Although the geographical regions (e.g., polar for most of the particle fluxes except for the most energetic cosmic rays), times (e.g., daytime for solar flare UV and x-ray bursts), and altitude ranges affected are generally understood, the consequences are by no means yet known. Whereas the resulting electron density enhancements obviously affect our use of the ionosphere, there are known atmospheric chemistry effects (including stratospheric and mesospheric ozone chemistry perturbations and suggestions of possible influences on high-altitude clouds) that require more study. The cause-and-effect chain can be examined by modern cosmic-ray and solar particle detectors and sensitive atmospheric measurements (available in some cases from the newest experiments within the Earth sciences community). Indeed, the ionization link has consistently recurred as a possible explanation for solar variability effects on climate through some nonlinear process. No previous period of high solar activity has been so well endowed with facilities and resources for establishing or refuting the significance of such mechanisms.

The preceding discussion has broad implications beyond the study of space physics. For example, the consequences of solar variability on Earth lead us to ask how these variations affect other planets in our solar system. What happens on a planet like Mars, which lacks a protective magnetic shield or substantial atmosphere like Earth 's? How have Mercury's surface and atmosphere been altered over time by the variable solar irradiations at close range? To what extent are the giant planets and their satellites immune to “space weather”?

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