Theoretical Prediction of an Observed Solar g -Mode

Abstract

This Letter considers the weak but persistent radial velocity variations measured by the Global Oscillations at Low Frequencies instrument on the Solar and Heliospheric Observatory satellite at 75.55 minutes (220.6 μHz), which is very close to our new theoretical solar model period prediction of 75.15 minutes (221.8 μHz) for the angular degree l = 2, g3-mode. The triplet splitting for this mode indicates that the central slow solar rotation has a frequency of 0.36 μHz. Our solar model, using the latest physical input data, is evolved to match the present solar mass, radius, luminosity, and surface composition, and it predicts, as best as currently possible, the p-mode oscillation frequencies for many l-values. Our nonadiabatic eigensolutions also show that l = 1 and 2 g-modes of radial order 4 and higher, with periods about 86 minutes (193 μHz) and 131 minutes (127 μHz), respectively, and longer, have deep radiative diffusion variations that damp their linear theory growth, making their existence and observation unlikely. Four l = 3 g-modes are calculated to be pulsationally unstable, but their detectability for observations with no angular resolution on the solar surface seems unreasonable. All these g-modes seem significantly excited by radiation flow blocking at the bottom of the solar convection envelope (where the convective timescale, about 30,000 minutes, is much longer than the g-mode period) plus some regular hydrogen ionization κ-effect near the solar surface. From p-mode pulsation driving experience, it is likely that this hydrogen κ-effect driving is overestimated, because it is destroyed by time-dependent convection. For our low radial order g-modes, time-dependent convection may produce a little damping and some driving between 15,000 and 30,000 K.