Are solar maximum fan streamers a consequence of twisting sheet structures?

Druckmüller

et al. 2010

ApJ

Self Cite

Using observations of the corona taken during the total solar eclipses of 2006 March 29 and 2008 August 1 in broadband white light and in narrow bandpass filters centered at Fe x 637.4 nm, Fe xi 789.2 nm, Fe xiii 1074.7 nm, and Fe xiv 530.3 nm, we show that prominences observed off the solar limb are enshrouded in hot plasmas within twisted magnetic structures. These shrouds, which are commonly referred to as cavities in the literature, are clearly distinct from the overlying arch-like structures that form the base of streamers. The existence of these hot shrouds had been predicted by model studies dating back to the early 1970s, with more recent studies implying their association with twisted magnetic flux ropes. The eclipse observations presented here, which cover a temperature range of 0.9 to 2 ×10 6 K, are the first to resolve the long-standing ambiguity associated with the temperature and magnetic structure of prominence cavities.

Section: Introductionmentioning

confidence: 99%

Total Solar Eclipse Observations of Hot Prominence Shrouds

Druckmüller

et al. 2010

ApJ

Self Cite

“…Since the average and standard deviation of brightness, as functions of height, have been calculated for large groups of pixels, the process does not amplify noise within an image. The NRGF has been used as a tool for revealing coronal structure in many studies (Morgan & Habbal 2007a, 2007b, 2010bHe et al 2009;Wang et al 2010;Kienreich et al 2009;Lugaz et al 2009;Frazin et al 2009;Habbal et al 2007Habbal et al , 2011, for example) and has been further developed in the sophisticated Fourier NRGF (Druckmüllerová et al 2011).…”

Section: The Normalizing Radial Graded Filter (Nrgf)mentioning

confidence: 99%

Automatically Detecting and Tracking Coronal Mass Ejections. I. Separation of Dynamic and Quiescent Components in Coronagraph Images

Byrne

2012

ApJ

Automated techniques for detecting and tracking coronal mass ejections (CMEs) in coronagraph data are of ever increasing importance for space weather monitoring and forecasting. They serve to remove the biases and tedium of human interpretation, and provide the robust analysis necessary for statistical studies across large numbers of observations. An important requirement in their operation is that they satisfactorily distinguish the CME structure from the background quiescent coronal structure (streamers, coronal holes). Many studies resort to some form of time differencing to achieve this, despite the errors inherent in such an approach-notably spatiotemporal crosstalk. This article describes a new deconvolution technique that separates coronagraph images into quiescent and dynamic components. A set of synthetic observations made from a sophisticated model corona and CME demonstrates the validity and effectiveness of the technique in isolating the CME signal. Applied to observations by the LASCO C2 and C3 coronagraphs, the structure of a faint CME is revealed in detail despite the presence of background streamers that are several times brighter than the CME. The technique is also demonstrated to work on SECCHI/COR2 data, and new possibilities for estimating the three-dimensional structure of CMEs using the multiple viewing angles are discussed. Although quiescent coronal structures and CMEs are intrinsically linked, and although their interaction is an unavoidable source of error in any separation process, we show in a companion paper that the deconvolution approach outlined here is a robust and accurate method for rigorous CME analysis. Such an approach is a prerequisite to the higher-level detection and classification of CME structure and kinematics.

“…Morgan & Habbal (2007a, 2007b established links between observed structures in coronagraph observations (streamers) with structures viewed in extreme UV in the chromosphere and low corona. QSRT maps will give a much-improved constraint on the shape and position of structures in the corona, and enable a better interpretation of the coronal evolution from the Sun into the heliosphere.…”

Section: Applications For Qsrtmentioning

confidence: 99%

Mapping the Structure of the Corona Using Fourier Backprojection Tomography

Lugaz

2008

ApJ

Estimating the structure, or density distribution, of the solar corona from a set of two-dimensional white-light images made by coronagraphs is a critical challenge in coronal physics. This work describes new data-analysis procedures which are used to create global maps of the coronal structure at heights where the corona becomes approximately radial ( 3 R ). The technique, which is named Qualitative Solar Rotational Tomography (QSRT), uses total brightness white light observations, processed with a suitable background subtraction and a Normalizing Radial Graded Filter (NRGF). These observations are made with high frequency by the Large Angle and Spectrometric Coronagraph Experiment (LASCO) C2 coronagraph, which allows a standard Fourier-transformbased tomographical reconstruction. In this paper, we first test the technique using a model corona. QSRT is then applied to a set of observations made during Carrington Rotation (CR) 2000-2001 March 16 to 2003. Since the maps are constructed from data which are normalized using the NRGF process, QSRT cannot give electron density directly. Nevertheless, the tests using the model corona demonstrate the technique's ability to give a good qualitative reconstruction of the coronal structure at high latitude, with decreasing but acceptable accuracy at the equator. These tests also demonstrate QSRT's insensitivity to noise. For the LASCO C2 observations, good agreement is found between synthetic images calculated from the reconstructed corona and the original observations, and good agreement is found between the distribution of density in a QSRT reconstruction and that found using a global MHD model. Despite their lack of quantitative information on absolute electron density, the resulting maps (which are constructed directly from high-resolution coronal data observed at the appropriate height), contain useful information on the distribution of density in the corona.