Aircraft observed microphysical evolution of ice particles and melting layer in the stratiform clouds on 24 August 2019 over Hebei province, China

Scientific understanding of evolution of microphysical properties of ice particles in the melting layer and below for stratified clouds is of great significance for the development of cloud precipitation parameterization, precipitation forecast and weather modification in China. Based on aircraft observations of stratiform clouds in Hebei province on 24 August 2019, the evolution of microphysical properties of particles in negative temperature cloud layers and below the melting layer are analyzed. The study shows that ice particles in the negative temperature layer in the cloud are mainly aggregates, and graupel particles exist in some areas. In the melting layer, the concentration of medium sized particles (600—1500 μm) increases, indicating that the melting rates of ice phase particles with different sizes are different. It is found that the melting rate of particles in the region of high relative humidity (RH≥95%) is faster than that in the region of low relative humidity (RH＜95%). In the region of low relative humidity, surface melting on particles leads to evaporation and latent heat absorption, which reduce ambient temperature and slow down the melting rate of particles. The intercept of precipitation particle spectrum distribution in the melting layer of high relative humidity area is larger than that in the low relative humidity area and the slope is similar to that in the low relative humidity area. It is found that the intercept and slope of the negative exponential spectrum distribution of precipitation particles in the melting layer are greater than those in the negative temperature layer. The particle spectrum distribution parameter N_0 detected by HVPS below 0℃ layer is positively correlated with λ, and the linear function can better fit the relationship between them. For precipitation particles whose D_\mathrmm\mathrma\mathrmx is Larger than 1000 μm, λ is negatively correlated with D_\mathrmm\mathrma\mathrmx , and the power function can fit their relationship well. Numerical simulation results show that there are mixed phase particles in the cloud below the 0℃ layer, and observations and simulations show that the medium particle number concentration is higher below the 0℃ layer. The intercept of precipitation particle mean spectrum in the classification scheme is consistent with observations, but the slope is greater than the observed result. In this work, the microphysical characteristics of particles in the melting layer in the cloud have been more deeply understood by combining aircraft observations and model simulations.