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Improved Determination of the Location of the Temperature Maximum in the Corona  

Joseph Lemaire   Submitted: 2017-01-13 06:07

The most used method to calculate the coronal electron temperature [Te(r)] from a coronal density distribution [ne(r)] is the scale-height method (SHM). We introduce a novel method that is a generalization of a method introduced by Alfvén (Ark. Mat. Astron. Fys. 27, 1, 1941) to calculate Te(r) for a corona in hydrostatic equilibrium: the "HST" method. All of the methods discussed here require given electron-density distributions [ne(r)] which can be derived from white-light (WL) eclipse observations. The new "DYN" method 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 applications of the SHM method and DYN method give comparable distributions for Te(r). Both have a maximum [Tmax] whose value ranges between 1-3 MK. However, the peak of temperature is located at a different altitude in both cases. Close to the Sun where the expansion velocity is subsonic (r < 1.3 R) the DYN method gives the same results as the HST method. The effects of the other free parameters on the DYN temperature distribution are presented in the last part of this study. Our DYN method 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: Joseph Lemaire, Koen Stegen
Projects: None

Publication Status: Solar Physics, Volume 291, Issue 12, pp.3659-3683
Last Modified: 2017-01-13 06:08
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Improved Determination of the Location of Temperature Maximum in the Corona  

Joseph Lemaire   Submitted: 2016-09-14 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: shm-method. 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 hst-method. 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 dyn-method 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 dyn-method 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 shm-method and dyn-method give comparable distributions for Te(r). Both have a maximum, Tmax , whose value ranges between 1-3 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 dyn-method give the same results as the hst-method. The effects of additional free parameters on the dyn-temperature distribution are presented in the last part of this study: (1) the super-radial expansion rate of flow tubes, (2) the relative concentration of α particles, as well as (3) the ratios of ion and electron temperatures. Our dyn-method 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: 2016-09-17 07:05
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Improved Determination of the Location of the Temperature Maximum in the Corona
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