Exploring the global shock scenario at multiple points between sun and earth: The solar transients launched on January 1 and September 23, 1978 |
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Authors: | DB Berdichevsky DV Reames C-C Wu R Schwenn RP Lepping RJ MacDowall CJ Farrugia J-L Bougeret C Ng AJ Lazarus |
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Institution: | 1. NASA/GSFC, Greenbelt, MD 20771, USA;2. University Alabama, Huntsville, AL 35899, USA;3. Max-Planck-Institut für Aeronomie, D 37191 Katlenburg-Lindau, Germany;4. University New Hampshire, Durham, NH 03824, USA;5. Observatoire de Paris, Meudon, France;6. MIT Space Science, Cambridge, MA 02139, USA |
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Abstract: | We revisit the transient interplanetary events of January 1 and September 23, 1978. Using in-situ and remote sensing observations at locations widely separated in longitudes and distances from the Sun, we infer that in both cases the overall shock surface had a very fast “nose” region with speeds >900 and >1500 km−1 in the January and September events, respectively, and much slower flank speeds (∼600 km−1 or less), suggesting a shock surface with a strong speed gradient with heliospheric longitude. The shock-nose regions are thus likely efficient acceleration sites of MeV ions, even at 1 AU from the Sun. Our 3D magnetohydrodynamics modeling suggests that a 24° × 24° localized disturbance at 18 solar radii injecting momentum 100 times the background solar wind input over 1 h can produce a disturbance in semi-quantitative agreement with the observed shock arrival time, plasma density and velocity time series in the January 1978 event. |
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Keywords: | Gradual SEP events Collisionless shocks Shock MHD modeling |
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