Listening to the waves
Analysis of ‘inaudible’ infrasound high in the stratosphere can improve weather forecasting and climate models, Dr Pieter Smets (Faculty of Civil Engineering and Geosciences) believes. Ocean waves can be a good source of this infrasound.
Geophysicist Dr Pieter Smets, who also works for the Royal Netherlands Meteorological Institute (KNMI) in the group of Prof. Läslo Evers, is interested in the climatic conditions in the stratosphere, the atmospheric layer situated at an altitude of between 10 and 50 kilometres. Hardly any data are available on wind force and temperature above 30 kilometres. Climate models and weather forecasts could be improved with more understanding of this atmospheric region.
Wind forces and temperatures can be deduced by analysing infrasound that has travelled through these atmospheric layers. Or so concludes Smets who recently defended his PhD thesis Infrasound and the Dynamical Stratosphere, A new application for operational weather and climate prediction.
Infrasound, sound with a frequency below 20 Hertz, is measured with arrays (series) of highly sensitive microbarometers. Sources of infrasound are often large and powerful, like meteors, explosions, earthquakes and – importantly - ocean waves.
Dozens of microbarometers have been set up in the Netherlands and around the world to listen to the infrasound.
An especially interesting use of the research is the study of sudden stratospheric warmings – dramatic events in which the midwinter stratosphere changes into a temporary summer-like situation over the course of a few days. “Before climate scientists can incorporate these kinds of phenomena in their models, we need to do a lot more work,” Smets warns.
Smets captured infrasound that was produced by the eruption of volcanoes, amongst which the eruption of Mount Tolbachi in Russia in 2013. Läslo Evers and Pieter Smets will continue in the same line of work but will use continuous background noise of infrasound created by ocean waves instead.
Photo (c) ESA
Sources of infrasound are often large and powerful, like meteors, explosions, earthquakes and – importantly - ocean waves.