Dr Angus McEwan was interviewed in 2011 for the Interviews with Australian Scientists series. By viewing the interviews in this series, or reading the transcripts and extracts, your students can begin to appreciate Australia's contribution to the growth of scientific knowledge and view science as a human endeavour. These interviews specifically tie into the Australian Curriculum sub-strand ‘Nature and development of science’.
The following summary of Dr McEwan’s career sets the context for the extract chosen for these teachers’ notes. The extract discusses two experiments performed by Dr McEwan; one which explained the phenomenon of the Quasi Biennial Oscillation and another which was simulating convection in clouds. Use the focus questions that accompany the extract to promote discussion among your students.
Angus McEwan was born in Alloa, Scotland in 1937. In 1947, after the early death of his father, Angus McEwan immigrated with his mother and three brothers to Melbourne, Australia. McEwan attended Upwey High School and then Melbourne High School finishing with a leaving certificate. Too young for university, McEwan completed a diploma in engineering at Caulfield Technical School. After his National Service, McEwan got a job at the Aeronautical Research Laboratories in Melbourne. A cadetship enabled him to extend his studies at the University of Melbourne where he graduated with a BEMech (Hons) (1960). McEwan was then awarded a Vacuum Oil Scholarship to complete his masters, MEngSc (1962). McEwan again went to work for the Aeronautical Research Laboratories on heat transfer problems.
A desire to change direction in his research found McEwan on his way to Cambridge with a CSIRO Fellowship and, later, a Public Service Board Scholarship. He graduated with a PhD in 1966 for his work on the distortion changes in turbulence as flow goes over a step. He also worked with the legendary Sir Geoffery (‘GI’) Taylor on liquid surfaces in electric fields. McEwan then returned to Australia and the Aeronautical Research Laboratories to work on hypersonic re-entry problems (1966-69). He then joined the CSIRO Division of Meteorological Physics (later Atmospheric Research) supported by a Queen Elizabeth II Fellowship (1969-71). In 1971 McEwan was appointed as a senior research scientist with the task of creating a geophysical fluid dynamics laboratory within this Division (1971-81). During this period, in 1975, McEwan was invited as a Rossby Fellow to the Woods Hole Oceanographic Institution, USA where he worked on internal waves. In 1981 McEwan was appointed to chief of the new CSIRO Division of Oceanography (1981-95) to be established in Hobart. Following his term as chief, McEwan served as senior science advisor to the Commonwealth Bureau of Meteorology (1995-2005).
In addition to his research, and several roles in the advancement of Australian marine science, McEwan was active in the UNESCO Intergovernmental Oceanographic Commission (IOC). He served in a number of capacities including; Australian delegate to the (IOC) (1982-2004), member (1982-90) and then chairman (1987-90) of the IOC Committee on Climatic Changes and the Ocean, representative of the Global Ocean Observing System (GOOS) steering committee (1995-2003), chairman of the Intergovernmental GOOS committee (1998-2001) and chair of the Oceanographic Data Exchange Policy group (2001-02).
Dr Angus McEwan was elected a Fellow of the Australian Academy of Science in 1982 and served on its Council from 1997-2000. He was elected to fellowship of the Australian Academy of Technological Sciences and Engineering in 1994.
In 1977, you worked with Alan Plumb, who was an import from the UK to Melbourne, on a new theory of the Quasi-Biennial Oscillation. This work turned out to be perhaps your biggest contribution to science and certainly a big output of the GFD laboratory that you had established there. Tell us about that.
The quasi-biennial oscillation is a phenomenon in the atmosphere. In the equatorial stratosphere there is a zonal jet of air circulating the globe. It has been found to alternate in direction between EastWest and WestEast, with a period of approximately two years. In other words, you get a quasi-biennial oscillation.
It occurs not exactly at two years. That annoyed everybody.
Yes, it annoyed everybody because people produced abundant theories about this thing, but it didn’t fit the theories because the oscillation period was not exactly two years. During the early seventies, explanations were developed of how this change in direction might occur. One in particular by Holton and Lindzen was that there were upward travelling waves emerging from the tropopause. You can imagine that the turbulent troposphere is bumping around against the base of the stratosphere, and these waves travelling upwards would produce an alternating jet.
Alan Plumb improved on this by a few essential differences in the theory which took into account the fact that the waves, as they travel upwards, would be dissipated and their momentum would be deposited at elevated levels within the jets of the stratosphere. The important thing was that these waves bumping up and down on the bottom of the stratosphere were composed of waves that travelled in both Easterly and Westerly directions. The waves that were travelling in the same direction as the jet would be absorbed as a process of ‘critical layer absorption’. Basically, what would be happening would be that the frequency of the waves would approach zero in relative terms, whereas the waves going in the opposite direction would go straight through the jet. So we got a preferential process of depositing momentum in the Easterly and Westerly directions. The consequence of that would be that the jet would grow, getting stronger at the lower altitudes, until it was reversed in sign, where the waves that were going in the other direction would then start to be absorbed.
Okay. So that was the theory.
The idea was to make an experiment which would prove this theory. Basically, we had an annular tank of water, stratified so that waves could be generated in it. We generated waves at the bottom of the tank by having a set of pistons which deformed the bottom, and waves would travel in both directions around the tank as a result. We threw the switch and waited for something to happen. What happened was exactly as predicted by the theory: a jet would form going in one direction and then, as we continued to force these waves, gradually the jet would be built up in strength at the bottom and then start flowing in the other direction.
Why is it close to two years? Is it just happenstance?
Yes, it is happenstance. In other words, it is decoupled from the fact that the earth is rotating. So there is nothing special about the fact that it reverses direction every year and a little bit.
Changing tack a bit, you came back to Melbourne after being in Woods Hole and you started working on simulating convection in clouds. Tell us about those experiments.
Clouds form and rise and are visible because the water vapour that is contained in the air at low levels condenses. The condensing process liberates heat inside the cloud and it encourages or helps it to grow to higher levels. People imagined that clouds were a bit like mushroom clouds and would rise with the buoyancy that they started with. Theories were produced to describe this. Stewart Turner, for example, worked on such things, as did Bruce Morton.
So the key difference to the theory of Morton, Taylor, Turner and so forth was that you were simulating the latent heat release and buoyancy production due to the cloud’s rising.
If you are doing an experiment in water, which is what I was doing, you would be trying to release the buoyancy conditionally as it rose. In other words, you would be releasing more buoyancy the higher it got. The way I did that was to saturate the blob of fluid, which was supposed to be the cloud, with a fairly insoluble gas. Air is a fairly insoluble gas, but I used other gases as well. At a certain height, the gas in solution would come out of solution in the form of very fine bubbles. You can see this kind of thing happening in Guinness. If you look at a glass of Guinness after it has just been poured, you will see that there is a white layer which rises. I think it is nitrogen gas that they saturate Guinness with. I made experiments which would do just that – release the buoyancy as they rose. And sure enough, the clouds produced in this way closely resembled real cumulus clouds in the atmosphere. But there were measurement problems and, unfortunately, something intervened in my proceeding with this experiment.
So, Angus, you are making clouds in reverse. The water became the air and the bubbles were being used for water droplets. It is all back to front.
Yes, that’s right.
Select activities that are most appropriate for your lesson plan or add your own. These activities align with the Australian Curriculum strands ‘Science Understanding’, ‘Science as a Human Endeavour’ and ‘Science Inquiry Skills’, as well as the New South Wales syllabus Stage 4 Science outcome 4.6.6 and 4.9.4 and Stage 5 Earth and Environmental Science outcome 8.4.1. You can also encourage students to identify key issues in the preceding extract and devise their own questions or topics for discussion.
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