Photospheric Downflows: How Deep, How Coherent, How Important?

Abstract

While convection in the solar envelope globally transports the incident radiative flux from the interior, the local dynamics of granulation as seen at the photosphere is dominated by radiative cooling and downflow formation. Here we examine the stability of such downflows with depth and their importance to acoustic excitation. We find that downflow plumes, even in a quiescent adiabatic environment, are subject to vigorous secondary instabilies causing detrainment of fluid from the plume region. It seems unlikely that they are coherent to the bottom of the solar convection zone. We also find that plume initiation by rapidly localized cooling results in both monopolar and dipolar acoustic emission. The mechanism is distinct in that pressure fluctuations are induced thermodynamically by radiative loss as well as dynamically by fluid motion.