| We carried out an experiment to analyze the QBO observed in the tropical
stratosphere. The QBO-like flow oscillation is visualized along with the gravity wave that
causes the oscillation. The gravity wave is visualized by the moíre method. By
WKB approximation, propagation of the internal gravity wave was calculated using the mean
flow obtained experimentally, and was compared to that observed in the experiment. The
patterns of the internal gravity wave agreed fairly well with each other. Also, the
estimated momentum flux convergence agrees with the acceleration of the mean flow. These
results show the validity of the WKB approximation, even in cases where the structure of
the mean flow is relatively small compared to the wavelength. |