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

Abstract

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.