High small ice concentration in stratiform clouds over Eastern China based on aircraft observations: Habit properties and potential roles of secondary ice production

The microphysical properties of supercooled liquid droplets (SLDs) and ice particles of stratiform mixed-phase clouds over Eastern China are characterized using carefully post-processed airborne data. The majority of sampled clouds were precipitating with ice particles and were frequently mixed with SLDs at cold temperature. While the concentration of large ice crystal (> 600 μm in diameter, the same below) was low (up to 3 L−1), the concentration of smaller ice particle (> 50 μm) was high (up to 300 L−1). Such particles with high concentration cannot be a result of the recirculation of pre-existing aged ice and thus secondary ice production (SIP) was likely occurring over the stratiform clouds at temperatures between −16.9 °C and −6.4 °C. The statistical analyses show that concentrations of tiny, hexagonal and irregular ice crystals were significantly greater in updraft than those in downdraft regions, suggesting that updrafts not only provide a favorable environment for the growth of cloud particles, but also promote the multiplication of the above young-age small ice (50–100 μm) where SIP is commonly occurring. Since the criteria for the other SIP mechanisms are difficult to meet for this light-riming stratiform without deep convections, this analysis indicates that shattering during droplet freezing might thus be an important SIP source at temperatures between −15 °C and −9 °C. This study should provide a precise opportunity for parameterizations of mixed-phase stratiform clouds associated with the SIP processes and effects of updraft and temperature. •The SIP is likely occurring over the stratiform at T between −16.9 °C and −6.4 °C.•The splintering during riming process is not an important SIP in this study.•Concentrations of tiny, hexagonal and irregular ice crystals are significantly greater in updraft regions.•The shattering during droplet freezing process is an important SIP source for the studied stratiform (−15 °C