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Fig.1 shows the zonal mean temperature (contours) and difference between the final product and the warm up (colours), for the last three months of the overlap year, October - December 2009. In the troposphere and lower stratosphere, between 1000 hPa and 10 hPa the differences are small (less than 0.2 K). From the mid-stratosphere into the mesosphere, the differences are larger, but generally below 2 K. However, in some places the differences are larger. Near the equator, at about 1 hPa the final product is more than 2K warmer than the warm up, whereas above, the final product is generally more than 2 K colder, and its more than 5 K colder at about 0.05 hPa. In addition, this colder region spreads into the northern hemisphere near 0.5 hPa, and the southern hemisphere above 0.05 hPa. Differences of more than 2 K are also apparent in both polar regions above about 0.3 hPa.
A similar comparison for the transition from 1988 to 1989 in ERA-Interim reveals slightly larger differences below 10 hPa, in the region of the South Pole and near the equator. The differences in the mid to upper stratosphere (10 to 1 hPa) are similar to those in the 2009/2010 ERA5 transition, with a similar magnitude and concentrated at low latitudes. The differences in the ERA-Interim transition in the lower to mid mesosphere (1 to 0.1 hPa, with the latter being the top of the ERA-Interim domain) are generally smaller than in the ERA5 transition, having a magnitude less than 2 K, except near the equator at about 0.8 hPa where the magnitudes exceed 3 K.