Contributed Talk - Splinter Activity
Connecting chromospheric emission to photospheric magnetic field
Theodosios Chatzistergos1, Ilaria Ermolli2, Sami K. Solanki1,3, Natalie A. Krivova1
1Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
2INAF Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monte Porzio Catone, Italy
3School of Space Research, Kyung Hee University, Yongin, Gyeonggi 446-701, Republic of Korea
Solar full-disc photographs in Ca II K line have been taken since 1892 at various observatories around the globe. Such images are considered as good tracers of the photospheric magnetic field due to the good spatial correspondence between the brightness excess in Ca II K images and strong magnetic fields found in magnetograms. Numerous studies found a power law relationship between the Ca II K brightness and the photospheric line-of-sight magnetic field strength. Still, there is no general agreement between the parameters derived in these studies, and even the existence of such a relationship has been debated. However, all previous studies were limited to rather few images, low quality observations, or isolated regions on the solar disc. We reassess the relation between the photospheric line-of-sight magnetic field strength and the Ca II K excess brightness using high-quality full-disc and almost co-temporal SDO/HMI magnetograms and Rome/PSPT Ca II K observations covering half a solar cycle. We also test the derived relationship by employing it for a reconstruction of unsigned magnetograms from the Ca II K observations.