Stratiform clouds contribute significantly to spring and fall precipitation over northern China. These clouds are mostly multilayered mixed-phase clouds with various ice crystal habits. The complexity of ice particle habits in natural clouds is related to the variety of temperature and relative humidity and the resultant particle growth modes. Riming—snow growth by the collision of supercooled droplets that subsequently freeze—is significant to both ice particle growth and precipitation formation.

In a recently published study in Advances in Atmospheric Sciences, Dr. HOU Tuanjie and his team from the Institute of Atmospheric Physics, Chinese Academy of Sciences, present in-situ observations of ice particle growth modes and habits in a stratiform cloud case from cloud imaging probes. The aircraft-observed moderate-rimed dendrites and plates, as well as dendrite aggregation and capped columns, suggested that aggregation coexisted with riming and played an important role in producing many large particles.

Clouds consisting of altocumulus (classified as middle clouds between 2 and 6 km) and stratocumulus (classified as low clouds at heights below 2 km). (Image by HOU Tuanjie)

The team investigated the ability of two microphysical schemes in the Weather Research and Forecasting model to simulate the stratiform rainfall event, and examined the underlying factors responsible for the precipitation differences by analyzing hydrometeor mass contents, ice particle riming degree, and fall speeds. An analysis of the surface precipitation temporal evolution indicated faster precipitation in the Morrison scheme, while the Predicted Particle Properties (P3) scheme indicated slower rainfall by shifting the precipitation pattern eastward toward what was observed. P3 simulated the stratiform precipitation event better as it captured the gradual transition in the mass-weighted fall speeds and densities from unrimed to rimed particles. 

Citation: Hou, T. J., H. C. Lei, Z. X. Hu, J. F. Yang, and X. Y. Li, 2020: Simulations of microphysics and precipitation in a stratiform cloud case over northern China: Comparison of two microphysics schemes. Adv. Atmos. Sci., 37(1), 117-129, https://doi.org/10.1007/s00376-019-8257-0.

Media contact: Ms. LIN Zheng, jennylin@mail.iap.ac.cn