Quiet Sun chromosphere
I plan to investigate of the impact of photospheric dynamics in active regions on the chromosphere and the transition region (TR). This includes research topics in quiet Sun and active regions through the solar atmosphere. While our understanding of the quiet Sun chromosphere has significantly improved after the Carlsson & Stein (1997) simulations, we have to find out the important mechanisms which make the active region chromosphere so much bright, structured, and dynamic. We investigate the emergence of the magnetic flux in the solar surface, accompanied with small-scale reconnections, hot explosive events like Ellerman bombs, and a spectrum of bright structures in the chromosphere and the TR. It is important to compare the chromospheric reaction in small ephemeral regions and vigorous flux emergence in active regions. The goal is to find out the relation between dynamics of the photosphere, the chromosphere, and the TR during a flux emergence process.
Active Region chromosphere
The next research topic concerns a detailed explanation of the active region chromosphere and TR. While plage magnetic field has been measured in photosphere a long time ago, the nature of their enhanced chromospheric emission compared to the quiet Sun was not truly understood. Active region moss observed in the TR are associated with plage regions. The flux of mass, energy and momentum is transferred to the upper atmosphere (moss) via the lower atmosphere (plage). The heating processes are however different in the moss and plage, even if they are related. Strongest magnetic filed in active regions appear in sunspot umbrae. Umbrae and light bridges are very active in chromosphere. The three minute umbral oscillations in the umbra results in strong emission in the core of strong chromospheric lines, known as umbral flashes. Umbrae and light bridges sometimes harbor strong ejections like Hα surges. We lack high-resolution thermal and magnetic field measurements of the umbral chromosphere (in particular middle and upper chromosphere). We want to establish a thermal and magnetic connectivity with simultaneous measurements in the photosphere, the chromosphere, and the TR. The goal is to explore the basic mechanisms responsible for the deposit of mass and energy in the chromospheric and transition region.
Sunspots
Although we have over 400 years of sunspot observations, fine structure of sunspots and the solar cycle is still an important topic of research. I have studied the formation and evolution of sunspots and their solar cycle variation in the past using a variety of the ground and space telescopes. There are several important questions concerning the fast evolution of sunspot fine structure in different layers of the solar atmosphere. Surges, cavities, and light bridges are just a few highly dynamic events related to sunspot chromosphere. While there have been a lot of progress in simulating quiet Sun, active region simulations are not there yet. The interplay between the strong magnetic field and solar surface plasma presents a variety of plasma features (instabilities, waves, ..).
Solar-stellar physics
There are many phenomena which takes too long time like Maunder minimum. We cannot wait another billion years to understand how the rotational and magnetic properties of the Sun evolve. Instead, we look for Sun-like stars and sample a diverse set of such stars with various ages. This way, we learn about the long-term trends in solar variations, e.g. what is the chance of a super flare event? The Sun is located in-between the branch of active stars and the branch of inactive stars. It is not clear how long this evolutionary phase will last.