We divided into two main
subgroups: those identifying and studying solar & IP sources of the storms
and those studying solar surface magnetic fields.
Sciences questions we
addressed:
1) Can we infer the magnetic
field structure (Bz south) from
photospheric magnetograms?
2) What are the primary
characteristics that make a CME geoeffective?
3) What types of ICMEs are most geoeffective and
why?
4) What is the relationship
between solar filaments and the ICME flux ropes?
5) What is the best way to
predict the intensity of geomagnetic storms?
6) Why do some storms have
no associated CMEs?
7) Why don't some
Earth-directed CMEs cause storms?
Did not address: No weaker storms are included; we
have no control group.
Preliminary Results of
WG1 (referenced to Question no.)
1) Surface magnetic fields
and eruptions (see file “WG1 mag fields summary.ppt”)
2) Solar & IP source
identifications
- Not yet completed but we made good progress.
- List sources in 3 categories of confidence.
- List by type of geoeffective
structure, with emphasis on what leads to or causes the Bs field region.
3) IP parameters considered
to be most geoeffective:
VBs, Bz,
epsilon best for comparision to Dst,
in that order.
3, 6) We
found that 5 of the storms were caused only by corotating
interaction regions (CIRs); i.e., they had no ICME
material. CIRs are the interface region between slow
and high-speed solar wind flows. The latter are related to sun-centered coronal
holes. Maybe 5 more of the storms were caused by CIRs
with some ICME involvement. This was a surprising result.
3) Types of geoeffective ICMEs:
- Bs field is the most important parameter determining Dst. It can occur in a shock, the
sheath region between the shock and ejecta, an ICME,
or a CIR.
- Enhanced density is important at times when in a sheath
or ICME, most notably in the Jan. 97 event. It can lead to increased dynamic
pressure.
5) How can we predict the
intensity of storms?
- A difficult problem but we made some progress.
- There is a relation between the total mag.
flux and speed of the eruption; i.e., faster CMEs
produce bigger storms.
- Compression; strong ejecta
field
- The total flux under the H-alpha flare ribbons during an
eruption can be used to est. the flux in the erupting CME. Studies show that
the higher the flux, the higher the CME speed. The
total erupting flux has also been est. assuming that the feet of the flux rope
= the area of assoc. dimming regions on the surface. Best example is #3, the
May 15, 1997 event.
- Also there is a relation bet. total
B and Bs fields.
- Use the potential mag. field at
to derive a first order estimate of flux that left the sun as a CME.
-
Previous studies have shown a good correlation between the orientation of
erupting filaments and associated Flux Rope/mag.
clouds at 1 AU. But relation may depend on phase of cycle.
Finally, we had a good
discussion about solar-IP MHD models following a presentation by Nick Arge.