Solar magnetic flux tube simulations with time-dependent ionization

Abstract

In the present work we expand the study of time-dependent ionization previously identified to be of pivotal importance for acoustic waves in solar magnetic flux tube simulations. We focus on longitudinal tube waves (LTW) known to be an important heating agent of solar magnetic regions. Our models also consider new results of wave energy generation as well as an updated determination of the mixing length of convection now identified as 1.8 scale heights in the upper solar convective layers. We present 1D wave simulations for the solar chromosphere by studying tubes of different spreading as a function of height aimed at representing tubes in environments of different magnetic filling factors. Multilevel radiative transfer has been applied to correctly represent the total chromospheric emission function. The effects of time-dependent ionization are significant in all models studied. They are most pronounced behind strong shocks and in low-density regions, i.e. the middle and high chromosphere. Concerning our models of different tube spreading, we attained pronounced differences between the various types of models, which were largely initiated by different degrees of dilution of the wave energy flux as well as the density structure partially shaped by strong shocks, if existing. Models showing a quasi-steady rise of temperature with height are obtained via monochromatic waves akin to previous acoustic simulations. However, longitudinal flux tube waves are identified as insufficient to heat the solar transition region and corona in agreement with previous studies.

Chromospheric Activity in 55 Cancri: I. Results from Theoretical Wave Studies

“…However, significantly larger shock strength are encountered in wave models based upon frequency spectra; this is a consequence of shock-shock interaction also readily identified in previous works (e.g., Cuntz 1987;Carlsson & Stein 1995;Ulmschneider et al 2005;Fawzy et al 2012). This process is especially evident in LTW models -noting that in some instances (although only temporarily) shock strengths of M sh ∼ > 20 are found.…”

“…Following subsequent work by Stein et al (2009a,b), who employed detailed 3-D convective models, the value of αML = 1.8 has become increasingly established; it has also been previously used by Fawzy et al (2012). For 55 Cnc this approach yields an acoustic wave energy flux of FAC = 3.3 × 10 7 erg cm −2 s −1 with a representative wave period of PAC = 60 s. This latter value has also been adopted for our monochromatic wave simulations intended for comparison with the more detailed models based on wave spectra; see Fig.…”

Chromospheric activity in 55 Cancri: II. Theoretical wave studies versus observations

“…The chromospheric Ca II fluxes are computed by considering non-local thermodynamic equilibrium (NLTE) and partial redistribution (PRD). In addition, effects originating from time-dependent ionization (TDI) have been taken into account as well; see Rammacher & Ulmschneider (2003) and Fawzy et al (2012) for details. The self-consistent treatment of TDI (especially for hydrogen) greatly impacts the atmospheric temperatures and electron densities (especially behind the shocks); it also affects the emergent Ca II fluxes.…”

Solar Irradiance Variability and Climate

“…Krivova, J.D. Haigh due to the drop in density, finally dissipating their energy at shocks in the chromosphere (e.g., Carlsson & Stein 1997;Fawzy, Cuntz & Rammacher 2012). Other forms of heating may also be taking place, but are not discussed further here.…”