Long-range Forecasting (continued)

At that time Charney was working with von Neumann at the Princeton Institute for Advanced Study where, with collaborators, von Neumann had developed the ENIAC (see Burks, A. W. et al, 1946).

Willet referred us to a useful article on climate change by C. E. P. Brooks (1951) in the Compendium of Meteorology. This gave a comprehensive review of geological and historical evidence of climate change and suggested causes for the changes which had occurred. The article contains 36 references to papers on the subject including that of Milankovitch in the Handbook of Climatology of Koppen and Geiger 1930.

Willet's reticence in assessing the progress made in long-range forecasting was useful in increasing my understanding of climate. He indicated that without a knowledge of the processes which produce fluctuations of weather, and fluctuations within climate, on time scales from days to years to centuries, millennia and further, there was little hope of improvement in short-range or long-range forecasting.

He also caused me to wonder whether fluctuations within climate from year to year, decade to decade, century to century could be part of climate rather than an indication of climate change.

I have suggested that the use of random numbers to create a synthetic meteorological time-series in which apparent trends and cycles will appear can serve as a warning against impulsive conclusions when such trends and cycles appear in a natural time series. Synthetic time series of precipitation using random numbers could produce models containing an apparent advance and retreat of glaciers and the filling and drying-out of inland lakes. This would suggest that these changes may result from fluctuations within climate rather than from climate change.

Synoptic Meteorology

There was considerable emphasis on the basic processes involved in the development and movement of fronts and pressure systems with discussions on heating and cooling of the atmosphere, dynamics, geostrophic and gradient winds, horizontal divergence and vertical motion. Weather forecasting was mentioned with emphasis on the factors influencing air temperature, wind, precipitation, visibility, cloudiness and particularly cloud ceiling and fog.

The development of the pressure field was a prominent part of the lectures with considerable emphasis on pressure tendency, isallobars, cyclogenesis and the influence of upper air patterns.

It was useful to have the work of Petterssen, Sutcliffe, Rossby, Sawyer and Palmer reviewed in a formal manner and to have discussions of the basic equations of motion, divergence and vorticity.

After my Australian experience in the application of frontal theory, which appeared to still be an important part of synoptic analysis and prediction in North America, I asked Austin whether the Scandinavian frontal model was relevant in the North American and North Atlantic region. My lecture notebook records that he replied that examples appeared "every now and again".

One aspect of his lectures that I found particularly interesting was his discussion of streamlines and trajectories. This emphasised the dangers in making assumptions that both were similar, particularly when pressure gradients were weak and pressure systems moved quickly.

When I plotted some trajectories associated with moving anticyclones in Australian latitudes I realised that, in many cases, it would be difficult for the classical frontal model to be applied. This conclusion had been reached by Kidson (1947) and Palmer (1942) for the Southern Ocean and for southern areas of Australia although the observational data they used was very scanty. Palmer postulated that most fronts over southern Australia were occluded, which seemed reasonable as many zones of cloud were observed at middle and high levels.

It seemed that great care needed to be taken in applying the term 'front' to any zone delineating a change in wind direction or a zone of cloud or precipitation. The possibility that classical warm and cold fronts were likely to occur in southern Australia 'every now and again' seemed worth remembering but it seemed desirable to use different designations for the other significant wind changes, cloud lines, etc. In CAO we had learnt that fronts of the classical type were likely to be found in the vicinity of Southern Ocean oceanic convergence, especially in the Heard Island region.

Bureau of Meteorology