, Volume 94, Issue 3, pp 461-493

Large-Eddy Simulation Of Radiation Fog

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Abstract

In order to study the three-dimensional structure of radiation fogand to obtain a basic understanding of its generation mechanism,a numerical experiment is performed with a large-eddysimulation model and compared with the observation at Cabauw in the Netherlands. After confirming that the results are insatisfactory agreement with the observations, the structure of thefog and its generation mechanism are examined in more detail.

Before the fog forms, the atmosphere is stable and an inversionlayer exists almost adjacent to the ground surface. As the fog grows, however, the stratification is destabilized and a mixed layerdevelops gradually. The longwave radiative cooling near thefog top contributes to the destabilization more than thecondensational heating does.

The evolution of the fog can be classified into three stagesaccording to the behaviour of turbulent kinetic energy (TKE):formation, development, and dissipation stages.The fog layer has different flow structures at each stage.During the formation stage, longitudinal rolls similar tostreaks in channel flows appear near the ground surface.The development stage is characterized by an initiation oftransverse bands due to Kelvin–Helmholtz instability anda sudden increase of TKE. During the dissipation stage, longitudinalrolls and polygonal cells due to convective instability are organized.