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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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Presentation Transcript
outline
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?
limb cme

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
slide4

CME ‘Cone’ Geometry

radial velocity

b

a

h

radius

α

latitude

Xie et al. 2004

CME parameters calculated from analysis of SOHO images

longitude

slide6

Problem: Ellipses are “freeform” – no constraints on eccentricity vs offset

Cone ½ Angle = 83 degrees (full Angle 166 !!)

slide7

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)
slide8

Again: Which ellipse ?

Cone ½ Angle

30 degrees

45 degrees

60 degrees

factor 2 difference

in velocity

if only one side view
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
a single side view always has problems
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?