CHARACTERISTICS OF STABILITY PARAMETER OBSERVED AT 1.1M ABOVE THE GROUND

Abstract

In this paper, the author intended to make clear the dependences of wind speed (U) and net radiation (Rn) above the bare ground on stability parameter measured by sonic anemometer thermometer. As the stability parameter, we take ζ evaluated from z/L, withz=1.1 m. In the calculation of ζ, L is Obukhov's scale height defined by L=_??_. Here, κ(_??_0.40) is von Karman's constant, θ is the absolute temperature, g is the acceleration of gravity, U* is the friction velocity and T, * is the scaling temperature. The following results were obtained. Values of show systematical diurnal change taking positive values at night and negative values at daytime. They correspond to the stable and unstable conditions respectively. Whenζ reverses the sign, the outgoing net radiation is balanced with the incoming. The decrease of log|ζ| with increasingU is occurred by increasing turbulent mixing as shown in Fig. 5-a and Fig. 5-b. The relation between log |ζ|and Rn is approximately linear in the case ofζ 0, namely under the stable condition, as shown in Fig. 6-b, it is expressed by the equation log|ζ|=-0.050Rn-1.096. These relationships mean that the closer Rngets to zero, the smallerlog|ζ|becomes. Un-der the unstable conditions, the ratio of Rn/log|ζ|is remarkably large. The correlation between log|ζ|andRn is larger than that between log |ζ|andU. Under the stable conditions, on the other hand, large correlation is observed between log |ζ| andU as given in Table 2. From the facts described above, it can be concluded that the stability para-meter is estimated from the relationships between U and Rn as shown in Fig. 7. A tentative classification of the relations between U and Rn is given in Fig. 8.