FIGURE 27 Computer simulations of gravity wave seeding of the ionosphere. Reproduced from Huang and Kelley (1996) with permission of the American Geophysical Union.

systems much more predictable. The hope is that by the next solar cycle maximum when GPS and other space-based systems are truly a part of everyday life, military and commercial users will have access to severe space weather information. For example, if the postsunset ionosphere is very high and has detectable wiggles on the bottom edge to the west of your location, you are pretty certain that severe communication disruptions are on the way.

At mid-latitudes our knowledge of the underlying physics is much less but so is the severity of the weather. The gravity wave effects are known to be present and some severe weather has been reported, particularly over Japan (Figure 28) where the powerful middle upper atmospheric (MU) radar system has been trained in the most sensitive orientation (perpendicular to the magnetic field). Some turbulent upwellings of ionospheric plasma have been seen, especially in summer and at solar minimum, which are too far off-equator to be the same Rayleigh-Taylor process discussed above.

These violent ionospheric storms have also been attributed to gravity wave seeding of the so-called Perkins instability in which energy is drawn from the background current system in the ionosphere. Much more work is needed to justify this claim, but the National Science Foundation program called CEDAR (Coupling Energetics and Dynamics of Atmospheric Response) is a beginning.