A note on the deficiency of NCEP/NCAR reanalysis surface winds over the equatorial Indian Ocean

Abstract

The seasonal cycle and intraseasonal variability of the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP) reanalysis surface winds over the Indian Ocean (IO) are assessed by comparing them with in situ surface observations from two moored buoys and winds from the SeaWinds scatterometer on the QuikSCAT satellite. The buoys are located in the central Bay of Bengal and eastern Arabian Sea. Both QuikSCAT and NCEP wind products reproduce closely the seasonal cycle and intraseasonal variability (10-60 day) in the in situ observations. In the equatorial IO, however, the seasonal mean NCEP wind speeds can be 2-3 m s^-1 smaller and the amplitude of intraseasonal variability only about half that of QuikSCAT winds. The systematic errors of NCEP zonal winds are comparable to the annual mean or amplitude of the seasonal cycle in the equatorial IO. It is suggested that the systematic error of mean and intraseasonal variability of reanalysis winds is related to systematic error in the NCEP analysis of precipitation.