The importance of the ice phase in the atmosphere - for the global water cycle, for chemical processes, for energy exchanges - has been well recognized for many decades. Research to understand the processes involved in how ice forms has been intense, yet the complexity of the problem makes progress slow. Difficulties arise from the many pathways that exist for the nucleation of ice particles, and from the complicated dynamic situations in which those processes are embedded. There are important shortcomings in observations, and also in the theoretical underpinnings of the relevant components of numerical models. The great variety of conditions in which ice particles are formed in tropospheric clouds dictates that observations be collected in a wide range of conditions and that those observations be analyzed to isolate the most likely mechanisms for ice particle formation in the different situations.
The goal of this project is to apply an observational approach to delineating and quantifying ice initiation processes in clouds, and to support analysis of observation with model calculations. Use will be made of observations made with in situ instrumentation, and the Wyoming Cloud Radar, which were mounted on the Wyoming King Air and the NSF/NCAR C-130 research aircraft for a series of field projects over the past decade that, among other activities, included observations in ice-phase and mixed-phase clouds. New observations also will be obtained in the ICE-L field campaign of 2007. Included in these observations will be data from the newly-developed Wyoming Cloud Lidar. This new analysis of past aircraft observations, along with analysis of new observations from ICE-L, will provide much new information on ice initiation. The remote sensing instruments (radar and lidar) on board the aircraft complement the data from the in situ sensors in a very effective way, both with respect to defining the spatial distribution of the concentrations and sizes of hydrometeors, but also for the definition of the dynamic context of the in situ measurements. The cloud types included in the study are wave clouds, mountain cap clouds, and stratiform clouds. Features relevant to the question of ice initiation have been already identified in each of these cloud types and provide the starting points for the work. In addition, there will be a focus on the presence, in the stratiform cloud types, of highly localized sources of ice which exhibit spatial intermittency but temporal continuity.
The research will have the broader impacts of enhancing the involvement in research of participating young scientists and students in work related to ice initiation, under the guidance of a veteran researcher. There will be significant impacts in the continued development of the Wyoming King Air and the Wyoming Cloud Radar, both of which are available to the wider NSF research community via the NSF Atmospheric Sciences Lower Atmospheric Observing Facility.
