The role of turbulent heat flows of the atmospheric boundary layer in the formation of radiation fogs
Abstract
Introduction. The article presents an approach to forecasting the evolution of radiation fog by determining the turbulent heat fluxes in the fog formation layer. Utilizing high temporal resolution data from atmospheric radio sondes at Lindenberg station, a database of radiation fog cases has been established. Based on the frequency of different types of stratification of the atmospheric boundary layer, it has been found that the formation of radiation fog is associated with the development of a near-surface inversion layer, where the upper boundary fluctuates between 200 and 800 meters.
The aim of the study. The purpose of the work is to determine the role of turbulent heat flows in the boundary layer of the atmosphere in the formation of radiation fogs and their influence on the temporal evolution of fogs in order to evaluate the use of their characteristics as a prognostic criterion.
Relevance of the research. Stems from the need to develop new effective approaches to fog forecasting at the local level, using highly informative predictors available in operational practice with further integration of the resulting techniques into specialized platforms. In addition to the already worked out predictors (synoptic situation, cloudiness, wind, humidity), the formation and evolution of radiation fogs are influenced by turbulent flows of heat and moisture in the boundary layer of the atmosphere, which are a relatively little-studied but important factor in improving the effectiveness of their forecasting
Analysis of recent research and publications. The forecast for the formation of radiation fog typically involves comparing the minimum air temperature with the temperature needed for fog formation. While the forecast for the former is generally well-developed, challenges in predicting the latter primarily stem from the need to determine the additional decrease in temperature (after it reaches the dew point temperature around sunset) that is necessary for the condensation of a specific amount of water per unit volume of air, which will ensure that the critical value of horizontal visibility is achieved.
Highlighting previously unsolved problems. Thus, the specified criterion likely enables the forecasting of fog evolution, as visibility fluctuations within it are associated with the vertical restructuring of temperature-humidity stratification. Prior to the formation of fog and at the beginning of its existence, condition (2) is satisfied, leading to the development of a surface inversion, a deterioration of visibility near the ground, and, at the same time, a reduction in the effective radiation of the underlying surface.
Results and discussion. The choice of the procedure for calculating the turbulence coefficient for fog cases should consider the characteristics of the synoptic situations favorable for their formation and the temperature stratification in the atmospheric boundary layer. Determining the turbulence coefficient for cases of radiation fog formation should ideally be conducted for a layer whose thickness encompasses the entire near-surface stabilizing layer (excluding the surface layer). The criterion for determining its upper boundary is proposed to be the averaged values of the upper limits of the stabilizing layers in the presence of radiation fogs.
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