This paper is concerned with comparing sets of analyses. The baroclinic transients in the reanalyses of the Data Assimilation Office (DAO) of the National Aeronautics and Space Administration (NASA) are compared to those in the operational analyses of the European Centre for Medium Range Weather Forecasts (ECMWF) for the winters of 1985/86 through 1992/93. The data are consistently filtered to a T42 resolution by a combination of spatial interpolation and spectral transforms, and are filtered with a band-pass (BP) filter to retain periods of 2-8 days.
The vertical and horizontal shears of the winter seasonal mean flow are very similar in the two sets of analyses. The variances of meridional velocity and vorticity are consistently weaker in the NASA DAO reanalyses than in the ECMWF analyses during the last four winters.
A difference in vertical structure of the transients is seen in the BP variance and BP meridional heat flux, with the ECMWF analyses giving values larger (smaller) at upper (lower) levels. The ECMWF poleward heat flux, at 200 hPa is larger over both oceanic waveguides, and at 850 hPa it is larger over northeastern North America, but it is weaker over the Pacific waveguide.
The BP available potential to kinetic energy conversion is considerably weaker in the DAO results for all winters, and this difference intensifies during the later winters. Locally the differences in BP vertical heat flux are as large as 50% at 850 hPa in the Atlantic waveguide and 35% at 500hPa in the Pacific waveguide. The BP variance in vertical velocity in the DAO analyses is only about 50-60% of that in the ECMWF analyses.
The total diabatic heating in the NASA analyses has much smaller values in the mid-troposhere compared to the lower troposphere. The smaller mid-tropospheric heating rates are much weaker than estimates of heating from the ECMWF analyses given by Sardeshmukh, (1993).
The BP variance of temoperature gradient is larger at 850 hPa in the ECMWF analyses over land (particularly over northeastern North America and Asia) and somewhat smaller over the oceans. At 500 hPa this variance is considerably stronger in the ECMWF results over the oceanic waveguides, particularly in the last four winters. This is apparently due to the improvements in the assimilation of satellite radiances in the ECMWF system in which the synoptic temperature structure of the first guess is not smoothed excessively.
The fields of meridional and vertical velocity BP variance are computed as a function the horizontal truncation limit for all limits in the range T2 to T42. The added variance contributed by incrementing the global wavenumber by one is given by the derivative of the variance with respect to wavenumber. Substantial differences between analyses (the ECMWF being stronger) are evident at T15 truncation.
last update: 1 April 1996
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