Change of the Large-Scale Atmospheric Circulation Over the North Hemisphere During 1900-2010

Abstract:

The change of atmospheric circulation over the North Hemisphere from decade to decade during the XX century until recent decade was studied. The Fourier series expansion of fields of pressure at the middle level of the troposphere is used in the analysis of change of atmospheric circulation in time and space. The shift of the atmospheric circulation from decade to decade at ± 20 degrees from its position of the 1930-1939 was found. The period of shift between the east (+20 degrees) and the west (-20 degrees) positions is about 50-60 years.

The displacement of circulation to the west corresponds to the cold winters over the Northern Hemisphere (as it was at the middle of the 20th century) and displacement to the east corresponds to the warming (as it was at the end of the century). The displacement of the large-scale circulation of atmosphere to the east at the end of the century over the Northern Hemisphere corresponds to the warming. In the beginning of the twenty-first century large-scale atmospheric circulation again shifted to the west to the circulation with the colder winters. That is the reason for appearance of the frosty winters in the recent years. Continuing displacement of the circulation over the North Hemisphere to the west direction will correspond to the colder winters in future.

The influence of new factors of the climate change of the hemisphere is also shown. They are the “bands of heat” (elongated positive anomaly of surface temperature) which have appeared on the background of the general atmospheric circulation in last decades. They have the permanent geographical position during the month and more. These “bands of heat” differ from moving warm air flows from the south and also they caused increasing of temperature in the troposphere. The synoptic conditions along the bands form the dangerous weather events.