Vertical Structure and Dominant Horizontal Scales of Baroclinic Waves in the NASA DAO and NCEP Reanalyses

Abstract

Abstract The reanalyses of the Data Assimilation Office (DAO) of the National Aeronautics and Space Administration (NASA) are compared to those of the National Centers for Environmental Prediction (NCEP) with regard to the vertical structure and important horizontal scales of the baroclinic transients. Attention is focused on the eight Northern Hemisphere winters of 1985/86–1992/93 and on (bandpass) transients of timescales 2–8 days. The local seasonal mean vertical shear (normalized by the square root of the static stability) is very similar between the two sets of analyses. The upper-level vorticity gradient (dominated by the meridional derivative) also shows little sensitivity to which reanalysis is used. The condition for barotropic instability (change of sign of total vorticity gradient) is satisfied. The vertical structure of bandpass kinetic energy, meridional sensible heat flux, and variance of temperature gradient all show consistent differences between the NCEP and NASA reanalyses, with the NCEP...