Structure of the Atmospheric Boundary Layer Derived from Airborne Measurements of the Energy Dissipation Rate

[摘要] To clarify the structure of the atmospheric boundary layer, airborne measurements were carried out above the Kanto Plain in the vicinity of Tokyo, in March and August, 1972. We analised characteristics of the atmospheric boundary layer, using the rate of turbulent energy dissipation ε, which can be calculated from the isotropic region of the power spectrum, where an airplane can be regarded as a fixed platform. We define Hε, which is the height where ε decreases rapidly, as a thickness of the atmospheric boundary layer. Hε in many cases coinsides with the base height of inversion layer Hi during daylight measurements. Hε from sunrise to about 1500 hrs can be described as a function of the root of an integral quantity of insolation, which shows Hε is strongly correlated with the heat flux from the ground. We clarified relations between vertical temperature profiles and characteristics of turbulance. In the atmospheric boundary layer up to Hε or Hi, temperature profiles show nearly neutral stratification, even when a free convection is predominant. However profiles of ε show the difference between a free convection case (AA (strong), A (moderate)), and a forced convection case (B). In case AA and A, ε is nearly constant up to Hε (averaging ε∼z-(1/3-5); z, height) and it is independent of wind velocity U. On the other hand in case B, ε decreases with height linealy, and proportional to U3. R.M.S, of vertical turbulence σω is proportional to ε1/3 in both case AA (including A) and case B. The profiles of the eddy coefficient Kz obtained by Hanna's equation show that in case AA and A, Kz is almost constant up to Hε, in case B, Kz has its peak at some level.

[学科分类] 大气科学