High-resolution spectroscopy of a surge in an emerging flux region

Abstract

Aims. The regular pattern of quiet-Sun magnetic fields was disturbed by newly emerging magnetic flux, which led a day later to two homologous surges after renewed flux emergence, affecting all atmospheric layers. Hence, simultaneous observations in different atmospheric heights are needed to understand the interaction of rising flux tubes with the surrounding plasma, in particular by exploiting the important diagnostic capabilities provided by the strong chromospheric Hα line regarding morphology and energetic processes in active regions. Methods. A newly emerged active region NOAA 12722 was observed with the Vacuum Tower Telescope (VTT) at Observatorio del Teide, Tenerife, Spain on 11 September 2018. High-spectral resolution observations using the echelle spectrograph in the chromospheric Hα λ6562.8 Å line were obtained in the early growth phase. Noise-stripped Hα line profiles yield maps of line-core and bisector velocities, which were contrasted with velocities inferred from Cloud Model inversions. A high-resolution imaging system recorded simultaneously broad-and narrow-band Hα context images. The Solar Dynamics Observatory (SDO) provided additional continuum images, line-of-sight (LOS) magnetograms, and UV/EUV images, which link the different solar atmospheric layers.Results. The active region started as a bipolar region with continuous flux emergence when a new flux system emerged in the leading part during the VTT observations, resulting in two homologous surges. While flux cancellation at the base of the surges provided the energy for ejecting the cool plasma, strong proper motions of the leading pores changed the magnetic field topology making the region susceptible for surging. Despite the surge activity in the leading part, an arch filament system in the trailing part of the old flux remained stable. Thus, stable and violently expelled mass-loaded ascending magnetic structures can co-exist in close proximity. Investigating the height dependence of LOS velocities revealed the existence of neighboring strong up-and downflows. However, downflows occur with a time lag. The opacity of the ejected cool plasma decreases with distance from the base of the surge while the speed of the ejecta increases. The location at which the surge becomes invisible in Hα corresponds to the interface where the surge brightens in He ii λ304 Å. Broad-shoulders and dual-lobed Hα profiles suggests accelerated/decelerated and highly structured LOS plasma flows. Significantly broadened Hα profiles imply significant heating at the base of the surges, which is also supported by bright kernels in UV/EUV images uncovered by swaying motions of dark fibrils at the base of the surges. Conclusions. The interaction of newly emerging flux with pre-existing flux concentrations of a young, diffuse active region provided suitable conditions for two homologous surges. High-resolution spectroscopy revealed broadened and dual-lobed Hα profiles tracing accelerated/decelerated flows of cool plasma along the multi-threaded structure of the surge.

High-resolution spectroscopy of an erupting minifilament and its impact on the nearby chromosphere

“…The parameters are derived by inverting the contrast profiles of the structure, which are taken in reference to an average absorption profile taken from a nearby quiet-Sun region, free from prominent absorption structures (see e.g., black line in Figure 5a). Typical structures that have been treated with CM are chromospheric mottles or fibrils see (e.g., Tsiropoula & Schmieder 1997;Tziotziou et al 2003), filaments (e.g., Kuckein et al 2016), arch-filament systems (González Manrique et al 2017) and surges (Verma et al 2020). In this study, as already mentioned, contrast profiles were processed by applying an iterative PCA process to remove noise before feeding the CM inversion scheme.…”

“…These are attributed to strong downflows after the eruption and indicate that the corresponding spectral profiles are not only redshifted but also highly asymmetric. Since the BVHM is sensitive to motions lower in the chromosphere (Dineva et al 2020;Verma et al 2020), these strong downflows are attributed to the interaction of the minifilament material with the chromosphere below. In the following, we will discuss these profiles in detail and the regions where they occurred.…”