The Early Evolution of Solar Flaring Plasma Loops

Abstract

Plasma loops are the elementary structures of solar flaring active regions and dominate the whole process of flaring eruptions. Standard flare models explain evolution and eruption after magnetic reconnection around the hot cusp-structure above the top of plasma loops very well; however, the early evolution of plasma loops before the onset of magnetic reconnection is poorly understood. Considering that magnetic gradients are ubiquitous in solar plasma loops, this work applies the magnetic-gradient pumping (MGP) mechanism to study the early evolution of flaring plasma loops. The results indicate that early evolution depends on the magnetic field distribution and the geometry of the plasma loops, which dominate the balance between the accumulation and dissipation of the energy around loop tops. Driven by MGP process, both of the density and temperature as well as the plasma β value around the looptop will increase in the early phase of the plasma loop’s evolution. In fact, the solar plasma loops will have two distinct evolutionary results: low, initially dense plasma loops with relatively strong magnetic fields tend to be stable for their maximum β value, which is always smaller than the critical value β<βc, while the higher, initially diluted solar plasma loops with relatively weak magnetic fields tend to be unstable for their β values, exceeding the critical value β>βc at a time of about one hour after the formation of the solar-magnetized plasma loop. The latter may produce ballooning instability and may finally trigger the following magnetic reconnection and eruptions. These physical scenarios may provide us with a new viewpoint to understand the nature and origin of solar flares.