The aim of this proposal is to accumulate a databank of information on X-ray brightenings and their relationship to photospheric fields, so that we can make predictions on when and where eruptions will occur. This requires observations over several hours across different features (coronal holes, quiet Sun, small active regions) on the solar disk.
Analysis of MDI and STEREO data suggests that eruption and coronal brightenings are activated by twisting photospheric flows at supergranule junctions (Innes et al, A&A, 2008). We have several examples where vortices in photospheric flows, computed by tracking granules in MDI continuum images, seem to be dragging mixed polarity magnetic fields together. Subsequently small CME-like eruptions are seen from the same supergranule junction in EUVI/STEREO images. With SOT/FG continuum images we are able to track the photospheric flows with much better resolution and, together with XRT, we are able to see smaller events in detail. The rate for small (5” and 15 min) X-ray events is 1-2 events per hour in the SOT field-of-view for the quiet Sun. To see the build-up phase of events we require at least 8 hours of observation, the turnover time of supergranulation.
Last September we obtained an 8 hour run with SOT, XRT, SUMER and MDI which we are currently analyzing. The data quality is excellent and will give good insight on the spatial and temporal correlation of the vortex X-ray link in a region of quiet Sun. Unfortunately the SOT/FG sequence was not ideal for tracking photospheric flows since it was done with alternating 30 s and 90 s time delays. We are therefore asking for a repeat of the run using continuous 60 s cadence. Tests have shown that to obtain underlying supergranulation flows, 60 s cadence is optimal. We would also like to obtain simultaneous, high cadence EIS observations in transition region and coronal lines.
Both the Soho instruments SUMER and MDI (HR) are essential. SUMER because it provides high quality spectra showing the transition region dynamics, at least along the 300”x1” slit. MDI because it provides the line-of-sight magnetic field and Doppler velocity as well as continuum images for computing the photospheric flow across the full XRT field of view. In addition MDI images will be used to obtain sub-surface flows using local helioseismology techniques.
We are asking for FG/SOT , C-Poly/XRT and EIS observations, to be taken together with HR MDI and SUMER for three 8 hour observations between March 31 and Apr 14, 2009. If possible there should be one run on each of the three features - quiet Sun, coronal hole and active region. |
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