Trends in frequency and persistence of atmospheric circulation types over Europe derived from a multitude of classifications

Abstract

The aim of this study is to quantify changes of atmospheric circulation over Europe using a large number of classifications of circulation types that were collected and developed within the COST733 Action ‘Harmonisation and Applications of Weather Types Classifications for European Regions’. Circulation changes over Europe are studied in terms of changing seasonal frequency and persistence of daily circulation types in the period September 1957–August 2002. The extensive collection of both subjective and objective (computer‐assisted) catalogues of circulation types in 12 European domains serves as a platform for comparison of different classification methods, varying numbers of circulation types, sequencing of input sea‐level pressure data, and spatial scale of circulation processes. The overall picture of frequency and persistence trends is consistent with two large‐scale tendencies: strengthening and eastward shift of the North Atlantic Oscillation, and a northwestward shift of storm tracks. There is, however, a limited consistency in the trends between individual classifications. This inconsistency leads us to the recommendation that results of climatological analyses based on a single classification should not be generalized and overinterpreted; it is highly advisable to simultaneously use multiple, and as many as possible, classifications in climatological studies.

Weekly to multi‐month persistence in sets of daily weather patterns over Europe and the North Atlantic Ocean

“…WP frequencies of occurrence are likely modulated by lower‐frequency (slowly varying) physical processes, such as large‐scale atmospheric teleconnection patterns and land‐atmosphere interactions. For example, studies have associated variations in the North Atlantic Oscillation (NAO) with changes and trends in the frequencies of WPs from a range of classifications (e.g., Stefanicki et al ., ; Casado et al ., ; Kučerová et al ., ). In particular, during the 1990s the NAO entered a more positive phase (Ostermeier and Wallace, ), which means an increased pressure gradient between the teleconnection's high and low pressure centres near the Azores and Iceland, respectively, resulting in a strengthening of the prevailing westerly flow.…”

“…An exception found by Kučerová et al . () is for some classifications during the summer over the eastern Mediterranean, which show a mean persistence of up to 52 days, which the authors state reflects the classifications’ unrealistic temporal behaviour. We propose a less strict assumption, allowing for limited numbers of different WPs to break up occurrences of the WP(s) under consideration.…”

“…WP persistence has been much less researched and has focussed on changes and trends in mean persistence over time (Stefanicki et al ., ; Werner et al ., ; Kyselý, ; Kyselý and Domonkos, ; Kyselý and Huth, ; Kyselý, ; Blenkinsop et al ., ; Cahynová and Huth, ; Casado et al ., ; Kučerová et al ., ). Missing from the literature is analysis of the longest persistent sequences of WPs and the implications for atmospheric circulation and hydro‐climatic variables.…”

Variation of macro‐circulation forms over the Atlantic‐Eurasian temperate zone according to the Vangengeim‐Girs classification

“…The data summarized in Table provides, through the example of V‐G classification, an answer to the question, formulated by Kučerova et al (), about the influence of “the number of synoptic situations” (here: nCEs) and their persistence (tCEs) on the annual frequency of particular circulation forms. These interrelations are different for the V‐G zonal (W) and meridional (E, C) macroforms.…”

“…The long‐term fluctuations of V‐G tCEs do not show an increase in persistence similar to that observed around 1990 in Hess‐Brezowsky classification (Kyselý and Huth, ). Our observations confirm the subsequent conclusions of the authors who state that the increase in HB type persistence is an artefact (Huth et al , ; Kučerova et al , ).…”