The Maple Leaf –  Defence Stories

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By Major Craig Cutting, The Royal Regiment of Canadian Artillery School

For anyone, including the residents of the communities surrounding 5th Canadian Division Support Base Gagetown (5 CDSB), who may be curious as to why they hear the thunder of Howitzers differently on any given day, the intent of this article is to explain how and why guns are heard differently in good weather and in bad, during the day and night.

Atmospheric effects on sound

Atmospheric effects, comprised of four major factors (wind, temperature, humidity and cloud cover) have a large impact on sound.

Wind

Wind alters sound propagation by ‘bending’ the sound wave. At lower elevations, wind travels more slowly due to terrain features such as hills and trees. At higher elevations, wind travels faster as it is unimpeded. Therefore, if you are downwind from a source, you will hear louder noise levels than someone standing upwind.

Temperature

On a hot day, the air is warmest near the ground, and decreases in temperature at higher altitudes. This causes sound waves to refract upward, away from the ground. On a cold day, this temperature gradient will reverse, having the opposite effect. Therefore, at night when it is cooler, a listener will experience raised noise levels compared to midday when it is warmer.

Humidity

As humidity increases, so too does the percentage of water molecules in the air. Because water molecules have less mass than nitrogen and oxygen, the air becomes less dense, allowing sound to travel faster. Therefore, a relative humidity increase will result in a raised noise level at the listener’s location.

Cloud cover

On a clear day, sound waves will propagate into the atmosphere and eventually dissipate. However, on a cloudy day, the sound waves will be reflected from the clouds back to the ground, and will therefore result in a raised noise level at the listener’s location. For example, on a cool, cloudy, humid evening in the spring, guns will be heard from much farther away, especially if downwind, compared to a dry, hot, clear afternoon.

The Royal Regiment of Canadian Artillery School, located within 5 CDSB, provides the Canadian Army with combat-capable soldiers and officers ready to meet the operational and domestic requirements of the Canadian Armed Forces.

To provide world-class training within a challenging modern battlefield, guns fire by day and night, in all weather conditions.