Abstract
Context.
The solar corona exhibits a pronounced temperature inversion, with plasma temperatures increasing by a factor of 100 from the chromosphere to the corona. The atmosphere below the corona hosts spatially sparse and temporally intermittent heating events, whose role in establishing this temperature inversion remains debated.
Aims.
We investigate how the combined effects of spatial sparsity and temporal intermittency of stochastic heating events shape the temperature inversion in coronal loops within a kinetic framework.
Methods.
We introduce stochastic thermal boundary conditions at the base of the transition region, together with a surface coarse-graining procedure. In the collisionless case, two stationary regimes are analytically modeled, depending on whether the timescale of heating events is shorter or longer than the electron or proton loop crossing time. Coulomb collisions are then incorporated through a reduced approach that captures their cumulative effect as an attenuation of the suprathermal population with height.
Results.
In the absence of collisions and in the short timescale regime, spatial filling factor and temporal intermittency enter symmetrically through a single effective parameter that controls the weight of suprathermal particles. A temperature inversion develops both within individual heated loops and at the coarse-grained level. When collisions are included, the temperature inversion persists, but collisional effects significantly reduce the coronal density. In the long timescale regime, where loop temperatures are nearly uniform, the temperature inversion is governed solely by the spatial filling factor. In this regime, Coulomb collisions do not significantly modify affect the coronal temperature and density. The system thus remains in a low plasma-beta regime, with density and temperature profiles consistent with observations.
Conclusions.
Spatially sparse and temporally intermittent heating can self-consistently generate suprathermal distributions and a temperature inversion within a kinetic framework. The robustness of the long timescale regime contrasts with the stronger collisional constraints affecting the short timescale regime.
