Long-range Forecasting (continued)

This comprehensive review of attempts to make extended period and long-range forecasts based on the wide variety of indices and indicators referred to in the previous paragraph did not create much optimism for success. One problem was to find a method of verifying such forecasts many of which were somewhat circumlocutionary. The lectures provided a salutary message that extended period and long-range forecasts needed a comparison with observed atmospheric conditions over lengthy periods.

In view of the current interest in the Southern Oscillation and El Niņo it is interesting to note that Willet's lectures referred us to investigations of the oscillation of pressure indices as a method of long-range forecasting. Gilbert Walker had computed the oscillation of the difference in pressure between 'centres of action' in the North Atlantic, North Pacific and Southern Oceans where he believed there may be teleconnections with rainfall in adjacent continents. He found that the Southern Oscillation showed a significant correlation with Indian rainfall. Willet referred us to Supplement No 39 of the US Weather Bureau's Monthly Weather Review for further details.

The lectures by Willet in the third semester dealt with historical and geological evidence of climatic change. This part of the course was to prove valuable in the 1970s when the subject became a matter of widespread public interest.

Figure 26 Diagram in circular 30/1403 on climatic change issued 11 December 1974 by W. J. Gibbs, Director of Meteorology. It illustrates the time scales of fluctuations in climate, a subject featured in the lectures by Hurd Willet at the Massachusetts Institute of Technology in 1951–52.

Willet's lectures also discussed the evidence of the 200 year data bank of reliable meteorological observations, the 2000 year historical record and the geological eras extending back as far as 750 million years.

He suggested that this information indicated possible cycles in climate over the last 200 years and that historical evidence of variation in the extent of Arctic and Antarctic pack ice, and of inland lakes and glaciers may provide evidence of, or be the cause of, variability of climate. He pointed out that periodic fluctuations of the number of sunspots on the sun was also considered to be a likely cause of climatic fluctuations and that the geological evidence of past ice ages demonstrated a scale of climatic variability with much larger amplitude and much longer periodicity.

Bureau of Meteorology