On the basis of reanalysis data and hydrodynamic modeling the spatial-temporal features of Wallace-Gutzler circulation indices, calculated at daily intervals, are studied. The circulation index extremes are interpreted as "weather regimes" with the alteration closely related to the low frequency variability of the atmospere. The outliers and extreme values are studied using nonparametric statistics and exploratory techniques. On the basis of the experiments performed assessments of the potential predictability of the outlier and extreme value characteristics for the summer and winter seasons are given.
The spatial and temporal relationships between sea surface temperature anomalies (SSTA) in the North Atlantic and the large-scale mid-troposphere circulation features in the Northern Hemisphere during the summer and the winter seasons are investigated. Results are based on atmospheric circulation indices (CI), introduced by Wallace and Gutzler for physical reasoning the low frequency atmospheric oscillations. Extreme levels and extreme situations in the mid-troposphere were defined and the SSTA composite charts were constructed with backward lags from 0 to 3 months. Analysis shows that several CI extreme phases of different signs are associated with synchronous and asynchronous SSTA composites of statistically separable types, or even antipodes, which may be interpreted as the intraseasonal influence of the ocean on the large-scale mid-troposphere anomaly features. Noteworthy is the role of the North Atlantic tropical zone in formation of ridges and blocking situations both in synchronous and asynchronous aspects. The North Atlantic SSTA relations to the West Atlantic Oscillation are shown to be significantly weaker that the same to the East Atlantic Oscillation.
The features of the spatial and temporal distribution of the main meteorological values in the Northern Hemisphere in 2019 are considered. A brief description of climate change on the background of long-period variability of extreme meteorological phenomena, which identified by WMO climate indices, is given. Quartile analysis and nonparametric Mann-Kendall criterion are used to assess the significance of changes in the frequency and intensity of extreme meteorological phenomena in different regions of Russia. The increase in the growth of the average temperature in the Northern Hemisphere in the spring and summer of 2019 compared to 2018 and early 2019 is noted. The prolonged large-scale anomalies of weather regimes were observed in the warm period of 2019: heatwaves in Western Europe, in the south of European Russia, in Siberia, Alaska, and as well heavy rainfall in the Irkutsk region and in the south of the Far East. Possible mechanisms of weather and climate changes in the Northern Hemisphere are discussed. The focus is on the Arctic, which is the most vulnerable to climate warming. It is concluded that, with an abundance of physical hypotheses, there are many contradictions and uncertainties in the study of the mechanisms of weather and climate variability. Solving the problems requires further research based on modern technologies, the development of satellite monitoring systems and hydrodynamic modeling.
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