The study reconstructs circulation processes for the northwestern part of the Russian Plain with Pinus Sylvestris ring width chronologies from Novgorod.
48 cores taken from 24 living pines were used. The plot is located within the temperate climatic zone within the interstream area of two Msta river confluents. As a growth parameter the latewood width was used and measured with a microscope.
The age trend in growth was removed by using both exponential and linear functions. By means of principal component analysis initial data were transformed to a new set of variables. The first three principal components were accepted for further regression.
For revealing a coniferous growth dependence on circulation conditions the classification of macrocirculation processes in extratropical latitudes of the Northern Hemisphere developed by Dzerdzeevskii was used. This is based on the ratio of meridional and zonal components of circulation i.e. corresponding directions of cyclone and anticyclone tracks. According to this scheme each homogeneous process over the entire hemisphere is called an 'elementary circulation mechanism' (ECM). The set of 44 ECMs was designed.
The full schedule of successive changes in the ECM subtypes over the period 1899-1971 was used. According to the classification, all ECMs are divided into two groups for warm (April-September) and cold (October-March) periods.
According to the 1st PC temporal variability the period may be divided into three general parts: 1899-1929, a slow growth increase, corresponding to the northern meridional circulation epoch of the Dzerdzeevskii classification; 1930-1949, an abrupt and intensive growth increment, corresponding to the zonal circulation epoch; 1950-1971, a slow growth decrease, corresponding to the southern meridional epoch.
The radial growth of trees reflects intrasecular climatic anomalies caused by global circulation changes. Favorable conditions during the warm period are a decreasing precipitation and relatively good heating. These conditions are produced by a northward shift of Azores High and its ridge spreading to the East up to the Urals. Unfavorable conditions are southern cyclone breakthroughs causing overmoisting. During the cold period, the eastward air transfer over Europe accompanied by cyclonic activity along the Northern European coast is favorable which prevents the rest of Europe from Arctic intrusions. Any meridional transfer forcing forming less stable temperature regime produces unfavorable conditions.
It worth mentioning finally that there are only a few ECMs among the 44 subtypes that correlate with tree growth. It should be kept in mind that we dealt with regional features of hemispheric processes. Only those ECMs which produce extreme conditions may be revealed from tree growth series. Similar local synoptic conditions may be produced by different ECMs. In the past any growth increase or decrease can only be assumed to result from a set of ECMs. If we have a network of chronologies we are able to reconstruct each ECM exactly and try to reproduce the ECM their temporal dynamics.
The obtained strong response to regional manifestation of circulation changes within the Northern Hemisphere (expressed in terms of different circulation epochs) makes it possible to reconstruct circulation features of the historical past.