3. Vitinsky-Kuklin-Obridko Solar Cycle Phase Classification

[9]  As we are interested in isolating the solar cycle extreme phases in the GCR intensity modulation and as this solar cycle is very similar to that in R_Z, we looked at the known SC phases classifications for the photospheric (and nearby) activity and found that of Ju. I. Vitinsky, V. G. Kuklin, and V. N. Obridko (VKO) [Obridko and Shelting, 1992, 2003; Vitinsky et al., 1986] to be the best as an initial point.

[10]  First, let us describe some terms we widely use. The development of the solar cycle can be described as the interaction of the toroidal ( T, B_j ) and poloidal ( P, B_r ) subphotospheric magnetic fields and the alternating transition of the energy from T to P fields and back. Accordingly at the photosphere one can see the phenomena of the T branch of solar activity (sunspots with the ordered toroidal magnetic fields and other objects (active regions) linked to them) and those of the P branch (much weaker but large-scale poloidal magnetic fields at the polar latitudes and between the active regions, also polar faculae, etc).

Figure 2

[11]  In Figure 2 the Carrington rotation-averaged sunspot area (available at http://science.nasa.gov/ssl/PAD/SOLAR/greenwch.htm) (Figure 2a) and latitude range occupied by the spots (Figure 2b) are shown for each hemisphere (the solid curves for Northern and the dotted ones for Southern Hemispheres) for 1980-1999, the polarity of the sunspots (the sign of B_j ) being also reflected by the thickness of the lines. The line-of-sight component of the north and south polar photospheric magnetic field as seen from the Earth (available at http://sun.stanford.edu/ wso/) is depicted in Figure 2c. Also shown by the shading are the periods isolated by Obridko and Shelting [2003] as the extreme phases.

[12]  Without going into details, we can give the following brief description of the solar cycle main phases (according to Vitinsky et al. [1986] but using our ( T and P ) terms): (1) min, t_Dm < t mD, the minimum phase, the period when the sunspots with the old and new azimuthal polarities ( B_j ) coexist; the strength of the T phenomena reaches its minimum, while that of the P branch attains its maximum; (2) Asc, t_mD< t < t_Am, the ascending phase, the period when both T and P phenomena are pronounced, characterized by the spontaneity of the activity; (3) Max, t_AM< t < t_MD, the maximum phase, the period when the strength of the P phenomena reaches its minimum and their dipole-like polarity changes sign, while the T branch is at its maximum with the pronounced double-peak structure; (4) Des, t_MD< t < t_Dm, the descending phase, when again both T and P phenomena are pronounced but characterized by the recurrence of the activity.

[13]  The boundaries of the main phases ( t_mA, t_AM, t_MD, t_Dm ), introduced by Vitinsky et al. [1986] as the reference points of the solar cycle) are determined for the last solar cycles by Obridko and Shelting [2003] from the careful study of the sunspots, polar faculae, filaments etc. and widely using the data (available at http://sun.stanford.edu/&nbsp;wso/) on the large-scale magnetic fields both on the photosphere and at the base of the heliosphere. It is this particular interest in the very important for the heliosphere solar P phenomena, that determined our choice of the above classification as the best initial point in our search for the SC phases in the GCR intensity modulation.