Evaluation of the atmospheric moisture and hydrological cycle in the NCEP reanalyses. Technical note

An evaluation is carried out of the moisture fields, the precipitation P and evaporation E, and the moisture transport and divergence in the atmosphere from the global atmospheric National Centers for Environmental Prediction (NCEP) reanalyses produced with four-dimensional-data assimilation. The moisture fields are summarized by the precipitable water which is compared with analyzed fields from NVAP based primarily on Special Sensor Microwave Imager (SSM/I) over the oceans and rawinsonde measurements over land, plus TIROS Operational Vertical Sounder (TOVS). The moisture budgets are evaluated through computation of the freshwater flux at the surface E - P using residual techniques from the divergence of the total moisture transport, and this is compared with the reanalysis E - P that is based upon a 6-hour integration of the assimilating model and thus depends on the model parameterizations. The P field is evaluated using Xie-Arkin Global Precipitation Climatology Project (GPCP) estimates. An atlas presents climatological means for the period 1979 1995 (17 years) and standard deviations for annual, seasonal and monthly values, and the differences between estimates.