UCAR Communications


staff notes monthly

March 2003

A smooth ride to Juneau:
RAP maps wind shear and turbulence at isolated airport

That ubiquitous air travel safety announcement about fastening seatbelts and placing seats in their upright positions has a special meaning when it comes to flying into Juneau International Airport. The local wind shear and turbulence are notorious because the mountains that tightly encircle the airport produce a complex wind-flow pattern that literally rattles passengers who travel in and out of Alaska’s small capital city.

Two airplanes—a University of Wyoming King Air and an Alaska Airlines 737-400—gather data on RAP’s prototype system.

As the project manager for the FAA-sponsored Juneau Wind Project, Bob Barron of the Research Applications Program hopes to give travelers a smoother, safer ride.

Bob and his colleagues are developing a prototype warning system that issues up-to-the-minute alerts about wind shear and turbulence to air traffic controllers, airline dispatchers, and pilots. The goal is to warn pilots in time to prevent injuries to passengers and crew. RAP designed a similar system that’s operating at Hong Kong’s Chek Lap Kok Airport.

“It’s great that NCAR can use its scientific and technical expertise to contribute to society on this day-to-day operational level,” Bob says.

RAP’s Bob Barron and Deirdre Garvey.

The RAP team used anemometers and wind profilers to set up the Juneau warning system. The devices use vector mathematics to create a comprehensive picture of surrounding winds and to determine the danger these winds pose to airplanes and passengers.

A wind profiler is an upward-looking radar that can measure turbulence, wind speed, and wind direction. It gives researchers a profile of horizontal winds and turbulence at 60-meter (200-foot) increments up to about 2.5 kilometers (1.5 miles). An anemometer also measures wind speed and wind direction, but its measurements are at a single point near the ground.

The team placed the anemometers and wind profilers at a variety of locations ranging from the airport’s runways to the surrounding mountains. Many sites were chosen for their proximity to flight paths, while others were placed upstream to monitor incoming air before it reaches the airport.

RAP is working with the Atmospheric Technology Division to locate and operate the instruments. From 1996 to 1997, ATD collected wind data for several months to explore wind patterns and ultimately determine the best locations for the wind profilers in Juneau. ATD’s Steve Cohn has helped ensure the accuracy and proper functioning of the Juneau wind profilers, analyzing data with RAP’s Steve Mueller, Andrew Weekley, Cory Morse, and Kent Goodrich.

By boat or plane

Despite a population of barely more than 30,000, Juneau has a busy airport. This is because, unlike Rome, no roads lead to Juneau. The only ways in or out are by boat or plane. From apples to zucchini, supplies travel through the airport along with people.

This high volume of traffic, coupled with unusually dangerous winds, brought Juneau International Airport to the attention of the FAA. The area has two major airflows: a warm south to southeast wind from the Gulf of Alaska and a north to northeast wind bringing cold air from the interior. Under certain wind conditions, the only way to fly out of Juneau is by making a slow, 180-degree turn just after takeoff while turbulent winds coming over the mountains buffet the aircraft.

For several years, RAP has worked with the FAA, Alaska Airlines, the Univeristy of North Dakota, the University of Oklahoma, and the University of Wyoming to collect data in Juneau. In 1998, 2000, and 2002, RAP and university staffers traveled to Juneau to collect wind data that have been used to build and refine the warning system. This past winter, two airplanes, the University of Wyoming’s King Air and a larger Alaska Airlines Boeing 737-400, gathered data to fine-tune the prototype system.

The planes were used to correlate ground-system readings with actual data from the planes. For further accuracy, the Doppler on Wheels—a truckborne radar owned jointly by NCAR and the University of Oklahoma that measures radial wind speed—confirmed the data.

With the cold winter weather and rough traveling conditions in Juneau, Bob jokes that a lot of people have suffered on the project. But everyone involved understands that the focus of the new system is safety. Turbulence is a major concern for the airlines. In one serious incident in Juneau, a 737 departing the airport fully loaded with passengers encountered a wind hazard and rolled over more than 90 degrees. Fortunately in this case, the pilots were able to get the airplane back upright just a few hundred feet above the ground and complete their departure. The Juneau warning system is designed to provide alerts that will allow pilots to avoid these types of hazardous areas.

It will also help airlines save money. Turbulence costs U.S. airlines an estimated $100 million each year in injuries and operational disruptions such as delays and rerouting. In Juneau, high winds can last from 2 to 72 hours, and wind information can help airlines adjust their routes and schedules to optimize usage of the airport.

The warning system features sophisticated technology. “The wind profilers have two computers,” explains RAP’s Deirdre Garvey. “One is part of the profiler and the other is a Debian Linux computer running the RAP algorithms.” The anemometers and wind profilers transmit data to a central location at the airport, where final data analysis is performed. There is also a wind information system in Juneau running a set of RAP algorithms and sending the data to various remote locations in Juneau. Despite all this technology, in the end, it is up to the pilot to decide how to respond to the warnings.

RAP hopes to have the prototype completed and handed over to the FAA by 2004. The FAA will then modify the system to fit its long-term needs. In the meantime, RAP staffers will continue to refine the prototype alert system and check it for accuracy.

Until the warning system is up and running, people will be sure to remember to pull their seat belts tight on their next trip to Juneau. Bob sighs, “NCAR never seems to send me to a place where the weather is nice.” •Ellen Leslie

Hong Kong system

Before the Juneau project, RAP built a similar warning system at Hong Kong’s Chek Lap Kok Airport (above in an artist’s illustration), which is scheduled to be completed as shown in 2040. Without this warning system, called the Windshear and Turbulence Warning System (WTWS), research showed that one in 700 flights would encounter severe wind shear and one in 2,500 would encounter severe turbulence. With the WTWS system installed, unexpected windshear and turbulence are rarely encountered. The WTWS is equipped with a suite of wind shear and turbulence detection algorithms. It processes data from anemometers and a terminal Doppler weather radar.

Also in this issue...

Archives launching instrument collection

Vin Lally wins prestigious ballooning award

Short takes

A special evening with an intimate of the atmosphere

Delphi Question: PTO, health benefits, and diversity training

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