Solar Activity and Weather - Is there a Connection?
The Sun radiates an immense amount of heat and light. A small fraction of this is intercepted by the Earth, and makes life possible on this planet. It also creates the weather. If there was no Sun there would be no weather (and no life) on the Earth. For many years the Sun was regarded as a constant star - a producer of a fixed amount of heat and light. Variations in the weather or the seasons are produced primarily because of the tilt of the Earth's orbit. In summer the Sun is more nearly overhead at noon, whereas in winter it is lower in the sky and appears for a shorter interval of time. However, not all summers are the same, and neither are all winters. Some years bring drought, others may bring flooding. This is of vital concern to many, particularly the person on the land. And so it was when we began to discover that the the Sun is not truly a constant star that many began to wonder whether these variations of the solar orb may have something to do with changes in the weather. Do sunspots or solar flares or other related phenomenon influence the weather? By weather, here we are referring to the tropospheric weather - what happens in the first 10 km or so of our atmosphere.
Much research has been conducted over many decades in an attempt to link sunspots or other forms of solar activity to the weather. The subject is often extremely popular with the media. Countless hours have been spent in trying to convince the world that droughts or floods are the consequence of an unprecedented outburst of solar fury. Unfortunately, for each paper published showing a relationship between the floods of some year and sunspots, there can usually be found a contradictory paper showing either no relationship or perhaps a relationship between sunspots and a drought of the same year. Some scientists believe there may be a small connection between weather disturbances and solar activity. Still others believe there is very little connection. The reason why many scientists have difficulty accepting that solar activity has a major affect on our weather is very simple. Even a large solar eruption (either a coronal mass ejection or a flare) - although a gigantic explosion by Earth standards - only releases an amount of energy comparable to what the whole Sun emits in a few seconds. In other words, solar activity is only a very small variation of the total solar output. Much larger variations in the received sunlight at the Earth's surface are due to the Earth's tilt and its elliptical orbit.
For people wanting a practical method of forecasting the weather, a statement by the eminent Australian meteorologist Barrie Pittock should be borne in mind:
"there is at present little or no convincing evidence of statistically significant or practically useful correlations between sunspot cycles and weather or climate on intermediate time scales. This conclusion seems justified despite massive literature on the subject ... evidence suggests that if ... more data and better analyses ... succeed in verifying ... significant relationships, they will ... account for so little of the total variance in the meteorological record as to be of little practical value."
There is evidence of some very small short term effects (within days) and also some long term climatic effects (of the order of centuries). However, none of these offer much hope to the weather forecaster.
The two classic references below contain many additional references within their covers, for those who are interested in following up this subject.
- John R Herman and Richard A Goldberg, Sun, Weather and Climate NASA Special Publication SP-426, NASA (Washington DC, 1978).
- Geophysics Study Committee NRC, Solar Variability, Weather and Climate, National Academy Press (Washington DC, 1982), ISBN 0-309-03284-9.
Material prepared by Richard Thompson