Excitation of arctic and antarctic oscillations by torsional oscillations

Important elements of the general atmospheric circulation are Arctic and Antarctic oscillations (AO, AAO) that define weather and climatic anomalies at high and middle latitudes of both hemispheres. Characteristics of these oscillations vary with time and depend on solar and geomagnetic activity that enables us to address these modes as one of the elements of solarterrestrial relations. However, the immediate cause of excitation of oscillations is still uncertain. The analysis of possible mechanisms and the search for factors influencing excitation of oscillations are under way. In the work presented here, the correlation between Arctic/Antarctic oscillations (AO, AAO) and torsional variations in the atmosphere was revealed. Crossing polar-frontal zones of both hemispheres, low-frequency zonal velocity fluctuations cause variations in AO and AAO indexes of the same sign as zonal velocity anomalies. Torsional variations are quasiregular; their typical time scale is from 10 to 20 days. They propagate with the velocity of ~ 4 m/s corresponding to the group velocity of barotropic Rossby waves in the meridian direction. Data for 2000 year show that torsional variations propagated southward in the Northern Hemisphere for the most part over Eurasia, while in the opposite direction - from south to north - over the Western Hemisphere