Gravity Wave Spectra in the Lower Stratosphere Diagnosed from Project Loon Balloon Trajectories

Area of Science:

• Atmospheric Science
• Geophysics
• Aeronomy

Background:

• Project Loon utilized super-pressure balloons launched since 2013 for global internet coverage.
• These balloons operated at altitudes of 18-21 km, collecting data on winds and pressure fluctuations in the lower stratosphere.
• This dataset provided a unique opportunity to study atmospheric gravity waves.

Purpose of the Study:

• To analyze gravity waves using data from 1,560 Project Loon balloon flights.
• To derive and characterize the kinetic energy and temperature perturbation spectra of these waves.
• To compare findings with existing atmospheric models and balloon analyses.

Main Methods:

• Divided 1,560 Loon flights into 3,405 two-day segments for gravity wave analysis.
• Derived kinetic energy spectra from horizontal balloon motion.
• Estimated temperature perturbation spectra from pressure variations, fitting data to a power-law function.

Main Results:

• Both kinetic energy and temperature spectra exhibited a -1.9±0.2 power-law dependence in the 3-50 cycles/day intrinsic frequency range.
• The modal temperature was found to be higher (0.77 K average in the tropics) than currently used in gravity wave parameterizations.
• Highest amplitude waves were observed over mountainous regions, tropics, and high southern latitudes, with minimal height variation.

Conclusions:

• The study provides valuable empirical data on gravity wave characteristics in the lower stratosphere.
• Findings suggest a need to update gravity wave parameterizations in atmospheric models.
• Results are consistent with previous, more limited super-pressure balloon studies.