Loop 2 profiles

The animation shows the loop temperature, density, pressure, and velocity for a 1D coronal loop simulation published in this submitted paper. This simulation is initialized with an approximate static equilibrium solution under uniform heating, which relaxes to a proper equilibrium before a spatially dependent, exponential heating term is gradually introduced at t = 10⁵ s. The first frame begins from a state where the loop has stabilized into a repeating thermal nonequilibrium (TNE) cycle. The first time step is at peak temperature during one TNE cycle, about 11.8 hours (13 thermal times) after exponential heating was fully implemented in the simulation. As the condensation forms, note the apparent isobaric evolution. This discrepancy likely reflects how a local instability saturates within the context of a global simulation. Each zone appears to evolve at nearly constant density during the linear phase, potentially resulting in only minor local pressure loss—perhaps too subtle to register in the full-loop pressure profile. As the perturbation amplitude grows and nonlinear effects set in, we hypothesize that the surrounding plasma dynamically compensates for emerging pressure imbalances. This adjustment could give the impression of an isobaric condensation process, even though the underlying instability originated under isochoric conditions.

Critical isochoric cooling rate

This animation shows the evolution of isochoric Λ_c for the same loop as above. Here, Loop 2 begins in the stable regime (Λ(T) < Λ_c). However, over the next few hours, the cooling rate, Λ(T) (black line), increases and eventually surpasses the critical cooling rate, isochoric Λ_c (blue line). The red highlighted portions of the black lines indicate where Λ(T) > Λ_c, indicating instability. Around 3.6 hours later, a dense, cool condensation forms within the loop. This event aligns with theoretical expectations: based on the isochoric growth rate, the timescale for instability is approximately 6.6 hours. Thus, our analysis points to the cause of condensations in TNE loops being the exponential growth of CC modes.

Acknowledgements

This simulation was run using the ARGOS code and was provided by James Klimchuk and Manuel Luna. Though not published, this run was part of the study for their paper.