Analysis of cold anomalies observed over Turkey during the 2018/2019 winter in relation to polar vortex and other atmospheric patterns

The mid-latitudes are exposed to outbreaks of Arctic cold air almost every winter. A stretch of below-normal temperatures prevailed over Eastern Europe, the Balkan Peninsula, parts of Mediterranean region and Turkey in the 2018/2019 winter. Extremely low temperatures associated with cold-air advection and considerable snowfalls were observed in parts of Turkey, especially during December and January. This study aims to investigate the association of observed cold anomalies with changes in the upper atmospheric conditions, especially considering polar vortex weakening, from December 2018 to January 2019, when the cold anomalies were more persistent over the country. The findings indicate that the observed cold anomalies during the two-month period were caused by several factors, including northerly and north-westerly Arctic air mass advection from an omega block pattern and polar vortex split, respectively. A persisting ridge across Western Europe caused meridional flow channels from the Arctic region to extend far towards the south. In addition, a deep upper low developed over north-eastern Europe and pushed a strong cold front towards east-central Europe, the Balkan Peninsula and Turkey. The polar vortex split was not as persistent across Eurasia as across North America but still led to cold anomalies, especially in early January 2019. Following the polar vortex split, an Arctic cold advection moved downstream and reinforced the southward displacement of the Siberian high, leading to extended cold anomalies and a stretch of below-normal temperatures over Turkey. An omega blocking pattern across the Western and Northern Europe also enhanced the northerly and north-westerly cold-air advection. In addition, a few intense cut-off lows, which moved across the eastern Mediterranean and Black Seas, intensified the local cold-air advection effects. The negative phase of the arctic oscillation corresponded well with the period of extremely cold temperatures observed over Europe during the 2018/2019 winter. The impact of the North Atlantic Oscillation variability on the cold anomalies portrayed a conflicting result for Turkey when compared to the Northern US, Canada and Northern Europe, where the cold-air outbreaks are usually associated with its negative phase. It is also likely that the decreasing Barents-Kara Sea ice favoured Ural blocking that led below-normal temperatures that impacted Eastern Europe and Turkey.