In order to speed up production, ERA5 is being produced by several parallel experiments, each covering a different period, which are then appended together to create the final product. The disadvantage of this approach, is that there can be discontinuities in the final product at the transition points between the different experiments. Here, we document the transition at the end of 2009 and the beginning of 2010. Each experiment begins with a warm up year, which does not become part of the final product, but does overlap with the preceding experiment. This overlap facilitates a comparison of the two experiments to see how well they have converged to a common solution.
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| Fig. 1 Zonal mean temperature difference, for the final ERA5 HRES product minus the warm up for October to December 2009. | Fig. 2 | Fig. 3 |
Fig. 1 shows the ERA5 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 to the stratopause (from 10 hPa to 1 hPa), the differences are larger, but generally below 2 K, except near the equator at about 1 hPa where the final product is more than 2K warmer than the warm up. In the mesosphere (from 1 hPa to 0.01 hPa), the final product is generally more than 2 K colder than the warm up near the equator, 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, but of different signs, are also apparent in both polar regions above about 0.3 hPa.
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