Why does the Sun, our nearest star, have a hot atmosphere?
Seminar Hall 31, 2nd Floor, Main Building
Abstract:
The solar atmosphere is a complex and dynamic region that consists of several layers, including the photosphere, chromosphere, transition region, and corona. These layers are interconnected and exhibit a wide range of physical processes, including wave coupling and dynamics. MHD wave coupling refers to the transfer of energy between different layers of the solar atmosphere through MHD waves. The different types of MHD waves that are observed in the solar atmosphere include fast/slow magnetoacoustic waves and Alfven waves. These waves are often excited by the turbulent convective motion of the plasma in the photosphere consisting of disordered plasma motions across a wide variety of lengthscales and/or timescales. These plasma motions can be rotating, such as intergranular vortices, vertical, such as global p-modes, or they can be random. Influenced by the topology of omnipresent magnetic fields throughout the solar atmosphere, these motions excite various MHD waves that travel to higher solar atmospheric layers. MHD waves have been considered a potential candidate for maintaining high-temperature plasma since their theoretical prediction decades ago. MHD waves and oscillations are now known to exist throughout the solar atmosphere, spanning a wide range of spatial scales and wave periods, thanks to recent solar observations.
The dynamics of the solar atmosphere are also strongly influenced by these waves. For example, magnetoacoustic waves are important in transporting energy and mass from the lower layers of the solar atmosphere into the corona, where they can contribute to the heating of the corona. Alfven waves are believed to play a key role in the acceleration of the solar wind, which is a stream of charged particles that flows out from the Sun and fills the entire solar system. Overall, MHD wave coupling is an important process in the solar atmosphere that can lead to energy transfer and heating of the plasma and can have important consequences for the dynamics and evolution of the solar atmosphere.