Climate signatures in long-term seismo-acoustical measurements in the earth, atmosphere and oceans

Speaker: Läslo G. Evers, head of the R&D Seismology and Acoustics department at KNMI and Professor of Seismo-Acoustics at Delft University of Technology

A global network of seismic, infrasound and hydro-acoustic sensors is in place for the verification of the Comprehensive Nuclear-Test-Ban Treaty. This so called International Monitoring System (IMS) has been build up since 1996 to monitor the earth on the occurrence of nuclear test explosions. To date 90% of the IMS is complete, which will eventually consist of 321 monitoring facilities.

The propagation of acoustic waves in the atmosphere and ocean depends on the temperature. With the IMS, temperature changes in the deep ocean and upper atmosphere can be passively probed, there where other observations are sparse. The atmosphere and ocean are changing on a wide variety of timescales. The hydro-acoustical and infrasound component of the IMS can sense such changes, each second over periods of tens of years. Such long term measurements of oceanic and atmospheric variability enable the study of climate change.

Infrasonic waves passively probe the entire atmosphere. The challenge is to unravel temperature variability (long term increases and decreases) with surface based recordings. As a reference, seismic signals are used which remain unchanged as a function of time. A so-called seismo-acoustic analysis uses both seismic and infrasonic signals, where changes in the recordings can be attributed to changes in the medium. The latter being temperature changes in the troposphere and stratosphere.

To illustrate the contribution of the IMS to climate studies, over 15 years of IMS seismic, infrasonic and hydro-acoustical recordings will be shown. The seismo-acoustic analysis performed with the recordings reveals long term changes in atmospheric temperature.

Simultaneously a temperature increase in the troposphere and decrease in the stratosphere can be passively sensed. Changes in the deep-ocean temperature are also retrieved on the basis of an analysis of the ambient noise.