The ECMWF produces daily analyses through combination of a short-range forecast with observational data based on four-dimensional variational assimilation (ECMWF 2004). A resolution of T511L60 was used until February 2006, then a major resolution upgrade was introduced on February 1, 2006 by increasing the horizontal resolution to T799 and the vertical resolution to 91 levels (Untch et al. 2006). ECMWF analysis fields are operationally used as reference data in the WegCenter/UniGraz processing system, at a resolution of T42L60 until February 2006 and of T42L91 since then, at four time layers per day (00 UTC, 06 UTC, 12 UTC, 18 UTC). ECMWF climatologies were produced from the individual analyses at the same resolution as CHAMP climatologies for the same time span.
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