دانلود رایگان مقاله رفتار شناوری مغناطیسی در مدل های حمل و نقل شار دینامو

Abstract

One important ingredient of flux transport dynamo models is the rise of the toroidal magnetic field through the convection zone due to magnetic buoyancy to produce bipolar sunspots and then the generation of the poloidal magnetic field from these bipolar sunspots due to the Babcock–Leighton mechanism. Over the years, two methods of treating magnetic buoyancy—a local method and a non-local method—have been used widely by different groups in constructing 2D kinematic models of the flux transport dynamo. We review both these methods and conclude that neither of them is fully satisfactory—presumably because magnetic buoyancy is an inherently 3D process. We also point out so far we do not have proper understanding of why sunspot emergence is restricted to rather low latitudes.

6. Conclusion

Our discussion has been restricted to kinematic dynamo models in which the velocity field is assumed to be given. Although we so far do not have anything that can be called the standard model of the solar dynamo even within the framework of kinematic models (Choudhuri, 2008), flux transport dynamo models developed by different groups have lots of common features. While there is a controversy on the nature of the meridional circulation at present, it is still not clear whether a serious revision of existing dynamo models will be required. Another uncertainty about the value of turbulent diffusion seems to be resolved now in favor of higher diffusivity (such that the diffusion time scale is a few years) because only with such diffusivity it is possible to model various aspects of cycle irregularities (Choudhuri, 2015). Whether turbulent pumping is important for the solar dynamo is another question. However, since the inclusion of turbulent pumping does not change the results of high-diffusion dynamo models too much (Karak and Nandy, 2012), this is presumably not a large source of uncertainty.