why a sun-earth line coronagraph is best doug biesecker noaa/swpc
Post on 25-Dec-2015
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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
• Headed away from Earth
• Definite miss• No geomagnetic
storm
Partial Halo CME
• Glancing blow at Earth
• Probable hit– Harder to predict
• Weaker, shorter geomagnetic storm
• Headed directly at the Earth
• Definite hit• Strongest, longest
geomagnetic storm
Halo CME
Classic CME Descriptions
longitude
radial velocity
latitude
radius
CME ‘Cone’ Geometry
CME parameters calculated from analysis of SOHO
images
Xie et al. 2004
ba
h α
Latitude (deg) Longitude (deg) Cone ½ Angle (deg) Radial distance (Rs)
b 9.1 2.3 43.2 14.7c 9.4 1.3 26.9 22.3d 0.7 0.2 4.4 132.4e 3.8 1.7 20.3 29.0f 20.8 -37.8 83.0 12.3
Problem: Which ellipse ?
Problem: Ellipses are “freeform” – no constraints on eccentricity vs offset
Cone ½ Angle = 83 degrees (full Angle 166 !!)
• 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)
Cone ½ Angle
30 degrees 45 degrees 60 degrees
factor 2 difference in velocity
Again: Which ellipse ?
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
POS Ambiguity is the differencebetween a hit and a miss
Is it possible to tell the differenceBetween a Full and partial Halo?
A single side view always has problems
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