期刊名称：Tellus A: Dynamic Meteorology and Oceanography
电子版ISSN：1600-0870
出版年度：2001
卷号：53
期号：1
页码：35-55
DOI：10.3402/tellusa.v53i1.12178
摘要：The targeting procedure developed at ECMWF is used to make ensembles specially designedfor northern Europe and parts of the north Atlantic Ocean. A total of 35 ensembles are integrated,consisting of 20 winter cases and 15 summer cases in 1997, each consisting of 20 membersplus one control forecast. The ensembles are run up to day 10, and the ensemble spread insidethe target area continues to increase all through the 10 days. Two distinct regimes of increasecan be found, the first increase is consistent with the perturbations moving in and through thetarget area, it is hypothesised that the latter increase in ensemble spread around forecast day 5–7is connected with increasing non-linearity. The performance of the experimental ensembles iscompared to the operational ensemble prediction system (EPS) at ECMWF, both with all 50members and with only 20 members. The spread increases when the number of members in theensemble prediction system is increased, and the spread increases inside the target area whentargeting is applied.We find that the increase in spread when going from EPS with 50 membersto the targeted ensembles is larger than when going from 20 to 50 ensemble members of theoperational sets. Clearly targeting must be an option when predicting for a sub-domain of thehemisphere. Looking at other measures, such as the Brier skill score (BSS), relative operatingcharacteristic (ROC) curves and cost/loss analyses, the impact of the targeting is modest forthe winter cases, but the impact for the summer cases is evident. For the winter cases a largepart of the operational perturbations were located in the same area as the targeted perturbations,and the differences for the two sets are small. For the summer cases the operational perturbationswere mostly split between two locations and hence the targeting will give results differing morefrom the operational.
