M. Cristina Rabello-Soares
We present evidence that the sound-speed variation with solar activity has a
two-layer configuration, similar to the one observed below an active region,
which consists of a negative layer near the solar surface and a positive one in
the layer immediately below the first one. Frequency differences between the
activity minimum and maximum of solar cycle 23, obtained applying global
helioseismology to the Michelson Doppler Imager (MDI) on board SOHO, is used to
determine the sound-speed variation from below the base of the convection zone
to a few Mm below the solar surface. We find that the sound speed at solar
maximum is smaller than at solar minimum at the limit of our determination (5.5
Mm). The min-to-max difference decreases in absolute values until ~7 Mm. At
larger depths, the sound speed at solar maximum is larger than at solar minimum
and their difference increases with depth until ~10 Mm. At this depth, the
relative difference is less than half of the value observed at the lowest depth
determination. At deeper layers, it slowly decreases with depth until there is
no difference between maximum and minimum activity.
View original:
http://arxiv.org/abs/1110.5596
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