Coupled Groups ofg‐Modes in a Sun with a Mixed Core

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Abstract
Groupsof linear g-modescansumtocreatenonlinear motioninsmall''hotvolumes''(diameter � 10Mm)nearthe solarcenterthathelpdrivethemodes.Weexploretheconsequencesof couplingonlyinthehotvolumeswherethetime- averagedrateof 3Heburningcandoubleiftemperatureoscillationsexceed10%.Anticipatinglargelocal motionsinthe core, we impose a mixed shell r ¼ (0:10 � 0:03) Ron an otherwise standard solar model before computing g-mode solutions. Mixing is rapid (T106 yr) in this shell, with slower mixing somewhat beyond. Ifl is the principal spherical harmonic index, a set of g-modes for any singlel � 5 with six consecutive radial harmonics can be excited with nearly linear thermal amplitudesAT � 0:05 throughout the star. But far smaller thresholds for excitationare actually expected when sets for many values of l can be computed simultaneously. This is a new kind of stellar instability whose effectivenessriseswiththenumberof activemodes.Eachsetrotatesrigidlyandmaximizesthereleaseof nuclearenergy from its hot volumes. There is some evidence for their rotation rates in the long solar activity record. The upward wave fluxpoweredbythehotvolumeshasalsobeensuggestedtoexplainthe1.3yrreversingflowstentativelydetectedbelow the Sun's convective envelope. An analog using uncoupled modes is also investigated based on an observation that indicates g-mode activity up to l � 20. If all modes in that range had linear amplitudes of only AT � 0:0015, their combined effect would give positive growth rates to dozens of low harmonic g-modes. Subject headinggs: stars: oscillations — Sun: interior — Sun: oscillations

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