GOES-8/9 Satellite Derived Wind Products

General Information on Derivation and Image Displays of GOES-8/9 High Density Winds

(1) Satellite-Derived Winds Production

High density winds are produced at six hourly intervals from both the GOES-8 and GOES-9 satellites, operated by the National Oceanic and Atmospheric Administration (NOAA). The two satellites are the latest geostationary weather satellites operating in the U.S., and employ the latest technology in spacecraft and instrument capabilities. They orbit the earth directly over the equator, at a speed equal to the earth's rotation. To an observer on the ground, they would appear stationary (thus the term geostationary). GOES-8 is fixed relative to longitude 75W, providing coverage over the Eastern U.S., Central and South America, and the Atlantic Ocean, and GOES-9 is fixed relative to longitude 135W, to provide coverage over the Western U.S. and Pacific Ocean.

Satellite images of clouds, water vapor fields and surface features are obtained by instruments capable of measuring infrared energy emitted by the earth's atmosphere and surface, as well as reflected sunlight in the visible spectrum. The amount of infrared energy reaching the satellite's instruments is affected by the surface temperature, and the vertical temperature and humidity structure of the atmosphere. Two distinct frequencies (or channels) of infrared energy are used in the derivation of the high density winds. One is highly correlated with atmospheric moisture (designated the 'water vapor' channel), and the other with the temperature of the land, oceans and clouds (known as the 'window' channel).

Wind estimates are produced by tracking features in the GOES-8/9 water vapor and infrared window channel data, (clouds) and are designated as ' water vapor` and 'cloud drift' winds. Automated pattern recognition software is used to detect and track features in three successive images, each 30 minutes apart. Each wind vector, consisting of speed and direction, is assigned a height above the earth's surface based on the infrared energy signatures and guidance from corresponding numerical weather forecast parameters.

(2) High Density Winds Images

The high density wind images presented on this web site are generated every six hours using an automated procedures which produce GIF files using the satellite-derived wind estimates and GOES-8/9 satellite imagery. The cloud drift winds are plotted over an image of the GOES-8/9 'window' channel, using shades of gray. Relatively warm areas, such as land regions during the day and tropical ocean regions, are represented by darker shades of gray. Colder areas, such as clouds, ice and land regions at night, are depicted by lighter shades of gray. Cloud heights are correlated with temperature, with lower clouds (such as cumulus and stratus) being warmer, and higher clouds (such as cirrus) being colder. Therefore, low clouds will appear as relatively darker shades of gray, and high clouds as lighter shades of gray. Careful examination of the high density cloud drift wind images will reveal that the winds at higher altitudes correspond to higher, colder clouds, and lower altitude winds correspond to lower, warmer clouds.

(3) Evaluation of High Density Winds Accuracy and Quality

For more information contact:

Donald G. Gray, Chief, FPDT Donald.G.Gray@noaa.gov

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