Ewan Short: studies in land-sea breeze

After studying the physics of fluid flow in his honours year, Ewan resolved to study atmospheric science at a graduate level. Read about his research and experiences as a graduate student.

Ewan Short is a PhD candidate in the School of Earth Sciences:

"Studying science provides tools for understanding objective reality, which both empowers action and promotes intellectual self-defence. These tools have perhaps never been more important than in today's world, which is characterised by complex global problems, information saturation, and many powerful players indifferent to truth. While modern scientific research is by necessity hyper-specialised, the instincts, habits, and values that you develop from studying science are almost universally applicable.

I began my undergraduate studies in development economics, but quickly found the subjective nature of the discipline did not suit my personality, so transferred into a science degree with a mathematics major. After studying the physics of fluid flow in my honours year, I learned that a major application of this field is to weather and climate prediction, and so resolved to study atmospheric science, also known as meteorology, at a graduate level.

During my masters degree at the University of Melbourne, I learned about meteorological processes like the land-sea breeze. This breeze occurs along coastlines, and is associated with the daily cycle of heating and cooling of the land surface, which produces winds that blow from seas onto land during the afternoon and evening, and from land back out to sea during the night and early morning.

To better understand this phenomena, I produced an animation of Richard Rotunno’s 1983 solution to a set of equations that describe a highly simplified tropical land-sea breeze. These equations are simple enough that they can (mostly) be solved by hand to produce an equation for wind as a function of time. Using the programming language python, numbers can then be plugged into this equation to produce a dataset for animation.

Scientists following Rotunno hypothesised that the wave structure of Rotunno’s solution might be partly responsible for the rainfall that can be seen to propagate away from coastlines in tropical regions. My masters supervisors Claire Vincent and Todd Lane were among the first to resolve these processes in realistic, high resolution computer simulations of the weather around Malaysia, Indonesia and New Guinea, one of the rainiest regions of the planet. Claire won an award from the Australian Research Council Centre of Excellence for Climate System Science for a paper on this simulation.

The figures below are from this paper, and show cross sections of the atmosphere extending perpendicular to the north coast of New Guinea. The purple contours give the amount of liquid water, indicating the presence of clouds and rain. The temperature anomalies resemble the waves in Rotunno's solution, with warmer temperatures in red associated with winds blowing from the sea onto land (sea-breeze), and the cooler temperatures in blue are associated with winds blowing from the land out to sea (land-breeze). These temperature anomalies affect rainfall offshore, because it is harder for moist air near the surface to rise and condense when the air is warmer than usual above (left hand figure), but easier when the air is cooler than usual above (right hand figure). These processes can also be observed in a 3D animation of Claire’s simulation results.

The goal of my masters research was to look for observational evidence for these processes. This was challenging as weather observations generally aren’t taken over the open ocean. My supervisors and I therefore used satellite scatterometers to observe ocean surface winds remotely. Satellite scatterometers work by emitting microwave radiation from space, which is reflected off wind-induced ocean waves and returned to the satellite. We also used satellite precipitation radar to measure surface rainfall.

The datasets produced by these instruments allowed us to create these figures, which show the same cross section through New Guinea as Claire’s figures above, although now the vertical axis is time rather than height. The red and blue shading indicates winds blowing offshore and onshore, respectively, and the grey contours give the average precipitation over multiple months.

These figures show precipitation indeed propagates offshore with the land-breeze, likely due to the cool anomaly revealed in Claire’s simulation. The figures were published in my masters thesis, and in a paper for the academic journal, Monthly Weather Review. Getting a research paper published was something I had never dreamed of accomplishing, and helped create funding and supervision opportunities down the line. Both my supervisors and the broader research community were highly supportive of my publication efforts, and seeing my work survive the peer review process provided a lot of personal satisfaction, and the motivation to continue to do research as a PhD student.

Over time, I've learned that while scientific study will never provide perfect understanding, it certainly allows you to progress your understanding, no matter what your level or ability. I believe everyone should be encouraged and supported to continuously develop these skills. While studying science at university, particularly completing a research project of your own, will greatly accelerate your understanding of the scientific approach, there are also many free resources that can take you a long way on your own. In my late teens I discovered a public domain recording of Einstein's ‘Relativity: The Special and General Theory’, which he wrote to introduce his ideas to a general audience. I listened to this recording on my MP3 player repeatedly, trying (and mostly failing) to understand general relativity.

I also encourage people to look directly at research publications, and other challenging material, for themselves, no matter what their background or education level. In my late teens I started reading papers from diverse fields to help me understand the everyday challenges I was facing in my own life. Usually I would only understand a few lines of the abstract and the concluding paragraph, but I still gained a sense of the state of the knowledge within that field, and the background material I’d have to learn to understand the research more fully. I think the key thing with endeavours like this is to try, and not get scared off by the things you don't understand. The goal isn’t for everyone to understand everything about every field, but to better diffuse scientific knowledge, culture and values into as much of society as possible."