A MODEL FOR THE FORMATION OF SOLAR PROMINENCES

We propose a model for the formation of prominence condensations in hot coronal loops. Previous studies have concentrated on cooling the hot plasma by decreasing the coronal heating rate. The difficulty with such models is that when the heating decreases, most of the loop mass is lost by draining onto the chromosphere. We argue that a prominence condensation is likely to be due to an increase in the heating. The key idea of our model is that the heating increase is spatially dependent so that it is localized nearer to the chromospheric footpoints than to the loop midpoint. We present results of numerical simulations of hot loops that are initially heated uniformly, and then undergo heating increases that are concentrated away from the loop midpoint. The temperature at the midpoint first increases, but eventually it collapses to chromospheric values as a result of chromospheric evaporation. Hence, we obtain the curious result that increasing the heating causes cooling. The resulting densities and time scales agree well with observations. The implications of this model for coronal heating and prominence structure are discussed.