SOHO Status Report - February 2003
Operations and Archiving
All instruments are nominal and SOHO science operations are progressing smoothly. Links to the SOHO archives (including mirrors) are accessible at URL: http://soho.estec.esa.nl/data/
Science Highlights
From 27 October to 1 November 2002 the 12 th SOHO Workshop was held jointly with the annual meeting of the Global Oscillation Network Group (GONG) on the topic "Local and Global Helioseismology: The Present and Future". It focused on the study of the interior of the Sun from a seismic perspective and the prospects for similar study of solar-like stars. The Workshop provided an excellent opportunity for the scientific community to pause and reflect on the status of this fertile field, with more than half a solar cycle of SOHO and GONG observations. More than 120 participants discussed over 100 papers addressing a wide variety of topics, including the observational status of low-, medium-, and high-degree p-mode characterization, low-frequency g-mode detection, solar structure and dynamics, mode excitation and damping, and advances in local helioseismology.
One of the most interesting papers presented was the SOHO/MDI discovery that supergranulation undergoes oscillations, supporting waves with periods of 6-9 days. This explains the long-standing puzzle of why supergranules appear to rotate faster around the Sun than the plasma. Supergranulation is a pattern of horizontal outflows at a distinct scale of 30 Mm and an apparent lifetime of 1 day, outlined by a network of magnetic features. While it is believed that supergranulation corresponds to a preferred cellular scale of thermal convection, the dynamics of supergranulation is not understood. In particular, there was no explanation for the observation that the pattern appears to rotate faster around the Sun than the magnetic features. Gizon et al. (January 2, 2003 issue of Nature, Vol 421, p. 6918), based on a study of MDI data, show that supergranules have wavelike properties, with the waves being predominantly prograde, which explains the apparent super-rotation of the supergranulation pattern.
Researchers have compared ion-cyclotron resonance model calculations with UVCS observations of effective temperatures of nine ions spanning a broad q/n range. They found good agreement between the observed and calculated Teff values, which provides further evidence in support of the ion-cyclotron mechanism for the heating and acceleration of the fast solar wind in polar coronal holes.