Main Objective: The aim of this project is to infer the full magnetic field vector along coronal loops through coronal rain observation.
Scientific Justification: Coronal rain is the direct observational signature of the thermal instability mechanism in the solar corona. It corresponds to cool and dense (spanning chromospheric to transition region conditions) partially ionised clumpy plasma falling along coronal loops. Recent studies show that this phenomenon has a ubiquitous presence above active regions (Antolin & Rouppe van der Voort 2012, Antolin et al. 2015).
One of the unique features of tracing coronal rain is that it is currently the highest resolution method to trace out the coronal magnetic field vector. By tracking the clumps both global and local reconstruction of the coronal magnetic field topology can be achieved. The aim of this project is to take one step further in this direction and use the coronal rain properties to infer the full magnetic field vector along the coronal loops. To achieve this goal we aim at co-observing in various magnetically sensitive lines:
- At the SST (for which the observers will be N. Freij and P. Antolin): we will conduct full polarimetric observations in the Ca II 8542 line, combined with H-alpha spectrometric observations of the rain. Coronal rain is commonly observed in H-alpha, and has also been previously observed in the Ca line with FISS at the NST (Ahn et al., 2014), with TIP-II at the VTT (Collados et al., 2014) and also with the SST (Scullion et al. 2016, in prep.). Previous spectropolarimetric observations in which coronal rain is present can also be found in Schad (2013).
- With Hinode/SOT (SP+BFI) we aim at observe coronal rain and measure at high resolution the magnetic field strength at the photospheric footpoints of the loops. This will allow in turn to perform magnetic field extrapolations. Comparison between these extrapolations and the coronal rain paths will serve as a test for the extrapolation methods and also as a means to estimate the non-potentiality of the active region.
- With IRIS and Hinode/EIS we aim at studying the change in the thermodynamic evolution of the rain, as it cools through the transition region down to chromospheric temperatures, and also to perform coronal MHD seismology. Indeed, since transverse MHD waves are commonly observed in rainy loops (Antolin & Verwichte 2011), we also aim at observing these waves at high resolution, especially at the apex of the loops. Having the slit crossing the loops close to the apex is essential, since it allows to detect the presence of resonant absorption and dynamic instabilities (Okamoto et al. 2015, Antolin et al. 2015b). The detection of transverse MHD waves will allow to perform coronal seismology, which will therefore serve as an additional and independent measurement of the coronal magnetic field.
- With Meudon/MSDP continuous H-alpha spectrometric observations will be performed over a larger field-of-view, thereby complementing the SST observations above. |
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