The Effect of the Horizontal Component of the Angular Velocity of the Earth's Rotation on Inertia-Gravity Waves

Journal of the Meteorological Society of Japan. Ser. II

Kaoru SATO¹  Yuki YASUDA¹ 

[1] Department of Earth and Planetary Science, The University of Tokyo

关键词: inertia-gravity wave;    traditional approximation;    angular velocity of the Earth's rotation;    tropopause;    hodograph;    form stress;   

DOI  :  10.2151/jmsj.2013-102

学科分类：大气科学

来源: Meteorological Society of Japan

【 摘 要 】

 By using a linearized Boussinesq model on the tangent plane in the mid-latitudes, how the effect of the horizontal component of the angular velocity of the Earth's rotation (fH-effect) modifies the characteristics of inertia-gravity waves is examined. The fH-effect widens the range of the intrinsic wave frequency. A physical interpretation of this modification is made in terms of restoring forces. There are cases in which the rotational direction of the hodograph with time is anticlockwise (clockwise) even in the Northern (Southern) Hemisphere, unlike the case of fH = 0. Considering the form stress over the potential temperature surface, the sign of the vertical group velocity can be the same as that of the vertical phase speed, unlike the case of fH = 0, because the fH-effect can reverse the direction of the form stress through the vertical force balance. The minimum frequency increases with the buoyancy frequency (N) for fH ≠ 0, when the latitude and the direction of the wavevector are fixed. This fact indicates that waves trapped in a weakly stratified layer (WSL) exist, where N is low. Using an idealized vertical profile of N in the form of a square well, the trapped wave solution is derived. The solution is composed of two plane waves in the WSL, while it decays exponentially outside. Using operational radiosonde data in Japan, it is shown that there is a persistent WSL slightly below the tropopause where the climatological minimum value of N (Nmin) is about a half times lower than the typical tropospheric value (~0.01 s−1). The Nmin value is not sufficiently small to form trapped waves having wavelengths in a realistic range within a few days, because the condition of Nmin < 0.001 s−1 is necessary. Thus, such trapped waves are rarely observed in the WSL slightly below the tropopause.

【 授权许可】

Unknown