Magnetohydrodynamics

Abstract

State-of-the-art MHD calculations reveal acceptable agreement with observational data for the height profile of the temperature $T(h)$ in the transition region of solar corona. Simultaneously, the velocity of the solar wind $U(h)$ has also been calculated. The developed method gives the possibility at given frequency dependent spectral density of Alfv\'en waves (AW) coming from chromosphere $\mathcal{W}(\omega)$ to calculate both height profiles $T(h)$ and $U(h)$. In agreement with the concepts of the self-induced opacity of plasma with respect of AW, the narrow width $\lambda$ of the transition region is determined by the fast temperature increase of the viscosity $\eta(T,B)$. After more than 70 years of development of Solar physics, the Alfv\'en hypothesis of heating of the solar corona by AW has remained without alternatives; none of other mechanisms can explain $ab$ $initio$ the value of $\lambda$. The performed MHD analysis explains the height dependence of the non-thermal broadening of the chromospheric spectral lines and predicts angular dependence of this broadening with respect of position in solar disc. One can expect significant impact of MHD analysis in the interpretation of the long expected data from Parker Solar Probe.