Edward N. Lorenz was born in 1917 and has been Professor of Meteorology at Massachusetts Institute of Technology, Cambridge, USA, since 1962.
Henry Stommel was born in 1920 and since 1945 has been at Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA, where he is senior scientist.
As the earth rotates, the sun heats the atmosphere and the sea, causing movements in both these media. Therefore, theories about the large scale motions of the atmosphere and the sea have much in common. However, the most important difference between them is the fact that while the sea is limited in its horizontal movement by the continents, the winds in the atmosphere are only partially restricted by mountain ranges which cause turbulent flows as the air ascends over them. Moreover, the lower part of the atmosphere (12-15 km from the earth´s surface) is driven primarily by the heating of the underlying surface, whereas the ocean movements are driven from above by the thermal contrast generated by solar heating and through the effects of winds on the sea surface.
In trying to understand complex phenomena such as the motions of the atmosphere and the sea, scientists have been greatly helped by simple laboratory experiments. If a rotating fluid in a circular container is heated at the outer rim (equivalent to the earth´s equator) and cooled in the center (analogous to the polar regions) quite different patterns of surface motions are established at different rates of rotation. Some show long waves similar to those that are found along the jet stream at temperate latitudes in the atmosphere. Lorenz has shown how the number of waves that are created depends upon the rate of rotation and the thermal contrast. He further explains why the rather sudden swift from a given number of waves around the container to another pattern does not entirely depend on the absolute rate of rotation but is governed by whether the liquid is accelerating or decelerating.
Lorenz has also studied the internal interplay between waves. The mathematics that is required for this is non-linear systems dynamics. With the aid of computer experiments Lorenz has been able to elucidate some important mechanisms by which one motion pattern can rather rapidly change to another. This work has increased our understanding of the factors that may be responsible for characteristic changes in the dynamic patterns of atmosphere. As an integral part of this research Lorenz has also made important contributions to the filed of non-linear differential equations, which was the subject of the Crafoord prize of 1982.
Lorenz has also tried to answer the question of how far ahead it is possible to make weather forecasts. He has shown how the internal instability of the atmosphere motion systems puts an upper limit on the forecast period. In addition, Lorenz has clarified how energy transformations in the atmospheric-motion system can most appropriately be described.
Henry Stommel is not only one of the leading theoreticians in the field of modern oceanography but has also made an important contribution to the development of a series of large internationally coordinated programmes for the collection of oceanographic observations.
Even as a young research assistant Stommel formulated a simple model for the movements of the sea which explained the strong ocean currents that are found along the western side of the ocean basins, for example the Gulf Stream. This formed the starting point for his most important contributions to our understanding of the general circulation of the sea. Devising laboratory experiments similar to those that served as a basis for Lorenz´s work, Stommel showed the way in which the rotation of the earth effectively limits the motions in the interior parts of an ocean basin and how compensating currents are primarily formed along the ocean boundaries, i.e. the coasts. With these findings as a starting point, Stommel explained why there is southward coastal current in the deep sea below the Gulf Stream. Today, from measurements obtained with the aid of drifting buoys in the deep sea and from studies of the movement of air pollutants, primarily halocarbon compounds (freons), dissolved in sea water, we know that surface water settles as deep water between Iceland and Greenland, and travels in deep coastal currents all the way to the coast of Brazil, where it shows up at a depth of two to three thousand meters a few decades later.
Stommel´s many fruitful ideas and initiatives in starting large research expeditions have been of very great importance in extending our knowledge of the large scale circulations of the seas during the last 35 years.
Crafoord lectures will be held on September 28 at 15.00 and on September 29 from 09.30 throughout the day. In addition to the Crafoord prize a sum of 370 000SEK will be awarded as grants within the same filed of geosciences.
The Crafoord fund was constituted in 1980 when Mr. and Mrs. Crafoord donated a large sum to the Academy. The fund will support scientific research work within the fields of mathematics and astronomy, geosciences, biosciences (especially ecology) and polyarthritis.