Corona & solar wind

Sources of solar wind:

Since 1973, when Krieger et al. identified a coronal hole as the source of a high speed stream, people have been searching for localized regions, within holes, where fast wind might originate. As for sources of slow wind, these are, as of today, not fully identified. In this research area, Arcetri is involved along different lines:

• Hinode, STEREO, SDO have shown that X-ray jets are, in coronal holes, much more numerous than predicted on the basis of previous observations. These are small-scale, short lived ejections, that resemble larger scale flare events. A question we are trying to answer is: do X-ay jets contribute to the mass and energy flux of the wind?Satellite studies, within this area, focus on the nature of jets, on their physical parameters (that can be identified via spectroscopic techniques), and their evolution in time and spatially along the ejection, and extend to other transient CHs structures (e.g. plumes) and their role in solar wind origin and maintenance.

Images of the jet that occurred in the southern polar CH on July 1, 2008, and was imaged by HINODE/XRT in two filters

• One of the slow wind sources may reside at the edge of Active Regions (ARs), as scintillation measurements had suggested. Space experiments, like HINODE, allowed observations of ARs in the low corona, revealing the occurrence of outflows, whose behavior at higher levels is, however, difficult to predict: is outflowing plasma falling back or does it become part of the wind? In this area we analyze data acquired by UVCS/SOHO at high coronal levels (order of 2 solar radii) above Active Regions, to examine whether outflows reach these altitudes, hence supporting the hypothesis that one of the slow wind components originate from ARs.
  Long-term behavior of these flows, over an AR lifetime, or over a solar cycle, are further issues that can be examined.