Observations Pertaining to Ice Production in Natural and Seeded Wintertime Orographic Clouds (Invited Presentation)

The overarching goal of the Seeded and Natural Orographic Wintertime clouds-the Idaho Experiment (SNOWIE) project is to gain an improved understanding of the key natural dynamical and microphysical processes within orographic winter storms and to identify the physical processes by which cloud seeding with silver Iodide (AgI) may impact natural cloud evolution and precipitation development. The SNOWIE data set provides a unique opportunity to directly observe the impact of increased aerosol loading, specifically with well-characterized INPs, on the microphysical evolution of mixed-phase clouds.

We examine several cases from SNOWIE, comparing and contrasting the microphysical characteristics of perturbed and natural clouds that evolve in identical environments. Our analyses rely on detailed in situ observations of hydrometeor size, concentration, and phase partitioning, collected onboard the University of Wyoming King Air (UWKA) during repeated passes through cloud. The in situ observations are augmented with vertical profiles from an airborne high-resolution W-band cloud radar (WCR) and a polarization backscatter cloud lidar (WCL) on the UWKA. The analysis will show that in many cases, the addition of AgI as a highly active INP at modestly warm temperatures dramatically increases production of ice beyond the natural state of the cloud and rapidly transitions super-cooled liquid into ice through both riming/accretion and the Findeisen-Bergeron process. Which process dominates appears to depend on many factors including the initial natural state of the cloud and the condensate supply rate after ice has been initiated. We also will demonstrate that the amount of natural ice present limits the ability to detect a change in cloud microphysical characteristic, if such a change even exists. Lastly, we explore the conditions by which natural clouds may be more or less susceptible to modification through the addition of INPs. This work has implications leading to a greater understanding of aerosol loading for both intentionally and unintentionally modified clouds.