Turbulent and Gravity Wave Transport in the Free Atmosphere
Abstract
Turbulent fluxes and related parameters in the free atmosphere are estimated from aircraft data obtained in SESAME and CABLE. Estimated eddy diffusivities and mixing lengths are found to decrease rapidly with increasing gradient Richardson number (Ri) at small Ri, and then decrease more slowly at large Ri. The eddy Prandtl number increases with increasing Ri. This suggests that the generation of TKE by the pressure correlation term becomes more significant as the stability increases. A simple representation of the eddy diffusivities in the free atmosphere is proposed by using an asymptotic mixing length and a nondimensional function of Ri . Tests of this formulation in a column model indicates that nocturnal CAT may become significant near the low level jet above NBL. This constitutes the first systematic study of the residual layer above NBL. The momentum flux by orographic gravity waves and the turbulent heat flux in the wave breaking regions are estimated from aircraft data sets from two days in ALPEX. The calculation of these fluxes allows the first direct comparison between gravity wave momentum transport models and observed fluxes. Toward this goal, the gravitywave stress supersaturation theory by Lindzen (1988) is generalized for the application to verticallyvarying mean flows. The wave momentum flux estimated from the generalized model agrees well with the observations for both the cases with and without a critical level. The wave breaking leads to convectively unstable regions of 1020 km wide where the magnitude of the observed upward turbulent heat flux can be approximated by using the flux gradient relationship in which the mixing length and modified shear are derived from the generalized wave stress supersaturation condition. The effective height (h_{e }) of the surface topography varies substantially between the two days. Our sensitivity tests tentatively suggesth_{e} = { bf min} [ h_0, 0.32 {U_0over N_0}], close to that proposed by Stern and Pierrehumbert (1988), where h_0 is the mountain height, and U_0 and N_0 are the surface wind and stratification.
 Publication:

Ph.D. Thesis
 Pub Date:
 January 1990
 Bibcode:
 1990PhDT.......186K
 Keywords:

 TURBULENT FLUXES;
 WAVE BREAKING;
 Physics: Atmospheric Science