Quasi-Lagrangian measurements in the lower stratosphere reveal an energy peak associated with near-inertial waves

[1] In March 2001, three superpressure balloons were launched from Kiruna, Sweden (67.9degrees N, 21.1degrees E). The balloons drifted for several weeks in the stratospheric polar vortex at about 19 km. The corresponding trajectories exhibit cycloid-like patterns due to the presence of near-inertial waves. Consistently, it is found that the intrinsic-frequency spectra of the horizontal velocity components are enhanced around the inertial frequency in reference to the generally assumed power-law distribution. A large spectral gap is also found between gravity waves and Rossby waves in the polar stratosphere, in contrast to the continuum found in the equatorial lower stratosphere.