Precipitation field experiment underway in western NC

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Mike Moss

NASA, NOAA and Duke University got started last week on a sizable field experiment over an area just to our west that covers parts of four states, mainly comprising the central and southern mountains, foothills and western Piedmont.

The project is called the Integrated Precipitation and Hydrology Experiment, or IPHEx, and is focused on measuring the amounts and distribution of precipitation in those areas of rugged topography in much greater detail than is routinely available, using the enhanced data to provide "ground truth" to validate observations from a new satellite, and tying all that data to more detailed hydrological measurements (streamflows, lake levels, water supplies, etc).

The program got going on May 1 and will continue into mid June. The overall idea is to improve greatly on the typical measurements of rainfall that come from gauges at airports and cooperative observing sites, along with estimates from operation NWS Doppler radars. These resources do a pretty good job overall, but do have limitations in mountainous or near-mountainous terrain, since the topography helps induce large local variations, measurement sites are limited due to difficult access in many areas, and the uneven terrain can result in blocking of the routine radar measurements.

To shore things up, the research teams have added more rain gauges and stream gauges, along with instruments to measure rainfall drop-size distributions. They are also bringing in at least three additional radar units to supplement coverage in the area, all of which use dual polarization (like our Dual Doppler 5000) and one of which includes dual-frequency technology to improve characterization of precipitation measurements.

They'll also bring in two airborne platforms, a NASA ER-2 (adapted from the U-2 spy plane) to measure precipitation below from an altitude of about 65,000 feet, and a Citation jet from the University of North Dakota that will fly through the clouds to make microphysical measurements of raindrops, ice crystals and other particles involved in the process.

A part of the reason for all this is to help verify and validate measurements from a recently launched satellite mission called the Global Precipitation Measurement (GPM) Core Observatory that will form a key foundation for a network of precipitation measuring satellites from the U.S., Japan, France, India, and European Union.

In addition, the data will hopefully result in increased ability to forecast and measure precipitation over rough terrain, and to increase the reliability and accuracy of hydrologic models and methodology used to translate expected or observed rainfall amounts in regards to their impacts, whether economic in terms of agriculture and water supply, or as regards safety in the way of river or flash flooding (we've had some in our area lately) or landslides (tragic examples in the news recently from Oso, Washington and Ab Barak, Afghanistan).

Of course, it takes time for these kind of campaigns to progress from data collection and reduction, to analysis and research, and finally into improved operational products and techniques, but this project looks like one that should be a good foundation for those kinds of effort for years to come.

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