Quasi-biennial oscillations in the N-S asymmetry of solar activity
Authors:
O.G. Badalyan, V.N. Obridko, J. Sykora
Image & caption:
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Image caption::
(Above) Time course of the N-S asymmetry (blue) and the sums of QBO amplitudes (red), as averaged over the entire range of heliolatitudes. The thick smoothed lines are obtained by "a method of filtration"; (Below) Latitude dependence of the negative correlation coefficient between the N-S asymmetry in the coronal green line brightness and the sum of three QBO amplitudes.
Description:
The north-south (N-S) asymmetry of solar activity was investigated using data on the coronal green line brightness, the total number and the summary area of sunspots, all over 1939-2001. Similar time variations on both the short- (1.5 - 3.0 years) and the long-term (~ 12 years) scales were identified in the asymmetry of all the studied indices within the sunspot formation zone 0° -30°. Quasi-biennial oscillations (QBO) in the the N-S asymmetry of all the indices were clearly detected and then analyzed. Within the sunspot formation zone 0° -30° the properties of the QBO in the N-S asymmetry of the indices were found to be very similar. It was revealed that the QBO are much better expressed in the N-S asymmetry of the indices than in the indices themselves. Except of that, power of the QBO in the N-S asymmetry of three examined indices appears to be in an anti-phase with the magnitude of the N-S asymmetry itself. This effect is evident for all the three investigated indices over the whole range of solar latitudes, and decreses distinctly only in the latitudinal interval of 40° - 50°. Generally speaking, nature of the N-S asymmetry of solar activity remains unexplained (the same for manifestations of the QBO within this N-S asymmetry). As a rule, the dynamo theories do not consider the N-S asymmetry, assuming completely identical behavior of activity in both solar hemispheres. However, the above and similar findings repeatedly stress the need to consider them when any dynamo theory of solar activity is constructed.
Reference:
Proc. of the 11th European Solar Physics Meeting – The Dynamic Sun: Challenges for Theory and Observations, ESA SP-600 (December 2005), Compact Disc
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