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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, is generally larger than the 2009/2010 ERA5 transition differences in the lower latitudes of the troposphere and stratosphere. The largest values of the spread are located in the mid to upper stratosphere, at lower latitudes, where values exceed 0.8 K. This region merges into a second area of relatively large uncertainty, in the mesosphere northern mid-latitudes of the northern hemispheremid-mesosphere, where values exceed 0.7 K in the mid-latitudes of the mid-mesosphere. In general, the spread in the mesosphere is smaller than the ERA5 transition differences.
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