Isotope composition of macrocirculation processes responsible for precipitation in the Altai mountains

Abstract

An estimation of changes in the precipitation over the Altai mountains in 1959-2016 was carried out using the Mann-Kendall-Sneyers test. It was found that the precipitation has a step change in 1980. The step change point of precipitation in the Altai mountains coincides with the beginning of «zonal epoch of elementary circulation mechanisms» for the Siberian sector according to Dzerdzeevskii’s classification. B.L. Dzerdzeevskii considered 41 subtypes of elementary circulation mechanisms (ECMs) based on analysis of maps of baric topography at the 500 hPa level. To reveal the role of various ECMs in the Altai precipitation, we calculated the contribution of the ECMs which correspond to the Siberian sector to the precipitation. It was found that the most significant contribution to the precipitation regime of the Altai mountains was provided by the «West zonal and southern meridional» circulation group. The maximal contribution to the precipitation of 2016 was given by the «West zonal and southern meridional» circulation group (26.8%). The precipitation of this ECM group is characterized by the heaviest isotope composition (δ18O -9.85‰ and δD -78.65 ‰) relatively to the values obtained for the other circulation groups. In the ECM of this group of circulations the precipitation is most often caused by southern cyclones coming from the Aral-Caspian region, the waters of which have the heaviest isotope composition.