Dynamic Meteorology IV

I found it somewhat surprising that Lettau was a modest lecturer, in view of his distinguished reputation as a mathematician and researcher. His patient manner showed respect for his students, whom he obviously wished to be well informed on the subject of turbulence. He gave us assignments from time to time and I remember my dismay when one assignment asked us for comments on the relevance of the Heisenberg uncertainty principle. Knowing absolutely nothing of that principle I hastily repaired to the MIT library so I could disguise that lack of knowledge.

Lettau began his first lecture by explaining that the space and time scales of turbulence had a very wide range. He also gave examples of expert definitions given at a conference on turbulence at MIT earlier in 1951 which demonstrated that it was extremely difficult to describe the nature of turbulence with words. In later years I was to read a comment by Stephen Schneider recounting that at a seminar on climate the participants decided to begin by spending a few seconds agreeing on a definition of climate. After more than an hour of spirited discussion participants agreed that it would probably be best defined as the synthesis of weather.

When I was appointed Director of Meteorology in 1962 I determined to maintain an active scientific interest in at least one branch of meteorology and chose the subjects of climate, rainfall and drought. During the course of this work I suggested a definition of climate (Gibbs, 1987), a matter I believe to be of considerable importance. How can we study climate change unless we agree on what we mean by climate?

Bureau of Meteorology