Abstract
Cloud properties and the Earth’s radiation budget are defined as essential climate variables by the Global Climate Observing System (GCOS). The cloud albedo is a measure for the portion of solar radiation reflected back to space by clouds. This information is essential for the analysis and interpretation of the Earth’s radiation budget and the solar surface irradiance. We present and discuss a method for the production of the effective cloud albedo and the solar surface irradiance based on the visible channel (0.45–1 μm) on-board of the Meteosat satellites. This method includes a newly developed self-calibration approach and has been used to generate a 23-year long (1983–2005) continuous and validated climate data record of the effective cloud albedo and the solar surface irradiance. Using this climate data record we demonstrate the ability of the method to generate the two essential climate variables in high accuracy and homogeneity. Further on, we discuss the role of the cloud albedo within climate monitoring and analysis. We found trends with opposite sign in the observed effective cloud albedo resulting in positive trends in the solar surface irradiance over ocean and partly negative trends over land. Ground measurements are scarce over the ocean and thus satellite-derived effective cloud albedo and solar surface irradiance constitutes a unique observational data source. Within this scope it has to be considered that the ocean is the main energy reservoir of the Earth, which emphasises the role of satellite-observed effective cloud albedo and derived solar surface irradiance as essential climate variables for climate monitoring and analysis.
Highlights
Clouds play a dominant role within the Earth’s radiation budget [1,2,3,4]
The large regional differences in the trends demonstrate the risk of using ground stations with specific spatial distribution for the monitoring and analysis of climate change
A method for the generation of the effective cloud albedo and the solar surface irradiance based on the visible channel (0.45–1 μm) of the Meteosat Visible and InfraRed Imager (MVIRI) instruments on-board the first generation of Meteosat satellites has been presented and discussed
Summary
Clouds play a dominant role within the Earth’s radiation budget [1,2,3,4]. The warming effect induced by the increase of greenhouse gases might be modified by changes in the Earth’s albedo on a regional or global scale. Changes in the variability, and extremes of the cloud albedo could lead to a substantial change of the planetary albedo. Without clouds the Earth’s albedo would be halved. The reflected solar energy would drop from ∼100 to ∼50 W/m2 and the absorbed solar energy would increase from ∼240 to ∼290 W/m2 [2,4]. In a non-cloud Earth this effect could only partly be compensated by an increase of the emitted thermal radiation.
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