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Register a new userA revised cone model and its application to non-radial prominence eruptions
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Q. M. Zhang
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The traditional cone models achieve great success in studying the geometrical and kinematic properties of halo coronal mass ejections (CMEs). In this paper, a revised cone model is proposed to investigate the properties of CMEs as a result of non-radial prominence eruptions. The cone apex is located at the source region of an eruption instead of the Sun center. The cone axis deviates from the local vertical by an inclination angle of $theta_1$ and an angle of $phi_1$. The length and angular width of the cone are $r$ and $omega$, respectively. The model is successfully applied to two CMEs originating from the western limb on 2011 August 11 and 2012 December 7. By comparing the projections of the cones with the CME fronts simultaneously observed by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) and the Extreme-Ultraviolet Imager (EUVI) on board the ahead Solar TErrestrial RElations Observatory (STEREO), the properties of the CMEs are derived, including the distance, angular width, inclination angle, deviation from the plane of the sky, and true speed in space. This revised cone model provides a new and complementary approach in exploring the whole evolutions of CMEs.
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We report on a statistical study of prominence eruptions (PEs) using a catalog of these events routinely imaged by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) in the 304 r{A} pass band. Using an algorithm developed as part of an LWS project, we have detected PEs in 304 r{A} synoptic images with 2-min cadence since May 2010. A catalog of these PEs is made available online (https://cdaw.gsfc.nasa.gov/CME_list/autope/). The 304 r{A} images are polar-transformed and divided by a background map (pixels with minimum intensity during one day) to get the ratio maps above the limb. The prominence regions are defined as pixels with a ratio $ge$2. Two prominence regions with more than 50% of pixels overlapping are considered the same prominence. If the height of a prominence increases monotonically in 5 successive images, it is considered eruptive. All the PEs seen above the limb are detected by the routine, but only PEs with width $ge$15{deg} are included in the catalog to eliminate polar jets and other small-scale mass motions. The identifications are also cross-checked with the PEs identified in Nobeyama Radioheliograph images (http://solar.nro.nao.ac.jp/norh/html/prominence/). The catalog gives the date, time, central position angle, latitude, and width of the eruptive prominence. The catalog also provides links to JavaScript movies that combine SDO/AIA images with GOES soft X-ray data to identify the associated flares, and with SOHO/LASCO C2 images to identify the associated coronal mass ejections. We examined the statistical properties of the PEs and found that the high-latitude PE speed decreased with the decreasing of the average polar magnetic field strength of the previous cycle.
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Theoretical descriptions of observable quantities in cosmological perturbation theory should be independent of coordinate systems. This statement is often referred to as gauge-invariance of observable quantities, and the sanity of their theoretical description is verified by checking its gauge-invariance. We argue that cosmological observables are invariant scalars under diffeomorphisms and as a consequence their theoretical description is gauge-invariant, only at linear order in perturbations. Beyond linear order, they are usually not gauge-invariant, and we provide the general law for the gauge-transformation that the perturbation part of an observable does obey. We apply this finding to derive the second-order expression for the observational light-cone average in cosmology and demonstrate that our expression is indeed invariant under diffeomorphisms.
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