Quantitative constraints on secondary ice production in stratiform mixed-phase clouds using synergistic lidar-radar observations

Abstract. Secondary ice production (SIP) remains a major source of uncertainty in numerical models, particularly for single-layer, stratiform mixed-phase clouds (MPCs), owing to limited quantitative microphysical observations in nature. These clouds, consisting of a supercooled liquid layer and ice virgae below, provide an ideal natural laboratory for investigating cloud microphysical processes. We analyzed the ice multiplication factor (IMF) from 11 stratiform MPC cases based on lidar-radar synergistic observations and advanced retrieving approach associated. IMF was calculated as the ratio of the ice crystal concentration at 180 m below the base of supercooled liquid layer, to the ice nucleating particle concentration at cloud-top level. Two typical cases with different temperatures in supercooled liquid layer (T_SL) were studied. The first case was relatively warm with T_SL of -6.8 ~ -6.3 °C, showing a relative high IMF of 36.2; while, the second one was colder with T_SL of -10.6 ~ -8.7 °C, exhibiting a much lower IMF of about 3.0. For statistics, the IMF exhibits a distinct temperature dependence, remaining close to 1 when the T_SL is below -8 °C, and increasing to 351.8 as the T_SL approaches -5 °C. Additionally, Stronger SIP was associated with smaller ice particles above -8 °C, with a Pearson correlation coefficient of -0.73 between the IMF and the particle maximum diameter. These findings suggest the Hallett–Mossop process plays a significant role in SIP under relatively warm conditions, providing an invaluable observational constraint for improving SIP representations in numerical weather prediction and global climate models.