An analysis of the synoptic and climatological applicability\ud of circulation type classifications for Ireland

摘要

Circulation type classifications compiled as part of the COST733 Action, ‘Harmonisation and Application\udof Weather Type Classifications for European Regions’, were evaluated based on their ability to describe variations in\udsurface temperature (maximum and minimum) and precipitation across the Irish landmass. In all 16 different classification\udschemes, representative of four general approaches in synoptic typing (leader algorithm, optimization scheme, predefined\udtypes, eigenvector analysis) were considered. Several statistical measures variously quantifying performance in arranging\uddaily observations into clearly defined homogenous groups were employed. Based on the results it was not possible to identify\uda single optimum classification or general approach in synoptic typing. This is related to inconsistencies in performance with\udrespect to the specific target variable and statistical measures used; the results were also shown to be conditional on the number\udof circulation types (CTs) as well as spatiotemporal dependencies in performance. However, the study did indicate that those\udtyping schemes based on predefined thresholds (Litynski, GrossWetterTypes, LambWeather Type) – along with the Kruizinga\udand Lund classifications – were better able to resolve surface temperature. With respect to precipitation those classifications\udderived using some optimization procedure (simulated annealing, Self Organizing Maps, k-means clustering) were consistently\udamong the best-performing schemes. In capturing the relationship between synoptic-scale circulation and precipitation the\udimportance of incorporating somemeasure of vorticitywas highlighted; in contrast the inclusion of discrete directional patterns\udwas shown to be important for resolving variations in local temperature. The classifications generally performed best for\udwinter, reflecting the closer coupling between circulation and surface conditions during this period. Spatial patterns in the\udsynoptic–climatological relationship were more apparent for precipitation. In this case those more westerly/south-westerly\udstations open to zonal airflow exhibited a stronger response to circulation variability.