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Abstract: Although systematic measurements of the solar polar magnetic field exist onlyfrom mid 1970s, other proxies can be used to infer the polar field at earliertimes. The observational data indicate a strong correlation between the polarfield at a sunspot minimum and the strength of the next cycle, although thestrength of the cycle is not correlated well with the polar field produced atits end. This suggests that the Babcock Leighton mechanism of poloidal fieldgeneration from decaying sunspots involves randomness, whereas the otheraspects of the dynamo process must be reasonably ordered and deterministic.Only if the magnetic diffusivity within the convection zone is assumed to behigh, we can explain the correlation between the polar field at a minimum andthe next cycle. We give several independent arguments that the diffusivity mustbe of this order. In a dynamo model with diffusivity like this, the poloidalfield generated at the mid latitudes is advected toward the poles by themeridional circulation and simultaneously diffuses towards the tachocline,where the toroidal field for the next cycle is produced. To model actual solarcycles with a dynamo model having such high diffusivity, we have to feed theobservational data of the poloidal field at the minimum into the theoreticalmodel. We develop a method of doing this in a systematic way. Our modelpredicts that cycle 24 will be a very weak cycle. Hemispheric asymmetry ofsolar activity is also calculated with our model and compared withobservational data.



Author: Jie Jiang, Piyali Chatterjee, Arnab Rai Choudhuri

Source: https://arxiv.org/







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