A Physicist looks at Weather

© Fernando Caracena, 2015

1. Introduction

The weather has been on the minds of humans since prehistory. Hunter gathers planned around anticipated weather changes that were associated with the change of seasons. Ancient farmers, of course, read the sky for favorable weather. Ancient mariners watched for storms. Today, weather programs on televison are a necessary part of TV programming. People are interested in the weather; want to know more about it; and understand how it works. And so was I as a child. When in high school, I used to climb to the top of a hogback ridge near my house to watch the weather from the top. I had many interests then, mostly in the sciences. My main interest was in physics. I saw the weather as a complex of physical processes in a gaseous fluid.


The study of the atmosphere and weather is called meteorology; but the term is often loosely applied. In this field, the various functions that are kept separately defined in other areas are all run together. Technical fields are usually organized in three levels: science, engineering, and technology. The term meteorology and meteorologist are often applied to all three levels: the guys that take weather observations, the TV weather guy or gal, the guy that encodes algorithms for weather predictions and displays, and the weather forecaster. They all call themselves meteorologists and what they do, meteorology. When I worked at weather research, I had to keep correcting others from referring to me as a meteorologist. I would tell them that I was a physicists working on weather related problems. There was a difference in focus there.

Scientists Who were interested in Weather

Aristotle , who is considered the father of meteorology wrote a book called Meteorology. He would be considered more of a philosopher, or perhaps a natural philosopher. But we could mark the beginning of the study of weather as a science with Aristotle. In those ancient days there was also interested in weather forecasting, but it was more like astrology compared to astronomy today.  Theophrastus  compiled a book on weather forecasting, called the Book of Signs.

A painting of Benjamin Franklin by Benjamin West

A painting by Benjamin West (1738-1820), showing Benjamin Franklin flying a kite in a thunderstorm. From Wikimedia, in the public daomain.

Who has not heard of Benjamin Franklin's famous kite experiment, which is dramatically portrayed by Benjamin West's painting (Fig. 1)? Franklin, who dabbled in various sciences, demonstrated that lightning is a form of electricity. He also experimented with a variety of electrical gadgets, which impressed visitors to his laboratory. A lucky person, he lived a charmed life. Some others trying to duplicate his experiments were electrocuted in the process.

Vilhelm Bjerknes,  a physicist at the University of Stockholm, developed a model of the operation of the Earth's atmosphere based on set of partial differential equations, called the primitive equations.  This model would become

a means of forecasting the weather based on computations made on observations as input. In the 1920s Lewis Fry Richardson made the first attempt to make a numerically based weather forecast for a couple of points in Europe by using Bjerknes's model. It may have been considered a beau geste at the time. It took about six months to calculate a six hour forecast for very limited places, and the calculation turn out wrong anyway. However, this effort recorded in the scientific literature charted a path that others would later follow successfully using the developing digital computer as the computational engine. In time, numerical weather forecasts were produced ahead of the forecast period, and covered large portions of the globe.

Carl-Gustaf Arvid Rossby a scientist who studied under Bjerknes produced the first operational numerical weather forecast in in 1954 in Sweden based on Bjerknes's model.

Today, numerical prognostic models are being improved and refined around the world by various groups, who are taking advantage of advances in computer science and technology. Does that mean that we understand the weather better? I think not. Numerical weather forecasts are based on approximate input and produce approximate output. A given forecast has only a limited probability of being right, and its likelihood of being correct diminishes with the advance time of the forecast. The longer range of the forecast, the more likely it is to be wrong.

For the above reasons, this post and future ones on this subject aim to satisfy some of the curiosity of the the reader, not to prepare the reader to do meteorology, but rather to gain some intuitive understanding of the weather, and how it works.

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