Circulation types for European regions (1948–2021)

Circulation types were calculated for five regions located across the central latitude strip of Europe (along the 50° latitude). The regions correspond to 5° × 5° longitude–latitude grid boxes stretching from Western to Eastern Europe, with centers at [5°E, 50°N], [10°E, 50°N], [15°E, 50°N], [20°E, 50°N], and [25°E, 50°N]. Circulation types (CTs) were derived from three circulation indices (flow strength, direction, and vorticity; Jenkinson & Collison, 1977). Circulation indices were calculated in a daily time step using the sea level pressure from the NCEP/NCAR reanalysis (Kalnay et al., 1996). Based on the Lamb (1972) catalogue, 27 CTs adjusted for each region were derived from the indices (Blenkinsop et al., 2009). A detailed description of the classification of daily patterns into CTs was published by Lhotka et al. (2020) for Central Europe, and the procedure was analogous for the other regions under study. Blenkinsop, S., Jones, P. D., Dorling, S. R. & Osborn, T. J. (2009). Observed and modelled influence of atmospheric circulation on central England temperature extremes. International Journal of Climatology, 29(11), 1642–1660. https://doi.org/10.1002/joc.1807 Jenkinson, A.F. & Collison, B. P. (1977). An initial climatology of gales over the North Sea. Synoptic Climatology Branch Memorandum 62, Meteorological Office, London, UK. 18 pp. Kalnay, E., Kanamitsu, M., Kistler, R., Collins, W., Deaven, D., Gandin, L., et al. (1996). The NCEP/NCAR 40-year reanalysis project. Bulletin of the American Meteorological Society, 77(3), 437–471. https://doi.org/10.1175/1520-0477(1996)077<0437:TNYRP>2.0.CO;2 Lamb, H. H. (1972). British Isles Weather Types and a Register of Daily Sequence of Circulation Patterns, 1861–1971. Geophysical Memoir, 116, HMSO, London (UK), 85 pp. Lhotka, O., Trnka, M., Kysely, J., Markonis, Y., Balek, J. & Mozny, M. (2020). Atmospheric Circulation as a Factor Contributing to Increasing Drought Severity in Central Europe. Journal of Geophysical Research: Atmospheres, 125(18), e2019JD032269, 585–594. https://doi.org/10.1029/2019JD032269