Parameterization of radiation fog-top height and methods evaluation in Tianjin

Abstract

Different methods have been developed to estimate the fog-top height of radiation fog and evaluated using the measurements obtained from a 255-m meteorological tower located in Tianjin in 2016. Different indicators of turbulence intensity, friction velocity (u*), turbulence kinetic energy (TKE), and variance of vertical velocity (σw2) were used to estimate the fog-top height, respectively. Positive correlations between the fog-top height and u*, TKE, and σw2 were observed, with empirical parameterization schemes H = 583.35 x u*1.12, H = 205.4 x (TKE)0.68, and H = 420.10 x (σw2)0.51 being obtained. Among them, σw2 is the most appropriate indicators of turbulence intensity to estimate the fog-top height. Compared with sensible flux and condensation rate, the new form of convective velocity scale (σw2) was the most appropriate indicator of buoyancy induced by radiative cooling, and the relationship H = 328.33 x w*1.34 was obtained. σw2 and with w*1.34, which represents the intensity of turbulence and buoyancy, were used to estimate the fog-top height. The relationship H = 396.26 x (σw + 0.1 x w*1.34)-16 was obtained, which can be used to accurately estimate the fog-top height. Moreover, the temperature convergence (TC) method was used to estimate the fog-top height; however, the results strongly rely on the threshold value.