A Numerical Study of the Formation and the Dissipation of Radiation Fogs

Abstract

The evolution of radiation fog has been investigated by numerical simulations. A onedimensional boundary layer model was adopted for the atmosphere.No moisture transport in the soil layer was assumed; the dew and falling droplets are assumed to be stored at the ground surface.The P3-approximation method was employed to incorporate the effect of radiative transfer into the boundary layer model.With the development of radiation fog, the radiative cooling rate increases greatly and temperature decreases rapidly just below the fog top. This effect accelerates the condensation of water vapor near the fog top and, consequently, increases the height and liquid water content of the fog. The sudden increase of downward radiative flux from the fog layer enhances the rise of surface temperature, and the temperature profile in the fog layer turns from stable into unstable.With the increase of instability of temperature stratification in the fog layer, eddy diffusivities also increase rapidly. This effect enhances the transport of water vapor from the surface to the fog layer, and the development of the fog is again accelerated.In contrast to that within the fog layer, the temperature profile above the fog layer remains stable; consequently a sharp temperature inversion appears near the fog top. The height of this inversion rises gradually as the height of the fog top increases. When the moisture stored on the ground surface is exhausted and the transport of water vapor from the surface to the fog layer vanishes, the surface temperature rises suddenly and fog begins to disappear from the lowest layer near the ground.

Numerical simulations of upslope fog observed at Beppu Bay in Oita Prefecture, Japan

“…A vertical‐growing fog such as radiation fog often produces a linear increase in the fog water content and the abrupt decrease at the fog top with height (Bergot & Guedalia, 1994; Boutle et al, 2018; Koračhin et al, 2005; Nakanishi, 2000). The fog life cycle is affected by the heat budget in the entire layer, such as the radiative cooling of the fog top, downward longwave radiation emitted from the fog droplets, and turbulent effects (Nakanishi, 2000; Ohta & Tanaka, 1986; Wilson & Fovell, 2018; Yang et al, 2018). Further studies should investigate the role of the interaction between radiation and turbulence in upslope fog life cycle.…”

“…Numerous observational and experimental studies have been conducted on radiation fog (e.g. Bari et al, 2015; Bergot & Guedalia, 1994; Duanyang et al, 2011; Mason, 1982; Meyer & Lala, 1990; Nakanishi, 2000; Ohta & Tanaka, 1986; Price, 2019; Roach et al, 1976), advection fog (e.g. de Wolf et al, 1999; Fan et al, 2003; Hung & Liaw, 1981; Liu et al, 2016; Pithani et al, 2019; Yang et al, 2018), and steam fog (Heo & Ha, 2010; Khvorostyanov et al, 2003; Magono et al, 1974; Raymond & Schmit, 1989; Saunders, 1964).…”

Phase Function Mean Properties at Visible and Infrared Wavelengths within a Sample of 239 Fog Spectra

“…On the other hand, the great number of processes which control the formation and evolution of a fog gives rise to a great variety of droplet size spectra, and consequently to a great dispersion of the related optical quantities (Pilie et al, 1975), which are thus poorly indicative in practical problems, such as the measurement of transmission in fog (Bruscaglioni et al, 1984), the measurement of scattering with nephelometers (Gazzi et al, 1985), the lidar measurements (Carnuth and Reiter, 1986), the design of new instruments (Gerber, 1984), the definition of the order of magnitude of the quantities entering the radiative transfer equation within the numerc 1992, Meteorological Society of Japan ical fog models (Ohta and Tanaka, 1986). In all these cases the behavior of the mean optical quantities with wavelength, together with the relevant range of variation, within proper fog groups, can be of greater use for locating the limits within which an instrument or a model will operate.…”

Physical and Optical Properties of Fog at 74 Wavelengths from 0.35 to 90μm within a Sample of 239 Spectra

“…Theoretical and computational difficulties make this task so formidable (Brown, 1980;Forkel et al, 1987) that attempts have been made to avoid the determination of a size spectrum through an explicit treatment of the microphysics, as well as the computation of the related quantities. On the one hand, parameterizations of these quantities have been set up and verified (Corradini and Tonna, 1980;Tonna and Valenti, 1983), while, on the other hand, typical spectra and typical values of desired quantities have been determined and used (Deirmendjian, 1969;Tampieri and Tomasi, 1976;Kunkel, 1983;Ohta and Tanaka, 1986).…”