Caption:Example of a typical Hα Line Scan of solar off-limb spicules (in emission) and on-disk counterparts (in absorption) performed on 4 May 2005 with the GREGOR Fabry-Perot Interferometer (GFPI, Puschmann et al. 2006, A&A 451, 1151) deployed at the German Vacuum Tower Telescope (VTT) – Reconstructed Hα narrow-band images at consecutive spectral positions around the Hα line core.
Further information:The question how the outer solar atmosphere is heated from solar photospheric temperatures of about 5800K up to solar chromospheric and coronal temperatures of about 20.000K and millions of degrees respectively, remained without any satisfying answer for centuries. The density in the solar atmosphere drops fast in the photosphere, where the opacity reduces so much that the solar plasma becomes transparent to radiation. Therefore, it seems to be impossible to transfer energy to the outer solar atmosphere by radiation. Different energy transport mechanisms are apparently required. Spicules are highly dynamic jet-like structures best observed at and beyond the solar limb in chromospheric lines such as Hα (6563 Å), Ca II H (3968.5 Å) and Ca II IR (8542 Å). Provided that spicules possess on-disk counter parts, they could be one of the main drivers for the solar chromospheric heating. Type I spicules might be the result of photospheric acoustic p-mode leakage between granular cells, providing significant energy to the chromosphere. Type II spicules might by the result of magnetic reconnection at photopheric level and be related to Alfvén waves (MHD waves). The time series of Hα line parameters, resulting from the post-factum application of the Multi-Object Multi-Frame Blind Deconvolution technique (MOMFBD,van Noort, M., Rouppe van der Voort, L., & Loefdahl, M. G. 2005, Sol. Phys., 228, 191) as part of the GREGOR Fabry-Perot Interferometer Data Pipeline iSPOR-DP (imaging Spectropolarimetric Parallel Organized Reconstruction Data Pipeline, Puschmann, K. G. & Beck, C. 2011, A&A, 533, A21) reveal the entire and detailed complexity as well as the overwhelming dynamics of spicules apparently covering the entire solar disk, thus confirming spicules as the potential driver of chromospheric heating, with an expected mass flux larger than 100 times that of the solar wind. Spicules seem to be the result of the interaction of the highly dynamic photospheric quiet-sun or active-region small-scale magnetic field, which is dominated by convective processes and is predominantly located in intergranular lanes and at meso- or supergranular scales.
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