The reason you hear the loudness of explosions from distant interceptors: sound waves spread

Since the current campaign began, many Israelis find themselves jumping in panic at the sound of a loud explosion that shakes the windows, even when the home command’s app is silent and the horns are not sounding.

This feeling, where the heart skips a beat and the whole house shakes, is the result of simple but powerful physics that takes place high above the clouds. When the Iron Dome system, or alternatively the Katz 2 and Arrow 3 systems, destroy an enemy missile, enormous energy is created at the meeting point.

This energy is translated into surface waves that move through space in the form of sound waves. Contrary to what many think, the sound does not stay at the point where the missile exploded, but it goes on a journey across the country. These sound waves are affected by many factors such as the height of the interception, the direction of the wind, the temperature in the different layers of the air and even the humidity.

The higher the intercept is carried out, as is often the case with ballistic missiles intercepted by an Arrow system, the more the sound waves can spread to a much greater radius. The explosion that takes place at an altitude of tens of kilometers releases a great air pressure that moves down and to the sides, and when it hits the ground or buildings, it sounds like a deep and strong boom that can be heard in Haifa even if the interception was carried out over the center of the country.

The main reason for the feeling of deception is the speed at which sound travels compared to light, but also the way the human ear interprets the intensity of noise. When a person hears a loud explosion that shakes the walls, the brain automatically translates this to imminent danger. In practice, the sound waves can be trapped between layers of air at different temperatures, a phenomenon that creates a sort of conduction tube that transmits the noise over vast distances without its intensity significantly fading.

Therefore, a resident of Tel Aviv can hear an explosion that he hears right over the street, while in practice the interception was carried out over the sea or in the lowlands. This is doubly true for interceptions of the Arrow 3 system, which are carried out outside the atmosphere or at its edge. There, in the absence of dense air, the energy released is enormous, and when it penetrates back into the denser layers of air, it creates a page effect that spreads very widely.

It is important to understand that the sound of the explosion is not an indication of the location of the fall. The warning systems of the Home Command are based on an accurate calculation of the missile’s trajectory and the estimated point of fall, and they do not activate an alarm just because a loud noise is expected to be heard. This gap between the silence of the horns and the deafening noise is the main source of anxiety among the public.

Apparently this is another successful interception

Another aspect that affects the intensity of the noise we hear is the topographical and architectural structure of the environment in which we are. In a city with tall and dense buildings, the sound waves tend to bounce off the walls and create an echo that increases the feeling that the explosion is close and ongoing.

Meanwhile, at night the sound tends to sound louder and reach farther due to a phenomenon called temperature inversion, in which a layer of cold air is trapped beneath a warmer layer, causing the sound waves to curve back toward the ground instead of dispersing upward.

The distance at which the boom is heard depends to a great extent on the strength of the explosive in the warhead of the interceptor missile and the intercepted missile. When it comes to a missile with a heavy warhead, the amount of energy that is released is such that it can shake windows at a distance of 50 kilometers or more. The fact that the public is not always aware of these distances means that every successful interception becomes an anxiety-inducing event for much wider circles than those who are in actual danger.

In the end, these explosive sounds are evidence of the Air Force’s deterrence and defense capability, and even if they are alarming, they indicate that the main threat, in most cases fortunately for us, was removed before it even reached its destination. The damages are mostly interception crises.