Alfvén Wave Connection between the Chromosphere and the Corona of the Sun: An Analytical Study

Abstract

Alfvén waves are closely relevant to the three outstanding problems in the solar corona: coronal heating, solar wind acceleration, and the fractionization of low first ionization potential (FIP) elements. There has been increasing observational evidence for the Alfvén waves, not only in the corona, but also in the chromosphere. Here we investigate the Alfvén wave connection between the chromosphere and the corona based on the analytical solution of Alfvén waves in a layer where Alfvén speed varies along magnetic field lines with a constant gradient. The wave transmission of the layer is determined by two parameters: the Alfvénic cutoff frequency and the dimensionless thickness of the layer. It is shown that the ponderomotive acceleration originating from Alfvén waves is always directed upward in the solar atmosphere with the peak occurring in the chromosphere-corona transition region in association with downward low-frequency waves. We also find that some velocity amplitudes observed in the chromosphere of quiet regions and all the velocity amplitudes observed in active regions fall short of the theoretical estimates obtained with the assumption that the Alfvén waves generated below the chromosphere transport upward the energy required for the corona. We suggest considering the possibility that the Alfvén waves responsible for the coronal heating and the FIP fractionization originate from above the chromosphere.

Keywords

• Magnetohydrodynamics
• Alfven waves
• Solar chromosphere
• Solar atmosphere