The subsurface radial gradient of solar angular velocity from MDI f-mode observations
- Cite this article as:
- Corbard, T. & Thompson, M. Solar Physics (2002) 205: 211. doi:10.1023/A:1014224523374
We report quantitative analysis of the radial gradient of solar angular velocity at depths down to about 15 Mm below the solar surface for latitudes up to 75° using the Michelson Doppler Imager (MDI) observations of surface gravity waves (fmodes) from the Solar and Heliospheric Observatory (SOHO). A negative outward gradient of around −400 nHz/R⊙, equivalent to a logarithmic gradient of the rotation frequency with respect to radius which is very close to −1, is found to be remarkably constant between the equator and 30° latitude. Above 30° it decreases in absolute magnitude to a very small value at around 50°. At higher latitudes the gradient may reverse its sign: if so, this reversal takes place in a thin layer extending only 5 Mm beneath the visible surface, as evidenced by the most superficial modes (with degrees l>250). The signature of the torsional oscillations is seen in this layer, but no other significant temporal variations of the gradient and value of the rotation rate there are found.