Characteristics of Internal Inertial Gravity Waves and Inertial Waves in the Lower Stratosphere Observed by the MU Radar

Abstract

The MU radar observations were carried out for continuous five days each in September 1985 and1986 to reveal characteristics of internal gravity waves in the upper troposphere and lower stratosphere. Hodograph analysis and rotary spectral analyses in the vertical direction and time series of the data lead to the following results; (i) Upward propagating and saturating internal inertial gravity waves (IIGWs) are evidently observed through out all the observations in the lower region of the stratosphere lying above the tropopause. The waves are quasi-monochromatic, and representative wave parameters are a horizontal scale of 200 km (ranging from 110 to 330 km), a vertical wavelength of 1 to 2.5 km, a wave amplitude of several ms -1, and a horizontal phase velocity of 3 ms -1. The vertical wavelength and wave amplitude decrease with increasing height and the waves disappear in the vicinity of the Jones' critical level around 19 km. (ii) Another kind of upward-propagating inertial gravity wave, an inertial wave whose period is very close to inertial period is observed at the zonal mean wind turning level, separately from IIGWs just above the tropopause. The horizontal and vertical wavelengths of the wave are about 1000 km and 2 km, respectively, and the wave amplitude about 3 ms-1.We discuss propagation and origin of IIGWs and the inertial wave based on the wave parameters obtained from analyses. From an estimation of the group velocity of IIGWs, it is indicated that IIGWs are advected by the zonal mean wind and then the observed waves around a height of 17 km at the MU radar site (34*51' N, 136*06' E) are likely to have originated more than 1000 km west of the site. Ray tracing of the wave packet on a meridional plane shows that the inertial wave may have been propagated from the tropical upper troposphere over a period of about a week.

Wave focusing and ensuing mean flow due to symmetry breaking in rotating fluids

“…The final approach to the bottom agrees with observed, predominantly downward inertial wave energy propagation, close to the inertial latitude (Leaman & Sanford 1975;d'Asaro & Perkins 1984). Significantly, inertial oscillations have been observed in the stably stratified, lower stratosphere (Thompson 1978;Ushimara & Tanaka 1990;Hu & Holzworth 1997), while they are inconspicuous in the much weaker stratified troposphere (Holton 1979), in agreement with the fact that the homogeneous spherical shell lacks such a trap.…”

“…Their behaviour and fate is relevant to all rotating fluids occurring in nature or industry, particularly, as shown in the experiment here, when through mixing they affect the wave's medium. Examples include stars (Gough & McIntyre 1998), planetary atmospheres (Bjerknes et al 1933;Ushimara & Tanaka 1990), planetary cores (Aldridge & Lumb 1987;Olson & Aurnou 1999), oceans and lakes (LeBlond & Mysak 1978) and fluid-filled spinning spacecraft (Manasseh 1992).…”