Seeded And Natural Orographic Wintertime Clouds: The Idaho Experiment (SNOWIE)
Aikins, Joshua 1 ; Friedrich, Katja 2
1 University of Colorado
2 University of Colorado
SNOWIE (Seeded and Natural Orographic Wintertime Clouds: The Idaho Experiment) was conducted between 7 January and 17 March 2017 in the Payette Basin in west-central Idaho. The overarching goal of SNOWIE is to understand the natural dynamical and microphysical processes by which precipitation forms and evolves within orographic winter storms and to determine the physical processes by which cloud seeding with silver iodide (AgI), either from ground generators or aircraft, impacts the amount and spatial distribution of snow falling across a river basin. This research allowed, for the first time, a quantitative evaluation of the effects of seeding in case studies and over a winter season and a determination of the impact on the water balance within a basin.
Our core scientific objectives are to: (1) Evaluate the role of mesoscale and microscale dynamics and of the underlying terrain in the formation, growth, and fallout of natural ice crystals in winter storms through observations; (2) Investigate how the natural snow growth process is altered as a result of airborne AgI seeding through both observations and model simulations, and (3) Evaluate the effects of ground seeding on snowfall amount and distribution.
Key observational facilities used during the SNOWIE campaign include two Doppler On Wheels (DOW) mobile X-band dual-polarization radars and the University of Wyoming King Air (UWKA) aircraft. The two DOWs were deployed on two mountain-top locations located on the western side of the Payette Basin, which allowed radar observations both upwind (west) and downwind (east) over the Payette Basin. The DOW radar observations allowed dynamical and microphysical processes to be observed in 4-dimensions during intensive observational periods (IOPs). The UWKA provided flight level measurements of basic atmospheric state (pressure, temperature, water vapor, and winds) as well as cloud microphysical measurements, including liquid water content and ice crystal concentrations, that can be used to verify numerical weather model output. The UWKA also carried the W-band Wyoming Cloud Radar (WCR), the Wyoming Cloud Lidar, and a new experimental Ka-band Profiling Radar (KPR). These airborne instruments allowed visualization of cloud and precipitation processes along wind-parallel transects over the Payette Basin.
Preliminary results from the SNOWIE field campaign include the best ever direct evidence of enhanced snowfall initiated from airborne cloud seeding, which was observed by the DOWs and the UWKA. More in-depth research will be performed on these cases in the coming years, but these observations are likely the best available to prove the effectiveness of glaciogenic cloud seeding with AgI.