The Hemispheric Asymmetry of Solar Activity During the Twentieth Century and the Solar Dynamo

Abstract

We believe the Babcock--Leighton process of poloidal field generation to be the main source of irregularity in the solar cycle. The random nature of this process may make the poloidal field in one hemisphere stronger than that in the other hemisphere at the end of a cycle. We expect this to induce an asymmetry in the next sunspot cycle. We look for evidence of this in the observational data and then model it theoretically with our dynamo code. Since actual polar field measurements exist only from 1970s, we use the polar faculae number data recorded by Sheeley (1991) as a proxy of the polar field and estimate the hemispheric asymmetry of the polar field in different solar minima during the major part of the twentieth century. This asymmetry is found to have a reasonable correlation with the asymmetry of the next cycle. We then run our dynamo code by feeding information about this asymmetry at the successive minima and compare with observational data. We find that the theoretically computed asymmetries of different cycles compare favourably with the observational data, the correlation coefficient being 0.73. Due to the coupling between the two hemispheres, any hemispheric asymmetry tends to get attenuated with time. The hemispheric asymmetry of a cycle either from observational data or from theoretical calculation statistically tends to be less than the asymmetry in the polar field (as inferred from the faculae data) in the preceding minimum. This reduction factor turns out to be 0.38 and 0.60 respectively in observational data and theoretical simulation.

14 pages, 6 figures

References in corpus (4)

• Predicting solar cycle 24 with a solar dynamo model
• Solar activity forecast with a dynamo model
• Exploring the Physical Basis of Solar Cycle Predictions: Flux Transport Dynamics and Persistence of Memory in Advection versus Diffusion Dominated Solar Convection Zones
• On Predicting the Solar Cycle using Mean-Field Models

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• Mean field models of flux transport dynamo and meridional circulation in the Sun and stars
• A theoretical study of the build-up of the Sun's polar magnetic field by using a 3D kinematic dynamo model
• Phase and amplitude asymmetry in the quasi-biennial oscillation of solar Halpha flare activity
• A theoretical model of the variation of the meridional circulation with the solar cycle
• Is the Hemispheric Asymmetry of Monthly Sunspot Area an Irregular Process with Long-Term Memory?
• North-South Asymmetry in Solar Activity and Solar Cycle Prediction, V: Prediction for the North-South Asymmetry in the Amplitude of Solar Cycle 25
• A Critical Assessment of the Flux Transport Dynamo
• The Extended Solar Cycle and Asymmetry of the Large-Scale Magnetic Field
• Hemispheric Distribution of Solar Active Regions During Solar Cycles 23-25