The atmospheric circulation characteristics favouring snowfall in an area with complex relief in Northwestern Greece

Abstract

The connection between atmospheric circulation over Europe and snowfall in Ioannina, Northwestern (NW) Greece, is examined. The study deals with 160 snow events, referring to the 56‐year period 1956–2011. For each of the events, the patterns of 500 and 1000 hPa geopotential height, 500 and 850 hPa air temperature, 1000–500, 1000–700 and 700–500 hPa thickness are constructed for the European area, whereas static stability K‐index, relative humidity at 500, 700 and 850 hPa levels and finally relative vorticity at 500 and 1000 hPa are also used for the Southeastern (SE) Mediterranean region, for the previous day (D‐1), the starting day (D) and the day following the cessation of snowfall (END). Factor analysis and cluster analysis are applied to the above datasets and the evolutions of the above circulation parameters are classified into eight clusters. Snowfall in NW Greece is generally associated with a low pressure system over the Ionian Sea combined with an anticyclone over Western or NW Europe, causing cold northwesterly flow in the lower troposphere over NW Greece. In the middle troposphere, a deep 500 hPa trough usually extends from Western Russia to Italy and the Ionian Sea. The eight atmospheric circulation structures differ mainly in the exact location and/or the intensity of the depression and/or the anticyclone, in the orientation of the 500 hPa trough axis and in the trajectories of the above synoptic systems between D‐1 and END days.

Characterization of snowfall events in the northern Iberian Peninsula and the synoptic classification of heavy episodes (1988–2018)

“…The synoptic situations were classified based on a Principal Component Analysis (PCA) coupled with K-mean clustering and the characteristic patterns of each group are represented by the patterns of the cluster centers obtained for four groups. The synoptic patterns associated with heavy snowfall show that a trough was present over the Iberian Peninsula, or F I G U R E 1 0 Average patterns for group IV: (a) geopotential height (m) and temperature (K) at the 850 hPa pressure level; (b) geopotential height (m) and temperature (K) at the 500 hPa pressure level; (c) mean sea-level pressure (Pa) and (d) geographical distribution of snowfall associated with the day closest to the cluster center [Colour figure can be viewed at wileyonlinelibrary.com] close by, and a low appeared over the Mediterranean Sea or Central Europe, which are similar to the circulation patterns related to heavy snowfall found by Esteban et al (2005) in Andorra (Pyreness) The low-level flow from N or NE in 85% of cases and the temperature at the 850 hPa pressure level was lower than −3 C in 70% of the cases, showing cold air advection from northern latitudes, which is also seen in other studies of occurrence of snowfall in southern Europe, as in Greece (Dafis et al, 2016). These results are in agreement with those reported by Bednorz (2011Bednorz ( , 2013 who studied snow in Polish-German and Central European lowlands.…”

“…The synoptic patterns associated with heavy snowfall show that a trough was present over the Iberian Peninsula, or close by, and a low appeared over the Mediterranean Sea or Central Europe, which are similar to the circulation patterns related to heavy snowfall found by Esteban et al . (2005) in Andorra (Pyreness) The low‐level flow from N or NE in ~85% of cases and the temperature at the 850 hPa pressure level was lower than −3°C in ~70% of the cases, showing cold air advection from northern latitudes, which is also seen in other studies of occurrence of snowfall in southern Europe, as in Greece (Dafis et al ., 2016). These results are in agreement with those reported by Bednorz (2011, 2013) who studied snow in Polish‐German and Central European lowlands.…”

“…Snow cover has been studied in Tibet (Gao et al ., 2012), the Loess Plateau in China (Jin et al ., 2015), the Atlas region (Boudhar et al ., 2010) and the Kashmir Valley in India (Mishra and Rafiq, 2017). Within Europe, most studies have been on the Artic (Wang et al ., 2005; Park et al ., 2011) and Northern and Central regions (Bednorz, 2004; Bulygina et al ., 2009; Henderson and Leathers, 2010; Szwed et al ., 2017), including the characteristics and classification of synoptic patterns associated with heavy snowfall (Babolcsay and Hirsch, 2006; Bednorz, 2011, 2013; Dafis et al ., 2016). By contrast, studies examining the snow within the western region of Southern Europe are less frequent and are mostly associated with mountainous areas.…”

Reconstruction of snow days based on monthly climate indicators in the Swiss pre-alpine region

“…In addition, knowledge of past climate is an essential key to understand aspects of climate extremes, such as excessive and/or deficient snow periods (Marty and Blanchet 2012) characterising the long-term natural variability of climate (Diodato et al 2018). In this way, access to snow days data is of value to support a wide range of ecological and environmental science research, including studies of the impact on human activities, livestock assets and infrastructures (Dafis et al 2016), and terrestrial water cycle trends and soil moisture processes (Wang et al 2018). Our understanding of the snowfall characteristics in several regions of the world is however reduced by the short records available and the poor knowledge of the complex, interacting factors involved in weather and climate modifications (Kunkel et al 2016).…”

Υδρονομία Ορεινών Λεκανών Απορροής Σε Περιβάλλον Κλιματικής Αλλαγής Στην Κεντρική Πίνδο

“…Περτούλι 5,7 7,3 3,0 0,6 0,0 0,0 0,0 0,0 0,0 0,0 0,8 4,3 21,7 (Στάθης 1998, Houssos et al 2007, Dafis 2016.…”