IPB University Professor: Atmospheric Temperature Inversion Allows the Boom from Anak Krakatau to Be Heard as Far as Bandung
The boom produced by the eruption of Mount Anak Krakatau was reportedly heard in several areas, including Bandung. According to Sonni Setiawan, SSi, MSi, a professor in the Department of Geophysics and Meteorology at IPB University, this phenomenon may have been influenced by an atmospheric temperature inversion layer.
“Atmospheric conditions, particularly when a temperature inversion layer is present, can cause sound waves from the eruption to travel farther and be heard more clearly at the surface,” said Sonni.
Impact on Sound Propagation
A temperature inversion is a condition in which air temperature actually increases with altitude. Under normal atmospheric conditions, air temperature generally decreases as altitude increases.
“A temperature inversion layer forms when the air near the surface cools more rapidly than the air above it. This cooling can result from radiative cooling at the surface, the inflow of cold, dry air via advection, or other meteorological processes,” he explained.
According to him, these conditions affect the propagation of acoustic waves. Sound is a wave that travels through the air, and its speed of propagation is influenced by temperature.
Temperature differences between atmospheric layers can cause sound waves to undergo reflection or refraction, and which of these is dominant depends heavily on vertical temperature variations.
If vertical variations in air temperature decrease, refraction becomes more dominant; conversely, if vertical variations in air temperature increase, reflection becomes more dominant.
“Under inversion conditions, the refraction of acoustic waves causes the wave path to curve back downward, so that sounds from distant sources can still be heard at the surface,” he said.
Topography as a Contributing Factor
In the context of the Anak Krakatau eruption, volcanic activity not only produces volcanic material but also releases energy in the form of acoustic waves. When these waves travel through an atmosphere with inversion conditions, the sound energy can be refracted and reflected, thereby extending the sound’s range.
“An inversion layer can make the sound of an eruption audible from farther away. Simply put, this condition is like the formation of a space that helps retain sound energy so that it does not immediately disperse into the upper atmosphere,” he said.
The region’s topography can also reinforce these conditions. Cool air tends to accumulate in basins or low-lying areas, thereby further supporting the formation of an inversion layer.
“The Bandung Basin is one of the regions that is topographically prone to the accumulation of cold air. When atmospheric conditions support the formation of an inversion, this region can act as a pathway that allows sound energy to travel farther,” he explained.
A Boom Does Not Always Indicate a Nearby Source
Wave energy reaching the receiving area can not only be heard as a boom but, under certain conditions, can also cause vibrations in nearby objects, such as window glass, doors, or parts of buildings.
This phenomenon indicates that the booms heard by the public do not always originate from a source located near their location. Eruptive activity as the energy source, atmospheric conditions as the propagation medium, and the region’s topography are factors that collectively determine how far the sound can be heard. (AS) (IAAS/EPK)
