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GEOPHYSICAL RESEARCH LETTERS, VOL. 29, NO. 24, 2223, doi:10.1029/2002GL015708, 2002

Effects of clouds on erythemal and total irradiance as derived from data of the Argentine Network

Alexander Cede

Institute for Medical Physics, University of Innsbruck, Austria


Mario Blumthaler

Institute for Medical Physics, University of Innsbruck, Austria


Eduardo Luccini

Instituto de Física Rosario (CONICET-Universidad Nacional de Rosario), Argentina and Facultad de Ciencias Exactas, Ingeniería y Agrimensura, Universidad Nacional de Rosario, Argentina


Rubén D. Piacentini

Instituto de Física Rosario (CONICET-Universidad Nacional de Rosario), Argentina and Facultad de Ciencias Exactas, Ingeniería y Agrimensura, Universidad Nacional de Rosario, Argentina


Liliana Nuñez

Servicio Meteorológico Nacional de Argentina, Argentina


Abstract

Ultraviolet (UV) erythemal and total (300–3000 nm) irradiance measurements of the Argentine Servicio Meteorológico Nacional Network were related to ground-based cloud observations. No geographical dependence was observed in the effects of each cloud-type on the irradiance, from tropical to Antarctic regions. For overcast conditions, median transmittance percentages with respect to the clearsky situation of 81%, 44% and 36% at high, medium and low clouds respectively for erythemal irradiance, and 83%, 30% and 23% for total irradiance were determined, similar to results at mid-latitudes of the Northern Hemisphere. Irradiance enhancement by broken cloud fields is more pronounced from 5 to 7 octas cloud coverage and can last even hours, with peak instantaneous values of 113% for erythemal and 133% for total irradiance, with respect to the very clean clearsky situation. In each case, the total irradiance is usually more attenuated and also more enhanced by clouds than the erythemal irradiance.

Published 28 December 2002.

Index Terms: 0320 Atmospheric Composition and Structure: Cloud physics and chemistry; 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3309 Meteorology and Atmospheric Dynamics: Climatology (1620).

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Citation: Cede, A., M. Blumthaler, E. Luccini, R. D. Piacentini, and L. Nuñez (2002), Effects of clouds on erythemal and total irradiance as derived from data of the Argentine Network, Geophys. Res. Lett., 29(24), 2223, doi:10.1029/2002GL015708.