neuer CME der Hammer...oder auch nicht...(give or take a day

[Ulrich Rieth]

http://www.spacew.com/cme/index.html

Event #17 - 17 April 2002
Issued: 22:45 UTC, 17 April 2002

SOURCE EVENT

17 April 2002
M2.6/2N Flare in Active Region 9906 - S14 W34 at 08:24 UTC
Type II: 818 km/sec
Estimated LASCO-derived Plane of Sky Velocity: 1,288 km/sec @ position angle 285 degrees
1,191 km/sec @ position angle 266 degrees
600 km/sec @ position angle 106 degrees

ESTIMATED TIME OF ARRIVAL OF SHOCK AT EARTH

Estimated Impact Window: 23:00 UTC on 18 April to 23:00 UTC on 19 April
Preferred Predicted Impact Time: 06:00 UTC, 19 April 2002
Estimated Shock Strength (0: Weakest, 9=Strongest): 6

Predicted Behavior of IMF at Shock Impact

At Shock Impact, the Interplanetary Magnetic Field is predicted to initially turn:
SOUTHWARD

EVENT #16 NOTES:

This is a difficult disturbance to compute arrival times for because there were two nearly simultaneous coronal mass ejections in the same region of the sky. The first and fastest CME is believed to be associated with the M2.6/2N flare from Region 9906 (S14W34). However, within several minutes of this event, a second CME was launched by Region 9905 (S15W83). Disentangling these two events in the LASCO imagery is difficult at best. If the fastest CME front actually belongs to 9905, then a shock may not reach the Earth until near 18:00 UTC on 19 April. Forecaster opinion in this case is guided by which event appeared to be the most energetic, which clearly appeared to be the M2.6/2N flare that occurred in Region 9906. But this does not necessarily mean the fastest CME is associated with it. Nevertheless, in the absence of a clearer solution, we are suggesting that the faster CME (responsible for the 1,288 to 1,190 km/sec POS velocity) is related to Region 9906 and the full halo CME, which may result in a moderately strong impact with the Earth during the early UTC hours of 19 April. The slower POS velocity at 106 degrees is attributed to the characteristics of the cone angle of the CME (and the trajectory of that portion of the Earth-directed mass). If this scenario holds true, the strength of the geomagnetic and auroral disturbance on 19 April may be stronger than what was observed on 17 April following the full halo CME of 15 April.

These predictions may be based on preliminary data and may be revised without warning. The predictions should not be used as a definitive indication of CME impact times or strengths and may frequently be in error. The proprietary methods used to estimate shock impact times are under continual development. Caution is advised.

[Peter Kuklok]

Ein HCS-Crossing wird auch erwartet *o.T.*