Improved Determination of the Location of Temperature Maximum in the Corona 

Joseph Lemaire Submitted: 20160914 14:29
There are different methods to calculate the coronal electron temperature, Te(r), from a coronal density distribution, ne(r); the most used one is the scale height method: shmmethod. We introduce a novel method, which is a generalization of a method introduced by Alfvén (1941) to calculate Te(r) for a corona in hydrostatic equilibrium: the hstmethod.
All methods discussed here require given electron density distributions, ne(r), that can be derived from white light (WL) eclipses and any tomographic or stereoscopic coronagraph observations. The new dynmethod determines the unique solution of Te(r) for which
Te(r → ) → 0 when the solar corona expands radially as realized in hydrodynamical solar wind models. The coronal electron density used in our dynmethod is approximated by a power law distribution of the heliographic distance r, which is similar to that introduced by Baumbach (1937). The empirical distributions of ne(r) and the expansion velocity, u(r), are extended up to 1 AU, by using the continuity equation of particle flux for given solar wind densities and bulk speeds at 1 AU which are parameters available from spacecraft measurements.
The applications of the shmmethod and dynmethod give comparable distributions for Te(r). Both have a maximum, Tmax , whose value ranges between 13 MK. However, the peak of temperature is located at different altitudes for both methods. Close to the Sun where the expansion velocity is subsonic (r < 1.3 RS) the dynmethod give the same results as the hstmethod.
The effects of additional free parameters on the dyntemperature distribution are presented in the last part of this study: (1) the superradial expansion rate of flow tubes, (2) the relative concentration of α particles, as well as (3) the ratios of ion and electron temperatures.
Our dynmethod is a new tool to evaluate the range of altitudes where the heating rate is maximum in the solar corona when the electron density distribution is obtained from WL coronal observations.
Authors: J.F. Lemaire, K. Stegen
Projects: None

Publication Status: Recently accepted for publication in SOLAR PHYSICS
Last Modified: 20160917 07:05




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