were: 1º S-10º N, 11º - 17º N, 18º - 26º N and 27º - 33º N. The pressure levels utilized in this study are 200, 150, 100, 70, 50, 30, 20, 10 and 5 hPa. For the zonal wind, the signal with the highest power was found in the 20 hPa level for the most equatorial band. It was observed a decrease of this signal from that layer to higher and lower levels and to higher latitudes. The signal found in the same band, for the temperature variable, was a maximum near the 30 hPa level, but it is not as well marked when compared to that of the zonal wind. The meridional wind variable did not show any signal of importance in this frequency range. Finally, a QBO signal was found in the Total Ozone for the most mid latitude band.Item Algunas características de las corrientes marinas en Golfo de Nicoya(Revista de Biología Tropical, 2004) Lizano, O; Alfaro, EThe spatial and vertical structure of the water currents and its relationship with the tidal cycles were studied using current meters in the Gulf of Nicoya. In the upper gulf, the vertical marine current differences increase as the depth increases. The water column at the station near Chira Island (upper gulf) shows the smaller changes in currents and in temperature. The flow at the station between San Lucas Island and Puntarenas (middle gulf) is the most stratified in this region. Currents with magnitudes over 100 cm/seg were measured during spring tides. Changes in the lags of the surface and bottom tidal flows were measured on the order of 100 minutes. In general, in this upper region the flows are toward the head of the gulf when the tide is flooding and toward the mouth when the tide is ebbing. In the lower gulf the circulation is more complex. Along an axis between Tárcoles and Negritos Islands, changes of velocity vectors are identified between surface and bottom. The current rotates in a different way in the water column in this region and their patterns cannot be explained only by the tidal cycles predicted for Puntarenas. These results demonstrate that the spatial and vertical variation of the marine currents of the Gulf of Nicoya is not only related to the thermohaline structure, but also to the tidal cycles and tide ranges that take place in this estuary.Item Algunas relaciones entre las zonas de surgencia del Pacífico Centroamericano y los Océanos Pacífico y Atlántico Tropical(Revista de Biología Tropical, 2001) Alfaro, E; Lizano, OIn order to explore the influence of the surrounding tropical oceans on the Central American Pacific coast, a Transfer Function Model was fixed to Sea Surface Temperature Anomalies (SSTA) of the Gulf of Tehuantepec, Papagayo, Panama and Quepos time series. As independent variables the following were used: Niño 3.4, Tropical North and South Atlantic indices. These models show that Niño 3.4 has the most important influence over the region when compared with the influence of the other indices, having positive correlation with all the SSTA series. It shows an influence of this index on the relative termocline’s depth in front of the Central American Pacific Coast.Item Análisis de las anomalías en el inicio y el término de la estación lluviosa en Centroamérica y su relación con los océanos Pacífico y Atlántico Tropical(Tópicos Meteorológicos y Oceanográficos, 1999) Alfaro, E; Cid, LIt is estimated the star, end and duration of the rainy season for 37 gauge stations located mainly on the Pacific Slope in Central America. The relation of these aspects with the sea surface temperature of the Tropical North and South Atlantic and Tropical Eastern Pacific was studied by means of a cross correlation and an anomalies analysis. The star of the rainy season was influenced mainly by the Tropical North Atlantic with early (late) starts related with warm (cold) conditions in this index. The Tropical Eastern Pacific was related mainly with the end of the rainy season with early (late) ends related with warm (cold) conditions in this oceanic zone. Finally, the Tropical North Atlantic was the main influence on the duration of the rainy season. It was observed a longer (shorter) period of rains related with warm (cold) conditions on this index.Item Aplicación de análisis multivariado al campo de anomalías de precipitación en Centroamérica(Tópicos Meteorológicos y Oceanográficos, 1999) Soley, F; Alfaro, EBecause climate signals have components in different time and space scales it is difficult to identify the causes of climate variability when only one or a few stations are analyzed. Multivariate analysis of one or several variables of stations with an adequate geographical distribution helps to identify the possible causes of variability, to separate in certain cases different time scales, and in quantifying the influence of those causes at different geographical points. Multivariate methods, such as principal components analysis, singular value decomposition and canonical correlation analysis were first applied to meteorological fields in the 1950’s and 1960’s. In the last ten years they have proved to be a valuable tool in the study of climate variability and their use has increased considerably. Vector Auto Regressive-Moving Average models are more recent and besides identifying the causes of variability they are also useful in forecasting. In this paper, we present the principles on which these methods are based and they are applied to the precipitation anomalies’ field in Central America. The results are interpreted within a discussion of the advantages and limitations of the different methods.Item Atmospheric forcing in the Eastern Tropical Pacific: A review(Progress in Oceanography, 2006) Amador, J; Alfaro, E; Lizano, O; Magaña, VThe increase in marine, land surface, atmospheric and satellite data during recent decades has led to an improved understanding of the air–sea interaction processes in the eastern tropical Pacific. This is also thanks to extensive diagnoses from conceptual and coupled ocean–atmosphere numerical models. In this paper, mean fields of atmospheric variables, such as incoming solar radiation, sea level pressure, winds, wind stress curl, precipitation, evaporation, and surface energy fluxes, are derived from global atmospheric data sets in order to examine the dominant features of the low level atmospheric circulations of the region. The seasonal march of the atmospheric circulations is presented to depict the role of radiative forcing on atmospheric perturbations, especially those dominating the atmosphere at low levels. In the tropics, the trade winds constitute an important north–south energy and moisture exchange mechanism (as part of the low level branch of the Hadley circulation), that determines to a large extent the precipitation distribution in the region, i.e., that associated with the Inter-Tropical Convergence Zone (ITCZ). Monsoonal circulations also play an important role in determining the warm season precipitation distribution over the eastern tropical Pacific through a large variety of air–sea–land interaction mechanisms. Westward traveling waves, tropical cyclones, low latitude cold air intrusions, and other synoptic and mesoscale perturbations associated with the ITCZ are also important elements that modulate the annual rainfall cycle. The low-level jets of the Gulf of California, the Intra-Americas Sea (Gulf of Mexico and Caribbean Sea) and Choco´, Colombia are prominent features of the eastern tropical Pacific low-level circulations related to sub-regional and regional scale precipitation patterns. Observations show that the Intra-Americas Low-Level Jet intensity varies with El Niño/Southern Oscillation (ENSO) phases, however its origin and role in the westward propagation and development of disturbances that may hit the eastern tropical Pacific, such as easterly waves and tropical cyclones, are still unclear. Changes in the intensity of the trade winds in the Caribbean Sea and the Gulf of Mexico (associated with eastern tropical Pacific wind jets) exert an important control on precipitation by means of wind–topography interactions. Gaps in the mountains of southern Mexico and Central America allow strong wind jets to pass over the continent imprinting a unique signal in sea surface temperatures and ocean dynamics of the eastern tropical Pacific. The warm pools of the Americas constitute an important source of moisture for the North American Monsoon System. The northeastern tropical Pacific is a region of intense cyclogenetic activity, just west of the coast of Mesoamerica. Over the oceanic regions, large-scale properties of key variables such as precipitation, moisture, surface energy fluxes and wind stress curl are still uncertain, which inhibits a more comprehensive view of the region and stresses the importance of regional field experiments. Progress has been substantial in the understanding of the ocean and atmospheric dynamics of the eastern tropical Pacific, however, recent observational evidence such as that of a shallow meridional circulation cell in that region, in contrast to the classic concept of the Hadley-type deep meridional circulation, suggests that more in situ observations to validate theories are still necessary. This paper is part of a comprehensive review of the oceanography of the eastern tropical Pacific Ocean.Item Composición de sedimentos en las Zonas Costeras de Costa Rica utilizando Fluorescencia de Rayos-X (FRX)(Revista de Biología Tropical, 2004) Salazar, A; Lizano, O; Alfaro, EUsing an energy dispersive X-Ray fluorescence analysis, simultaneous evaluation of K, Ca, Ti, Cr, Mn, Ge, Ni, Cu, Zn, Br, Rb, Sr and Pb in 74 marine sediment samples from the Costa Rica intertidal zones was conducted. Samples were collected between June 1999 and December 2001, from Caribbean and Pacific beaches of Costa Rica. Calcium and iron showed the highest abundances and are indicators of the natural origin of the sediments. Calcium is associated with biogenic processes such as coral reefs near the sampling sites and iron indicates a terrigenous origin. In general, the beaches of the Caribbean and North Pacific regions showed the greatest concentration of calcium. This is indicative of the abundant reef structures near these beaches. The beaches of the Central and South Pacific show the greatest iron concentrations, indicating an important lithosphere contribution and/or little contribution of calcium carbonate due to the poor development of coralline structures near the sampling sites. Finally, the analyses did not show evidence of elements associated with anthropogenic pollution. Only a northern section of Puerto Viejo beach showed high concentrations of lead, zinc and titanium, perhaps associated with hydrothermal sources.Item El Niño-Oscilación del Sur y algunas series de temperatura máxima y brillo solar en Costa Rica(Tópicos Meteorológicos y Oceanográficos, 1996) Alfaro, E; Amador, JSome characteristics of "El Niño-Southern Oscillation" (ENSO) and their possible relationship with the space and time distribution of anomalies of monthly values of maximum temperature and sunshine hours are analyzed for some selected regions in Costa Rica. Time series are firstly deseasonalized, then smoothed in order to decrease the contribution of less than a year period components. To carry out the study moving average techniques and Fourier analysis are used. Time series showed anomalies in the range of 0.5° to 1°C, that could be associated with ENSO events. The sunshine hours series presented some consistency with the results of maximum temperature, however, its behavior is more difficult to be interpreted. Almost all the maximum temperature series showed a positive trend in the order of 0.5°C during the last two decades consistent with the ides of a regional warming.Item Eventos Cálidos y Fríos en el Atlántico Tropical Norte(Atmósfera, 2000) Alfaro, ESe cuantifican los eventos cálidos y fríos en la región del Atlántico Tropical Norte, definida entre los 6-22° N y los 15-80° W, por medio del uso de los índices normalizados de temperatura superficial del mar (TSM). Se definió como evento cálido (frío) a aquel período de tiempo en el cual el índice de TSM, suavizado con un promedio móvil de cinco meses, permanece por encima (abajo) del cuarto (segundo) quintil por seis o más meses. La ocurrencia de eventos se mostró como aperiódica y con duraciones de gran variabilidad. Del período total de estudio, los eventos fríos ocuparon en promedio un 17% y los cálidos un 15.5%. En general, se notó que el primer semestre del año coincide con la mayoría de los comienzos tanto de eventos fríos como cálidos y que el segundo semestre coincide con la mayoría de los finales de eventos fríos y cálidos.Item Eventos Cálidos y Fríos en el Atlántico Tropical Sur(Tópicos Meteorológicos y Oceanográficos, 1999) Alfaro, E; Soley, FPor medio del uso de índices normalizados de temperatura superficial del mar (TSM), se cuantifican los eventos cálidos y fríos en la región del Atlántico Tropical Sur, definida entre los 2° N - 22° S y los 35° W - 15° E, la cual influye sobre el régimen de precipitación de la Vertiente Caribe de Costa Rica. Se definió como evento cálido (frío) a aquel período de tiempo en el cual el índice de TSM, suavizado con un promedio móvil de cinco meses, permanece por encima (abajo) del cuarto (segundo) quintil por seis o más meses. Al igual que en la región del Atlántico Tropical Norte, la ocurrencia de eventos se mostró como aperiódica y con duraciones de gran variabilidad. Del período total de estudio, los eventos fríos ocuparon en promedio un 37% y los cálidos un 15%. En general, no se notó una fecha preferencial ni para el comienzo ni para el término de eventos cálidos y fríos.Item Frecuencia de los ciclones tropicales que afectaron a Costa Rica durante el siglo XX(Tópicos Meteorológicos y Oceanográficos, 2003) Alvarado, L; Alfaro, EIt is studied the tropical cyclone frequency in the Caribbean Sea that affected Costa Rica during the XX century. None of the 125 cyclones passed over Costa Rica, being the closest track the 1993 tropical storm Bret. The 1988, category 5, hurricane Gilbert was the more intense, however the hurricane Joan during the same year is considered the cyclone with the most severe damage over Costa Rica. Hurricane Mitch in 1998 is cataloged as the cyclone with more damages in Central America and with more rain accumulated by topographic effects. The 40s (80s) was the decade with more (less) hurricane frequency. The modulation of this aspect could be the combination of interannual and interdecadal variability in the Eastern Tropical Pacific and Tropical North Atlantic. It is concluded that the intensity of a temporal in Costa Rica is not directly associated with cyclone’s magnitude because it depends also on the relative cyclone’s position and its velocity over the Caribbean Sea.Item Influencia del océano Atlántico tropical sobre el comportamiento de la primera parte de la estación lluviosa en Venezuela(Tópicos Meteorológicos y Oceanográficos, 2000) Rojas, M; Alfaro, EThe Statistical Ocean Model System, based in Canonical Correlation Analysis, was used to study the relationships between the Tropical Atlantic and Pacific Oceans and the precipitation anomalies in Venezuela for the first part of the rainy season during 1951-1995. The Tropical Atlantic Ocean had the main influence over the April-July (AMJJ) precipitation anomalies with annual cycles associated showing only one maximum in June, mainly. The atmospheric mechanism responsible for this oceanic modulation over the precipitation anomalies could be variations in the latitudinal position of the Inter-Tropical Convergence Zone.Item Modelo de estimación de viento para Bahía Coliumo, Chile Central. Gayana Oceanológica(Gayana Oceanológica, 1997) Calliari, D; Alfaro, ELas surgencias costeras en la costa de Chile central son causadas por la interacción entre el patrón de vientos dominante y la topografía local. En consecuencia, para interpretar los procesos oceanográficos costeros es sumamente útil contar con una buena medida o estimación de las componentes del viento local. Partiendo de series horarias, se construyó un modelo para estimar las componentes meridional (norte-sur) y zonal (este-oeste) del viento en Bahía Coliumo (36°32' S; 72°57'W), a partir del viento medido en la estación Bellavista (36°47' S; 73°07' W, Concepción) como variable independiente. Los modelos propuestos son: Uc(i)=0.280+0.200Ubv (i)+0.156 V¡",(i)+E¡Ci), Vc(i)= -0,460+0.253 U".,(i)+0.839 V",,(i)+E/i), para las componentes meridional y zonal, respectivamente. Estos modelos bivariados produjeron mejores estimaciones que los modelos con una sola de las componentes como variable independiente. La componente meridional fue con la cual se obtuvo la mejor correlación entre las series originales y la que presentó menor error en la estimación. Ello es de articular interés ya que dicha componente es la causante de las surgencias costeras.Item Predicción Climática de la Temperatura Superficial del Aire en Centroamérica(Ambientico, 2007) Alfaro, EItem Prediction of Summer Maximum and Minimum Temperature over the Central and Western United States: The Roles of Soil Moisture and Sea Surface Temperature(Journal of Climate, 2006) Alfaro, E; Gershunov, A; Cayan, DA statistical model based on canonical correlation analysis (CCA) was used to explore climatic associations and predictability of June–August (JJA) maximum and minimum surface air temperatures (Tmax and Tmin) as well as the frequency of Tmax daily extremes (Tmax90) in the central and western United States (west of 90°W). Explanatory variables are monthly and seasonal Pacific Ocean SST (PSST) and the Climate Division Palmer Drought Severity Index (PDSI) during 1950–2001. Although there is a positive correlation between Tmax and Tmin, the two variables exhibit somewhat different patterns and dynamics. Both exhibit their lowest levels of variability in summer, but that of Tmax is greater than Tmin. The predictability of Tmax is mainly associated with local effects related to previous soil moisture conditions at short range (one month to one season), with PSST providing a secondary influence. Predictability of Tmin is more strongly influenced by large-scale (PSST) patterns, with PDSI acting as a short-range predictive influence. For both predictand variables (Tmax and Tmin), the PDSI influence falls off markedly at time leads beyond a few months, but a PSST influence remains for at least two seasons. The maximum predictive skill for JJA Tmin, Tmax, and Tmax90 is from May PSST and PDSI. Importantly, skills evaluated for various seasons and time leads undergo a seasonal cycle that has maximum levels in summer. At the seasonal time frame, summer Tmax prediction skills are greatest in the Midwest, northern and central California, Arizona, and Utah. Similar results were found for Tmax90. In contrast, Tmin skill is spread over most of the western region, except for clusters of low skill in the northern Midwest and southern Montana, Idaho, and northern Arizona.Item Relaciones entre el inicio y el término de la estación lluviosa en Centroamérica y los Océanos Pacífico y Atlántico Tropical(Investigaciones Marinas, 1998) Alfaro, E; Cid, L; Enfield, DEn los últimos años diversos estudios han mostrado que las anomalías en los campos de temperaturas de los océanos Pacífico y Atlántico Tropical están relacionadas con variaciones, tanto en la intensidad como en la duración de la estación lluviosa sobre Centroamérica. En este trabajo se usaron, como variables independientes, distintos índices oceanográficos y atmosféricos, principalmente de las distribuciones de la temperatura superficial del mar (TSM) en los océanos Pacífico y Atlántico Tropical, para explicar las variaciones en las fechas de inicio (IELL) y término (TELL) de estación lluviosa sobre la región centroamericana. El índice del Atlántico Norte (ATN) y los índices IOS-Niño3 mostraron las mayores correlaciones con el IELL y el TELL, respectivamente.Item Relationships between the Irrigation-Pumping Electrical Loads and the Local Climate in Climate Division 9, Idaho(Journal of Applied Meteorology, 2005) Alfaro, E; Pierce, D; Steinemann, A; Gershunov, AThe electrical load from irrigation pumps is an important part of the overall electricity demand in many agricultural areas of the U.S. west. The date the pumps turn on and the total electrical load they present over the summer varies from year to year, partly because of climate fluctuations. Predicting this variability would be useful to electricity producers that supply the region. This work presents a contingency analysis and linear regression scheme for forecasting summertime irrigation pump loads in southeastern Idaho. The basis of the predictability is the persistence of spring soil moisture conditions into summer, and the effect it has on summer temperatures. There is a strong contemporaneous relationship between soil moisture and temperature in the summer and total summer pump electrical loads so that a reasonable prediction of summer pump electrical loads based on spring soil moisture conditions can be obtained in the region. If one assumes that decision makers will take appropriate actions based on the forecast output, the net economic benefit of forecast information is approximately $2.5 million per year, making this prediction problem an important seasonal summer forecasting issue with significant economic implications.