Three-Dimensional Morphology of a Coronal Prominence Cavity

Abstract

We present a three-dimensional density model of coronal prominence cavities, and a morphological fit that has been tightly constrained by a uniquely well-observed cavity. Observations were obtained as part of an International Heliophysical Year campaign by instruments from a variety of space-and ground-based observatories, spanning wavelengths from radio to soft X-ray to integrated white light. From these data it is clear that the prominence cavity is the limb manifestation of a longitudinally extended polar-crown filament channel, and that the cavity is a region of low density relative to the surrounding corona. As a first step toward quantifying density and temperature from campaign spectroscopic data, we establish the three-dimensional morphology of the cavity. This is critical for taking line-of-sight projection effects into account, since cavities are not localized in the plane of the sky and the corona is optically thin. We have augmented a global coronal streamer model to include a tunnel-like cavity with elliptical cross-section and a Gaussian variation of height along the tunnel length. We have developed a semi-automated routine that fits ellipses to cross-sections of the cavity as it rotates past the solar limb, and have applied it to Extreme Ultraviolet Imager observations from the two Solar Terrestrial Relations Observatory spacecraft. This defines the morphological parameters of our model, from which we reproduce forwardmodeled cavity observables. We find that cavity morphology and orientation, in combination with the viewpoints of the observing spacecraft, explain the observed variation in cavity visibility for the east versus west limbs.

The Physical Processes of CME/ICME Evolution

“…1, 2 and 3, can be described by physical models, which can reproduce observed properties and explain and predict their evolution. For CMEs with a common three-part structure, the magnetic field is commonly taken to be of the form of a twisted flux rope contained within an interior plasma cavity (e.g., Gibson et al 2010). The core of the structure is typically considered to be filament material that was supported by the magnetic field above the system's photospheric polarity inversion line (PIL) prior to the eruption.…”

A new look at a polar crown cavity as observed by SDO/AIA

“…In a recent paper by Gibson et al (2010), the authors studied the structure, shape, and evolution (mostly due to the solar rotation) in detail of a stable cavity observed by SOHO/EIT in the wavelength filter at 195 Å. They find that, based on a forward modelling approach, the cavity is darker than the surrounding owing to the depletion in density by a factor of about 2.…”

Magnetism and the Invisible Man: The mysteries of coronal cavities

“…. Gibson et al (2010) studied the 3D morphology of a cavity using observations at multiple wavelengths, vantage points, and covering multiple days. The cavity was modeled as a tunnel-like structure, with a Gaussian height (Figure 3, left) and elliptical crosssection.…”

“…Forland et al (2013) fit ellipses to all the EUV cavities in the survey, and found a strong tendency (93%) for cavity ellipses to be taller than they were wide. Building on the 3D morphology found by Gibson et al (2010), Schmit & Gibson (2011) extracted density of a coronal cavity from multiwavelength observations. The density was found to be approximately 30% depleted at the center of the cavity relative to the surrounding streamer at the same height.…”