Bulletin of Taras Shevchenko National University of Kyiv. Astronomy, no. 55, p. 22-29 (2017)

The alpha effect of Babcock-Leighton in the in the surface layers of the Sun

V. Krivodubskij, Dr. Sci.
Astronomical Observatory of Taras Shchevchenko National University of Kyiv, Kyiv

The paper reviews recent studies of cyclicity of magnetic activity of the Sun based on the αΩ-dynamo model. According to the αΩ-dynamo model the radial gradient of angular velocity ∂Ω/∂r acts on the poloidal magnetic field BP, as a result generating the toroidal magnetic field BT (Ω-effect). Meanwhile helical turbulence, acting on the toroidal field BT, regenerates new poloidal magnetic component of opposite sign – BP. Since the differential rotation ∂Ω/∂r is inherent in almost stable regularity in time, there is a functional dependence between the observed values of the poloidal BP and toroidal BT magnetic fields. Poloidal magnetic field BP in minimum epoch of the solar cycle (when field BP has maximum value) determines the amount of the generated toroidal magnetic field BT (which is responsible for intensity of the spots activity in the coming cycle). This allows us to predict the amplitude (Wolf numbers W) and the strength (the total area of spots) of cycle for the measured field BP at the beginning of the cycle. However, for a long time in past there were no detected the positive correlations between the characteristics of sunspots cycle (Wolf number or the total area of spots) and polar magnetic flux (which characterized the value of poloidal field BP) at the end of the cycle. In the terms of dynamo theory it was supposedly evidenced of the absence of functional dependence poloidal fields BP at the end of cycles on the toroidal field BT in maximum of cycles. As it turned out later, this was due to the fact that the surface α-effect of Babcock–Leighton (which defined by tilt angles of the bipolar magnetic fields, turbulent diffusion and meridional circulation, and causes the regeneration of the poloidal field) is characterized by random fluctuations in time and space. The situation, however, changed drastically after the introducing of the parameter of magnetic strength spots of cycle, which is a product of the area of spots cycle and tilt angles of the bipolar magnetic groups. By combining assimilation of the area of spots, the distance between the weighted canters of opposite magnetic polarity and the tilt angles, the functional dependence of polar magnetic flux (which is an indicator of poloidal field BP) on the assimilated parameter magnetic strength of sunspots (which describes the relative intensity of the toroidal field BT) was restored. Within the framework of the αΩ-dynamo this indicates that the surface α-effect of Babcock–Leighton leads to the generation of the poloidal magnetic
field at the end of the current cycle, and assimilated parameter of magnetic strength spots of cycle is an integral component for future forecasts of solar activity based on the dynamo models.

Key words
Sun, turbulence and magnetic fields, sunspots, cycles of activity, dynamo model, forecasts of solar activity

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DOI: https://doi.org/10.17721/BTSNUA.2017.55.22-29