Synoptic messages to extend climate data records

• Published in: Journal of Geophysical Research: Atmospheres 2012-04, Vol.117 (D7), p.n/a
• Main Authors: van den Besselaar, E. J. M., Klein Tank, A. M. G., van der Schrier, G., Jones, P. D.
• Format: Article
• Language: English
• Subjects: Climate change; Climatic data; data; Earth; Earth sciences; Earth, ocean, space; Environmental assessment; Exact sciences and technology; Geophysics; indices of extremes; precipitation; Regions; Scientific apparatus & instruments; synoptic messages; temperature; Time series; Weather forecasting
• ISSN: 0148-0227; 2169-897X; 2156-2202; 2169-8996
• DOI: 10.1029/2011JD016687

Synoptic messages (SYNOP) exchanged internationally for operational weather forecasting are regularly used to extend validated (quality controlled) daily climate time series to the present day, despite differences in measuring intervals and lack of validation. Here we focus on the effect of this on derived climate indices of extremes in Europe. Validated time series are taken from the European Climate Assessment & Dataset (ECA&D). Validated data and SYNOP over the period 01 April 1982 to 31 December 2004 are compared. The distribution of the difference series of validated data and SYNOP is skewed. Generally, minimum temperatures are lower or equal in the validated series, while maximum temperatures are higher or equal. This is at least partly due to the 24‐hour (validated data) versus 12‐hour (SYNOP) measuring intervals. The precipitation results are dependent on the difference between the measuring intervals of both time series. Time series of indices of extremes exhibit a non‐climatic inhomogeneity for several indices when SYNOP are used to extend the validated series, leading to spurious trends. The sizes of the trends in pure validated and pure SYNOP series are generally in good agreement, but the absolute values of the indices show an offset. Accepting a trend error of 10%, the averaged winter minimum and maximum temperature and the number of tropical nights (minimum temperature >20°C) in summer allow only a very small fraction of SYNOP in the extended series (about 5–10%), while for the other indices studied here a larger fraction can be used (up to 50%). Key Points Bias between validated series and synoptic messages In general impossible to reproduce exact min. and max. temperatures from SYNOP Offset in indices of extremes and trends when using blended data series