Analysis of moisture variability in the European Centre for Medium‐Range Weather Forecasts 15‐year reanalysis over the tropical oceans

We compare European Centre for Medium‐Range Weather Forecasts 15‐year reanalysis (ERA‐15) moisture over the tropical oceans with satellite observations and the U.S. National Centers for Environmental Prediction (NCEP) National Center for Atmospheric Research 40‐year reanalysis. When systematic differences in moisture between the observational and reanalysis data sets are removed, the NCEP data show excellent agreement with the observations while the ERA‐15 variability exhibits remarkable differences. By forcing agreement between ERA‐15 column water vapor and the observations, where available, by scaling the entire moisture column accordingly, the height‐dependent moisture variability remains unchanged for all but the 550–850 hPa layer, where the moisture variability reduces significantly. Thus the excess variation of column moisture in ERA‐15 appears to originate in this layer. The moisture variability provided by ERA‐15 is not deemed of sufficient quality for use in the validation of climate models.