Evaluation of soil moisture in the NCEP-NCAR and NCEP-DOE global reanalyses

This study compares soil moisture analyses from the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) global reanalysis (R-1) and the later NCEP-Department of Energy (DOE) Atmospheric Model Intercomparison Project (AMIP) global reanalysis (R-2). The R-1 soil moisture is strongly controlled by nudging it to a prescribed climatology, whereas the R-2 soil moisture is adjusted according to differences between in model-generated and observed precipitation. While mean soil moisture fields from R-I and R-2 show many geographic similarities, there are some major differences. This study uses in situ observations from the Global Soil Moisture Data Bank to evaluate the two global reanalysis products. In general, R-2 does a better job of simulating interannual variations, the mean seasonal cycle, and the persistence of soil moisture, when compared to observations. However. the R-2 reanalysis does not necessarily represent observed soil moisture characteristics well in all aspects. Sometimes R-I provides a better soil moisture analysis on monthly time scales, which is likely a consequence of the deficiencies in the R-2 surface water balance.