Microphysical Characteristics of Winter Mixed-Phase Stratiform Clouds and Summer Convective Clouds in the Rocky Mountain Region Based on Airborne Measurements

The microphysical characteristics of mixed-phase stratiform and convective clouds are different but have not been well considered in numerical models, leading to uncertainties in modeling clouds and precipitation. To improve our understanding of the difference in microphysics between mixed-phase stratiform and convective clouds and obtain quantitative results for model evaluation and parameterization, the microphysical characteristics of continental winter mixed-phase 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) projects. The particle images and Particle Size Distributions (PSD) were measured using 2D cloud and 2D precipitation probes, Liquid Water Content (LWC) was measured using the King hot-wire probes, and Ice Water Content (IWC) was calculated based on the particle spectrum. The main findings are as follows: (1) Between −30°C and 0°C, the LWC in summer convective clouds is an order of magnitude higher than that in winter stratiform clouds, and the IWC in summer convective clouds is 1–2 orders of magnitude higher than that in winter stratiform clouds. Supercooled liquid water was observed near the convective cloud top. The LWC in summer convective clouds increases with the decrease in temperature from 0°C to −20°C, while the LWC in winter stratiform clouds decreases with the decrease in temperature. The liquid fraction in summer convective clouds is smaller than that in winter stratiform clouds, indicating rapid ice production. (2) Both winter stratiform and summer convective clouds had large spatial variability in their phase distribution. As the temperature decreased from 0°C to −30°C, ice in winter stratiform clouds grew through the Bergeron process, and the water-dominated zones transformed into the mixed-phase and ice-dominated zones. The phase distribution was complicated in summer convective clouds, indicating a complex 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 decreased, the ice PSDs in both winter stratiform and summer convective clouds broadened. (4) The observed particle images in winter stratiform clouds were irregular at temperatures lower than −20°C. Meanwhile, between −20°C and −10°C, the ice was dendritic and irregular, and at temperatures warmer than −10°C, the ice was mainly needle-shaped, columnar, and irregular, indicating that 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 strong updrafts of summer convective clouds, a high LWC and large liquid fractions were observed. The IWC had no obvious correlation with vertical velocity, indicating that the efficiency of glaciation in HiCu clouds was independent of vertical velocity.