Proceedings with Extended Abstracts (single PDF file) - Radio ...

MU RADAR ESTIMATION OF DOWNWARD TURBULENTOZONE FLUXES NEAR THE TROPOPAUSENikolai M. Gavrilov (1) and Shoichiro Fukao (2)(1) Saint-Petersburg State University, Atmospheric Physics Department, Petrodvorets, St.Petersburg, 198504, Russia, gavrilov@pobox.spbu.ru(2) Kyoto University, Center for Atmospheric and Space Research, Uji, Kyoto 611, Japan,fukao@kurasc.kyoto-u.ac.jp1. IntroductionOne of the important problems is the role of gravity waves and turbulence in diffusion ofozone and gas species in the tropo-stratosphere. It is supposed recently that the mainmechanism of the transport of admixtures influencing the ozone layer between thetroposphere and the stratosphere is the general circulation of the atmosphere creating upwardmotions near equator and downward motions at the middle and high latitudes [Holton, 1990].Alternatively, a sharp change of vertical temperature gradient near the tropopause can make asharp increase in the amplitudes of IGWs propagating upwards from the troposphere. It canlead to IGW breaking and to the generation of increased turbulence, which can make themiddle latitude tropopause more transparent for the diffusive transport of the admixtures frombelow. In this paper, we studied this mechanism of IGW and turbulence influence on theatmospheric admixtures transport through the tropopause using a numerical model, whichdescribes IGW propagation and turbulence generation in the non-homogeneous atmosphere.The numerical model described by Gavrilov and Fukao (1999) is used to study thepropagation of IGW harmonics generated by hydrodynamic sources in the atmosphere. Itgives the integral energy characteristics of a spectrum of IGW harmonics with variousfrequencies, horizontal phase speeds and directions of propagation. The model includes IGWgeneration on the Earth surface and inside the atmosphere, realistic vertical profiles of themean wind and temperature, IGW dissipation, destruction of waves and generation ofturbulence. The results of numerical calculations are compared with the measurements ofparameters of IGWs and turbulence in the tropo-stratosphere with Japanese MU radar.2. Numerical simulation of wave induced turbulent diffusivity near the tropopause.Sharp increase of vertical temperature gradient at the tropopause may lead to a sharpincrease in the amplitudes of IGWs propagating upward from the troposphere. Such IGWsmay break and generate increased turbulence, which may make the middle latitude tropopausemore transparent for the diffusive admixtures transport. Such diffusive admixtures transportmay make an alternative to the traditionally assumed circulation with upward flux ofatmospheric mass from the troposphere to the stratosphere in the equatorial region and itsdownward flux in the middle and high latitudes. In this study, we made evaluations of therelative importance of this mechanism of IGW and turbulence influence on the admixturestransport through the tropopause using a numerical model, which describes the IGWpropagation and turbulence generation in the inhomogeneous atmosphere.The model calculates the integral characteristics of a spectrum of wave harmonics withdifferent frequencies, horizontal phase speeds and directions of propagation. The model isbased on the wave action balance equation for every wave harmonic [see Gavrilov, 1997;Gavrilov and Fukao, 1999]. Calculation of the coefficients of turbulent diffusion produced bybreaking IGWs is made using the model by Gavrilov and Yudin [1992]. Previouslyverifications of the model by Gavrilov and Fukao [1999] showed that the model reproducesthe seasonal cycles of the amplitudes of IGW zonal wind variations having a maximum in234