GPS Detection and Energy Estimation of the Ionospheric Wave caused by the July 13th, 2003 Explosion of the Soufriere Hills Volcano, Montserrat

Abstract

Volcanic explosions or shallow earthquakes are known to trigger acoustic and gravity waves that propagate in the atmosphere at infrasonic speeds. At ionospheric heights, coupling between neutral particles and free electrons induces variations of electron density detectable with dual-frequency GPS measurements. Using GPS data collected in the Caribbean, we identified an ionospheric perturbation following a major volcanic explosion at the Soufriere Hills Volcano (Montserrat, Lesser Antilles) on July 13, 2003. Spectral analysis reveals peaks centered at 1 mHz and 4 mHz, similar to previous observations and consistent with theory, suggesting both gravity and acoustic wave components. We retrieve a horizontal velocity of ~24 m/s for the acoustic component, which, implies upward propagation at ~33°, consistent with ray tracing results.

We model the acoustic wave using a N-wave pressure source at ground level combined with ray-tracing to propagate the neutral pressure wave; this accounts for the dispersive characteristics of the atmosphere while conserving total acoustic energy. Plasma velocity is derived from neutral velocity using a finite difference solution of the magneto-hydrodynamic momentum equation. The continuity equation for charge densities is used to compute corresponding electron density variations, which are then numerically integrated along satellite-to-receiver line-of-sights, simultaneously accounting for the satellite displacements. We minimize the misfit between observed and model waveforms to estimate a total acoustic energy release of 1.53 10¹⁰J for the primary explosion event at Soufriere Hills Volcano associated with the peak dome collapse. This method can be applied to any explosion of sufficient magnitude, provided GPS data are available at near to medium range from the source.