Numerical Simulations of Solar Chromospheric Jets Associated with Emerging Flux

Abstract

We studied the acceleration mechanisms of chromospheric jets associated with emerging flux using a two dimensional magnetohydrodynamic (MHD) simulation. We found that slow mode shock waves generated by magnetic reconnection in the chromosphere and the photosphere play key roles in the acceleration mechanisms of chromospheric jets. An important parameter is the height of magnetic reconnection. When magnetic reconnection takes place near the photosphere, the reconnection outflow collides with the region where the plasma beta is much larger than unity. Then the plasma moves along a magnetic field. This motion generates a slow mode wave. The slow mode wave develops to a strong slow shock as it propagates upward. When the slow shock crosses the transition region, the transition region is lifted up. As a result, we obtain a chromospheric jet as the lifted transition region. When magnetic reconnection takes place in the upper chromosphere, the chromospheric plasma is accelerated due to the combination of the Lorentz force and the whip-like motion of magnetic field. We found that the chromospheric plasma is further accelerated through the interaction between the transition region (steep density gradient) and a slow shock emanating from the reconnection point. This is an MHD effect which has not been discussed before.

Flux Emergence (Theory)

“…(70)), the slow-mode wave mechanism likely plays a role in the further evolution of the jet. Takasao et al (2013) presented Living Reviews in Solar Physics http://www.livingreviews.org/lrsp-2014-3…”

A Three-dimensional Magnetohydrodynamic Simulation of the Formation of Solar Chromospheric Jets with Twisted Magnetic Field Lines

“…Magnetic reconnection has also been suggested as an energy source for acoustic wave generation (Uchida 1969;Pikel'ner 1969Pikel'ner , 1971Heggland et al 2009;Singh et al 2011;González-Avilés et al 2017). The magnetic reconnection model has the advantage of chromospheric jets being accelerated by both the shock wave and the Lorentz force (Takasao et al 2013). …”

Observational study on the fine structure and dynamics of a solar jet. I. Energy build-up process around a satellite spot

“…According to this unified model (Shibata 1999), the characteristic temperature and velocity of an explosive phenomenon are determined by where the magnetic energy is released through the magnetic reconnection, which is possible to be triggered anywhere as long as in the magnetized plasma. In fact, the reconnection in the chromosphere produces the cool jet such as Hα jet, as reproduced by Takasao et al 2013, and that in the corona follows the hot jet such as EUV jet or Xray jet, as reproduced by Nishizuka et al 2008 andMiyagoshi &Yokoyama 2004. Note that the physical mechanisms driving those diverse jets are different from each other; for example, the cool jet reproduced by Yokoyama & Shibata 1995 is driven by the Lorentz force, while that of Takasao et al 2013 are driven by the interaction between the slow-mode shock and the transition layer.…”