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Why a Sun-Earth line Coronagraph is Best

Why a Sun-Earth line Coronagraph is Best. Doug Biesecker NOAA/SWPC. Outline. Use classic Full Halo, Partial Halo, Limb morphology to determine Earth impact Need secondary observations to resolve near side - far side ambiguity X-ray flare, X-ray/EUV image, H-alpha image

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Why a Sun-Earth line Coronagraph is Best

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  1. Why a Sun-Earth line Coronagraph is Best Doug Biesecker NOAA/SWPC

  2. Outline • Use classic Full Halo, Partial Halo, Limb morphology to determine Earth impact • Need secondary observations to resolve near side - far side ambiguity • X-ray flare, X-ray/EUV image, H-alpha image • Classic cone model can be used to derive CME parameters needed to drive WSA-Enlil • Need a constraint on CME width • Right now, more than one view is required, but there is hope • CME’s seen from the side have longitude ambiguity at least, and are unresolved at worst • Don’t know if Earth will get hit by the CME • Will polarization data resolve this? • Is there a preferred angular separation?

  3. Classic CME Descriptions Limb CME Partial Halo CME Halo CME • Headed away from Earth • Definite miss • No geomagnetic storm • Headed directly at the Earth • Definite hit • Strongest, longest geomagnetic storm • Glancing blow at Earth • Probable hit • Harder to predict • Weaker, shorter geomagnetic storm

  4. CME ‘Cone’ Geometry radial velocity b a h radius α latitude Xie et al. 2004 CME parameters calculated from analysis of SOHO images longitude

  5. Problem: Which ellipse ?

  6. Problem: Ellipses are “freeform” – no constraints on eccentricity vs offset Cone ½ Angle = 83 degrees (full Angle 166 !!)

  7. Full 3D graphics solution – can only represent ‘correct’ cones originating at the Sun • Need to know the cone angle • Big problem since cone angle inversely proportional to velocity (roughly)

  8. Again: Which ellipse ? Cone ½ Angle 30 degrees 45 degrees 60 degrees factor 2 difference in velocity

  9. What if we only have one Coronagraph ?

  10. If only one side view… • Answers below vary depending on s/c-Sun-Earth angle • CME latitude is well determined • CME Width and Earthward velocity are usually well determined, though can still be problematic • CME longitude remains ambiguous, if not unknown • Radial propagation is a bad assumption • Need to test this – I have the data to do so

  11. A single side view always has problems POS Ambiguity is the difference between a hit and a miss Is it possible to tell the difference Between a Full and partial Halo?

  12. CME Analysis Tool (CAT)

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