Using the International Monitoring System infrasound network to study gravity waves

International audienceThe infrasound network of the International Monitoring System (IMS) has been designed for the detection of atmospheric pressure fluctuations produced in the [0.02 Hz-4 Hz] frequency range. However, the majority of the measuring chains used in this network also record pressure fluctuations at lower frequencies. The objective of this paper is to demonstrate the accuracy of IMS pressure measurements in the gravity wave band, whose period usually ranges from a few minutes to 24 hours. Application examples such as the monitoring of worldwide gravity wave time-spectra and the characterization of surface pressure fluctuations produced by atmospheric tides are presented. This study opens the way to the analysis of gravity waves using IMS data, which constitute a unique and accurate set of pressure measurements

Surface pressure fluctuations produced by the total solar eclipse of 1 August 2008

International audienceDuring a solar eclipse, the Moon's shadow progressively occults a part of the Earth from the solar flux. This induces a cooling in the atmospheric layers that usually absorb the solar radiation. Since the eclipse shadow travels within the atmosphere at supersonic velocity, this cooling generates a planetary-scale bow-wave of internal gravity waves. The purpose of this article is to estimate the surface pressure fluctuations produced by the passage of the 1 August 2008 total solar eclipse and to compare these pressure fluctuations with those recorded by a temporary network of microbarographs and by the infrasound stations of the International Monitoring System. The surface pressure fluctuations expected at all the measurement sites are estimated using a linear spectral numerical model. It is shown that the cooling of both the ozonosphere and the troposphere can produce detectable pressure fluctuations at the ground surface but that the tropospheric cooling is likely to be the predominant source. Since the expected eclipse signals are in a frequency range that is highly perturbed by atmospheric tides and meteorological phenomena, the pressure fluctuations produced by these synoptic disturbances are characterized and removed from the recorded signals. Low-frequency gravity waves starting just after the passage of the eclipse are then brought to light at most measurement sites. The time-frequency characteristics of these waves are similar to those obtained from the model, which strongly suggests that these waves were produced by the passage of the 1 August 2008 solar eclipse

Comparaison de 10 lignées commerciales de mâles terminaux : Caractéristiques des carcasses

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Comparaison de 10 lignées commerciales de mâles terminaux : Croissance et efficacité alimentaire

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