On the Stability of Solar Photospheric Magnetic Flux Tubes

Abstract

In the quiet solar photosphere, most of the magnetic flux is in the form of small-scale intense magnetic flux tubes. It is believed that the intense flux tubes are formed by the convective collapse, which is a kind of the convective instability in a magnetic flux tube. Thus, the nature of the instability has been investigated by many authors. From linear theory it was found that the stability is determined by β (the ratio of gas pressure to magnetic pressure in the flux tube); if β β c) evolves into an intense flux tube (β < β c) in a static equilibrium, due to the convective collapse, carrying out the nonlinear calculations. However, he adopted the adiabatic approximation which is not valid in the photospheric region. Thus, we investigated the nonlinear and the long term evolution of the convective instability in a weak flux tube, adopting thin flux-tube approximation (Roberts, Webb 1978). The radiative heat exchange was iaken into account adopting Newton’s law of cooling.