A comparative study of observed Northern Hemisphere circulation statistics based on GFDL & NMC analyses. Part 1: the time-mean fields.

The time-mean fields in the two data sets are found to be generally in excellent agreement over the North American and Eurasian continents, where a dense observing network exists. The deviations between the data sets are large over the oceans and northern Africa, where the GFDL analyses give relatively weaker zonal wind speeds in the jet exit regions, stronger ageostrophic motions in the meridional direction, lower temperatures in the subtropical lower troposphere, and higher temperatures above the subtropical tropopause. The maximum local deviations are on the order of 10-15 m s^-1 for zonal wind, 6-8 m s^-1 for meridional wind, 50-70 m for geopotential height, and 2-4^oC for temperature. These discrepancies are associated with much weaker standing eddy kinetic energy, and much stronger equatorward transports of geopotential energy by the stationary waves in the GFDL analyses. The intermonthly variability of the monthly mean fields in the GFDL set is generally weaker over the oceans.-from Authors