Browsing by Author "Hidalgo, H"

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    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, H
    Air 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.
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    Changes in Meteorological Variables in Coronel Oviedo, Paraguay, During the Total Solar Eclipse of 3 November 1994
    (Earth, Moon and Planets, 1996) Fernández, W; Hidalgo, H; Coronel, G; Morales, E
    Solar global radiation, air temperature, relative humidity, and wind speed were measured in Coronel Oviedo, Paraguay, within the path of totality of the eclipse of 3 November 1994. Global radiation decreased gradually as the sun was being eclipsed and became negligible during the totality, then increased to their normal values. Surface air temperature decreased significantly, about 3 ‡C, with the lowest value occurring about 7 minutes after totality. Relative humidity, because of its dependence on temperature, increased as a consequence of the temperature decrease. Surface wind speed decreased gradually during the eclipse, as a result of the cooling and stabilization of the atmosphere. Although atmospheric pressure was also measured, it was not possible to record pressure changes clearly associated to the eclipse, since the pressure sensor was only able to detect pressure variations of at least 1 hPa.
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    Changes in solar irradiance and atmospheric turbidity in Costa Rica during the total solar eclipse of July 11, 1991
    (Earth, Moon, and Planets, 1993) Fernández, W; Castro, V; Wright, J; Hidalgo, H; Sáenz, A
    Solar global radiation was measured in several places in Costa Rica during the total solar eclipse that occurred on July 11, 1991. In two of these places, Puntarenas and Santa Cruz, measurements in the ultraviolet range (295-385 nm) were also taken. In Santa Cruz, a normal incidence pyrheliometer with Schott filters OG530 and RG630 was used to measure direct solar radiation in its whole range, and in the 530-2800 nm and 630-2800 wavebands respectively. Global radiation, and consequently direct, diffuse and irradiance in any of the wavebands considered, decreased gradually as the sun was being eclipsed and reached zero during de totality, the increased to their normal values. Data registered in Santa Cruz were used to determine Angstrom’s atmospheric turbidity parameters α and β. Computations show that between 13:00 and 14:30 LT (local time), α decreased and β increased significantly. This indicates that atmospheric turbidity was high and large particles were more abundant than small ones. The size of hygroscopic particles increased during the eclipse when temperature decreased and relative humidity increased in a comparatively short time.
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    Distribución Espacio-temporal de la Ocurrencia de Tormentas Eléctricas en Costa Rica
    (Tópicos Meteorológicos y Oceanográficos, 1997) Fernández, W; Hidalgo, H
    Se realiza un análisis del número de días con tormentas para la estación meteorológica del Aeropuerto Juan Santamaría y de los días con tormentas en el periodo 06-18 horas para las otras seis estaciones sinópticas de Costa Rica. En la cuenca del Pacífico, se encontró que las distribuciones estacionales del número de días con tormentas en el periodo 06-18 horas son similares a las correspondientes distribuciones de la precipitación. Esto se debe a que la lluvia es producida principalmente por convección diurna. En la cuenca del Caribe, esto no ocurre de tal forma, porque llueve principalmente durante la noche y la mañana con excepción de la estación Limón (en la cuenca del Caribe), el número anual de días con tormentas en el período de 06-18 horas está en el rango de 86-108. Se estimó, utilizando relaciones ernpíricas, que entre el 12,2% y el 14,7% del número total de relámpagos van a tierra. El valor máximo del número total de relámpagos (intracloud y a la tierra) por km2 por mes, considerando las diferentes estaciones meteorológicas y exc1uding la estación de Limón, varía entre 7 para Liberia a cerca de 10 para Nicoya. Los s totales anuales están entre cerca de 33 (Liberia) y cerca de 52 (Nicoya). Excluyendo también Limón, el número de descargas de rayos a tierra por km2 al mes varía entre 0,96 para Puntarenas y 1,15 para Nicoya. Los s totales anuales se sitúan entre cerca de 4,6 (Palmar Sur) y cerca de 6,4 (Nicoya).
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    Mediciones climáticas de humedad del aire en los trópicos, con termistores y la ecuación sicrométrica
    (Tópicos Meteorológicos y Oceanográficos, 1997) Castro, V; Hidalgo, H
    Se probaron dispositivos electrónicos para medir la humedad del aire con sensores de capacitancia higroscópica durante periodos superiores a un año en condiciones tropicales en Costa Rica. Algunos de ellos mostraron una deriva de calibración que produjo errores de hasta un 20% de humedad relativa tras varios meses de uso. Para presentar una alternativa de bajo coste para las mediciones electrónicas de la humedad del aire en los trópicos, se utilizaron dos termistores como termómetros de palanquilla húmeda-seca. Las mediciones simultáneas con un aspiropsicrómetro Assmann y los termistores mostraron que las temperaturas medias de cinco minutos estaban dentro de 0,2°C y las humedades relativas dentro del 2%. Los termopares de cobre-constantan arrojaron resultados similares. Se demostró que los termistores son apropiados para ser utilizados año tras año, según las necesidades de las estaciones climatológicas, sin necesidad de sustituirlos ni recalibrarlos.