ON SOLAR P-MODE FREQUENCY-SHIFTS CAUSED BY NEAR-SURFACE MODEL CHANGES

The effect on p-mode frequencies of changing the near-surface structur e of solar models is investigated. As is well known, changes confined to the near-surface region have little effect on the low-frequency p m odes: this is as one would expect from a simple asymptotic description which shows that these modes have upper turning points located well b eneath the photosphere. However, some examples of structural changes s how that, if the changes are viewed at fixed fractional radius (an Eul erian description), the small frequency shifts at low frequency come a bout through near-cancellation of different contributions which are in dividually much larger than the resultant shifts themselves; the reaso n is that even so-called near-surface changes extend substantially bel ow the upper turning points of these modes. We demonstrate that the co rresponding changes at fixed fractional mass (a Lagrangian description ) are confined much closer to the surface, so that the small frequency shifts come about in a natural way.