In this paper, the microphysical relationships of 8 dense fog events collected from a comprehensive fog observation campaign carried out at Pancheng（32.2 N, 118.7 E） in the Nanjing area, China in the winter of 2007 are investigated. Positive correlations are found among key microphysical properties（cloud droplet number concentration, droplet size, spectral standard deviation, and liquid water content） in each case, suggesting that the dominant processes in these fog events are likely droplet nucleation with subsequent condensational growth and/or droplet deactivation via complete evaporation of some droplets. The abrupt broadening of the fog droplet spectra indicates the occurrence of the collision-coalescence processes as well, although not dominating. The combined efects of the dominant processes and collision-coalescence on microphysical relationships are further analyzed by dividing the dataset according to visibility or autoconversion threshold in each case. The result shows that the specific relationships of number concentration to volume-mean radius and spectral standard deviation depend on the competition between the compensation of small droplets due to nucleation-condensation and the loss of small droplets due to collision-coalescence. Generally, positive correlations are found for diferent visibility or autoconversion threshold ranges in most cases, although negative correlations sometimes appear with lower visibility or larger autoconversion threshold. Therefore, the compensation of small droplets is generally stronger than the loss, which is likely related to the sufcient fog condensation nuclei in this polluted area.
Parameterization of entrainment-mixing processes in cumulus clouds is critical to improve cloud parameterization in models,but is still at its infancy.For this purpose,we have lately developed a formulation to represent a microphysical measure defined as homogeneous mixing degree in terms of a dynamical measure defined as transition scale numbers,and demonstrated the formulation with measurements from stratocumulus clouds.Here,we extend the previous work by examining data from observed cumulus clouds and find positive correlations between the homogeneous mixing degree and transition scale numbers.These results are similar to those in the stratocumulus clouds,but proved valid for the first time in observed cumulus clouds.The empirical relationships can be used to parameterize entrainmentmixing processes in two-moment microphysical schemes.Further examined are the effects of secondary mixing events on the relationships between homogeneous mixing degree and transition scale numbers with the explicit mixing parcel model.The secondary mixing events are found to be at least partially responsible for the larger scatter in the above positive correlations based on observations than that in the previous results based on numerical simulations without considering secondary mixing events.
