``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
Publication Status: Journal of Atmospheric and Solar-Terrestrial Physics (in press)
Last Modified: 2011-02-06 18:43
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
Publication Status: published in ApJ
Last Modified: 2008-09-23 20:59
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
Publication Status: ApJ 664, L131 (2007)
Last Modified: 2007-07-26 05:55