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Sound waves are longitudinal waves in which the particles of the medium travel parallel to the sound waves propagating through it. These waves generate compressions and rarefactions in alternating patterns. The speed of the sound wave depends on the characteristics of the medium that it propagates. The sound waves cannot travel through a vacuum, but they are able to propagate through solids, liquids and gases.
Effect of wind on Sound Waves
The difference between the two atmospheric zones causes the movement of wind which is the flow of air. The wind can flow or move in the same direction as the sound signal or in the opposite direction, depending on which they can accelerate the speed of sound. If the case is with short distances, then the wind does not have significant effects on sound waves, but for long distances, the wind has the tendency to bend or spread out the sound signal causing it to get refracted. The temperature influences the density of the air, which in turn influences the speed of sound. Air is considered the perfect gas, and it is said that the lower the temperature, the higher the density and lower the velocity. The sound waves are refracted as a result of the decrease in the speed and change in the path of sound waves. The refraction of sound waves and refraction of light can be similar.
Refraction of Sound waves
Refraction above ground level-
Refraction of sound waves is a concept that deals with the bending or spreading of the sound signal in a medium. This phenomenon of bending sound waves affects the speed of the sound. If the wind is travelling in the same direction as the sound, then the sound wave is refracted. The natural temperature gradient of the atmosphere can also influence the refraction of sound. During the night or when the clouds are denser, temperature inversions take place that can affect the wind’s temperature and flow.
The temperature of the wind increases along with the elevation; then, the sound waves are refracted back to the ground. Hence, this is the reason the sound can be clearly heard at night rather than during the day over long distances.
- Case 1- When the wind is blowing in the same direction as the sound, the sound is refracted towards the ground. The conditions are, therefore, favourable for sound propagation.
- Case 2- However, when the wind is blowing in the opposite direction to the sound, the sound wave is refracted upwards, and losses of 20 dB or more can be observed depending on the conditions.
- Case3- During windy days, there is an effective change that influences the speed of sound waves because the wind flows faster at greater heights at a distance from the ground level.
When a person speaks with the wind (same direction), the waves are refracted downward to the ground, and thus the sound is carried farther along with the wind. But when they speak into the wind (opposite direction), the sound waves are refracted upwards, and the voice is lost.
Refraction of sound in the ocean-
The temperature gradient decreases as we go deeper into the ocean. The temperature increases as the depth of the ocean increases. Under certain circumstances, the sound waves are refracted downward originating from underwater, opposite to the shadow effect in the air. As reported by marine biologists, the refraction of sound in oceans helps marine animals to communicate with one another over a long distance.
Conclusion-
The speed of sound varies as per the characteristics of the substance through which it is travelling. Sound waves transport energy, and the pattern of disturbance has the information that propagates from one point to another. The speed of the sound wave depends on the characteristics of the medium that it propagates. The effect of wind on sound waves is studied to determine the high energy sound waves that occur due to the changes in the atmospheric conditions. It also helps in designing the navigating equipment for submarines, tracking ships and aircraft.
The effect of wind plays an important role in understanding the geographical variations, forecasting weather and communicating over distances which are employed in the astronomical processes. This type of research is still under study for creating new approaches and innovative ideas that will help in medical and drug delivery processes.
