they can also be severe in near-equatorial regions, where convective overturning and enhanced electron densities in the ionosphere can amplify the scintillations.

Satellite and Space Systems Hazards

Transient populations of energetic (MeV) protons, which enhance the Van Allen belt radiation for weeks to months following the arrival of a fast CME, potentially can affect the operation of spacecraft, including spacecraft in the highly populated geosynchronous orbit. For example, protons of these energies are known to contribute to single-event upsets in spacecraft electronics.3 Transient population protons can also reach higher latitudes than the typical inner radiation belt protons and may pose an additional radiation hazard to the crew of the International Space Station (ISS). 4 Peak levels of extravehicular activity will occur during the construction phase of ISS, which coincides with the upcoming solar maximum. These energetic protons are not taken into account in models of inner-zone protons, which are based on data taken during the maxima of solar cycles 20 and 21 (which were relatively mild compared with the maxima of solar cycles 19 and 22).

The current prediction for the upcoming (cycle 23) solar maximum is that its activity level will be comparable to that of the previous solar maximum in 1989-1991.5 The transient populations produced by CME-generated interplanetary shocks were discovered only at the last solar maximum (and rediscovered to have occurred in preceding solar cycles that had had scant documentation), and so there is little calibrated predictive capability for the upcoming solar maximum. Earlier limited spacecraft coverage (both upstream in the solar wind and within the appropriate radiation belt region of the magnetosphere) supplied few constraints for dynamic models.

Power Grids

On March 13, 1989, the Hydro-Quebec Power System experienced a catastrophic failure resulting from its interaction with geomagnetically induced currents (GICs). The cause was probably the arrival of an interplanetary disturbance produced by a CME days earlier on the Sun. Although the Hydro-Quebec incident was the greatest problem of its kind during the previous solar maximum, less severe geomagnetic storms in September 1989 and October 1991 also created power system anomalies. In the Hydro-Quebec case, geomagnetic fluctuations had apparently coupled electromagnetically into the system, producing transformer saturation at many sites and causing voltages in the system to exceed safety margins. Widespread power blackouts that accompany such events produce a variety of problems. Oak Ridge National Laboratory assessed the potential impact of a widespread blackout in the Northeast United States as a result of a slightly more severe March 1989-type storm event. Its estimate of the impact to

3  

Space Studies Board, National Research Council, Space Weather: A Research Perspective, 1997. This report is not available in hard copy; it may be viewed on the World Wide Web at the following address:<http://www.nas.edu/ssb/cover.html>.

4  

Space Studies Board, National Research Council, Radiation Hazards to Crews of Interplanetary Missions: Biological Issues and Research Strategies, National Academy Press, Washington, D.C., 1996.

5  

J.A. Joselyn, J.B. Anderson, H. Coffey, K. Harvey, D. Hathaway, G. Heckman, E. Hildner, W. Mende, K. Schatten, R. Thompson, A.W.P. Thomson, and O.R. White, “Panel Achieves Consensus Prediction of Solar Cycle 23,” Eos, Trans. Am. Geophys. Union, 78:205, 211-212, 1997.



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