The Weather Guys

What is brontology?

Brontology is the scientific study of thunder.

All thunder results from lightning.

A bolt of lightning rapidly heats the air around it, which causes the air to quickly expand and generate a sound wave we call thunder.

This sound wave travels through the atmosphere, and how it travels is a function of the atmospheric conditions.

Some thunder sounds loud and crisp, while in other cases it rumbles and lasts a few seconds.

The sound of thunder is a function of how far away the lightning is from us.

Sound waves interact with objects in multiple ways.

As sound waves move through the atmosphere, they are absorbed by molecules in the air.

The waves can bend around objects, such as trees and leaves, or be absorbed by those objects.This muffles the sound.

Rapid changes in wind speed or wind direction can influence the direction of a sound wave, which can also affect whether we hear it.

As sound waves travel through the open air, they can change the direction in which they are traveling.

In the lower atmosphere, the temperature of the air generally is cooler with increasing height above the ground.

Cooler air over warmer air causes the sound wave to bend upward away from the ground. In this condition, we may see the lightning but not hear the thunder.

We refer to this as heat lightning; we see the light but don’t hear the thunder because the sound wave never reaches our location.

An acoustic shadow zone is an area in which the sound wave does not propagate.

You can be in an acoustic shadow with heat lightning.

— Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month.

How do we gain knowledge about the atmosphere?

It is easy to assume that current, well-accepted scientific knowledge about anything was originally discovered by the grace of inspired geniuses armed with vastly superior intelligence than the average thinking person.

In reality, very often the key ingredient is a roving curiosity and the determination to think about something for a long time.

For instance, the fact that the flow around mid-latitude cyclones (large, organized winter storms) is counterclockwise in the Northern Hemisphere was known long before it was physically understood.

Benjamin Franklin, the first great American scientist, was very interested in a number of meteorological phenomena. He undertook voluminous correspondence with his family in Boston while he was in Philadelphia. By comparing notes about the weather in those letters, Franklin came to recognize that stormy days with northeasterly winds in Philadelphia tended to occur just before such days in Boston.

Further, he noted that when such northeasterly winds were occurring in Boston, the winds were often from the northwest or west in Philadelphia. From these observations, he concluded not only that the flow around the storms was counterclockwise but that the storms were moving entities.

Today, we continue to acquire basic knowledge of the atmosphere combining careful measurements, detailed analyses, and computer-aided simulations. The path to understanding is very often “non-linear” as in this example. That makes it particularly difficult to accurately predict what the exact benefits and applications of basic research might turn out to be. That is why the pursuit of basic research is a fantastic investment with a guaranteed return.

— Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month.

There are spring and summer afternoons when very thin clouds appear overhead and turn the sky a bit white. These types of skies are physically interesting in at least two ways that are worthy of note.

First, the whiteness is a function of the fact that the cloud cover is a thin cirrus cloud. Cirrus clouds are composed of tiny ice crystals that scatter visible light without preference for any of the colors of the visible spectrum (the colors of the rainbow). This particular property is shared by snowflakes as well as by haze droplets. Individual snowflakes look clear but even a small collection of them is white since all of the light that hits the collection of snowflakes is scattered in all directions equally. The same is true of haze droplets which are most common in the summertime in southern Wisconsin.

Second, even the presence of such a thin deck of high clouds (or a thin haze layer) can substantially lower the high temperature of that afternoon. Often, record high temperatures in the summer occur on days with very little cirrus cloud and very little haze in the sky.