The Observation of Ice-Nucleating Particles Active at Temperatures above–15°C and Its Implication on Ice Formation in Clouds

A series of measurements of ice-nucleating particles (INPs) were performed at two sites in Beijing. At the Beijing Meteorological Service (BMS) site, which was an urban site, no INPs were found to be active above–15°C. However, at the Yanjiaping (YJP) site, which was a rural site, the concentration of INPs active at temperatures above–15°C was found to be as high as 1.73 g–1. Two parameterizations were constructed by respectively fitting the data obtained at BMS site and YJP site. The two parameterizations, as well as another parameterization from the literature, were implemented into a parcel model to investigate the effect of INPs active above–15°C on phase partitioning in mixed-phase clouds. At a vertical velocity of 0.01 m s–1, which is typical for stratiform clouds associated with frontal systems, the INPs active above–15°C nucleate ice crystals at low levels. The growth of these ice crystals remarkably reduces both the maximum liquid water mixing ratio and the altitude where the maximum liquid water mixing ratio is reached. When the vertical velocity of the parcel is increased to 0.1 m s–1 or an even higher value, the evolution of liquid water mixing ratio is not controlled by the INPs active above–15°C but those active below–15°C.