An evaluation of recent performance of ECMWF's forecasts
Thorpe, Alan ; Bauer, Peter ; Magnusson, Linus ; Richardson, David
Since the end of 2009 the anomaly correlation coefficient (ACC) measure of the skill of ECMWF’s high-resolution forecasts (HRES) for the northern hemisphere extra-tropics has been essentially constant – that is, not showing an increase in ACC values for over 3 years. A number of new model cycles have been introduced in this period. Pre-operational testing of the new cycles demonstrated increases in skill resulting from the improvements to the data assimilation, model resolution and representation of physical processes, as regularly reported in the ECMWF Newsletter and on the ECMWF website. Why, then, does the operational HRES skill not reflect these improvements? If the interpretation of this period – hereafter referred to as a pause – were to be that the skill of the ECMWF HRES has reached a plateau then this is not in accord with our scientific expectations! Consequently the pause is worthy of some investigation and comment.
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