KEY ISSUES OF THE SOLAR TRANSITION REGION TO BE ADRESSED BY THE SOLAR ORBITER

摘要

The transition region is the thermal contact between the dense and cold chromosphere and the hot and tenuous corona. As such, the spectral emission lines formed in the region potentially contain information on the phenomena occurring in both. This diagnostic potential is increased since the transition region is geometrically quite small and since the radiative transfer is relatively simple for these lines. The transition region thus presents us with the possibility of making observations that can elucidate the still not understood energetics and dynamics of the corona and the chromosphere. On the other hand, the nearly discontinuous rise in temperature and the fact that plasma beta passes through β = 1 close to the transition region practically ensure that wave phenomena such as reflection and refraction will occur. It is also certain that time-dependent phenomena and the topology of the magnetic field are factors that contribute to the complications in unraveling the nature of the dynamics of these regions. There is a large contrast between network and internetwork emission throughout the outer layers of the Sun (indeed it is not certain that any material at coronal temperatures is in thermal contact with the internetwork at all), while at any given location the emission varies with time on several different time scales. In the internetwork there is, perhaps, general agreement that acoustic waves play an important role in powering the emission stemming from the upper chromosphere. In the network the acoustic power seems suppressed and in the upper regions of the Solar atmosphere magnetic phenomena, such as rapid reconnection or the dissipation of high frequency Alfven waves surely contribute to the heating. We will discuss the various phenomena expected in the transition region in the context of observations possible with the Solar Orbiter.