Pr Peter J. Cargill

Modeling the Radiative Signatures of Turbulent Heating in Coronal Loops

The statistical properties of the radiative signature of a coronal loop subject to turbulent heating obtained from a three-dimensional (3D) magnetohydrodynamics (MHD) model are studied. The heating and cooling of a multistrand loop is modeled and synthetic spectra for Fe XII 195.12, Fe XV 284.163, and Fe XIX 1118.06 ? are calculated, covering a wide temperature range. The results show that the statistical properties of the thermal and radiative energies partially reflect those of the heating function in that power-law distributions are transmitted, but with very significant changes in the power-law indices. There is a strong dependence on the subloop geometry. Only high-temperature radiation (?107 K) preserves reasonably precise information on the heating function.

Profiles of heating in turbulent coronal magnetic loops

Context. The location of coronal heating in magnetic loops has been the subject of a long-lasting controversy: does it occur mostly at the loop footpoints, at the top, is it random, or is the average profile uniform? Aims. We try to address this question in model loops with MHD turbulence and a profile of density and/or magnetic field along the loop. Methods. We use the Shell-Atm MHD turbulent heating model described in Buchlin & Velli (2007, ApJ, 662, 701), with a static mass density stratification obtained by the HydRad model (Bradshaw & Mason 2003, A&A, 401, 699). This assumes the absence of any flow or heat conduction subsequent to the dynamic heating. Results. The average profile of heating is quasi-uniform, unless there is an expansion of the flux tube (non-uniform axial magnetic field) or the variation of the kinetic and magnetic diffusion coefficients with temperature is taken into account: in the first case the heating is enhanced at footpoints, whereas in the second case it is enhanced where the dominant diffusion coefficient is enhanced. Conclusions. These simulations shed light on the consequences on heating profiles of the complex interactions between physical effects involved in a non-uniform turbulent coronal loop.