Main Objective: Discriminating between two main scenarios for penumbra formation
Scientific Justification: Currently, there are two main explanations for penumbra formation. Leka & Skumanich (1998) suggested that emerging, horizontal field lines could be trapped and form a penumbra rather than continuing to rise to higher layers, due to the presence of the overlying magnetic canopy in the emerging region. In contrast, Shimizu et al. (2012) and Romano et al. (2013, 2014), based on their observations of signatures of penumbra formation around pores in the chromosphere appearing earlier than in the photosphere, suggested that the field lines of the magnetic canopy, already existing at a higher level of the solar atmosphere and overlying the pore, may be responsible for the formation of the penumbra if they sink down into the photosphere and below the solar surface. In order to discriminate between these two scenarios, we plan to perform a coordinated observing campaign with GST, Hinode and IRIS. Moreover, we aim to investigate also the physical mechanism which is able to trigger the Evershed flow in
the penumbral filaments during their settlement.
To this purpose, we have been allocated GST time on October 2019.
Our targets will be active regions during formation (if any) or pores.
Backup program: quiet-Sun flux emergence at disc center.
Leka, K. D., & Skumanich, A. 1998, ApJ, 507, 454
Romano, P., Frasca, D., Guglielmino, S. L., et al. 2013, ApJL, 771, L3
Romano, P., Guglielmino, S. L., Cristaldi, A., et al. 2014, ApJ, 784, A10
Shimizu, T., Ichimoto, K., & Suematsu, Y. 2012, ApJL, 747, L18 |
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