THE RELIABILITY OF THE SURFACE AIR TEMPERATURE AND GEOPOTENTIAL HEIGHT DATA AND THEIR LONG-TERM CHANGES IN THE 20CR PROJECT.

The reliability of surface air temperature (SAT) and 500 hPa geopotential height (H500) of the recent 20CR project data has been evaluated on daily, seasonal and longer timescales for western and eastern parts of Eurasia. The mean daily difference (between 20CR and observations) is up to 1°C in autumn-winter season and 2°C in the springsummer season. For stations located in Western Eurasia the difference appears to be generically similar for selected stations in Eastern Eurasia region. The regional differences are more obvious for H500 and exceed several decameters. Nevertheless, the correlations between daily reanalysis data and observations look quite reliable and vary from about 0.65 to 0.95 over western and eastern Eurasian regions. Thus, the results confirm the validity of the modern approach used in the 20CR project and demonstrate a fairly good reliability of the reanalysis results for climate research. That’s why, long-term trends of the frequency of blockings over Eurasian region and midlatitude SAT linear trends has been analysed for the 1875-2012 period. It was found the positive long-term trend of the frequency of winter blockings over Eurasian region accompanied by warming over most part of the Northern Hemisphere mid-latitudes. [ABSTRACT FROM AUTHOR]