On the Fluctuation of the Temperature and Turbulent Structure near the Ground

[摘要] Vertical flux of heat and momentum in the lowest layer, which are significant quantities in the micrometeorology, are expressed symbolically as ρCp_??_and ρ_??_ respectively, (where u' and w' are fluctuation components of velocity and T' is temperature fluctuation). Lately, due to the progress of instrumentation and calculating machine, the flux has come to be measured in its original form, that is, as the cross-correlation of two fluctuating quantities. In this procedure, it becomes a significant problem to decide the sampling time and time lag of the measuring instrument. To solve the above problem, structures of u'-, w'- and T'-fluctuations are measured and analysed. In the range of small eddies, similarity hypothesis in the locally isotropic turbulence holds well in three fluctuating quantities. The author stresses that sampling time of 1 minute, thougt it seems by far shorter than the ordinarily used one, is sufficient to cover the large eddy which is effective to the gradient diffusion. It is noted that in the large eddy which is effective to the turbulent transfer of heat, the state of turbulence deviates very far from the local isotropy.

[学科分类] 大气科学