Quantifying the dust impacts on the ice generation in supercooled stratiform clouds

 
Poster PDF

Authors

Zhien Wang — University of Colorado
Damao Zhang — Pacific Northwest National Laboratory
Ming Zhao — National Oceanic and Atmospheric Administration
Andrew Heymsfield — National Center for Atmospheric Research (NCAR)

Category

Aerosol-Cloud-Radiation Interactions

Description

Dust particles are known as one main source of ice nuclei (IN). However, there are large uncertainties in the effectiveness of dust particles as IN. In this study, we combine ground-based and satellite active remote sensing to evaluate dust impacts on ice generation in supercooled stratiform clouds. Multi-year ground-based observations at Barrow, Alaska, show that springtime arctic stratiform mixed-phase clouds are often influenced by long-range transport of Asian dust. When cloud-top temperature is colder than -15°C, this seasonal dust influence results in significantly lower liquid mass partitions than the other seasons in the mixed-phase clouds. Four years of collocated Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) and CloudSat measurements are used to find mid-level stratiform clouds embedded in dust layers. Results showed that ~98% dusty mid-level stratiform clouds are in mixed-phase at cloud-top temperature around -15°C, while the non-dusty similar clouds in the same geographical region only reach this magnitude of mixed-phase occurrence until ~-30°C. To quantitatively evaluate the impacts of dust particles on the ice generation, we explored the relationship of ice number concentration and layer maximum radar reflectivity with in situ measurements, 1D ice particle growth models, and 3D cloud resolving model simulations. Results indicated that ice crystal number concentration in mixed-phase stratiform clouds can be estimated from CloudSat and CALIPSO measurements within uncertainties of about a factor of 2 statistically. By comparing estimated ice concentrations in the dusty and non-dusty stratiform clouds, it was found that dust can enhance ice number concentrations in stratiform mixed-phase clouds at a given temperature by a factor of 2 to 5, and the dust ice enhancement is strongly a function of dust concentration and mineralogical composition. The fraction of dust activated as IN is also estimated from CloudSat and CALIPSO measurements and compared with laboratory and modeling results. Although there are inherent uncertainties in the remote sensing approaches, it provides a much-needed global view on dust impacts on the ice generation.