Why a Sun-Earth line Coronagraph is Best

Doug BieseckerNOAA/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. 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 ?

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 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

CME Analysis Tool (CAT)