Granular-Scale Elementary Flux Emergence Episodes in a Solar Active Region

Abstract

We analyze data from Hinode spacecraft taken over two 54-minute periods during the emergence of AR 11024. We focus on small-scale portions within the observed solar active region and discover the appearance of very distinctive smallscale and short-lived dark features in Ca II H chromospheric filtergrams and Stokes I images. The features appear in regions with close-to-zero longitudinal magnetic field, and are observed to increase in length before they eventually disappear. Energy release in the low chromospheric line is detected while the dark features are fading. Three complete series of these events are detected having remarkably similar properties, i.e. lifetime of ≈12 min, maximum length and area of 2-4 Mm and 1.6-4 Mm 2 , respectively, and all had associated brightenings. In time series of magnetograms a diverging bipolar configuration is observed accompanying the appearance of the dark features and the brightenings. The observed phenomena are explained as evidencing elementary flux emergence in the solar atmosphere, i.e small-scale arch filament systems rising up from the photosphere to the lower chromosphere with a length scale of a few solar granules. Brightenings are explained as being the signatures of chromospheric heating triggered by reconnection of the rising loops (once they reached chromospheric heights) with pre-existing magnetic fields as well as to reconnection/cancellation events in U-loop segments of emerging serpentine fields. The characteristic length scale, area and lifetime of these elementary flux emergence events agree well with those of the serpentine field observed in emerging active regions. We study the temporal evolution and dynamics of the events and compare them with the emergence of magnetic loops detected in quiet sun regions and serpentine flux emergence signatures in active regions. Physical processes of the emergence of granular-scale magnetic loops seem to be the same in quiet sun and active regions being the difference the reduced chromospheric emission in quiet sun attributed to the fact that loops are emerging in a region of lower ambient magnetic field density and therefore interactions and reconnection are less likely to occur. Incorporating the novel features of granular-scale flux emergence presented in this study we advance the scenario for serpentine flux emergence.

Magnetic field emergence in mesogranular-sized exploding granules observed with sunrise/IMaX data

“…Taking advantage of the v10 emergence that presents transverse field, we found a magnetic loop emerging in the FOV, whose associated footpoints separate from each other with a velocity of ∼3 km s −1 , in agreement with Martínez González & Bellot Rubio (2009) andVargas Domínguez et al (2011). The footpoints present downflows, indicate mass draining along the legs of the loops, making their ascent to less dense layers possible.…”

“…Carried out with the MURaM code (Vögler et al 2005), which solves the radiative MHD equations on a Cartesian grid, this numerical experiment places a rising fluxtube with a twist parameter λ = 0.25 at z = −3.9 Mm. The simulation domain has horizontal dimensions of 24 Mm × 18 Mm and height of 5.76 Mm, with a total magnetic flux of 10 20 Mx.…”

Evidence of Twisted Flux-Tube Emergence in Active Regions

“…Recently, Valori et al (2012) studied the emergence of an AR and found that the first manifestations of the emergence occur in the form of small bipoles, which are consistent with the sea-serpent scenario. The characteristic size of the bipoles can be associated with the instability wavelength (see also Bernasconi et al, 2002;Otsuji et al, 2011;Vargas Domínguez, van Driel-Gesztelyi, and Bellot Rubio, 2012). As the flux continues to emerge in this way, coalescence and reconnection leads to the formation of larger flux concentrations and the observation of pores, sunspots, and faculae (see Toriumi, Hayashi, and Yokoyama, 2012, and references therein).…”

Small-scale magnetic features in active region NOAA 11024

“…Ïîñ ëå ïî ÿâ ëå íèÿ íà ñî -ëíå÷ íîì äèñ êå ýòà îá ëàñòü áûñ òðî ðàç âè âà ëàñü, óñëîae íÿ ëàñü åå ìàãíèò íàÿ ñòðóê òó ðà. Ñîã ëàñ íî äàííûì [44,45] â íåé ïðî èñ õî äèë òàê íàçû âà å ìûé çìå å âèä íûé âû õîä ìàã íèò íî ãî ïî òî êà íà áîëü øèõ è ìà ëûõ ìàñ øòà áàõ, ÷òî âû çâà ëî áîëü øîå êî ëè ÷åñ òâî ýðóï òèâ íûõ ÿâ ëå íèé, ìàëåíü êèõ âñïû øåê, áîìá Ýëëåð ìà íà è âûáðîñîâ.…”