Evaluating microbarom source models using infrasound recorded on a stratospheric balloon

The global International Monitoring System (IMS) network continuously detects coherent ambient infrasound noise between 0.1 and 0.5 Hz. This noise, referred to as microbaroms, is generated by second order non-linear interaction of ocean waves. Various source models have been developed in earlier works; e.g. Brekhovskikh et al. (1973) and Ardhuin & Herbers (2013) who considered a source directivity effect in infinite depth ocean, and Waxler (2007) who investigated the radiation model in finite depth ocean from monopolar sources. De Carlo et al. (2020) proposed a two-dimensional energy spectrum ocean wave model accounting for bathymetry and source directivity effects. First comparisons between the observed and modelled directional microbarom amplitudes at IMS infrasound stations show first order agreement. In order to further evaluate these models, microbarom observations from the Carolina Infrasound secondary payload on board the NASA Ultra Long Duration Balloon flight in 2016 (Bowman and Lees, 2018), that flew over spatially extended microbarom source regions along the Antarctic Circumpolar Current, are compared with the modelled source energy flux. The simulated source strength power spectrum is integrated over an extended source region beneath the balloon and compared with the observed one. The relative importance of modelled source parameters (e.g. bathymetry, launching ray parameters) is assessed. In this presentation, we describe the infrasound observations on the balloon and the supporting microbarom source models, and discuss the implications of these results on the remote estimation of the acoustic energy flux from the ocean surface to the upper atmosphere.