What is the influence of solar activity on the weather? Dr. Richard Head, who was the weather forecaster for The Old Farmer's Almanac for a quarter-century, answers this question and more.
Dr. Head had a master of science degree in aeronautics, a master of science in meteorology, and a Ph.D. cum laude (for which he studied the spontaneous condensation of supersaturated vapors) from the California Institute of Technology. He was published many times on the subjects of aerodynamics, plasma propulsion, solar activity, and related areas, and during the Mercury Program of the 1960s, he served as chief scientist at the NASA center in Cambridge, Massachusetts. Dr. Head passed away in January, 2006.
Q. Are modern Almanac forecasts really based on a so-called "secret formula"?
A. The Almanac's founder, Robert B. Thomas, did develop a formula for forecasting the weather, and I believe that it was refined by several of the editors who followed him. That formula still exists in a black tin box at the Almanac offices in Dublin, New Hampshire. While it's interesting to read and may have some validity, it's far too simple and broad to be useful in making our specific temperature and precipitation forecasts today for 16 regions in the United States and five across Canada.
Q. Was this old formula based on woolly bears and that sort of thing?
A. It was based on a variety of factors: old weather lore brought over from Europe and modified to fit the weather in the colonies, the effects of various phases of the Moon, careful weather observations, and the study of various plants and animals that seemed able to foretell the weather. It also involved a complex series of cycles, including those having to do with the number of sunspots on the Sun.
Q. So how does the Almanac make weather forecasts today—or is that still a secret?
A. No, I have no reticence in indicating the major factors that enter into the Almanac forecasts because I would like to encourage others to pursue these subjects. I can say that the first factor associated with the influence on the weather is solar activity. My research and the research of others have shown it to be significant.
Q. By "solar activity," do you mean sunspots?
A. The subject of sunspots' influence on our weather has been both touted and ridiculed for centuries and is still a hotly debated topic. In late 1979 and early 1980, the Nimbus 7 and Solar Maximum Mission satellites, respectively, began measuring the daily mean solar irradiance and showed that the solar constant is not a constant but does vary with activity on the Sun, of which sunspots are one manifestation. So, yes, solar activity includes sunspots.
Q. What, then, do you take into consideration besides sunspots?
A. The visible, ultraviolet, X-ray, and radio wavelength emissions from the Sun, for instance. I also consider the geomagnetic activity, the solar wind, and, yes, the high-speed streams that appear to be associated with coronal holes and open magnetic field lines in conjunction with the eruption of solar flares.
Q. You feel that all this solar activity directly influences our weather?
A. With respect to the weather side of the so-called solar-terrestrial relationship, one of the long-term indicators of the effect of changes in the radiant energy from the Sun on the Earth's climate is the change in the orbital parameters defining the motion of the Earth about the Sun and the mounting evidence that these changes were the cause of past ice ages.
In the shorter term, in addition to the so-called Little Ice Age during the late 17th and early 18th centuries, when there was little or no sunspot activity for about 70 years, various investigators have found increasing evidence for an approximate 22-year period of rainfall in certain regions and drought in other regions (including the mid-western part of the United States) that appears to be related to a double sunspot cycle or, more specifically, to the 22-year magnetic cycle on the Sun.
Q. Do you take into account anything else besides solar activity?
A. Many other factors influence Earth's weather - the extent of snow and ice cover; the surface temperature of the oceans and the velocity of their major currents; the type of ground cover and the soil moisture content; the amount and type of cloud cover as it affects the reflection and absorption of the incoming solar radiation and the absorption of the outgoing infrared radiation from the Earth; the effect of major fires or the ejecta from major volcanic eruptions; and the dynamic state of the atmosphere and its composition - including infrared absorbing molecules such as water vapor, carbon dioxide, methane, and oxides of nitrogen.
That's just naming a few of the things that we take into account. We don't profess to understand or always incorporate all of these and other factors into our Almanac forecasts. However, we are continually striving to improve our methods.
Q. What might long-range weather predicting will be like when The Old Farmer's Almanac's age is doubled? Like in 2192?
A. Well, we'll have far more detailed coverage of all weather elements around the globe by then—including the various depths of Earth's atmosphere as well as the oceans. We'll also know so much more about the radiant energy coming from the Sun. Then add incredibly expanded computer capabilities. Besides orbiting space platforms, there will doubtlessly be weather observatories on the Moon, out of the influences of our atmosphere and magnetosphere. By 2192, I'm sure that we'll also be able to foretell more accurately major volcanic eruptions, ocean current changes, and so forth—all of which have profound effects on our weather.
Q. So in 200 years we'll be able to predict weather with 100 percent accuracy?
A. Perhaps. Unless once we assimilate all the data of the next 200 years, it turns out that a certain small percentage of weather phenomena occurs totally at random. If that's the case—and at this point we're a long way from knowing enough to know—then the maximum accuracy rate for weather forecasting would be 100 percent less whatever the "at random" percent factor might be, if indeed that factor exists at all.