Mesopause temperature perturbations caused by infrasonic waves as a potential indicator for the detection of tsunamis and other geo-hazards
Many geo-hazards such as earthquakes, tsunamis, volcanic eruptions, severe
weather, etc., produce acoustic waves with sub-audible frequency, so called
infrasound. This sound propagates from the surface to the middle and upper
atmosphere causing pressure and temperature perturbations. Temperature
fluctuations connected with the above mentioned events usually are very weak
at the surface, but the amplitude increases with height because of the
exponential decrease of atmospheric pressure with increasing altitude. At the
mesopause region (80–100 km height) signal amplitudes are about two to
three orders of magnitude larger than on the ground.
The GRIPS (GRound-based Infrared P-branch Spectrometer) measurement system operated by the German Remote Sensing Data Center of the German Aerospace Center (DLR-DFD) derives temperatures of the mesopause region by observing hydroxyl (OH) airglow emissions in the near infrared atmospheric emission spectrum originating from a thin layer at approximately 87 km height.
The GRIPS instrument is in principle suited for the detection of infrasonic signals generated by e.g. tsunamis and other geo-hazards. This is due to the fact that the infrasound caused by such events should induce observable short-period fluctuations in the OH airglow temperatures. First results obtained during a field campaign performed at the Environmental Research Station "Schneefernerhaus", Zugspitze (47.4° N, 11.0° E) from October to December 2008 are presented regarding potential sources of meteorological and orographical origin.
An adequate distinction of the overlapping infrasonic signatures caused by different infrasound sources in the OH temperature record is needed for the ascription to the proper source. The approach presented here could form a contribution to a hazard monitoring and early warning system.