Evolution of microflares associated with bright points in coronal holes and in quiet regions

Abstract

Aims. We aim to find similarities and differences between microflares at coronal bright points found in quiet regions and coronal holes, and to study their relationship with large scale flares. Methods. Coronal bright points in quiet regions and in coronal holes were observed with Hinode/EIS using the same sequence. Microflares associated with bright points are identified from the X-ray lightcurve. The temporal variation of physical properties was traced in the course of microflares.Results. The lightcurves of microflares indicated an impulsive peak at hot emission followed by an enhancement at cool emission, which is compatible with the cooling model of flare loops. The density was found to increase at the rise of the impulsive peak, supporting chromospheric evaporation models. A notable difference is found in the surroundings of microflares; diffuse coronal jets are produced above microflares in coronal holes while coronal dimmings are formed in quiet regions. Conclusions. The microflares associated with bright points share common characteristics to active region flares. The difference in the surroundings of microflares are caused by open and closed configurations of the pre-existing magnetic field.

Comparative Analysis of a Transition Region Bright Point with a Blinker and Coronal Bright Point Using Multiple EIS Emission Lines

“…where n e is the electron number density, h is the LOS path length, and S is the region containing the physically interesting plasma (Kamio et al, 2011). Under the assumption that the observed plasma is optically thin and in ionization equilibrium, the observed intensity of a single emission line along the LOS h is expressed as…”

“…Coronal BPs display a wealth of enigmatic dynamic behaviors that if found in TR BPs might provide new insights into plasma heating and acceleration. For example, coronal BPs show periodic flashes or flaring for which there is not currently a consensus model Kamio et al, 2011). The larger of the flaring BPs often exhibit eruptive behavior in the form of jets, thus contributing mass to the solar wind .…”

Observational Evidence of Magnetic Reconnection for Brightenings and Transition Region Arcades in IRIS Observations

“…They have important impacts on the heating mechanisms of the solar atmosphere. Such events take place in different atmospheric layers from the photosphere to the corona (Harrison 1997;Berger et al 2007;Chandrashekhar et al 2013), and ubiquitous in active regions, quiet Sun and coronal holes (Shimizu 1995;Zhang et al 2001;Kamio et al 2011). With the ground-based and space telescopes, photospheric BPs are often studied to investigate the condition of the convective flows in and below the photosphere (Feng et al 2013;Jafarzadeh et al 2014;Yang et al 2015Yang et al , 2016Ji et al 2016a,b).…”

Quiet-Sun Network Bright Point Phenomena With Sigmoidal Signatures

“…Coronal and transition region (TR) X-ray and extreme ultraviolet (EUV) bright points (BPs; e.g., Shibata et al 1992Shibata et al , 1996Shimojo et al 1996;Shimojo & Shibata 2000) that predominantly follow the bipole reconnection model as selfsimilar manifestations of large-scale active regions (ARs) are sources of jet phenomena that contribute directly to coronal heating and solar wind mass feeding (Kamio et al 2011;Orange et al 2014b;Tian et al 2014). Although at some coronal heights and temperatures, individual BP loops have been resolved (Kankelborg et al 1996), the spatial resolution of Sun-observing instruments have been insufficient to probe the formation and evolution of BPs due to the existence of unresolved fine structure (UFS) and the dynamics of the plasma and magnetic field environment (Zhang et al 2012).…”