SMEI direct, 3-D-reconstruction sky maps, and volumetric analyses, and their comparison with SOHO and STEREO observations

Abstract

Abstract. In this paper we present the results of the analysis of the late January 2007 Coronal Mass Ejection (CME) events recorded by the Solar Mass Ejection Imager (SMEI), the Solar TErrestrial RElations Observatory (STEREO), and the SOlar and Heliospheric Observatory (SOHO) spacecraft. This period occurs when the two STEREO spacecraft views are from close to Earth, and thus the views from both SMEI and the STEREO outer Heliospheric Imagers (HI-2s) coincide. Three-dimensional (3-D) analyses derived from SMEI data show many CMEs that have also been studied by others using short-term image subtractions (image-differencing techniques). During this interval we map several CME structures that are observed in both SMEI and the STEREO-A HI instruments. SMEI brightness analyses provided by shortterm image subtractions ("difference images") and, alternatively, subtractions of a mean-brightness fit over a long-time duration, both show the extents of the CMEs travelling outward above the East limb that erupted from the Sun on 24 and 25 January 2007. The SMEI 3-D-reconstructions not only enhance distinct features within the CME events, but also reconcile difference-imaging results with those where a long-term base has been removed. In the January 2007 example the structure as mapped by CME difference images traces the sharp intensity gradients at the front of the CMEs; generally brighter ejected material follows behind the location of the CME front, but shows poorly in these because of its larger angular extent. Using the long-duration background removal enables SMEI's 3-D analysis to determine a mass for this CME sequence North of the ecliptic.

Solar Mass Ejection Imager (SMEI) 3-D reconstruction of density enhancements behind interplanetary shocks: In-situ comparison near Earth and at STEREO

“…In general there is also a good correspondence between 2-D difference images obtained by the STEREO HI 2 instruments (the only remote images that can be directly compared with SMEI) with difference images observed by SMEI (e.g., Webb et al, 2009;Jackson et al, 2009). The brightness shock fronts that are also modeled generally appear segmented in the SMEI and HI-2 remote observations, but the bulk of these analyses come largely from difference images.…”

“…The brightness locations where a long-term base has been removed are shown to be generally located at different elongations than difference images provide . Thus there is a potential not only for the elongation of the brightness behind the shock response to be found at a different 2-D location relative to the ICME (these presumably follow the sharp gradients in bulk density as shown in Jackson et al, 2009), but this sharp gradient can also potentially be located at a different position along the line of sight. Since this location and the non-uniformity of the shock response for specific events is one of the objects of this study, comparisons of the 2-D responses from these analyses and the remotely-sensed brightness observations from both the SMEI and HI-2 instruments remain beyond the scope of this current article.…”

Three-dimensional reconstruction of heliospheric structure using iterative tomography: A review

“…There is an inherent difficulty in this since the true LOS brightness of the response from the bulk density of the CME model should be fit to measurements where only a very longterm (many day) base is removed. As shown in Jackson et al (2009), difference images tend to highlight the steep gradients usually at the fronts of CMEs, and are thus not representative of the bulk density that is encompassed by the models. Not only does this make bulk density interpretation difficult, but most likely it places Fig.…”

A Heliospheric Imager for Deep Space: Lessons Learned from Helios, SMEI, and STEREO

“…SMEI, now into its seventh year of operation, is the first true heliospheric imaging system to track CMEs outward from the Sun until they arrive at Earth Tappin et al, 2004). The photometric signals from SMEI allow 3D reconstructions and modeled 2D images (see, e.g., Jackson et al, 2006Jackson et al, , 2008aJackson et al, , 2009Buffington et al, 2008Buffington et al, , 2009aBisi et al, 2008a). The SMEI team has produced significant scientific results directly from the 2D sky map orbit differences (see, e.g., Tappin et al, 2004;Reiner et al, 2005;andWebb et al, 2006, 2009b;).…”

“…IPS observations taken using the Cambridge IPS array in the UK (Houminer, 1971), show structures that can be classified as either corotating or detached from the Sun (Gapper et al, 1982;Hewish and Bravo, 1986;Behannon, Burlaga, and Hewish, 1991). More recently, IPS data used in conjunction with tomographic threedimensional (3D) reconstruction techniques have shown the global shapes of heliospheric density and velocity structures including corotating regions and coronal mass ejections (CMEs) or their interplanetary counterparts (ICMEs) in the solar wind (see, e.g., Jackson et al, 1998;Kojima et al, 1998;Asai et al, 1998;Jackson, Hick, and Buffington, 2002;Jackson et al, 2003;Jackson and Hick, 2005;Tokumaru et al, 2007;Tokumaru, Kojima, and Fujiki, 2010;Bisi et al, 2007Bisi et al, , 2008aBisi et al, , 2008bBisi et al, , 2009aBisi et al, , 2009bJackson et al, 2008aJackson et al, , 2008bJackson et al, , 2009Jackson et al, , 2010. These tomographic analyses match in-situ spacecraft measurements from near-Earth spacecraft fairly well.…”