State Water Resources Research Institute Program

Project ID: 2007WY39B
Title: Detecting the Signature of Glaciogenic Cloud Seeding in Orographic Snowstroms in Wyoming Using the Wyoming Cloud Radar
Project Type: Research
Start Date: 3/01/2007
End Date: 2/28/2010
Congressional District: 1
Focus Categories: Water Quantity, Climatological Processes, Hydrology
Keywords: Cloud seeding, Cloud radar, Aircraft measurements, Weather modification
Principal Investigator: Geerts, Bart
Federal Funds: $ 22,173
Non-Federal Matching Funds: $ 123,636
Abstract: Much of Wyoming's water supply originates as winter snow, which mainly falls over the state's mountain ranges. As part of the Wyoming Weather Modification (WWM) initiative, a five-year pilot program funded by the State of Wyoming, efforts are under way to enhance winter snowfall by means of glaciogenic cloud seeding. It has long been known that silver iodide (AgI) crystals act as nuclei on which snow can grow under saturation relative to ice. Until recently no tools have been available to document the spatial structure of snow growth in seeded plumes, and thus, given the high natural variability in snowfall rates, the efficacy of the cloud seeding has been a subject of debate ever since it was first attempted several decades ago.

This proposal calls for the deployment of the University of Wyoming King Air (WKA) aircraft over the mountains of southeastern Wyoming, in coordination with WWM cloud seeding operations, in order to describe cloud-microphysical processes following the injection of AgI ice nuclei into cloud. The key instrument on board the WKA is the Wyoming Cloud Radar (WCR). The WCR is a multi-antenna polarization Doppler mm-wave radar. Millimeter-wave radar technology is rather new and the WCR is rather unique world-wide.

The WCR is ideally suited to detect a cloud seeding signature, to map the impact of cloud seeding within cloud, and to quantify seeding-induced snow growth. The WCR measures the size and motion of scatterers (supercooled water and/or snow) at extremely high spatial resolution. WCR data in a vertical plane above and below the WKA aircraft allow a view of snow growth down to ground level, and an interpretation of the fine-scale cloud structure above and below flight level in the context of flight-level measurements of supercooled water and ice crystal size and concentration. WCR polarization measurements in the horizontal plane can be used to distinguish between supercooled water and snow, as well as between snow habits.

The proposed work has never been done before simply because mm-wave radars did not exist a few decades ago, when intensive cloud seeding research was conducted, and because more recently federal funding for such research has been much reduced.

The proposed field work builds on an identical effort in early 2006, but in unseeded conditions. That pilot work, a collaborative effort with the WWM program and partly funded by a previous WWDC/USGS grant (Snider /Geerts, 2005), has lead to some spectacular findings on the fine-scale structure of orographic flow and on terrain-driven snow generation.

This proposal calls for further collaboration with the coupled airborne and ground-based field work planned under the WWM initiative. The WKA will document the evolution of a region, seeded by the WMI (Weather Modification, Inc) Cheyenne II aircraft, by means of horizontal and vertical WCR slices around the aircraft, and flight-level changes in liquid water content and snow size and mass. Twenty WKA flight hours are requested, in order to examine up to five different snowstorms, under different conditions of upstream stability, wind, and cloud age.

Progress/Completion Report, 2007, PDF
Progress/Completion Report, 2008, PDF
Progress/Completion Report, 2009, PDF

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