Magnetic gradient: a natural driver of solar eruptions

Abstract

Abstract It is well-known that a gradient will inevitably drive a flow. For example, a density-gradient may drive a diffusion flow, an electrical potential-gradient may drive an electric current in plasmas, and so on. What flow will be driven when a magnetic-gradient occurs in solar atmospheric plasmas? Considering the ubiquitous distribution of magnetic-gradient in solar plasma loops, this work demonstrates that the magnetic-gradient pumping (MGP) mechanism is valid, even in the partial ionized solar photosphere and chromosphere as well as in the corona. The magnetic gradient drives energetic particle upflows that carry and convey kinetic energy fromthe underlying atmosphere tomove upwards, accumulate around the looptop and increase the temperature and pressure, produce ballooning instabilities, and finally it leads to magnetic reconnections and eruptions around the looptop. This mechanism may explain the formation of the hot cusp-structures that can be observed above flaring loops in most preflare phases; therefore, the magneticgradient should be a natural driver of solar eruptions. Furthermore, we may also apply this mechanism to explain many other astrophysical phenomena, such as the cold of sunspot and the hot above it, the formation of solar plasma jets, type-II spicule, and fast solar wind above coronal holes, and also the fast plasma jets related to white dwarfs, neutron stars and black holes.