Solar variability and terrestrial weather

Abstract

The past four years have seen a growing interest in possible relations between terrestrial weather and solar or solar wind variability. Most of the work in sun‐weather (and climate) studies has sought correlations on three time scales: (1) climate changes over hundreds to thousands of years, related to longer term variations in the solar output, (2) climate changes correlated with the 22‐year solar cycle, and (3) weather variations on the scale of a few days, in response to transient solar events. While it has not been conclusively shown that there is a sun‐weather connection on any of these time scales, in each case there exists enough supporting evidence to suggest that further study is warranted. The most convincing evidence is that concerning long‐term climate changes which could be connected to changes in the solar luminosity below the threshold of all but the most recent observations, but still involving relatively large amounts of solar energy. Short‐term weather changes correlated with solar phenomena cannot be explained in this way, since the effect of such transient phenomena on the Sun's energy output is far too small. There remains, however, the possibility that such phenomena affect some sensitive links in the sun‐solar wind‐magnetosphere‐stratosphere‐troposphere causal chain, such that a small variation of the input can trigger relatively large‐scale consequences. Most of this review will be concerned with developments in the short‐time scale connections.