Inhibition of convective collapse of solar magnetic flux tubes by radiative diffusion

Abstract

Interaction of convection with a magnetic field leads to an intermittent distribution of magnetic flux¹. Such a process operating on the solar surface can lead to ‘equipartition’ fields of 700 G (ref. 2). These fields are further prone to a convective instability and eventually collapse to kilogauss intensity^3–5. I show here that radiative diffusion can inhibit this collapse to a varying degree, depending on the field strength and the thickness of the flux elements. As a consequence, one would expect the field strength of the photospheric magnetic flux elements to depend on their sizes. It is shown that at one end of such a distribution there would be kilogauss tubes with small dispersion in field strength and large dispersion in size. At the other extreme of the spectrum would be thin tubes of fairly constant size but with a wide range in field strength, from kilogauss intensities to the equipartition values of 700 G. High-resolution observations from space-borne telescopes should reveal the existence of the latter variety of tubes.