Have you ever made chocolate milk? If you added chocolate syrup to your glass of milk and just let it sit, in a few hours it would all mix together naturally. This process is called diffusion. However, if we stir the milk the chocolate quickly spreads throughout the milk. The stirring creates turbulence, and it is turbulence that actually mixes the chocolate with the milk.
Before going back to school to get my doctorate, I worked for the National Oceanic & Atmospheric Administration (NOAA) doing government research on atmospheric diffusion. This means I studied how air quality in our country is affected by pollution. How does our air become polluted? Toxic particles could be emitted from factory smokestacks or cars on the road, or even from a volcano. As these particles spread out, the concentration (or strength) of pollutants decreases, but at the same time they are diffused over a larger area of our atmosphere.
When I began my Ph.D. program at Georgia Institute of Technology, I took the opportunity to take my research in a new direction, and learned about atmospheric gravity waves. These waves can sometimes create turbulence. They are caused by anything from thunderstorms and tornadoes, to volcanic eruptions. We call them gravity waves or buoyancy waves. This research is important to the study of atmospheric diffusion, because gravity waves can create turbulence can increase the spread of pollutants in the air, just as stirring your drink with a spoon speeds up the mixing of chocolate milk.
The atmosphere is full of wave activity, but at very small amplitude-- unless you’re experiencing turbulence in an airplane, you can’t really feel the effect. But have you ever heard trees sometimes rustle at night, when there shouldn’t be any wind? This is caused by turbulence- air pockets being pushed up and down- making little gusts of wind. Theory tells us that at night the air should be relatively calm—there shouldn’t be any kind of turbulent activity. Since no one had really studied this phenomenon, it was accepted as a mystery. Well, I decided the best way to learn a subject is to write a book about it, so I wrote Introduction to Atmospheric Gravity Waves.
Now we realize that the more correct term for this turbulence is buoyancy waves, because the air is pushed up by buoyancy before it is pulled down by gravity. Normally, the density (or weight) of air is heavier close to the ground, and is less heavy higher up in the atmosphere. But a storm might come along and suddenly push a pocket of dense air up a few 100 meters. It would be heavier than the air around it, so it would drop back down where the air is even heavier, which pushes it back up again. This slow bouncing movement is called oscillation, and it creates the waves. The next time you jump on a trampoline, you can imagine yourself as the heavy air pocket, forcing your body up into the lighter air, and then being pulled back down by gravity, until the trampoline pushes you back up.
Since I saw my first science fiction movie, I wanted to become a scientist and get my Ph.D. Like a buoyancy wave, my plan was pushed up above everything else. In 1959 I began to study physics at University of California at Riverside. But as I completed my master’s at University of Washington in Seattle, the family I had started needed me more. I needed to get a job to support them, instead of finishing my Ph.D. This responsibility pushed my dream down out of the way. But my plan was still there, and later in life, when my first daughter was old enough to go to college, I went back too! Having my family responsibilities cared for, and a scholarship from NOAA, pushed my dream back up, so I finally finished my doctorate in 1989. Besides being a personal goal, completing my education made it possible for me to become a professor. Now I am able to “diffuse” the information I have learned to all my students!