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Ann. Geophys., 20, 917-935, 2002
www.ann-geophys.net/20/917/2002/
© European Geosciences Union 2002
Arrival times of Flare/Halo CME associated shocks at the Earth: comparison of the predictions of three numerical models with these observations
S. M. P. McKenna-Lawlor1, M. Dryer2,3, Z. Smith3, K. Kecskemety4, C. D. Fry2, W. Sun5, C. S. Deehr5, D. Berdichevsky6,7, K. Kudela8, and G. Zastenker9
1Space Technology Ireland, National University of Ireland, Maynooth, Co. Kildare, Ireland
2Exploration Physics International, Inc., Milford, New Hampshire, 03055, USA
3NOAA Space Environment Center, Boulder, Colorado, 80305, USA
4KFKI Research Institute for Particle and Nuclear Physics, Budapest, Hungary
5Geophysical Institute, University of Alaska, Fairbanks, Alaska, 99775, USA
6Emergent Information Technologies, Inc., Largo, Maryland, 20774, USA
7Laboratory for Extraterrestrial Physics, NASA, GSFC, Code 690, Greenbelt, Maryland, 20771, USA
8Institute for Experimental Physics, Kosice, Slovakia
9Space Research Institute, Moscow, 117997, Russia
Correspondence to: S. M. P. McKenna-Lawlor
(stil@may.ie)
Abstract. The arrival times at L1
of eleven travelling shocks associated both with X-ray flaring and with halo
CMEs recorded aboard SOHO/LASCO have been considered. Close to the Sun the
velocities of these events were estimated using either Type II radio records or
CME speeds. Close to the Earth the shocks were detected in the data of various
solar wind plasma, interplanetary magnetic field (IMF) and energetic particle
experiments aboard SOHO, ACE, WIND, INTERBALL-1 and IMP-8. The real-time shock
arrival predictions of three numerical models, namely the Shock Time of Arrival
Model (STOA), the Interplanetary Shock Propagation Model (ISPM) and the
Hakamada-Akasofu-Fry Solar Wind Model (HAFv.2) were tested against these
observations. This is the first time that energetic protons (tens of keV to a
few MeV) have been used to complement plasma and IMF data in validating shock
propagation models. The models were all generally successful in predicting
shock arrivals. STOA provided the smallest values of the "predicted minus
measured" arrival times and displayed a typical predictive precision
better than about 8 h. The ratio of the calculated standard deviation of the
transit times to Earth to the standard deviation of the measurements was
estimated for each model (treating interacting events as composite shocks) and
these ratios turned out to be 0.60, 1.15 and 1.02 for STOA, ISPM and HAFv.2,
respectively. If an event in the sample for which the shock velocity was not
well known is omitted from consideration, these ratios become 0.36, 0.76 and
0.81, respectively. Larger statistical samples should now be tested. The ratio
of the in situ shock velocity and the "Sun to L1" transit velocity (Vsh
/Vtr) was in the range of 0.7–0.9 for individual, non-interacting,
shock events. HAFv.2 uniquely provided information on those changes in the
COBpoint (the moving Connection point on the shock along the IMF to the
OBserver) which directly influenced energetic particle rise times. This model
also illustrated the non-uniform upstream conditions through which the various
shocks propagated; furthermore it simulated shock deformation on a scale of
fractions of an AU. On the spatial scale (300 RE ), where near-Earth
spacecraft are located, the passing shocks, in conformity with the models, were
found to be locally planar. The shocks also showed tilting relative to the
Sun-Earth line, probably reflecting the inherent directionality associated with
their solar origin.
Key words. Interplanetary physics (energetic
particles; interplanetary shocks; solar wind plasma)
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