Changes in air temperatures and atmosphere circulation in high mountainous parts of Bulgaria for the period 1941–2008

Abstract

Changes of air temperatures and atmosphere circulation at three high mountainous stations in Bulgaria are investigated for the period of 1941–2008. The three stations are located on peaks Musala, Cherni vrah and Botev, where air temperature data have good quality. Some missing data were recovered using the method of differences. A significant mean annual air temperature rise happened in high mountainous parts of Bulgaria — the warming is in the order of 0.7 °C for the entire period. The increase is very prominent particularly in the last 30 years. Main contributors to this overall tendency are summer months — June, July and August. To some degree, January also could be included in this group. November trend shows temperature rise at the beginning of the investigated period. One of the causes for such a tendency is atmosphere circulation in respective months. It also shows signs of considerable reorganization in both winter and summer. There is an increase of the cases of warm atmosphere patterns typical for winter, summer and autumn seasons in Bulgaria. Meridional circulation has essential significance for air temperatures during the cold half of the year. In January and June atmosphere circulation has a substantial influence on the thermal regime of air in high mountains of Bulgaria. In July, August and November this influence is reduced. There are no cycles in air temperatures for the investigated period.