Surface-based remote-sensing of clouds during ASCOS

Arctic clouds continue to confound our understanding of Arctic climate due to their complex interactions with aerosols, the frequent occurrence of liquid and ice together, and the multitude of formation and conversion mechanisms for hydrometeors of both condensed phases. During the late summer of 2008, unique measurements of Arctic cloudiness over the permanent ice pack were made as part of the Arctic Summer Cloud Ocean Study (ASCOS). Measurements from an icebreaker include those from a cloud radar, a precipitation radar, a 449-MHz wind profiler, a dual-channel microwave radiometer, ceilometers, a 60-GHz profiling radiometer, and radiosondes. These complementary measurements are utilized within a cloud retrieval and characterization algorithm that provides information on cloud occurrence and vertical boundaries, cloud phase, microphysical properties, and some in-cloud dynamical properties.

Over the course of the five week ASCOS campaign a variety of cloud conditions occurred including deep frontal systems with heavy snow, complex multi-layered systems, boundary layer fogs, and persistent low-level stratiform mixed-phase clouds. In all, clouds occurred more than 90% of the time. An overview of ASCOS cloud conditions will be given, which includes a full description of the vertical cloud distribution distinguished by cloud phase. In addition basic properties such as total condensed water and ice, hydrometeor characteristic sizes, and precipitation occurrence will be documented. Lastly, in-cloud vertical velocity information will be provided. All of these derived cloud products support detailed studies of the microphysical and dynamical mechanisms that are responsible for maintaining Arctic cloud layers over long periods of time. This comprehensive cloud information will also be used in coordination with detailed observations of aerosol properties made during ASCOS to study aerosol-cloud interactions and their role in the late summer, Arctic Ocean environment.