Series: Astronomy Unit Seminars
Speaker: Prof. Michael McIntyre (University of Cambridge)
Abstract: Over the past century, there has been a gradual but profound paradigm change in the way we think about global-scale atmospheric circulations and the eddy transport processes involved, especially those responsible for the global-scale eddy transport of angular momentum. In the first half of the 20th century, it was usual to think of the eddy momentum transport as "turbulent", because of the enormous Reynolds numbers involved. The new paradigm recognizes that wave-induced momentum transport -- "radiation stress" in the language of physics -- is dominant. This easily solves what used to be regarded as three great atmospheric-dynamics enigmas of the mid-twentieth century: first Victor Starr's "negative viscosity", second the cause of the "quasi-biennial oscillation", and third the extreme coldness of the summer mesopause at around 85 km altitude where one observes the world's highest clouds. The same paradigm change has recently led, moreover, to a breakthrough in understanding the Sun's internal differential rotation.
Some of the historical twists and turns well illustrate the "Michelson-Morley principle" that negative results in science can have far-reaching importance. Time permitting, I'll briefly report on current work with Stephen Thomson on the (seemingly rather different) problem of Jupiter's weather-layer jets.