Long-Term Cloud Cover Variations within the Region of Optical Observatories in the South of Eastern Siberia

Abstract

In the south of Eastern Siberia (Russia), there are optical observatories of the Institute of Solar-Terrestrial Physics SB RAS. The observatories are equipped with instruments to observe the Sun, near and deep space. The first one, Sayan Solar Observatory, is located in the mountains at the height of 2,000 m (51.67 N, 100.99 E). The second, Baikal Astrophysical Observatory, is on the southern bank of Lake Baikal (51.86 N, 104.86 E). These two observatories were built in the 60s-70s of the last century. The purpose of this work is to study the long-term dynamics of cloud cover within the region of the optical observatories. We used data of: Monthly mean Total cloud cover (TCC), High cloud cover (HCC), Low cloud cover (LCC) and Medium cloud cover (MCC) values derived from ECMWF ERA-Interim 1979-2018 [1] and Monthly mean TCC values derived from NCEP/NCAR Reanalysis Gaussian Grid 1948-2019 [2]. Both reanalysis projects show a long-term decline in the annual TCC values. For the summer season, negative trend is most obvious and typical for HCC, MCC, and LCC. In our opinion, the causes of the current changes should be searched for in the peculiarities of long-term variability of large-scale atmospheric circulation, particularly, in blocking activity.