Modern trends of changes in large-scale atmospheric circulation, significant for the long-term changes in river runoff in the in the north of East European Plain, are discussed. The analysis of spatial features of the correlation between precipitation and macroscale circulation modes, as well as their manifestations in the annual river runoff changes in the Severnaya Dvina catchment. The obtained linear regression and spectral estimates of the Scandinavian mode contribution to the annual runoff variability in the Severnaya Dvina basin show that the leading factor of its anomalies appear to be the strengthening/weakening of the westerly transport described by this circulation mode in the opposite phase.
Analysis of climatic characteristics, Palmer Drought Severity Index and largescale river runoff basing on observational data (CRUTEM.5, GISS, CRU TS4.05, CRU-scPDSI) and 20th century reanalysis (ERA20C, CERA20C) shows that the Early 20th Century Warming period, in particular 1930-s, in the East European Plain was marked by the strong long-lasting drought that have no analogues during the observation period. Atmospheric circulation patterns and the drivers of this phenomenon, as well as possible analogues in the period of modern climate warming, are studied.
The variability of the snow water equivalent (SWE) in the Northern Dvina basin was analyzed using data from route snow surveys and obtained from numerical experiments for calculating high spatial resolution (1x1°) WES using local heat/moisture exchange models SWAP and SPONSOR in the Northern Dvina basin. It is shown that the use of local models can significantly improve the description of snow cover characteristics and use them in predicting spring runoff. The differences in the spatial distribution of the areas of the maximum influence of SWE on spring runoff variability between observation and modeling data are discussed.
The structure of the winter 500hPa geopotential height variability over the Northern Hemisphere extratropical zone is studied based on observations and simulations in CMIP5 experiments. We consider the shares of variability explained by the EOFs, spatial features of the patterns for the first three EOF (1-3), and the principal components of the PC (1-3) during the period of global temperature growth in 1977-1999. It is shown that the models are weak enough to reproduce the spatial and temporal features of the observed atmospheric circulation variability over the Northern Hemisphere extratropical zone. The main differences are due to the fact that the centers of actions associated with the structure of the AO/NAO modes are only partially reproduced, and the PNA structure is not reproduced.
The ability of three 20th century reanalyses (NOAA20C, ERA20C and CERA20C) to reproduce the observed features of the atmospheric circulation structure in the Northern Hemisphere is being analyzed. The leading modes of seasonal mean sea level pressure variability for winter season are analyzed using three reanalyses and HadSLP2.0 empirical data for two periods - the Early 20th century warming and the ongoing warming. It is shown that in general the reliability of the reanalyses in the first half of the 20th century is significantly worse than in the modern period. The leading mode of winter circulation variability, Arctic oscillation, is well reproduced in reanalyses throughout the 20th century, whereas the second and, especially, the third leading variability modes are characterized by significant discrepancies both in different reanalysis and periods. Systematic differences for sea level pressure in atmospheric circulation centers of action in the Northern Hemisphere are revealed in reanalyses throughout the 20th century.
Empirical orthogonal functions (EOF) of the geopotential height of 500 hPa variability over the extratropical zone of the Northern Hemisphere in winter season on the base of 30-year running periods are examined in order to reveal change in the atmospheric circulation patterns for 1948-2018. Analysis of the first EOF patterns and their features associated with changes in the intensity and localization of the atmospheric centers of action shows significant shifts the regional structure of the geopotential height anomalies. Comparison of the first five EOFs contribution to the total variability for two periods: 1968-1997 (warming of temperate NH latitudes) and 1988-2017 (sharp warming of the Arctic), reveals definite changes in the structure of circulation variability at the turn of the 20th and 21st centuries, primarily the prevalence of their negative phase occurrence and the increasing role of regional centers of action, in particular ЭОΦ3 responsible for 56% of temperature variability in the northeast Atlantic and over the Barents sea.
The temperature anomalies in early summer in Western Siberia, including the extreme heat of 2012 and 2016, are studied in terms of variations in large-scale atmospheric circulation (according to Northern Hemisphere Teleconnection Patterns). Estimates obtained using multiple stepwise regression show that the observed temperature changes from the mid-20th century, including long-term change, inter-annual variation and extremes, can be explained by the anomalies of several circulation modes. Macro-scale atmospheric circulation from the late 1980s - early 1990s can be characterized as a weakening of the westerly circulation, which is naturally accompanied by an increase in the frequency of blocking and temperature anomalies. The extreme manifestation of this мacro-scale circulation was catastrophic heat in Western Siberia in 2012 and 2016.
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