Interannual variations and long-term trends in total ozone over the North Caucasus

Results of analysis of variations in the total column ozone content measured at the Kislovodsk High-Altitude Scientific Station are presented. The station is located at a height of 2070 m in the North Caucasus 50 km north of the Main Caucasian Ridge and Mt. Elbrus, the highest summit in Europe. The total ozone content has been measured since 1989 with the Brewer MkII #043 spectrophotometer using standard methods. The 31-year series of observations has made it possible to analyze interannual variations and long-term trends in total ozone. The multiple regression method taking into account data autocorrelation in a wide range of time scales has been used. Seasonally dependent estimates of linear trends and interannual variations in total ozone associated with effects of the 11-year solar cycle, the quasi-biennial oscillation (QBO) in the equatorial stratosphere, the North Atlantic Oscillation (NAO), and the El Nino-Southern Oscillation (ENSO) have been obtained. The trends in total ozone over the North Caucasus contrast in sign from the trends of zonal mean total ozone. The annual trend in total ozone at the station was positive in 1989-2002 (1.6% per decade) and negative in 2003-2020 (-1.2% per decade). The strongest trends are characteristic of spring; they reach 4% per decade (in absolute value). Changes in total ozone during the 11-year solar cycle are especially significant in summer and amount to about 4%. The QBO-related interannual variations of total ozone with amplitude of about 6% are manifested in the cold season. The total ozone variations due to the NAO are pronounced in the winter-spring period. The ENSO effect on total ozone is noticeable in summer and lags approximately a year behind variations in sea surface temperature in the Nino region so that total ozone decreases after El Nino events and increases after La Nina events. The obtained characteristics of total ozone variability point at the evidence of a special character of interannual and multiyear evolutions of total ozone over the North Caucasus.