Scientific justification: It is well-known that the fast solar wind originates from coronal holes. However, its source close to the solar ``surface'' is a matter of debate even in today's era of modern observations. Spicules and their higher ``associates'', macro-spicules are considered to be a dominant mechanism for mass injection in the higher solar atmosphere outside active regions. In the
last few years, there is increasing edidence favouring reconnection as the driving mechanism for macrospicules. Ulysses data show that the high-speed wind has some fine scale structure. Furthermore, a statistical study of macrospicules show that half are of an erupting-loop type while the other half are of a spiked-jet type. The erupting-loop observation fits the model whereby there is reconnection between small emerging loops and open-field lines, thereby giving linkage between macrospicules and the fast solar wind. We have recently reduced SUMER data which shows evidence of high velocity macrospicules. The recent STEREO data shows several large jet features, with durations typical of macrospicules.
At present, we are exploring the modelling of macrospicules using the VAC code, including 2 and 3-D MHD modelling. Appropriate magnetic structures are embedded in VAL IIIc atmosphere mimicking a series of magnetic features from one single vertical narrow flux tube to interacting inclined flux tubes driven with photospheric velocity signals (synthetic or measured). 2-D simulations clearly show the presence of jets developing both at null-points and at the most tilted field lines. We need observational input in order to re-fine the modelling efforts. Most data taken of these features are of the single instrument type, however, in order to make progress we need a multi-instrument approach via high
resolution imaging with SOT, XRT, TRACE and STEREO coupled with spectral data
with SUMER, CDS and EIS. Such data will provide imaging in the lower atmosphere (SOT, Ca II & G-band), transition region (TRACE, 1550A) and the corona (XRT), while the spectrographs provide data from the chromosphere and transition region (SUMER), and the transition region and corona (CDS & EIS).
Target: We request all instruments to be pointed ~20-30 arcsec inside the limb at
around x=0",y=930". |
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