No abstract

Multiannual changes in atmospheric column transparency based on measurements of direct solar radiation allow us to assess various tendencies in climatic changes. Variability of the atmospheric integral (broadband) transparency coefficient, calculated according to the Bouguer‐Lambert law and transformed to a solar elevation of 30°, is used for two Russian locations, Pavlovsk and Moscow, one Ukrainian location, Feodosiya, and three Estonian locations, Tartu, Tõravere, and Tiirikoja, covering together a 102‐year period, 1906–2007. The comparison of time series revealed significant parallelism. Multiannual trends demonstrate decrease in transparency during the postwar period until 1983/1984. The trend ends with a steep decline of transparency after a series of four volcanic eruptions of Soufriere (1979), Saint Helens (1980), Alaid (1981), and El Chichón (1982). From 1984/1985 to 1990 the atmosphere remarkably restored its clarity, which almost reached again the level of the 1960s. Following the eruption of Mount Pinatubo (June 1991), there was the most significant reduction in column transparency of the postwar period. However, from the end of 1990s, the atmosphere in all considered locations is characterized with high values of transparency. The clearing of the atmosphere (from 1993) evidently indicates a decrease in the content of aerosol particles and, besides the decline of volcanic activity, may therefore be also traced to environmentally oriented changes in technology (pollution prevention), to general industrial and agricultural decline in the territory of the former USSR and Eastern Europe after deep political changes in 1991, and in part to migration of some industries out of Europe.

The Meteorological Observatory of Moscow State University has been developing the ideas of Professor K. Ya. Kondratyev since 1955 by regular measurements of solar radiation in different regions of the spectrum and under conditions of natural illuminance, and also by monitoring various optical characteristics of the atmosphere. Observing the temporal series of solar integral radiation according to average cloud conditions has revealed a weak tendency to a decrease in direct, diffuse, global and reflected solar radiation and an increasing trend in absorbed radiation and net radiation over the past 50 years. This is expressed most distinctly in winter. The main reason for the negative tendency in solar radiation is the increase in cloud amount due to an increase in the recurrence of cyclonic activity.

The data on the radiation balance of underlying surface, its components, and main factors defining their variations are systematized and generalized for 50 years on the basis of continuous observations at the Meteorological Observatory of the Moscow State University. The climatic norms of radiation balance are obtained and its variability (diurnal, annual, and interannual) limits are estimated. The correlation dependences between its main components and factors influencing their variability are obtained and the probability of one or another diurnal radiation balance sum during the year is determined. The existence is demonstrated of the tendency toward the increase in the absorbed, effective, and atmospheric back radiation and terrestrial radiation balance mostly pronounced in the nighttime in winter months.

The temporal variability of the total atmospheric water content W and the connection of the coefficient of integral transparency P 2 , reduced to the air mass m = 2, with W and aerosol optical depth t l a , 0 at a wavelength of 550 nm were analyzed and studied from the observational data of the Meteorological Observatory of Moscow State University for 50 years . The regression equations between mean daily and monthly t l a , 0 and t 2 2 =ln P were derived in different months and seasons and can be used for retrieving t l a , 0 from the coefficient of the integral transparency for the temperate latitudes. The P 2 intervals are given for which these equations can be used.