NOAA 2003-019
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NOAA News Releases 2003
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A research instrument the size of a 27-inch television set that is carried aboard NOAA Hurricane Hunter aircraft has been determined to be the most accurate and reliable remote sensing device available for measuring hurricane force winds at the sea surface. The results come from a study by scientists from the Commerce Department’s National Oceanic and Atmospheric Administration (NOAA) and the University of Miami’s Cooperative Institute for Marine and Atmospheric Sciences.

Eric Uhlhorn of the University of Miami’s Cooperative Institute for Marine and Atmospheric Sciences, one of NOAA’s 11 joint and cooperative institutes, and Peter Black with NOAA’s Hurricane Research Division, have determined that the stepped-frequency microwave radiometer (SFMR), an instrument carried on NOAA hurricane hunters, is a top performer in measuring hurricane force winds at the sea surface.

It is the surface winds that impact coastal areas when hurricanes make landfall and one of the most important pieces of information gathered for hurricane forecasters and the emergency response community.

The study, published in the January 2003 issue of the Journal of Atmospheric and Oceanic Technology, determined that surface winds measured by the SFMR are comparable to the Global Positioning Systems (GPS) dropwindsonde measurements that are the current standard. GPS dropwindsondes are instrument packages designed to measure wind speed, temperature and humidity as they drop from the aircraft to the surface.

The benefit of the SFMR is that winds are continuously measured during research flights, allowing for more complete mapping of hurricane surface wind structure.

”The SFMR has been previously used as a research tool. With this new validation of its accuracy, it can now be used as a primary tool for measuring hurricane winds directly below the airplanes,” said Peter Black, co-author of the paper.

The SFMR data are incorporated in near-real time with other observations into a hurricane windfield map called H*Wind. H*Wind maps out the wind speeds in different regions of a storm.

"The SFMR appears to be an outstanding new instrument that will help hurricane forecasters estimate the radius of tropical storm and hurricane force winds as well as better estimate the maximum sustained surface winds in tropical cyclones. We are eager to see this instrument installed on hurricane reconnaissance aircraft," said Max Mayfield, director of the National Hurricane Center.

Scientists at the University of Massachusetts conceived and built the original SFMR. NOAA first tested the SFMR on research aircraft in 1980 during Hurricane Allen. After initial success, updated models have been used continuously on NOAA research aircraft since 1985.

NOAA’s Hurricane Research Division and the University of Massachusetts each operate an SFMR attached to the fuselage of NOAA’s two WP-3D Orion hurricane hunter aircraft. NOAA’s Office of the Federal Coordinator for Meteorology is in the process of funding an additional newly redesigned SFMR to be located under the wing of one NOAA WP-3D.

The SFMR allows for improvement in surface wind studies as it takes continuous measurements of surface winds, as compared to single point measurements from GPS dropwindsondes. The SFMR measurements are not hindered by mathematical errors, for example, when winds at flight level are extrapolated to estimations of the surface.

“We hope that one day all planes flying into hurricanes, including US Air Force Reserve Command’s WC-130J aircraft, will be outfitted with this technology,” said Black.

The SFMR works by sensing the high radiation emitted in the microwave band which naturally radiate from the sea surface. When hurricane strength winds blow over the ocean, they cause the waters to churn and create sea foam. This sea foam radiates a high level of microwave energy which increases with wind speed over the ocean surface.

The SFMR tunes into these microwave frequencies over a series of six channels. Computer models can then calculate the wind speed from these microwave measurements even in the presence of rain.

Uhlhorn and Black are research meteorologists working with the Hurricane Research Division of NOAA’s Atlantic Oceanographic and Meteorological Laboratory (AOML)in Miami, Fla. In addition to studying hurricanes and tropical storms, the scientists are among a cadre of researchers who fly into storms gathering data that are relayed to NOAA’s National Hurricane Center that issues warnings.

The Commerce Department’s National Oceanic and Atmospheric Administration (NOAA) is dedicated to enhancing economic security and national safety through the prediction and research of weather and climate-related events and providing environmental stewardship of our nation’s coastal and marine resources.

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