September 2, 2011, 12:00 pm - 1:00 pm

September 2, 2011, 12:00 pm - 1:00 pm

Coronal Rotation from UVCS/SOHO during Solar Cycle 23

Dr. Silvio Giordano, INAF Astronomical Observatory of Torino, Italy

The SOHO/UVCS instrument provides unprecedented high spatial resolution and almost regular time series of observations of the solar corona in the UV spectral region, which covers a complete activity cycle. The nearly daily UVCS observations have been analyzed to reconstruct intensity time-series of OVI 1032 and HI Ly-alpha 1216 spectral lines at different latitudes in the coronal region from 1.5 to 3.0 solar radii. By using both autocorrelation and spectral analysis techniques we establish the rotational characteristics of the solar corona from minimum to maximum phase of solar cycle 23 and the rotation rate as a function of latitude and height. The UV corona is found to rotate more rapidly and rigidly with respect to the underlying sunspots and photospheric plasma, however the coronal rotation period is observed to vary considerably from 1996 to 2006, with episodes of sudden acceleration and deceleration. We investigate a possible connection between the variations in rotation rate observed in the solar corona and the corresponding variations observed in the upper layers of the convection zone of the Sun as inferred by inversion of helioseismic data. The results suggest that, at least around the solar equator, the observed coronal variations in the rotation rate may reflect changes in the upper layers of the convection zone of the Sun.