An Assessment of long-term surface solar flux measurements in polar regions for trend detection

There exists a large database of daily broadband total (direct+diffuse) pyranometer measurements collected for use by the Global Energy and Water Cycle Experiment (GEWEX) Surface Radiation Budget project. These surface observations are used to validate solar radiative flux estimates that pre-date more modern Baseline Surface Radiometer Network (BSRN) measurements. The measurements from many of these sites are used to form the monthly averages available through the Global Energy Balance Archive (Gilgen and Ohmura, 1998). The usage of these measurements have been called into question because of documented problems with calibration and maintenance procedures, which renews the questions concerning the usefulness of these observations. Yet, there remains a large and long time series of such measurements. So, the question remains as to whether or not these measurements are useful for climate research and if so how to best use them.

For a limited number of sites in the Arctic we will determine the mean standard deviation and the long-term trends as a function of the characteristics of each site (e.g., latitude, surface ecosystem type, and elevation). Also, the seasonal and inter-annual variations of the surface fluxes from each site will be discussed. We apply the statistical techniques to the time series of measurements from these sites as developed by Weatherhead et al. (1998) to quantify the usefulness of these data for trend detection and variability analysis. These methods account for the uncertainties in the measurements and for gaps in the time series. We will attempt to match appropriate application strategies with the reliability of these data.