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Abstract

Abstract. We analyze the temporal behavior of Network Bright Points (NBPs) searching for low-atmosphere signatures of flares occuring on the magnetic network. We make use of a set of data acquired during coordinated observations between ground based observatories (NSO/Sacramento Peak) and the MDI instrument onboard SOHO. Light curves in chromospheric spectral lines show only small amplitude temporal variations, without any sudden intensity enhancement that could suggest the presence of a transient phenomenon such as a (micro) flare. Only one NBP shows spikes of downward velocity, of the order of 2 -4 Km/s, considered as signals of compression associated to a (micro) flare occurrence. For this same NBP, we also find a peculiar relationship between the magnetic and velocity fields fluctuations, as measured by MDI. Only for this point the B -V fluctuations are well correlated, suggesting the presence of magneto-acoustic waves propagating along the magnetic structure. This correlation is lost during the compression episodes and resumes afterward. An A6 GOES soft X-ray burst is temporally associated with the downward velocity episodes, suggesting that this NBP is the footpoint of the flaring loop. This event has a total thermal energy content of about 10 28 erg, and hence belongs to the microflare class.

Power halo and magnetic shadow in a solar quiet region observed in the Hαline

“…On the other hand, Judge et al (2001), using TRACE UV continua and Solar Ultraviolet Measurements of Emitted Radiation (SUMER) lines, have detected a deficit of acoustic power along with lower intensity values in the 2-3 min period range around the quiet Sun NBPs. This deficit, which they termed "magnetic shadow", had already been reported in previous studies (Kneer & von Uexküll 1986;Cauzzi et al 2000), but it has been further exploited in two-dimensional power maps in the past few years (Krijger et al 2001;Muglach 2003;Muglach et al 2005;Vecchio et al 2007;Reardon et al 2009). It is now generally accepted that the interaction of acoustic oscillations with the inclined magnetic field lines together with the location of the magnetic canopy are responsible for the formation of the power halos and magnetic shadows and may reflect common physical processes (McIntosh & Judge 2001;McIntosh et al 2003;Muglagh et al 2005;Moretti et al 2007).…”

“…The NBPs exhibit long period oscillations, around 300 s or higher (Deubner & Fleck 1989;Lites et al 1993;Cauzzi et al 2000), which are attributed to either magnetoacoustic waves (Deubner & Fleck 1990;Lites et al 1993) or to their erratic motions (Kneer & von Uexküll 1986;von Uexküll et al 1989). The same studies find that the most prominent periodicity in the IN is in the 3 min range (5.5 mHz), while higher frequencies even up to 40 mHz or more (De Forest 2004;Fossum & Carlsson 2006) have been reported.…”

Propagating Waves and Magnetohydrodynamic Mode Coupling in the Quiet‐Sun Network

“…These simulations achieved good agreement with the observed Ca ii H profiles, specifically in the production of Ca ii H 2V grains. By contrast, the network is known to show variations at frequencies 4 mHz (e.g., Damé, Gouttebroze, & Malherbe 1984;Lites et al 1993;Cauzzi, Falchi, & Falciani 2000), suggesting a different heating mechanism.…”

Chromospheric models of a solar flare including velocity fields

“…The emission properties and the velocity field of this flare have been analyzed in Cauzzi et al (1995Cauzzi et al ( , 1996. We remind here two of its most important characteristics:…”