The ARROW (AtmospheRic infRasound by Ocean Waves) product forms a database of coherent ocean-generated noise (so-called microbaroms) acoustic power in the atmosphere. Microbarom acoustic power is estimated from the Hasselmann Integral computed by the spectral wave model WAVEWATCH-III (r) at global scale in realtime. Public acoustic data is provided with a 6-month delay. ARROW was developed as part of Marine De Carlo’s PhD thesis (2018-2021), funded by the Commissariat à l’Energie Atomique et aux Energies Alternatives and directed by Fabrice Adhuin from IFREMER, Laboratoire d’Oceanographie Physique et Spatiale (LOPS).

In the framework of this thesis, a new theoretical description of the mechanism of infrasound generation connecting the pressure amplitude to the height and frequency wave oscillation has been proposed. Hence, the characterization of atmospheric ambient noise originating from the ocean with application to long-range acoustic propagation has been achieved. Between 0.1 and 0.6 Hz, infrasound signals recorded in the atmosphere are dominated by microbaroms. Microbaroms propagate through the atmosphere over thousands of kilometres due to low absorption and efficient ducting between the ground and the stratopause.

Different theoretical models have been developed to characterize the source of microbaroms, all based on the second-order nonlinear interaction of ocean waves. These interactions are represented by a quantity called the Hasselmann integral which is the integral over all directions of the product of the energy present in waves propagating in quasi-opposite directions, at a given frequency. From these considerations, a unified microbarom source and application to radiation patterns by ocean waves has been proposed by Marine de Carlo in 2020 ( https://doi.org/10.1093/gji/ggaa015 ). This theoretical work reviews earlier models and extends previous theories to the combined effects of both finite depth ocean and source directivity. Global modelling of microbaroms and comparison with infrasound observations of the International Monitoring System (IMS) set up to monitor compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT) shows that the water depth has a negligible effect for the near-horizontally propagating acoustic waves that dominate microbarom records ( https://doi.org/10.1029/2020GL090163 ).

Using the ARROW product, a better characterization of the coherent ambient noise allows to limit the number of false alarms, thus improving the detection capabilities of the IMS. Furthermore, comparisons between the simulated and microbarom signals globally and continuously observed provide a basis for investigation into geophysical inverse problems. Hence, one foreseen application is the assessment of Numerical Weather Prediction (NWP) models, which are poorly constrained in the middle atmosphere (~10-90 km). This application would pave the way for innovative atmospheric remote sensing method intended to feed data assimilation frameworks.