Nanjing University of Information Science Technology
As one of the main processes affecting cloud and fog, entrainment-mixing process has an important impact on the cloud/fog life cycle, precipitation formation, radiative transfer, aerosol indirect effect evaluation and so on. In this study, entrainment-mixing mechanisms in a radiation fog was discussed from the microphysical and dynamical perspectives, which not only improved the theoretical understanding of entrainment-mixing mechanisms, but also revealed the development and dissipation of radiation fog from a new perspective. By using the comprehensive field observational data in Nanjing during the 2006 and 2007 winter, entrainment-mixing mechanisms in nine fog cases were analysed. First, a radiation fog event during 10 - 11 December 2007 was studied to understand microphysical relationships and entrainment-mixing mechanisms during different phases in detail. Results showed that the extreme inhomogeneous entrainment-mixing was found in the mature phase, in which volume-mean radius changed slightly as number concentration and liquid water content decreased. The homogeneous entrainment-mixing was found in the rapid dissipation phase, in which all microphysical properties decreased simultaneously with positive correlations. Except for microphysical properties, the scale number was calculated as a dynamical measure for entrainment-mixing mechanisms. In the mature (rapid dissipation) phase, the scale number was small(large), indicating that the extreme inhomogeneous(homogeneous) entrainment-mixing was most likely to occur. Then the microphysical relationships of the other 8 fog events were examined, which indicated that volume-mean radius had positive correlations with liquid water content in general, i.e., homogeneous entrainment-mixing dominated. The research results were helpful to the development of parameterization schemes of entrainment-mixing mechanisms, and provided reference for the simulation and prediction of radiation fog.