Upper Atmosphere Heating From Ocean‐Generated Acoustic Wave Energy

Abstract

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 1 mW/m2, 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 0.05 mW/m2. This is about half the average value reported in previous ground‐based microbarom observations spanning 8 years. 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.

Infrasound and Gravity Waves Over the Andes Observed by a Pressure Sensor on Board a Stratospheric Balloon

“…Our study was based on the analysis of the National Aeronautics and Space Administration's ULDB mission data, described in Bowman and Lees (). The balloon was launched from Wanaka, New Zealand, on the 16 May 2016.…”

“…Therefore, these variations of background pressure need to be characterized, in order to not be mistaken with an atmospheric wave of interest. The noise sources can be summarized by the following equation from Bowman et al (): where different constituents are as follows: : stands for sensor motion, that is, vibrations, which is removed from the signal by combination of two channels from active microphones (Bowman & Lees, ). : corresponds to the outside electromagnetic interference, the associated noise is shown on the signal coming from the mechanically disabled sensor (Bowman & Lees, ). : depicts the intrinsic sensor electronic noise, which is reduced by using several identical sensors and combining their signal. : stands for the wind generated noise. Because the balloon is flying in the stratosphere, at neutral buoyancy, thus it experiences near zero differential air flow; hence, the wind noise is negligible (Bowman & Lees, ). : depicts the nonhydrodystatic pressure fluctuations, which come from the balloon's altitude variations.…”

“…The signal is detectable all over the world and consequently is part of acoustic background on Earth. It can be detected on the ground when tropospheric winds are low and stratosphere wind ducts refract them back toward the surface (Campus & Christie, ; Bowman & Lees, ; Landès et al, ).…”

Detecting Lightning Infrasound Using a High‐Altitude Balloon

“…The ULDB balloon position and height was recorded using an onboard GPS unit, and records show that the full flight included a full circumnavigation of the Southern Hemisphere (Bowman et al, ). The acoustic sensor package recorded data for the first 20 days of the flight, and the ocean microbarom was recorded throughout as well as other signals of unknown provenance (Bowman & Lees, ).…”

“…The microphones were not calibrated to the pressure and temperature conditions experienced during the flight, but their primary effect should be to lower the corner period of the sensors (Bowman et al, ). The acoustic waveforms presented here are high‐pass filtered at 0.6 Hz in order to remove high‐amplitude signals contributed from the ocean microbarom (Bowman & Lees, ), atmospheric gravity waves generated by thunder cloud convection (Blanc et al, ), and balloon oscillations (W. J. Anderson & Taback, ). (Unfiltered signals recorded by the acoustic package can be seen in Figure S1 in the supporting information.)…”