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Colliding sea surface waves generate the ocean microbarom, an acoustic signal that may transmit significant energy to the upper atmosphere. Previous estimates of acoustic energy flux from the ocean microbarom and mountain-wind interactions are on the order of 0.01 to 1mW/m(2), heating the thermosphere by tens of Kelvins per day. We captured upgoing ocean microbarom waves with a balloon-borne infrasound microphone; the maximum acoustic energy flux was approximately 0.05mW/m(2). This is about half the average value reported in previous ground-based microbarom observations spanning 8years. The acoustic flux from the microbarom episode described here may have heated the thermosphere by several Kelvins per day while the source persisted. We suggest that ocean wave models could be used to parameterize acoustically generated heating of the upper atmosphere based on sea state.

Plain Language Summary When two sets of ocean waves collide, they generate the sea surface equivalent of a gigantic subwoofer. The resulting low-frequency sound waves can travel across the planet and even heat the upper atmosphere. While this heating has been estimated using distant ground-based measurements, no one has actually measured the strength of the sound waves directly above the source. Using a microphone on a high-altitude balloon, we intercepted these upgoing waves and directly measured their energy content for the first time. We found that they carry an energy flux of about 0.05mW/m(2). For context, one would have to capture all the acoustic energy over a 1.2-km(2) region to illuminate a single 60-W lightbulb. Even so, the energy is sufficient to heat the upper atmosphere by several degrees Celsius per day. This is consistent with previous modeling studies.