Statistical and Dynamical study of the cold winter spells over the Balkan Peninsula.

Extreme temperature values are an issue that concerns every society around the world since their impact can cause serious problems even to public health. During the winter months, southeastern Europe and especially the Balkan Peninsula, is characterized by high temperature variability and is often affected by extreme weather events resulting in the creation of serious socio-economic problems. There is therefore a need to further study the causes that contribute to creation of such cold winter spells, so that in the future there will be the possibility of timely forecasting and therefore alerting in order to better prepare each society. The present work provides an extensive climatic analysis of the cold extreme sequences that occurred in the Balkan Peninsula. This climatology includes temporal variations and classification of extreme cold spells according to their source of creation and their characteristics. More specifically, the aim of this work is to study the temporal and spatial variability of the extreme cold spells and to determine the circulation conditions of the occurrences. Daily temperature data from 20 Balkan stations has been collected from the “European Climate Assessment and Datasets” (https://www.ecad.eu/) for the period 1958-2019 (62 years). A cold spell is defined as a sequence of at least 3 cold days, i.e. when the minimum air temperature is below than the 10^th percentile of the probability density function from the observation (i.e. Tmin<P10).  After identifying the extreme cold spells, the above parameters are used to describe each event, namely frequency, duration, severity and intensity. The most intense cold spells of have been studied in a synoptic analysis to investigate their fundamental dynamic characteristics and to examine their association with anomalies in the upper layer of the atmosphere. All in all, the proposed study aims to understand the atmospheric circulation conditions that exist in advance and during the extreme cold spells. In addition, the final concept will investigate to identify possible common circulation types associated with their occurrence so that in the future the early indications of such patterns can contribute the early prediction of corresponding extreme cold spells.