BMKG: The Sound Of Banging In Malang Was Caused By An Inversion Layer In The Atmosphere

Topographic map of Malang, East Java, which is a basin and hilly, which is prone to inversion layer formation. (Photo: Antara)

JAKARTA - The Meteorology, Climatology and Geophysics Agency (BMKG) said that the explosion that occurred in Malang, East Java was caused by an inversion layer in the atmosphere.

"Likewise with the sound of thumping that occurred several times in various regions, which has been a mystery. The cause is the presence of an inversion layer in the atmosphere, unless it is proven that there is a meteor," said BMKG Coordinator for Earthquake and Tsunami Mitigation Daryono in Jakarta, as reported by Antara. Between, Saturday, February 6.

He explained that in meteorology there is a term known as temperature inversion, which is the squeezing of the cold air layer by the warmer air layer in the atmosphere.

This air layer is formed when warm air rises above the colder air layer, then spreads and expands in the atmosphere. The heat sources can come from industrial activities, fires, traffic, the release of heat received by the sun, radiation from the earth's surface and others.

This phenomenon, he said, was actually unusual because under normal conditions the higher the air temperature, the cooler it should be, so that the phenomenon of inversion layer formation can only occur at a certain time as long as the conditions for its formation are met. The inversion layer can also form when there is a pressure anomaly in the atmosphere or there is hot air moving from another place.

Hot air and gases that are moving up into the atmosphere, he said, will be held back by this layer of warm air because they form a kind of hood (inversion cap) that covers the area and traps the gas and heat rising from the earth.

He gave a simple example, namely, if you are near an industrial area, you sometimes smell an unpleasant smell that lasts a long time in certain weather conditions. This is because gases or pollutants cannot rise to the atmosphere and are trapped under the inversion layer.

The inversion layer has been recognized as a factor in the haze disaster in a number of countries. The severe haze events in 1948 in Donora, Pennsylvania, (USA) and in 1952 in London, England, were caused by an increase in the inversion layer in the atmosphere. The London smog disaster lasted for a week and claimed the lives of up to 12,000 people.

However, gases and pollutant particulates are not the only thing held up by the inversion layer. Some people have reported hearing strange noises during the formation of the inversion layer in the atmosphere.

Sound waves coming from trains, cars, lightning, and other sound sources can bounce off the inversion layer so they can be heard elsewhere. This occurs because the inversion layer acts as an imperfect reflector of acoustic waves, radio waves and even light.

The inversion layer can also make the sound louder until it sounds farther away. Like honking a car horn in a closed garage, it's certainly louder than honking on a highway. This is because the sound is stuck in a narrow space.

The inversion layer makes the sound of lightning unable to spread upwards or spread in all directions, because it is trapped and can only spread to the surface of the earth. In this case the sound of lightning will be heard louder and can be heard far away in the area covered by the inversion layer. The sound of lightning is like traveling through an audio channel similar to a "tropospheric duct".

In theory, sound is a proven acoustic wave that can be reflected off an inversion layer. Under conditions of temperature inversion, sound waves are refracted downwards, and therefore can be heard over a greater distance.

This is the basic concept why the inversion layer can make the sound of lightning sound far away due to the multi reflection process. The sound of lightning when it is far away and under certain atmospheric conditions can change its "anatomy" so that it is no longer like the original lightning sound at the source, but can resemble a boom.

Apart from reflecting regular acoustic waves, the inversion layer is also capable of reflecting extreme mechanical and acoustic waves in the form of shock waves. So that it can spread sound and vibration effects in a more distant area.

Furthermore, he said, topography plays an important role in developing and resisting the inversion layer. Cold air can accumulate in valley basins or lowlands on the coast under certain weather conditions. So that areas with this kind of morphology are prone to inversion phenomena during the rainy season.

One of the many areas in Indonesia that is prone to the formation of an inversion layer is the Malang area. With a topography in the form of a basin surrounded by mountains, this area is vulnerable to temperature inversions under certain conditions, namely when cold air is trapped in the valley and a layer of warm air covers it from above.

When the Malang basin is covered with a layer of inversion, it is as if a "giant tunnel" was formed. Enough with a lightning incident that occurs nearby or from another place, the boom will spread along the valley and reflect repeatedly, similar to the formation of an echo, as reported by some Malang residents a few days ago, said Daryono.