STEREO observed stealth CME

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== Introduction ==
== Introduction ==
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[[Image:Where_is_STEREO-1Jun2008.png|300px|thumb|right|'''Figure 1''': Schematic view of the CME that erupted on June 1st 2008, projected on the ecliptic plane (top view). The separation angle between the A and B spacecraft was <math>53^{\circ}</math>. The CME traveled towards STEREO B and was clearly visible in coronagraph images from STEREO A.]]
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The twin [http://stereo.gsfc.nasa.gov/ STEREO] probes are two identical spacecraft, one flying ahead (A) of the Earth and one flying behind it (B). They were launched on Wednesday, October 25th, 2006 from Cape Canaveral, Florida. The separation angle between the two spacecraft increases as time progresses. This double observation allows us to view solar activity from two different vantage points. On June 1st 2008, the angle between STEREO A and STEREO B reached <math>53^{\circ}</math> (Fig 1). On this day, a [http://en.wikipedia.org/wiki/Coronal_mass_ejection coronal mass ejection] (CME) was observed by the STEREO A coronagraphs (Fig 2), while no trace of it was seen in the STEREO B images! This was very surprising, since STEREO B had full view on the eruption. This observation confirms earlier suspicions that CMEs exist that have no clear surface signatures.
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[[Image:STEREO-B_171.jpg|300px|thumb|right|'''Figure 1''': There was nothing on the Sun's surface  that warned us that a CME was about to erupt.]]
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[[Image:CME_1Jun2008_STEREO-A.png|200px|thumb|left|'''Figure 2''': Composite view from STEREO-A of the CME.]]
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== STEREO observation ==
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[[Image:Where_is_STEREO-1Jun2008.png|300px|thumb|right|'''Figure 2''': Schematic view of the CME that erupted on June 1st 2008, projected on the ecliptic plane (top view). The separation angle between the A and B spacecraft was <math>53^{\circ}</math>. The CME traveled towards STEREO B and was clearly visible in coronagraph images from STEREO A.]]
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The twin [http://stereo.gsfc.nasa.gov/ STEREO] probes are two identical spacecraft, one flying ahead (A) of the Earth and one flying behind it (B). They were launched on Wednesday, October 25th, 2006 from Cape Canaveral, Florida. The separation angle between the two spacecraft increases as time progresses. This double observation allows us to view solar activity from two different vantage points. On June 1st 2008, the angle between STEREO A and STEREO B reached <math>53^{\circ}</math> (Fig 2). On this day, a [http://en.wikipedia.org/wiki/Coronal_mass_ejection coronal mass ejection] (CME) was observed by the STEREO A coronagraphs (Fig 3), while no trace of it was seen in the STEREO B images! This was very surprising, since STEREO B had full view on the eruption. This observation confirms earlier suspicions that CMEs exist that have no clear surface signatures.

Revision as of 21:34, 26 May 2009

Introduction

Figure 1: There was nothing on the Sun's surface that warned us that a CME was about to erupt.
Figure 2: Composite view from STEREO-A of the CME.

STEREO observation

Figure 2: Schematic view of the CME that erupted on June 1st 2008, projected on the ecliptic plane (top view). The separation angle between the A and B spacecraft was 53^{\circ}. The CME traveled towards STEREO B and was clearly visible in coronagraph images from STEREO A.

The twin STEREO probes are two identical spacecraft, one flying ahead (A) of the Earth and one flying behind it (B). They were launched on Wednesday, October 25th, 2006 from Cape Canaveral, Florida. The separation angle between the two spacecraft increases as time progresses. This double observation allows us to view solar activity from two different vantage points. On June 1st 2008, the angle between STEREO A and STEREO B reached 53^{\circ} (Fig 2). On this day, a coronal mass ejection (CME) was observed by the STEREO A coronagraphs (Fig 3), while no trace of it was seen in the STEREO B images! This was very surprising, since STEREO B had full view on the eruption. This observation confirms earlier suspicions that CMEs exist that have no clear surface signatures.


Problem storms and stealth CMEs

For the majority of CMEs, especially fast ones, it is generally easy to identify a number of associated low coronal signatures. But there exist several examples of halo CMEs with no such associations. In the past decade indeed, a number of mild geomagnetic storms have been captured at Earth for which no clear solar source could be found. Up till now these "problem storms", as they were called, were quite a mystery. This STEREO observation proves that there exist indeed "stealth" CMEs - eruptions that are invisible when viewed face-on. The term "stealth" was chosen by a reporter who wrote an article about this event in the NewScientist. It refers to stealth technology, used by the military to make aircraft, ships etc. less visible to radar, infrared and other detection methods. A similar CME but with southward Bz could have caused a mild geomagnetic storm at Earth, an unpredictable one.

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