Heterogeneous Nucleation of Midlevel Cloud Layer Influenced by Transported Asian Dust Over Wuhan (30.5°N, 114.4°E), China

Midlevel cloud layers (2-7 km) pertinent to transported Asian dust layers were observed on 26 occasions from the polarization lidar measurements during the period from December 2012 to December 2013 over Wuhan (30.5 degrees N, 114.4 degrees E), China. The events mainly occurred in winter. Cloud layers were mostly detected (19 out of 26) on top of the aloft Asian dust layers. The boundary between cloud layer and dust layer appeared at altitudes of 4-7 km. The observed events are classified into three categories: (1) category A (6 cases), supercooled liquid cloud layers persistently existed without an evident sign of freezing; (2) category B (9 cases), supercooled liquid cloud appeared initially and then ice crystals formed on the boundary between the cloud layer and dust layer; (3) category C (11 cases), only a cloud containing ice crystals was present throughout while the pure liquid stage did not present previously, indicating that deposition nucleation might take place. Cloud top temperatures (CTTs) for heterogeneous ice formation ranged from -38.5 degrees C to -18.3 degrees C; no ice formation occurred with CTT warmer than -15 degrees C. After thousands of kilometers transport, ice nucleation efficiency of Asian dust over Wuhan substantially did not present a distinct change compared with that of pure dust. Key Points Heterogeneous nucleation of midlevel cloud pertinent to transported Asian dust frequently occur in winter over Wuhan Cloud top temperatures for dust-related heterogeneous ice formation range from -38.5 degrees C to -18.3 degrees C Ice nucleation efficiency of transported Asian dust over Wuhan is substantially similar to that of pure dust