Nanjing University of Information Science & Technology
Microphysical characteristics in mixed-phase stratiform and convective clouds are very different, but have not been well considered in numerical models. This is one of the sources leading to uncertainties in modelling clouds and precipitation. In order to improve our understanding on the difference in microphysics between mixed-phase stratiform and convective clouds, and to provide quantitative results for model evaluation and parameterization, The microphysical characteristics of continental mixed-phase winter stratiform and summer convective clouds in the mid-Rocky Mountain region are compared using data collected during the Ice in Clouds Experiment—Layer Clouds (ICE-L) and the High Plain Cumulus (HiCu) project. The particle images and particle size distributions (PSD) were measured using 2D-Cloud and 2D-Precipitation probes, the liquid water content (LWC) was measured using the King hot-wire probes, and the ice water content (IWC) is calculated based on the particle spectrum. The main findings are: (1) Between -30° and 0°C, the LWC in the summer convective clouds is an order of magnitude higher than that of the winter stratiform clouds, and the IWC in the summer convective cloud is 1-2 orders of magnitude higher. More supercooled liquid water was observed near the convective cloud top. The LWC in summer convective clouds increases with decreasing temperature from 0°C to -20°C, while the LWC in winter stratiform clouds varied in an opposite way. The liquid fraction in the summer convective clouds is smaller than that of the winter stratiform clouds, suggesting more rapid ice production. (2) Both the winter stratiform and summer convective clouds had large spatial variability in their phase distribution. As the temperature decreases from 0°C to -30°C, ice in the winter stratiform clouds grew through the Bergeron process, and the water-dominated zones transform to the mixed-phase and ice-dominated zones. The phase distribution was more complicated in summer convective clouds, suggesting complicated liquid-ice interaction. (3) The ice PSD in summer convective clouds was broader than that in winter stratiform clouds between 0°C and -30°C. As the temperature decreases, the ice PSDs in both winter stratiform clouds and summer convective clouds broadened. (4) The observed particle images in winter stratiform clouds were irregular at temperatures lower than -20°C, while between -20~-10°C the ice were dendrites and irregular, and at temperatures warmer than -10°C the ice were mainly needles, columns and irregular, indicating the ice grew through vapor diffusion and coalescence in winter stratiform clouds. In summer convective clouds, the ice mainly formed through drop freezing, riming and coalescence. (5) In stronger updrafts of summer convective clouds, higher LWC and liquid fraction were observed. The IWC had no obvious correlation with vertical velocity, indicating the efficiency of glaciation in HiCu clouds was not dependent on vertical velocity.