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Reanalysis data are very useful for studying the stratosphere. They can beused for analysis of long-term trends (temperature, wind speed, humidity,etc.) or analysis of global atmospheric dynamics, etc. There are variousreanalysis projects that provide outputs which are not identical. In thispaper, we mutually compare three of them, ERA-40, ERA-Interim and NCEP/NCAR,and compare them with balloon radiosonde observations from Prague, Port Hardyand Valentia stations. This comparison is done for wind speed and directionat pressure levels 100 and 10 hPa and for various periods between 1957 and2009. The results show that the differences between reanalysis vary. Windspeed data from all three analyses reasonably agree except for the 10 hPahistorical data before 1966 and particularly ERA-40 data at the end of thedata series (1998–2001). The quality of the ERA-40 10 hPa stratosphericwind data has been proven to be substantially worse over the last four ERA-40years of 1998–2001 (2002) compared to previous years, both in wind speed andwind direction. The reanalysis data results are compared with radiosondeobservations from Prague, Port Hardy and Valentia stations at 10 hPa for themonths of February between 1989 and 2009. The results show that there aresometimes surprisingly large differences, more for ERA-Interim versus Praguemeasurements. Differences in wind direction greater than 45°(outliers) between the reanalysis data and Prague observations in winddirection occur in Februaries predominantly when winds in Prague are in"minor" sectors, such as north, northeast and east (easterlies), whereas"major" sectors, particularly the dominant W (westerlies) wind sector,exhibit almost no outliers

Differences in mid-latitude stratospheric winds between reanalysis data and versus radiosonde observations at Prague