Comparison of 850‐hPa relative humidity between ERA‐40 and NCEP/NCAR re‐analyses: detection of suspicious data in ERA‐40

An exploratory study is performed on the 850‐hPa relative humidity data (RH850) extracted from the Re‐Analysis Project (ERA‐40) and National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) re‐analyses covering a domain centred on western Europe (60°W–60°E, 15°N–75°N). The largest deviations between the two data archives are observed over the North Atlantic Ocean. In addition, unrealistic values of RH850 are detected in the ERA‐40 re‐analysis at resolutions of both 2.5° and 1.125°. There is no strong correlation between RH850 provided by ERA‐40 and observations from radio sounding stations, thus ruling out a straightforward correction of the detected anomalous values.