It has been argued that the solar magnetic cycle consists of two main periodic components: a low-frequency component (Hale's 22-year cycle) and a high-frequency component (quasi-biennial cycle). The existence of the double magnetic cycle on the Sun is confirmed using Stanford, Mount Wilson and Kitt Peak magnetograph data from 1976 to 1996 (solar cycles 21 and 22). In the frame of the Parker's dynamo theory a model of the double magnetic cycle is presented. This model is based on the idea of two dynamo sources separated in space. The first source of the dynamo action is located near the bottom of the convection zone, and the second operates near the top. The model is formulated in terms of two coupled systems of non-linear differential equations. It is demonstrated that in the case of weak interaction between the two dynamo sources the basic features of the double magnetic cycle such as existence of two component and observed temporal variations of high-frequency component can be reproduced.Comment: 6 pages, 2 figure

The 11-year cycle of solar activity follows Hale's law by reversing the magnetic polarity of leading and following sunspots in bipolar regions during the minima of activity. In the 1996-97 solar minimum, most solar activity emerged in narrow longitudinal zones -'active longitudes' but over a range in latitude. Investigating the distribution of solar magnetic flux, we have found that the Hale sunspot polarity reversal first occurred in these active zones. We have estimated the rotation rates of the magnetic flux in the active zones before and after the polarity reversal. Comparing these rotation rates with the internal rotation inferred by helioseismology, we suggest that both 'old' and 'new' magnetic fluxes were probably generated in a low-latitude zone near the base of the solar convection zone. The reversal of active region polarity observed in certain longitudes at the beginning of a new solar cycle suggests that the phenomenon of active longitudes may give fundamental information about the mechanism of the solar cycle. The nonrandom distribution of old-cycle and new-cycle fluxes presents a challenge for dynamo theories, most of which assume a uniform longitudinal distribution of solar magnetic fields.

We have investigated the relationship between magnetic activity and coronal structures using soft X-ray data from the Yohkoh soft X-ray telescope and magnetic field data from the Kitt Peak Solar Observatory for the period of 1991-2001 and EUV data from the Solar and Heliospheric Observatory EUV Imaging Telescope for 1996-2001. The data are reduced to Carrington synoptic maps, which reveal two types of migrating structures of coronal activity at low and high latitudes in the time-latitudinal distribution. The low-latitude coronal structures, migrating equatorward, correspond to photospheric sunspot activity, and the high-latitude structures migrating toward the poles reflect polar activity of the Sun. We present the following new results: 1. The migrating high-latitude coronal magnetic structures are revealed in the soft X-ray data as complete bright giant loops connecting the magnetic field of the following part of active regions with the polar field. They appear during the rising phase and maximum of the solar cycle and show quasi-periodic impulsive variations with a 1-1.5 yr period. 2. The soft X-ray intensity of these loops has a strong power-law correlation with the photospheric magnetic flux. The power-law index, which on average is close to 2, shows variations with the solar cycle: it is higher for the period of the declining phase and minimum of solar activity than for the rising phase and maximum.