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| Fig. 1 Zonal mean temperature (C) of the final ERA5 HRES product (contours) and zonal mean temperature difference (C) for the final ERA5 HRES product minus the warm up (colours), for October to December 2009. The vertical coordinate is pressure of the model levels. | Fig. 2 Zonal mean temperature (C) of the final ERA-Interim product (contours) and zonal mean temperature difference (C) for the final ERA-Interim product minus the warm up (colours), for October to December 2009. The vertical coordinate is pressure of the model levels. | Fig. 3 Zonal mean temperature (C) of the ERA5 EDA control (contours) and zonal mean ERA5 EDA ensemble spread of temperature (C) (colours), for September to November 2009. The vertical coordinate is pressure of the model levels. |
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A similar comparison for the transition from 1988 to 1989 in ERA-Interim (Fig. 2) reveals that in the troposphere and stratosphere (from 1000 hPa to 1 hPa), the differences are, on the whole, of a similar magnitude to those in the 2009/2010 ERA5 transition, although ERA-Interim does exhibit transition differences lower down in the atmosphere. However, in the lower to mid-mesosphere (from 1 hPa to 0.1 hPa, with the latter being the top of the ERA-Interim domain), the differences in the ERA-Interim transition are generally smaller than in the 2009/2010 ERA5 transition, having magnitudes less than 2 K, except near the equator at about 0.8 hPa where the magnitudes exceed 3 K. The spread in temperature, for September - November 2009, in the ERA5 10 member ensemble (Fig. 3), which gives some indication of the uncertainty, shows that the largest values are located at lower latitudes, in the mid to upper stratosphere, where values exceed 0.8 K. This region merges into a second area of relatively large uncertainty, in the mesosphere of the northern hemisphere, where values exceed 0.7 K in the mid-latitudes of the mid-mesosphere.
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| Fig. 4 Zonal mean eastward wind (ms-1) of the final ERA5 HRES product (contours) and zonal mean eastward wind difference (ms-1) for the final ERA5 HRES product minus the warm up (colours), for October to December 2009. The vertical coordinate is pressure of the model levels. | Fig. 5 | Fig. 6 |
Fig. 4 shows the ERA5 zonal mean zonal wind (contours) and difference between the final product and the warm up (colours). In the troposphere and lower stratosphere, between 1000 hPa and 10 hPa, the only region with differences greater than 0.2 ms-1 is a latitudinally confined region near the equator, above about 50 hPa, where the differences of alternating sign are no larger than about 1 ms-1. From the mid-stratosphere to the stratopause (from 10 hPa to 1 hPa), the equatorial differences are slightly larger, with a larger latitudinal extent. However, in the mesosphere (from 1 hPa to 0.01 hPa), the differences are much larger, with peak values greater than 50 ms-1 near the equator at about 0.1 hPa and values greater than 2 ms-1 are widespread.
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