Centro de Investigaciones Geofísicas
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Item A climatic feature of the tropical Americas: The trade wind easterly jet(Tópicos Meteorológicos y Oceanográficos, 1998) Amador, JUsing data from the NCEP/NCAR Reanalysis global monthly means for the period 1982-1994, a previously not reported featura of the climate circulation of the tropical Americas is documented: The Trade Wind Easterly Jet. This jet develops in low levels (especially in 925, 850 and 700 mb) in the central part of the Caribbean Sea and from Mat to July, the wind increases to máximum and then, the mean current decreases from the later to September. Values in excess of 14 ms -1 are observed in the 925 mb zonal mean field during July. Basic dynamical estimares of horizontal wind shear show that this flow is barotropical unstable during the peak of the summer months at low levels, so, disturbances may grow from the mean kinetic energ of the flow. Cross circulations associated to the jet exit región are consistent with the low level vertical velocity (dp/dt) and a máximum of precipitation found in the earstern Carribbean near the Central American coast during the summer months.Item A comparative study of hurricanes Fifi (1974) and Greta (1978) and their associated rainfall distributions over Central America(Tópicos Meteorológicos y Oceanogáficos, 1996) Fernández, W; Vega, NA comparative study of hurricanes Fifi (1974), which had similar tracks but produced different rainfall distributions over Central America, was made. It was found that Fifi was much rainier in spite of being much less intense than Grete, The direct effect of the cyclones (produced by the convergent fields in the central parts and local orographic enhancement) and the indirect effect (the interaction of a westerly component flow induced by the presence of the cyclones with orography on the Pacific side of Central America) were also studied. It was found that the indirect effect is as important as the direct effect when accumulated rainfall amounts for a period of about three days are considered.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 A Numerical Simulation of the Martian Polar Cap Breeze(Earth, Moon and Planets, 1995) Fernández, WA mathematical model for the Marian polar cap breeze was constructed in part from work previously done by others on the terrestrial sea breeze. With this model a numerical simulation corresponding to the Southern Hemisphere winter season was made. The results obtained with the proposed model show that the Martial polar cap breeze is a well defined system with some similarities to the terrestrial breeze. At the time of maximum intensity, the largest values of vertical velocities are about 10 cm/s and occur at heights between 850-1250 m. The largest values of horizontal velocities are about 15 m/s. A "polar cap breeze front" is clearly discernible in the results. The rate of advance of this front is at an average of about 10 km/h.Item A Review of Downdrafts at the Rear of Tropical Squall Lines(Bulletin of the American Meteorological Society, 1982) Fernández, WThe observational evidence for the formation of downdrafts at the rear of tropical squall lines is reviewed. Some mechanisms, which have been proposed for the formation of such downdrafts, also are reviewed. Although the mechanisms are different, it is likely that in a tropical squall line system, all of them act together to produce the observed downdrafts.Item Air temperature and wind changes in Costa Rica during the total solar eclipse of July 11, 1991(Earth, Moon, and Planets, 1993) Fernández, W; Castro, V; Hidalgo, HAir temperature and wind measurements on the surface and in the free atmosphere taken during the total solar eclipse of July 11, 1991, are analyzed. Surface air temperature decreased significantly, 2 to 5ºC in general, with the lowest values occurring 10 to 30 minutes after totality. In some places, surface wind speed decreased gradually during the eclipse, as a result of the decrease of air temperature and temperature gradients. In other places, it increased due to local atmospheric conditions. A radiosonde launched at 13:26 LT (local time) appeared to have been affected by the moon's shadow at about 13 km height. At this altitude temperature was relatively lower than usual and the balloon carrying the radiosonde experienced an upward acceleration. Also at this altitude wind direction changed and wind speed decreased.Item 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 características de las tormentas tropicales y de los huracanes que atravesaron o se formaron en el Caribe adyacente de Costa Rica durante el periodo 1886-1988(Tópicos Meteorológicos y Oceanográficos, 1996) Lizano, O; Fernández, WSe estudian algunas características de las tormentas tropicales y de los huracanes en el Caribe adyacente a Costa Rica, en el área localizada entre 70-850 Oy 8-180 N. En particular, utilizando un registro para el período 1886-1988, se presentan análisis de frecuencias para los parámetros usuales que caracterizan a los huracnes: presión atmosférica en el ojo, magnitud del viento máximo y velocidad y dirección de desplazamiento. También se estudian las frecuencias con las que las tormentas tropicales y los huracanes se forman y atraviesan en dicha área.Item Algunas características espectrales de las oscilaciones en la atmósfera sobre el oeste del Caribe(Ciencia y Tecnología, 1982) Amador, J; Soley, F.JSe investigan los modos de onda dominantes en la troposfera del Oeste del Caribe mediante el uso de la transformada discreta de Fourier de la función de autocorrelación para diferentes parámetros y algunas estaciones del área. Los espectros de las series temporales de temperatura, geopotencial y las componentes zonal y meridional del viento fueron estimados utilizando datos de la Isla de San Andrés para el año 1972 y de la Isla del Cisne para los años 1970, 1971 y 1972. Los niveles isobáricos analizados corresponden a 850, 700, 500, 400 y 300 mb (excepto 400 mb para la temperatura). El período analizado para San Andrés y para la Isla del Cisne para cada uno de los años investigados es del 1 de junio al 30 de noviembre (una observación diaria a las 12 T.M.G.). Además del anterior, se calculó el espectro de la precipitación para un período en particular (1 de agosto al 26 de noviembre de 1972) para la estación de Limón, Costa Rica. Los espectros del viento zonal y la temperatura muestran en general una tendencia a una mayor contribución a la variancia total de la serie para períodos mayores que 10 días. Los espectros del geopotencial indican la existencia de dos picos predominantes (uno cerca de los 3 días y otro para períodos ligeramente mayores que 5 días), aunque se evidencia una moderada variabilidad en la posición de esos máximos para diferentes años y estaciones. Los espectros de la componente meridional presentan resultados sumamente interesantes. En algunos años y estaciones, los períodos de 3 a 5 días parecen ser dominantes y, aunque su intensidad o amplitud es variable, aparentan estar asociados con las características del flujo medio durante los años estudiados. Tanto para San Andrés como para la Isla del Cisne, es aparente la relación: menor amplitud de la señal u oscilación a mayor cortante vertical, especialmente la del flujo zonal. Todos los resultados anteriores son consistentes con los de Amador (1982) y sugieren que las características del flujo medio juegan un papel importante en la naturaleza y desarrollo de sistemas cuasi-ondulatorios en la región. Un resultado importante del presente trabajo es la forma en que se distribuye la variancia de la precipitación para Limón durante 1972. Este espectro muestra máximos comparables cerca de los 10 y 4 a 5 días. El último máximo y el pico en el rango de 3 a 5 días encontrado por Amador (1982) en la componente meridional del viento podrían estar asociados y permite suponer que las ondas de propagación este-oeste afectan de manera importante la distribución temporal de la precipitación en la región del Oeste del Caribe.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 Algunos datos históricos sobre eclipses de sol en Costa Rica en el Siglo XX(Polaris, 1991) Amador, J; Solano, FAnte la observación del gran Eclipse Total de Sol, del 11 de julio de 1991, que cubrió la mayor parte del país. Se repasa algunos datos históricos de eclipses ocurridos en Costa Rica durante el siglo 20.Item Algunos detalles y hechos históricos de los albores de la Física en Costa Rica: Parte I(Las Matemáticas en Costa Rica, 1990) Amador, J; Páez, J; Solano, FEn el período precolombino hay indicios de que hubo un desarrollo científico acorde a las necesidades de la época. Durante la Colonia los pobladores de nuestro territorio le dieron más importancia a la artesanía. Con la fundación de las primeras universidades Centroamericanas es que se da la estructura y elementos básicos para el desarrollo científico posterior.Item Algunos detalles y hechos históricos de los albores de la Física en Costa Rica: Parte II(Las Matemáticas en Costa Rica, 1990) Páez, J; Solano, F; Amador, JA mediados del siglo XVIII se tiene información documental confiable de que el costarricense Liendo y Goicoechea introdujo la Física Experimental en la Universidad de San Carlos en Guatemala. Su influencia en Costa Rica es poco conocida y merece un análisis posterior.Item Algunos detalles y hechos históricos de los albores de la Física en Costa Rica: Parte III(Las Matemáticas en Costa Rica, 1990) Solano, F; Amador, J; Páez, JA principios del siglo XIX con la fundación de la Casa de Enseñanza de Santo Tomás y la contratación del Bachiller Rafael Francisco Osejo se introdujeron las primeras nociones fundamentales de Física en Costa Rica. A pesar de que desde la creación de la Universidad de Santo Tomás en 1844 se dictaron algunos rudimentos de Física Teórica en la Cátedra de Filosofía y en 1852 se impartió en la Universidad un curso de Física, no fue sino hasta el período entre 1861 y 1862 (no está claro en cuál de los 2 años exactamente) que se establece formalmente la enseñanza de la Física en esa Casa de Estudios Superiores. Desde 1849 hasta 1865 distinguidos naturalistas contribuyeron a mantener vivo el interés por las ciencias naturales lo que tal vez permitió mantener activas las ideas de la época en relación con la Ciencia Física. Con la clausura de la Universidad de Santo Tomás se cierrra en Costa Rica un período lento e incipiente en el desarrollo de la Física en Costa Rica.Item An Application of Palmer's Drought Index to a Semi-Arid Tropical Region(Revista Geofísica, 1987) Suárez, M.E; Fernández, W; Fernández, WPalmer's Drought Index (PDI) was applied to a semi-arid region in Costa Rica. In the computations of the water balance, two modifications to Palmer's method were made. The method of Hargreaves was used to obtain potential evapotranspiration and the procedure of Thorntwaite and Mather to obtain potential runoff. The period of analysis in the region was from June 1972 to December 1983 (i.e. 138 months), of which 32% had drought conditions, with 7% mild, 11% moderate, 11% severe, and 3% extreme droughts (according to Palmer's classification). The values obtained for the PDI were tested againts reports from the pess concerning crop damage by droughts and a very good agreement was found. The dependence of the PDI on the available water capacity of the soil and the potential evapotranspiration is also discussed.Item An Evaluation of Theories of Storm Motion Using Observations of Tropical Convective Systems(Monthly Weather Review, 1979) Thorpe, A.J.; Fernández, WRaymond's (1975) wave-CISK model is applied to several tropical convective storms observed in Venezuela, the eastern Atlantic and West Africa to predict their propagation velocity. Similar calculations are carried out with Moncrieff and Miller's (1976) analytical model for tropical cumulonimbus and squall lines. A comparison of the model predictions with the observed values is made. In some cases the models give good predictions, but not in others. In general, Raymond's model underestimates the propagation speed of the storms, while the Moncrieff-Miller model overestimates it. Raymond's model is poor when the cloud bases are very low. This result indicates that over tropical oceans wave-CISK models cannot give good results unless the mass flux due to the plumes, which is equated to the mass flux across cloud base, is treated in a more realistic way. The Moncrieff-Miller model gives better results if the mean wind component along the direction of motion is used rather than the mid-level wind. The wave-CISK model and steady-state models of storm motion are then considered in conditions of constant wind shear. In particular, their predictions are compared over a wide range of shear values, using realistic thermodynamic soundings. Despite the obvious differences between the models, it is found that, for Richardson number small (R<1) and very large, they give comparable predictions for the storm velocity. It appears that a very good approximation for the wave-CISK model over the entire R range is to put the storm speed proportional to the shear, plus a constant. An important conclusion is that the ability of storms to propagate relative to the environmental flow can be reproduced in the linear wave-CISK model and thus may not be a fundamentally nonlinear effect. It is therefore crucial to further examine forcing mechanisms of convective overturning and, in particular, to clarify the relationship between CISK and the implicit forcing involved in the steady model.Item An integrated dynamic model for the volcanic activity at Poás volcano, Costa Rica(Bulletin of Volcanology, 1987) Casertano, L; Casertano, L; Cigolini, C; Morales, L; Montero, W; Gomez, M; Fernández, JA dynamic model for the activity of Poas Volcano, Costa Rica, is proposed. Data collected during a three-year period show that the volcanic processes occur within a small hydrothermal system. Heat is supplied by a magma body in the conduit and is transferred to the surface by fluid convection. Within a given volume of rock, pore pressure builds up due to the upward motion of fluids and the increase in vapor pressure when the temperature rises above the boiling point. Ultimately, the system becomes unstable when the pore pressure overcomes the total pressure. This leads to the assumption that the kinetic and thermal energies are proportional to the depth at which the mechanical equilibrium is disturbed. Laboratory experiments were performed by heating samples of the crater lake deposits. The preliminary results of these experiments show significant analogies with the low-energy activity of the volcano. Following this model we estimated that a phreatic explosion which reaches 200 m in height (comparable to the one observed by Francis et al. in 1978) originates at a depth of 70 m and a temperature of 180° C; these values agree with those reported in the literature. In addition, “magmatic” sulfur, which partitions into the rising hydrothermal fluids, reacts at lower temperature and higher to produce pockets of liquid sulfur in the conduit deposits and the lava dome. These pockets are subsequently erupted forming the pyroclastic sulfur.