RAL/EOL Seminar- Aviation hazard or precipitation enhancement opportunity? The implications of supercooled liquid water in wintertime clouds

The presence of supercooled liquid water (SLW) in clouds poses a serious threat to aviation due to the potential for aircraft icing. In fact, some wintertime clouds produce supercooled drizzle-size drops, also known as supercooled large drops (SLD), which pose a unique icing hazard for aviation. When clouds contain SLW, it is a sign that ice-phase precipitation formation processes are not efficient, and therefore such clouds might be suitable for potential precipitation enhancement via cloud seeding techniques.   Moreover, for over 60 years, water managers around the world have attempted to use cloud seeding to augment water resources. Yet, despite decades of research, clear evidence of the effectiveness of cloud seeding to enhance precipitation did not exist.

In recent years, new modeling capabilities have improved our ability to simulate orographic precipitation and new model parameterizations have been developed to simulate the physical effects of silver iodide (AgI) seeding.  Recent observational studies from the Seeded and Natural Orographic Wintertime clouds: the Idaho Experiment (SNOWIE) project have collected unprecedented measurements that demonstrate seeding with silver iodide produces ice crystals that grow and fall to the ground as snow. The measurements from SNOWIE provide a rich dataset for studying the impacts of cloud seeding on orographic precipitation, as well as for improving understanding of the natural physics in orographic clouds that influence precipitation formation. For example, how does natural ice form in orographic clouds and how well do we predict clouds with SLD icing conditions?

This seminar will provide highlights of research from SNOWIE that has advanced our understanding of natural and seeded orographic clouds.