Resonant coupling between the Earth and the atmosphere at frequencies where the solid Earthmodes overlap the fundamental modes of the atmosphere allows for the triggering of oscillatoryacoustic perturbations by ground excitation and vice versa. Here, we describe oscillatoryperturbations observed in the solid Earth (from volumetric borehole strainmeter data) and inthe atmosphere (from GPS-derived ionospheric total electron content) following the 2003 July13, Soufri`ere Hills Volcano explosion (Montserrat, Lesser Antilles). Spectral analysis showsan amplitude peak at 4 mHz for both data sets, with similar waveforms and signal duration.Using a normal mode summation technique, we show that both signals are explained by asingle explosive source in the atmosphere. Similarities in waveforms, in particular a doublewave train also reported after several other explosion-triggered atmospheric perturbations,result from the superposition of the dominant (fundamental) atmospheric modes that triggerresonant coupling with the solid Earth around 4 mHz.