Centro de Investigaciones Geofísicas

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Browsing Centro de Investigaciones Geofísicas by Author "Alvarado, L"

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    Climatología de la Atmósfera Libre sobre Costa Rica
    (Tópicos Meteorológicos y Oceanográficos, 2001) Alvarado, L; Fernández, W
    A time series of aerological data for the 1972-1989 period was used in order to obtain a climatoly of the free atmosphere over Costa Rica, actualizing and complementing a previous study (Grandoso et al.,1981). The analyzed dynamic and thermodynamic characteristics are the result of radiosonde direct measurements (pressure, temperature, mixing ratio and wind) and derived variables such as geopotencial, potential temperature (and hydrostatic stability), equivalent potential temperature (and convective stability), saturation equivalent potential temperature (and conditional stability), relative humidity, zonal and meridional components of wind, and vertical wind shear.
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    Evaluación de modelos numéricos de Tercera Generación para el pronóstico de oleaje en Centroamérica y México
    (Tópicos Meteorológicos y Oceanográficos, 2001) Lizano, O; Ocampo, F; Alvarado, L; Puig, J; Vega, R
    The evaluation and implementation of two public domain wave spectral models: SWAN and WAM to be used in hindcasting and forecasting in the Central American region are presented. The typical model characteristics are analyzed using simulations for simple bathymetric cases. The model responses are evaluated using boundary conditions in the Caribbean region including extreme meteorological conditions like hurricanes. Those natural phenomena’s are of great importance given the historical frequency impacts in the region. The SWAN model shows some difficulties to propagate wave energy in big areas generating some wave height and direction anomalies mainly around islands or in low interpolated depth values. The numerical schemes and the different model’s variable parameterizations are responsible for the different spatial energy propagation found in some applications in this study. An integrated system could be working for the whole region where the wave information is necessary in activities like fishing, marine transit and transport, port operations and tourist activities.
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    Frecuencia de los ciclones tropicales que afectaron a Costa Rica durante el siglo XX
    (Tópicos Meteorológicos y Oceanográficos, 2003) Alvarado, L; Alfaro, E
    It 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.
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    Relación de las anomalías climáticas de la atmósfera libre sobre Costa Rica y la variabilidad de las precipitaciones durante los eventos El Niño
    (Tópicos Meteorológicos y Oceanográficos, 2001) Alvarado, L; Fernández, W
    The main physical causes of the sharp seasonal and inter-annual changes in the two rainfall regimes of Costa Rica during El Niño events are explained by means of the results of Alvarado and Fernández (2001). It is found that the rainfall anomalies are associated with: (i) the persistence of the northerly winds in the lower troposphere and the intensification (weakening) of the easterlies in the summer (winter) period, whose interaction with topography enhances the Föhn effect, (ii) the development of anomalous westerly winds in the upper troposphere during summer, (iii) the sharp decrease of humidity in the lower troposphere and its increase at mid-levels, (iv) the shorter time of permanence over Costa Rica of the ITCZ and its location further South than usual on the Pacific, (v) the considerable increase in wind shear during winter and summer, (vi) the higher values in equivalent potential temperature (qe) and the higher elevation of the convectively unstable layer, which implies a greater potential for deep convection, (vii) the decrease in the tropical cyclone activity in the Caribbean Sea and its increase in the Pacific Ocean, and (viii) the greater convergence in Western Caribbean due to a greater dynamic instability associated to the intensification of the lower level jet.
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    Variabilidad interanual y estacional de la atmósfera libre sobre Costa Rica durante eventos de El Niño
    (Tópicos Meteorológicos y Oceanográficos, 2001) Alvarado, L; Fernández, W
    In this article the main climatic fluctuations of the free atmosphere over Costa Rica during El Niño events are diagnosed by means of using a composite technique of the anomalies of the meteorological fields. These climatic fluctuations include: (i) the greater warming (cooling) of the air in all the troposphere (stratosphere), (ii) the decrease in atmospheric pressure at the surface, (iii) the greater values of equivalent potential temperatue (θe) and the greater depth of the convectively unstable layer, (iv) the greater magnitude of the trade winds during the summer and their decrease during winter, (v) a more intense wind shear between winter and summer, (vi) the west (east) phase at the equator is reflected in Costa Rica as an intensification (weakening) of the dominant easterly winds, (vii) the CBO signal shows a spectral maximum in the 27 months period. It is more intense at 30 hPa and disappears completely at 100, where the period of the spectral energy maximum approximately coincides with the cycle of El Niño phenomenon.