PROGRESS IN ESTIMATING TOA AND SURFACE DATA PRODUCTS
During the past 30 to 40 years important progress has been made in determining components of the radiation budget over the entire globe at upper and lower boundaries of the atmosphere using satellite observations. In the 1960s and 1970s exploratory research was done on the basis of a scarce network of ground stations and data from a single satellite, beginning with the early TIROS and Nimbus series.
The investigations in the 1980s and 1990s made use of data from multiple satellites (e.g. ERBE and later CERES, complemented by ScaRaB; ISCCP uses up to seven satellites), and of modern ground-based observation networks (e.g. BSRN; SURFRAD, ARM, Skynet and Aeronet and many national efforts and international networks in several regions of the GEWEX CSEs).
The CERES project features improved angular sampling and convolution with MODIS data in the determination of TOA fluxes and ties these results consistently with a Surface and Atmospheric Radiation Budget (SARB) component.
The recently launched GERB on Meteosat 8 provides an interesting opportunity for inter-satellite "calibrations" and for better knowledge of the diurnal cycle of ERB components at TOA. These new activities present an opportunity for comparisons with and improvement of older methods that produce longer records. Climate modelers are also trying to evaluate their model performance by comparing their computational results against these observations.
THE NEED FOR AN ASSESSMENT
Several global data sets have been developed and are starting to be used by the research community. In the US and in Europe work has started on developing such data sets in an operational mode, providing them for the purposes of the GCOS.
One of the chief purposes of the international GEWEX program is to observe, understand and model the global hydrological cycle and energy fluxes. To date long-term radiative flux datasets have largely been analyzed independently of the water cycle, but modeling requires the proper integration and joint analysis of these data. Thus, the need to assess the remaining uncertainties of the radiative fluxes is crucial to the next step of integrating the observational understanding of the radiative and hydrological cycles.
Serious questions are being asked about the quality and reliability of these data sets, especially when used to monitor the small, slow changes of climate. These questions must be answered quantitatively with a systematic determination of possible improvements and uncertainty limitations.
This is an appropriate time for satellite communities, modelers and ground experiment specialists to meet together and explore possibilities to advance this subject by exploiting other experiences and also to consider how each community can help other.
INITIAL WORKSHOP TOWARDS ASSESSMENT
To this end, a workshop was held at the ETH in Zürich, Switzerland from 4 to 6 October 2004 to plan an assessment of the global, long-term radiative flux datasets to summarize current data quality and to identify areas of needed improvement in the analysis of the Earth's radiation balance and its variability. Its major tasks therefore were to:
- Obtain a complete overview of all available datasets on the radiation budget at TOA and at ground and their availability,
- Develop a strategy for assessment, particularly developing a basis for estimating the range of uncertainties in such data on various time and space scales, and
- Identify and solicit requirements from stakeholders.
The workshop developed the following assessment plan.
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