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Stereoscopy of extreme UV quiet Sun brightenings observed by Solar Orbiter/EUI  

Andrei Zhukov   Submitted: 2021-09-19 14:27

The 3D fine structure of the solar atmosphere is still not fully understood as most of the available observations are taken from a single vantage point. The goal of the paper is to study the 3D distribution of small-scale brightening events ("campfires") discovered in the EUV quiet Sun by the Extreme Ultraviolet Imager (EUI) aboard Solar Orbiter. We used a first commissioning data set acquired by the EUI's High Resolution EUV telescope on 30 May 2020 in the 174 Å passband and we combined it with simultaneous data taken by the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory in a similar 171 Å passband. The two-pixel spatial resolution of the two telescopes is 400 km and 880 km, respectively, which is sufficient to identify the campfires in both data sets. The two spacecraft had an angular separation of around 31.5 degrees (essentially in heliographic longitude), which allowed for the 3D reconstruction of the campfire position. These observations represent the first time that stereoscopy was achieved for brightenings at such a small scale. Manual and automatic triangulation methods were used to characterize the campfire data. The height of the campfires is located between 1000 km and 5000 km above the photosphere and we find a good agreement between the manual and automatic methods. The internal structure of campfires is mostly unresolved by AIA; however, for a particularly large campfire, we were able to triangulate a few pixels, which are all in a narrow range between 2500 and 4500 km. The low height of EUI campfires suggests that they belong to the previously unresolved fine structure of the transition region and low corona of the quiet Sun. They are probably apexes of small-scale dynamic loops heated internally to coronal temperatures. This work demonstrates that high-resolution stereoscopy of structures in the solar atmosphere has become feasible.

Authors: A. N. Zhukov, M. Mierla, F. Auchère, S. Gissot, L. Rodriguez, E. Soubrié, W. T. Thompson, B. Inhester, B. Nicula, P. Antolin, S. Parenti, É. Buchlin, K. Barczynski, C. Verbeeck, E. Kraaikamp, P. J. Smith, K. Stegen, L. Dolla, L. Harra, D. M. Long, U. Schühle, O. Podladchikova, R. Aznar Cuadrado, L. Teriaca, M. Haberreiter, A. C. Katsiyannis, P. Rochus, J.-P. Halain, L. Jacques, D. Berghmans
Projects: SO/EUI

Publication Status: A&A (in press)
Last Modified: 2021-09-20 14:03
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EIT Wave Observations and Modeling in the STEREO Era  

Andrei Zhukov   Submitted: 2011-02-04 07:49

``EIT waves'' are large-scale bright fronts observed propagating in the solar corona in association with coronal mass ejections (CMEs). An overview of the observed properties of large-scale wave-like fronts in the solar atmosphere (Moreton waves, EIT waves and similar phenomena observed in other wavelengths) is presented. The models proposed to explain these phenomena are reviewed. A particular emphasis is put on the recent EIT wave observations made by the STEREO mission (Solar-TErrestrial RElations Observatory) launched in October 2006. New key observational results and their implications for EIT wave models are discussed. It is concluded that no single model can account for the large variety of observed EIT wave properties. Prospects for future investigations of this complex phenomenon are outlined.

Authors: Andrei N. Zhukov
Projects: SoHO-EIT,STEREO

Publication Status: Journal of Atmospheric and Solar-Terrestrial Physics (in press)
Last Modified: 2011-02-06 18:43
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The Origin of Polar Streamers in the Solar Corona  

Andrei Zhukov   Submitted: 2008-06-16 07:47

We investigate the large-scale three-dimensional (3D) structure of the solar corona near the maximum of the 23rd solar cycle in an attempt to determine the origin of polar streamers. We use a model that allows us to simulate the quasi-stationary configuration of the large-scale coronal density distribution. The coronal neutral line, as given by the potential field source surface (PFSS) model, serves as a proxy for mid- and low-latitude current sheets. We investigate the contribution of possible polar coronal current sheets associated with large-scale photospheric magnetic neutral lines around the poles of the Sun (polar crown neutral lines). Positions of polar neutral lines are radially extrapolated outward to obtain the configuration of polar current sheets. Coronal plasma sheets are centered around introduced current sheets. Streamer positions during Carrington rotation 1965, near the activity maximum, are calculated. Simulated synoptic maps of the coronal brightness are compared with those obtained from observations by the LASCO C2 coronagraph on board the SOHO spacecraft. We demonstrate that polar streamers are ''classical'' streamers situated above low-lying loops (observed by SOHO EIT) connecting the regions of opposite magnetic polarity on two sides of polar crown neutral lines. Polar streamer configurations obtained from our model are close to those observed by LASCO. Our results suggest that the PFSS model cannot adequately describe the configuration of streamers during the epoch of high solar activity. The representation of the streamer belt as a single tilted and warped current sheet becomes questionable. Multiple coronal current sheets may better correspond to the observed streamer configurations.

Authors: A. N. Zhukov, F. Saez, P. Lamy, A. Llebaria, and G. Stenborg
Projects: SoHO-LASCO

Publication Status: published in ApJ
Last Modified: 2008-09-23 20:59
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Global Coronal Mass Ejections  

Andrei Zhukov   Submitted: 2007-06-22 04:15

Observations of the low solar corona in the extreme ultraviolet and in soft X-rays evidence a close relationship of coronal dimmings and coronal mass ejections (CMEs). Dimmings are usually interpreted as places of plasma evacuation during a CME. We characterize a CME by the apparent angular extent of associated dimmings above the solar limb and define a global CME as a CME with the total apparent extent of limb dimmings of more than 180 degrees. Several examples of global CMEs are discussed. All the global CMEs identified up to now are fast full-halo CMEs associated with X-class flares (if they originate on the front side of the Sun). We demonstrate that global CMEs involve an eruption of several magnetic flux systems distributed on a large spatial scale comparable to one-half of the solar disk (true angular width around 180 degrees). We discuss possible interpretations of the global CME phenomenon and challenges it presents to CME modeling. Our results suggest a nonlocal nature of the CME eruption mechanism.

Authors: A. N. Zhukov, I. S. Veselovsky
Projects: SoHO-EIT,SoHO-MDI

Publication Status: ApJ 664, L131 (2007)
Last Modified: 2007-07-26 05:55
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Abstracts by Author
Stereoscopy of extreme UV quiet Sun brightenings observed by Solar Orbiter/EUI
EIT Wave Observations and Modeling in the STEREO Era
The Origin of Polar Streamers in the Solar Corona
Global Coronal Mass Ejections

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