Oro temperatūros ekstremalumas Vilniuje 1777-2005 metais

• Main Author: Dikčius, Silvestras
• Other Authors: Bukantis, Arūnas
• Format: Master Thesis
• Language: Lithuanian; English
• Published: Institutional Repository of Vilnius University 2006
• Subjects: North Atlantic; North Atlantic oscillation
• Online Access: https://repository.vu.lt/VU:ELABAETD1924078&prefLang=en_US

With the intention of defining the features of thermal indicators and their variations we have to consider not only average monthly and annual temperatures, but also other important indicator – the extreme of air temperature. This work is intended to analyze the warmest and the coldest five and ten day streaks through the year. The purpose of this analysis is to find out the statistical and climatic indicators of warmest and coldest streaks in Vilnius over the period 1777 – 2005. Such tasks were set trying to implement this purpose: to find out the warmest and coldest five and ten day streaks dates and thermal indicators of each year, their long-term fluctuation tendencies and the atmospheric circulation conditions, which determined these periods, to estimate the influence of North Atlantic Oscillation (NAO) to the periods of the extreme air temperatures. Linear trends, moving averages and correlations of these parameters were analyzed. It turned out, that air temperature trends of the warmest periods are decreasing. The air temperature of five days periods was decreasing 0,0052°C/year, ten days periods – 0,0062°C/ year. Opposite tendencies were observed during the cold season. Linear trends of the coldest streaks were increasing, the air temperature of five days periods increased 0,009°C/year, ten day periods – 0,0072°C/year. These trends exceed statistical significance level. The amplitudes of the temperature between the warmest and the coldest periods decreased about 3,1°C. It shows that the climate becomes less continental. The dates through the warm season, when warmest periods were fixed, according to linear trends, have tendency of becoming earlier, but not in a statistically significant way. In the most cases, when the air temperature of the warmest periods was lower, they formed earlier than averagely and when the temperature was higher – later than averagely. The correlation between these parameters is high and statistically significant. The linear trends of the warmest periods and summer NAO indices have a common tendency of decline and strong correlation between them. When NAO is positive, the air temperature of the warmest five and ten day periods in many ways exceeded the average. The trend direction of the winter NAO indices is weakly positive, but not in a statistically significant way. However, the air temperature of the coldest periods is highly correlated with NAO and these parameters fluctuate synchronically. Most of the fluctuations have one phase: when NAO is positive, the temperatures of the coldest periods are higher than average and when NAO is negative, lower temperatures are fixed. Also observed, that the warmest periods were formed by the main four atmospheric circulation types, which explain 97% cases. The coldest streaks – by the main three atmospheric circulation types (83,7%). The coldest, as well as the warmest periods mostly formed, when Vilnius city was in southern or southwestern part of anticyclone.