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The study of infrasound (acoustic) and gravity waves sources and propagation in the atmosphere of a planet gives us precious insight on atmosphere dynamics, climate, and even internal structure. The implementation of modern pressure sensors with high rate sampling on stratospheric balloons is improving their study. We analyzed the data from the National Aeronautics and Space Administration Ultra Long Duration Balloon mission (16 May to 30 June 2016). Here, we focus on the balloon's transit of the Andes Mountains. We detected gravity waves that are associated to troposphere convective activity and mountain waves. An increase of the horizontal wavelengths from 50 to 70 km with increasing distance to the mountains is favoring the presence of mountain waves. We also report on the detection of infrasounds generated by the mountains in the 0.01-0.1 Hz range with a pressure amplitude increase by a factor 2 relative background signal. Besides, we characterized the decrease of microbaroms power when the balloon was flying away from the ocean coast. These observations suggest, in a way similar to microseisms for seismometers, that microbaroms are the main background noise sources recorded in the stratosphere even far from the ocean sources. Finally, we observed a broadband signal above the Andes, between 0.45 and 2 Hz, probably associated with a thunderstorm. The diversity of geophysical phenomena captured in less than a day of observation stresses the interest of high rate pressure sensors on board long-duration balloon missions.

Plain Language Summary The variations of pressure recorded on board a high-altitude balloon are analyzed to observe various phenomena. When the balloon is passing over the Andes at 33 km altitudes, different waves emitted below it are recorded. Waves produced by storms, atmospheric flows over the mountains, oceanic waves, and thunderstorms are identified in the records. Mountain waves observed by the balloon's instruments are compared to images of the same altitude range obtained by satellites. The poorly documented bass music created by winds in the mountains are observed in certain frequency range, and the sounds created by interfering oceanic waves are slowly decreasing from the coast. The variety of geophysical phenomena observed in less than 1 day demonstrate the power of such missions and instruments. Their interest is extending beyond Earth, because planets with dense atmosphere like Venus can be investigated with such kind of missions.