Halo CME on 20060816 - SOHO/LASCO C3 Data

COMMENTS: I expect that the axis of the corresponding MC (if indeed is present) should be oriented more or less parallel to the ecliptic (<45 deg) plane. The direction of the axial field should then be westward and the azimuthal field at the front edge of the ejecta should be southward, slowly turning northward as the event progresses. The MC is expected to right handed.

Since the speed is not very high I expect that the negative Bz will not much exceed -20nT (i.e Bz>= -20nT) thus it has a potential to produce a moderate to strong storm with the Dst index dropping down to about -150...-190nT. But this number is the worst case scenario which can be realized provided that we will have direct hit and the magnetic field at the front edge will consist of mostly Bz component.

I'm not sure what is the real Dst index at this moment but if it is indeed -100nT as reported by the World Data Center for Geomagnetism in Kyoto, then the predicted decrease of -150..-190nT should be from the base level of -100nT, therefore the final value of the Dst index could reach of about -300nT.

COMMENTS AFTER ARRIVAL: The ejecta arrived on early Aug 19 and it was not observed as a typical MC but it rather looked as a complex ejecta (Burlaga et al). I think that it was deflected southward (under the earth), missed the target and what we observed was an edge of it. However, I'll leave the final interpretation of ACE data to expects.
Some periods of relatively strong negative Bz were, nevertheless, observed and as a result the Dst index dropped by about 80 units reaching -180 at 2200UT on Aug 19.

1Numbers in red are estimates. Numbers in parenthesis (if any) are actual measured values
*These estimates should be compared to the observed 1 hour averaged ACE and Dst values

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    Automaticaly Generated on Thu Aug 17 10:36:55 2006
    Please, send questions and comments to Vasyl Yurchyshyn