In March 2001, three superpressure balloons were launched from Kiruna, Sweden (67.9°N, 21.1°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.