AIAA JOURNAL Vol. 43, No. 5, May 2005 Key Links in Space Weather: Forecasting Solar-Generated Shocks and Proton Acceleration C. D. Fry * Exploration Physics International, Inc., Huntsville, Alabama 35806 M. Dryer † National Oceanic and Atmospheric Administration, Boulder, Colorado 80305 W. Sun ‡ and C. S. Deehr § University of Alaska, Fairbanks, Alaska 99775 Z. Smith ¶ and T. R. Detman ** National Oceanic and Atmospheric Administration, Boulder, Colorado 80305 A. Aran †† Institut d’Estudis Espacials de Catalunya, E-08034 Barcelona, Spain D. Lario ‡‡ Johns Hopkins University, Applied Physics Laboratory, Laurel, Maryland 20723 B. Sanahuja §§ Universitat de Barcelona, E-08028 Barcelona, Spain and S.-I. Akasofu ¶¶ University of Alaska, Fairbanks, Alaska 99773 Forecasting the arrival of solar-generated shocks and accelerated protons anywhere in the heliosphere presents an awesome challenge in the new field of space weather. Currently, observations of solar wind plasmas and in- terplanetary magnetic fields are made at the sun–Earth libration point, L1, about 0.01 astronomical units (∼245 Earth radii) sunward of our planet. An obvious analogy is the pitot tube that protrudes ahead of a supersonic vehicle. The Advanced Composition Explorer and Solar and Heliospheric Observatory spacecraft, currently per- forming this function, provide about 1 2 –1 h advance notice of impending arrival of interplanetary disturbances. The signatures of these disturbances may be manifested as interplanetary shock waves and/or coronal mass ejecta. We describe a first-generation procedure, based on first-principles numerical modeling, that provides the key links required to increase the advance notice (or lead time) to days, or even weeks. This procedure, instituted at the start of the present solar cycle 23, involves three separate models, used in real time, to predict the arrival of solar-event- initiated interplanetary shock waves at the L1 location. We present statistical results, using L1 observations as “ground truth” for 380 events. We also briefly discuss how one of these models (Hakamada–Akasofu–Fry version 2) may be used with a model that predicts the flux and fluence of energetic particles, for energies up to 100 MeV, that are generated by these propagating interplanetary shock waves. Presented as Paper 2003-1226 at the AIAA Aerospace Sciences Meet- ing, Reno, NV, 6–9 January 2003; received 11 June 2004; revision received 14 October 2004; accepted for publication 26 October 2004. Copyright c  2005 by Exploration Physics International, Inc. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. Copies of this paper may be made for personal or internal use, on condition that the copier pay the $10.00 per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923; include the code 0001-1452/05 $10.00 in correspondence with the CCC. * Vice President, 6275 University Drive, Suite 37-105; gfry@expi.com. Member AIAA. † Scientist Emeritus, Space Environment Center; also Scientist Emeri- tus, Exploration Physics International, Inc., Huntsville, AL 35806; Murray. Dryer@noaa.gov. Associate Fellow AIAA, Retired. ‡ Research Scientist, Geophysical Institute; sun@jupiter.gi.alaska.edu. § Professor of Physics, Emeritus, Geophysical Institute; cdeehr@gi. alaska.edu. ¶ Physicist, Space Environment Center; Zdenka.Smith@noaa.gov. ** Physicist, Space Environment Center; Thomas.R.Detman@noaa.gov. †† Ph.D. Candidate; also Ph.D. Candidate, Departament Astronomia i Meteorologia, Universitat de Barcelona, E-08028 Barcelona, Spain; aaran@am.ub.es. ‡‡ NRC Senior Research Associate; David.Lario@jhuapl.edu. §§ Dean of Sciences, Departament Astronomia i Meteorologia; blai@ am.ub.es. ¶¶ Director, International Arctic Research Center; sakasofu@iarc.uaf.edu. I. Introduction G EOMAGNETIC storms and proton radiation hazards are two of the panoply of space weather concerns for modern tech- nology and human activities (cf. the National Academy of Sciences Decadal Study 1 ). We believe that they are amenable to fluid me- chanics efforts. We take the view that some energetic solar flares generate fast coronal mass ejections (CMEs), which, in turn, gener- ate shocks. These latter combinations, called interplanetary coronal mass ejections (ICMEs), interact with the Earth’s magnetosphere, spacecraft en route to Mars, and even the Martian environment itself. If the magnitude and polarity of the interplanetary magnetic field (IMF) became large and southward, a geomagnetic storm would take place at Earth within hours after shock impact. Prior to this initiating “storm sudden commencement,” indeed, beginning at the solar initiating source, the shock becomes an accelerator of protons (and also of heavier species that are not considered here) that spi- ral along the IMF outward toward Earth, possibly to Mars, and to outward-bound spacecraft. The forecasters’ objective is to predict the shock’s arrival time and, thereafter, the temporal profile of the polarity and magnitude of the IMF, as well as the flux and fluence of the shock-accelerated protons. A complementary scientific objective is the prediction of other solar wind properties such as density and temperature; however, these properties are of secondary concern to the opera- tional goals of the space weather forecasters. 987