Investigation of the effect of contrails on direct and diffuse irradiance

Abstract

In the present study we investigate the effect of contrails on global shortwave radiation. This investigation is performed using continuous hemispherical fish eye photographs of the sky, diffuse and direct shortwave measurements. These measurements have been performed at the solar observatory Kanzelhöhe (1540 m.a.s.l) located in the southern part of Austria during a period of one and half year. The time resolution of the measurements is one minute, which allows to accurately follow the formation-eventually the disappearance or the movement - of the contrails in the sky. Using the fish eye photographs we identified clear sky days with a high contrail persistence. We especially look at situations where the contrails were obstructing the sun. First results show that contrails moving between sun and observer/sensor may reduce the global radiation by up to 68%. In general we however observe that during days with a high contrail persistence the diffuse irradiance is slightly increased. Finally a statistic of the contrail persistence during the period of measurement is presented. In addition the maximum and mean reduction in global irradiance are shown as a function of sun obstruction duration by contrails. © 2013 AIP Publishing LLC.