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Boulder City, CO, United States

Gibson S.E.,HAO | Kucera T.A.,NASA | Rastawicki D.,Stanford University | De Toma G.,HAO | And 15 more authors.
Astrophysical Journal | Year: 2010

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. © 2010. The American Astronomical Society. A.

Kucera T.A.,NASA | Gibson S.E.,HAO | Schmit D.J.,HAO | Schmit D.J.,University of Colorado at Boulder | And 2 more authors.
Astrophysical Journal | Year: 2012

We analyze the temperature and EUV line emission of a coronal cavity and surrounding streamer in terms of a morphological forward model. We use a series of iron line ratios observed with the Hinode Extreme-ultraviolet Imaging Spectrograph (EIS) on 2007 August 9 to constrain temperature as a function of altitude in a morphological forward model of the streamer and cavity. We also compare model predictions to the EIS EUV line intensities and polarized brightness (pB) data from the Mauna Loa Solar Observatory (MLSO) Mark 4K-coronameter. This work builds on earlier analysis using the same model to determine geometry of and density in the same cavity and streamer. The fit to the data with altitude-dependent temperature profiles indicates that both the streamer and cavity have temperatures in the range 1.4-1.7MK. However, the cavity exhibits substantial substructure such that the altitude-dependent temperature profile is not sufficient to completely model conditions in the cavity. Coronal prominence cavities are structured by magnetism so clues to this structure are to be found in their plasma properties. These temperature substructures are likely related to structures in the cavity magnetic field. Furthermore, we find that the model overestimates the EUV line intensities by a factor of 4-10, without overestimating pB. We discuss this difference in terms of filling factors and uncertainties in density diagnostics and elemental abundances. © 2012 The American Astronomical Society. All rights reserved.

Hayashi K.,Stanford University | Liu Y.,Stanford University | Sun X.,Stanford University | Hoeksema J.T.,Stanford University | And 3 more authors.
Journal of Physics: Conference Series | Year: 2013

The Helioseismic Magnetic Imager (HMI) has made full-disk vector magnetic field measurements of the Sun with cadence of 12 minutes. The three-component solar surface magnetic field vector data are from the HMI observations with the data process pipeline modules, VFISV (Very Fast Inversion of the Stokes Vector, Borrero et al., 2011) for Milne-Eddington inversion and the minimum-energy disambiguation algorithm (Metcalf 1994, Leka et al, 2009). The models of the global corona and solar wind, such as the PFSS (potential-field source-surface) model and the MHD simulations, often use the maps of solar surface magnetic field, especially the radial component (Br) as the boundary condition. The HMI observation can provide new Br data for these model. Because of weak magnetic signals at the quiet regions of the Sun, the limb darkening, and geometric effects near solar poles, we need to apply an assumption to make a whole-surface map. In this paper, we tested two assumptions for determining Br at weak-field regions. The coronal structures calculated by the PFSS model with the vector-based Br are compared with those with the magnetogram-based Br and the corona observed by the SDO/AIA (Atmospheric Imaging Assembly). In the tested period, CR 2098, the vector-based Br map gives better agreements than the line-of-sight magnetogram data, though we need further investigation for evaluation. © 2013 Published under licence by IOP Publishing Ltd.

Fong W.,University of Colorado at Boulder | Chu X.,University of Colorado at Boulder | Lu X.,University of Colorado at Boulder | Fuller-Rowell T.J.,University of Colorado at Boulder | And 6 more authors.
EPJ Web of Conferences | Year: 2016

McMurdo station (77.8°S, 166.7°E), locating at the poleward edge of the auroral oval, provides great opportunities for researchers to study the interactions among neutral atmosphere, ionosphere and magnetosphere. More than four years of valuable data have been collected, leading to several new discoveries from the McMurdo lidar campaign. Presented here are the winter temperature tides and their responses to the magnetospheric sources. Winter temperature structures from the lidar observations are also presented for this high southern latitude. © 2016 Owned by the authors, published by EDP Sciences.

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