long-term statistics of arctic stratiform mixed-phase cloud properties based on radar observation

Mixed-phase stratiform clouds have strong impacts on the surface radiative flux budget in the Arctic region due to their frequent occurrence, large coverage and long life time. Getting the phase partitioning in mixed-phase clouds correct is important if models are to accurately represent the Arctic environment and their role in climate change. Currently most models tend to under-predict liquid amounts at the cold Arctic temperatures because they typically prescribe the liquid fraction based on the temperature profile. In order to improve the parameterization of phase partitioning, more parameters, including vertical air motion, should be considered

In this study, we use a month's data from the DOE-ARM KAZR profiling radar (Ka-band ARM Zenith Radar) together with other ground-based observational data to construct long-term statistics of cloud properties and their relationships with vertical air motion. The cloud properties considered, including cloud boundary, temperature, and liquid water path (LWPs) are retrieved directly from the ground-based measurements. Microphysical characteristics of these mixed-phase clouds, including liquid/ice reflectivities, vertical air motion, reflectivity-weighted mean fall speeds are extract from radar Doppler spectra based on a newly developed spectrum deconvolution algorithm. Separate statistics of the cloud microphysical properties are presented for up- and downdraft structures.

A total of 185 hours of stratiform mixed-phase clouds are classified into two types, warm- and cold-base clouds dependent on cloud layer temperature (higher or lower than -10 ºC). Both liquid drops and ice particles grow in the cold cloud updrafts where larger size ice particles are produced. Most ice particles fall from the cloud layer in the updrafts. The liquid evaporates in the downdrafts but the ice particles may still grow, even though the total ice reflectivity is less than in the updrafts. The warmer clouds tend to be shallower with weaker draft structures and lower reflectivities. As in the colder clouds, precipitation particles preferentially grew in the warm cloud updrafts, where the median reflectivity value is ~-28 dBZ and the reflectivity-weighted fall speeds 0.5 m/s. These results suggest that drizzle is the dominant precipitation from in these warmer clouds.