Systems fire an arrow into heart of the hurricane

Systems fire an arrow into heart of the hurricane




Electronics engineer John Hill, left, and technician Chris Hornbrook examine data aboard the G-IV hurricane hunter.


By predicting where a storm is heading, NOAA's flying computers give people time to get out of the way

By Frank Tiboni

GCN Staff

Airborne computer systems that have helped predict hurricane movement more accurately were instrumental in forecasting the track of Hurricane Floyd as it teased Florida, battered North Carolina and continued up the East Coast, a National Oceanic and Atmospheric Administration official said.

'The National Hurricane Center's ability to make a determination that Floyd would track north is due largely to these aircraft,' said Jim DuGranrut, chief of the Science and Engineering Division at NOAA's Aircraft Operations Center at MacDill Air Force Base, Fla.

Three NOAA aircraft flew 13 missions during Hurricane Floyd to gather data on the storm's pressure, temperature and humidity. Four systems aboard the aircraft process data and send it via a satellite link to the National Centers for Environmental Prediction in Camp Springs, Md. Forecasters there run computer models to predict a storm's path, DuGranrut said.

Destructive power

Floyd, at one time a Category 4 storm on the Saffir-Simpson scale with winds of 150 mph, turned northward after hitting the Bahamas and skirted major population centers on the Florida coast. The storm made landfall near Wilmington, N.C., on Sept. 16, packing 115-mph winds, then moved north, dumping heavy rains.

Most of the damage from Floyd was caused by flooding, with estimates exceeding $6 billion. Parts of North Carolina received 20 inches of rain. The hurricane also claimed 35 lives in the state.

NOAA uses two types of aircraft to acquire and process hurricane data. Two Lockheed Martin Corp. turboprop P-3s fly at 20,000 feet into a storm to monitor wind and pressure change; a Northrop Grumman Corp. Gulfstream G-IV jet flies at 45,000 feet around the storm to record changes in its upper atmosphere.

To predict a hurricane's path, the aircraft release 20 to 30 sensor devices known as dropwindsondes, from Vaisala OY of Helsinki, Finland, said Alan Goldstein, chief for the Data and Development Branch at NOAA's Aircraft Operations Center.

The 14-inch-long, 3-inch-wide cylinders, with a cardboard outer casing, contain sensors that measure temperature, pressure and humidity. Each also has a Global Positioning System receiver from the National Center for Atmospheric Research in Boulder, Colo., that measures wind speed and direction, Goldstein said.

Scientists pull a pin to activate the cylinders, then attach them via umbilical cords to the Airborne Vertical Atmospheric Profiling System for calibration. Then the scientists detach the cylinders, put them in a launch tube and flip a switch that drops them into the hurricane.

The devices immediately being sending telemetry over a UHF channel to AVAPS. The 450-MHz Pentium II computer, with 128M of RAM, a 10G hard drive and Microsoft Windows 98, processes the hurricane's pressure, temperature and humidity data, Goldstein said.

About 15 or 20 seconds after launch, the GPS receiver starts sending wind telemetry via the UHF channel to AVAPS.

The PC receives two samples of data every second as the cylinders fall at a rate of about 20 feet per second. The cylinders take about 14 minutes to reach the Earth's surface, Goldstein said.
Data receptors

AVAPS sends the data to two systems aboard the aircraft. In the G-IV, the data goes to the Main Aircraft Data System, a Sun Microsystems Sparcstation 5 running SunSoft Solaris 2.6. In the P-3s the information goes to the Research Aircraft Measurement System, a Hewlett-Packard 1000 running RTE-A, Goldstein said.

On the P-3s, scientists use 9-inch NTSC color monitors from Sony Corp. of America of Park Ridge, N.J., to display the data. On the G-IV, they use three Sun Sparcstation 5s that serve as X terminals, Goldstein said.

AVAPS also sends data on both aircraft to the Hurricane Analysis Processing System. The HP L9000 server running HP-UX provides a platform for NOAA scientists to display, filter, quality control and create the World Meteorological Organization's temperature drop message, Goldstein said.

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