Abstract
A satellite-based climate record of monthly mean surface solar irradiance (SIS) is investigated with regard to possible inhomogeneities in time. The data record is provided by the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) Satellite Application Facility on Climate Monitoring (CM SAF) for the period of 1983 to 2005, covering a disk area between ±70° in latitude and longitude. The Standard Normal Homogeneity Test (SNHT) and two other homogeneity tests are applied with and without the use of reference SIS data (from the Baseline Surface Radiation Network (BSRN) and from the ECMWF (European Centre for Medium-Range Weather Forecasts) ERA -Interim reanalysis. The focus is on the detection of break-like inhomogeneities, which may occur due to satellite or SIS retrieval algorithm changes. In comparison with the few suitable BSRN SIS observation series with limited extension in time (no data before 1992), the CM SAF SIS time series do not show significant inhomogeneities, even though slight discrepancies in the surface measurements appear. The investigation of the full CM SAF SIS domain reveal inhomogeneities related to most of the documented satellite and retrieval changes, but only for relatively small domain fractions (especially in mountainous desert-like areas in Africa). In these regions the retrieval algorithm is not capable of adjusting for the changes of the satellite instruments. For other areas, e.g., Europe, no such breaks in the time series are found. We conclude that the CM SAF SIS data record has to be further assessed and regionally homogenized before climate trend investigations can be conducted.
Highlights
The solar radiation incident at the Earth’s surface, denoted in the following as SIS, is a major contributor to the surface energy budget and, substantially determines the prevailing climatic conditions [1]
In most of the analyses, we focused on the Standard Normal Homogeneity Test (SNHT, Alexandersson [35]) to detect possible discontinuities in the investigated time series
For most of the analyses presented we rely on the SNHT, while excluding positive results for the first and the last ten months of a time series to take into account the mentioned sensitivity problem of this method
Summary
The solar radiation incident at the Earth’s surface, denoted in the following as SIS (surface incoming solar irradiance), is a major contributor to the surface energy budget and, substantially determines the prevailing climatic conditions [1]. Global high-quality observations of the incoming solar surface radiation are of major scientific and commercial interest. With the Baseline Surface Radiation Network (BSRN), established in 1992, highly accurate SIS measurements have become available at certain sites (currently more than 50). The BSRN data, intended for monitoring long-term changes of SIS and for the evaluation of satellite and climate model datasets [3], have been used in numerous studies dealing with the surface radiation budget [4] and the references therein
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