High-speed coronal rain

Abstract

Abstract. At high spatial and temporal resolution, coronal loops are observed to have a highly dynamic nature. Recent observations with SOHO and TRACE frequently show localized brightenings "raining" down towards the solar surface. What is the origin of these features? Here we present for the first time a comparison of observed intensity enhancements from an EIT shutterless campaign with non-equilibrium ionization simulations of coronal loops in order to reveal the physical processes governing fast flows and localized brightenings. We show that catastrophic cooling around the loop apex as a consequence of footpoint-concentrated heating offers a simple explanation for these observations. An advantage of this model is that no external driving mechanism is necessary as the dynamics result entirely from the non-linear character of the problem.

Physics of Solar Prominences: II—Magnetic Structure and Dynamics

“…Only the blue field lines match the requirements for thermal non-equilibrium to produce dynamic and stationary condensations consistent with observed prominence structure. Red field lines are too short; the helical black field line can host only a condensation sitting at the bottom of the dip; and green field lines are capable of hosting small, intermittent, short-lived condensations known as coronal rain (Müller et al, 2003(Müller et al, , 2005. Threedimensional MHD simulations of both the magnetic and the plasma structure with localized heating, radiation, and thermal conduction are needed to determine the full scope and applicability of thermal non-equilibrium to solar prominence plasmas.…”

Is it possible to model observed active region coronal emission simultaneously in EUV and X-ray filters?

“…(2) that are not stable (e.g., Serio et al 1981;Aschwanden et al 2001;Winebarger et al 2003;Müller et al 2003Müller et al , 2004Müller et al , 2005Karpen et al 2005Karpen et al , 2006. In principle, there are two types of instabilities that must be considered: a Rayleigh-Taylor instability occurs if ∇n e · g < 0, and thermal instability occurs if the heating and the thermal conduction near the loop apex are insufficient to balance the radiative losses, leading to the formation of a condensation and condensation-evaporation cycle for the coronal loop (Müller et al 2003(Müller et al , 2004(Müller et al , 2005. Aschwanden et al (2001) found following approximative criterion for the existence of stably stratified coronal loops, that…”

“…(12). Müller et al (2003Müller et al ( , 2004Müller et al ( , 2005 numerically studied three loops A115, page 4 of 19 with different lengths. The shortest heating scale-lengths for which stable solutions exist follow the stability criterion of Aschwanden et al (2001) quite closely.…”

“…The shortest heating scale-lengths for which stable solutions exist follow the stability criterion of Aschwanden et al (2001) quite closely. According to the results of Müller et al (2003Müller et al ( , 2004Müller et al ( , 2005 and also e.g. Klimchuk et al (2010), loops with shorter scale-lengths undergo the condensation-evaporation cycle during which the loop initially rapidly heats up and fills with plasma because of the chromospheric evaporation.…”

“…4.3, we found that the majority of the modeled warm loops, seen in the EIT 171 and 195 filters, have very short heating scale-lengths s Γ H . These loops are known to be thermally unstable and should undergo the condensation-evaporation cycle (e.g., Müller et al 2003Müller et al , 2004Müller et al , 2005Karpen et al 2005;Klimchuk et al 2010). In our model, the cyclic solutions are incorporated only by using their average over evenly distributed phases (Sect.…”