Ice Nuclei Samples on Filters: A New Technique for Analysis

As children, we lie in fields and stare at the clouds for hours, their form, the shapes they make, and the way they seem to play with the light in the sky are fascinating to us. However, despite of our early fascination with clouds, we know surprisingly little about clouds and cloud processes. This paper outlines a technique developed to look at the formation of ice in clouds as part of a larger effort to understand more about clouds and their role in the atmosphere. This work is still in the early stages of development, however preliminary results obtained thus far seem to reflect our current understanding of ice formation in clouds accurately. Introduction The attempt to understand climate and create General Circulation Models (GCMs) as a tool to predicting future states of the climate has generated a need for a better and more thorough understanding of many atmospheric processes. Within this context, the formation of ice crystals in clouds has proven to be one of the most difficult problems to surmount. Generally speaking, modeling the formation of ice in clouds has been difficult because the process by which ice forms in clouds is sensitive to temporal and spatial variations by a factor of 100 or 1000, making cloud ice formation difficult to generalize and difficult to model in the lab. A large portion of what makes understanding ice formation difficult is that the commonly held notion that pure freezes as 0° C is incomplete. Thermodynamics revels that because it is energetically unfavorable for ice crystals to form at warmer temperatures, homogenous (pure) water will not freeze until it reaches ~-40°C. However, in heterogeneous (impure) systems, which we more commonly observe, non-H2O materials can provide a substrate, or nucleus, on which water molecules can collect to form an ice-like aggregate. When these aggregates come into contact with any water that is below 0° C, they can act as a seed which causes the water to freeze. Because water is brought into clouds as a vapor, it is exceptionally homogenous. However, if the ice in clouds were homogenous, we would only expect to only find ice at temperatures around -40° C. However, experiments looking at the actual concentration of ice in clouds with respect to temperature