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 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 b a h α

Latitude (deg)Longitude (deg)Cone ½ Angle (deg) Radial distance (Rs) b c d e f 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 degrees45 degrees60 degrees factor 2 difference in velocity Again: Which ellipse ?

What if we only have one Coronagraph ?

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

CME Analysis Tool (CAT)