What's up with that?

The Empire ponders Juneau's puzzles, unravels its mysteries and contemplates its conundrums.

Posted: Thursday, January 23, 2003

Q: Every so often a large white utility truck equipped with what looks like revolving radar screens parks at the wetlands viewing park near Lemon Creek and sits there with the screens going round and round. What's up with that?

On the web

• Juneau wind observations

• How Doppler radar works

• National Center for Atmospheric Research

A: The big white truck you saw is a tourist, of sorts. It's a Doppler on Wheels mobile radar unit on loan from the University of Oklahoma, and for the past few months it's been scanning the skies around Juneau to take measurements of local winds.

The observations are part of a study to better understand and forecast the tricky wind conditions encountered by aircraft flying to and from the Juneau Airport, according to Bob Barron, an engineer with the National Center for Atmospheric Research in Boulder, Colo., and a member of the research team.

The Empire ran an article on the study last October, when the team's research season was beginning; it concluded its observations last Sunday and is headed home. The project's ultimate goal is to create a wind hazard warning index, and it initially included the Doppler on Wheels unit and two instrument-filled aircraft - an Alaska Airlines 737 and a King Air plane on loan from the University of Wyoming.

The Alaska Airlines plane left town, as planned, Nov. 19, after conducting numerous passengerless test flights. The King Air plane remained in Juneau for the duration of the project.

"What we're doing is taking measurements from both the airplanes and the Doppler on Wheels and correlating them to the turbulence and wind shear in the area," Barron said.

The Doppler unit works by sending out a radar signal and listening for its return - the frequency shift of that return, in particular.

The change in frequency allows the Doppler radar to determine if winds are blowing toward or away from the unit, and the time it takes for the signal to return provides data on how far away a shift in direction is occurring.

The ability to identify and pinpoint wind shift makes Doppler radar very useful for monitoring severe thunderstorms in the Lower 48. Tornado warnings are frequently issued based on Doppler-detected wind rotation in storm cells.

Barron said the Doppler truck and airplane observations provide two pieces of the weather puzzle that, when assembled, give a very complete picture of wind conditions.

"The aircraft can make very precise measurements about what's going on with the wind on its route of flight - but it only makes the measurements on its route of flight," he said. "The aircraft gives us very, very accurate measurements, but of limited coverage. The Doppler gives us lots of measurements on a (wide) temporal and spatial scale."

While the Mendenhall Wetlands pullout along Egan Drive was likely the most visible observation point for the Doppler on Wheels unit, there was a total of six spots used. The variety of observation points allowed the team to study the wind up different valleys and at different angles.

It's been clear, just from setting foot outside anytime in the past few months, that this winter has produced unusual weather conditions. Barron said the lack of snow and severe winter storms has hindered - but not harmed - the wind study project.

"It definitely has not been a typical winter," he said. "We haven't seen as many data cases as we'd liked to have seen."

But, Barron said, "we've collected a lot of good data. What we have will be very valuable to us."

The peak wind gust observed during the team's stay was 117 knots - more than 134 miles per hour - at the Sheep Mountain station above Thane on the afternoon of Jan. 4. Barron said the most impressive statistic from that event was not the maximum speed, but the gustiness. That 117-knot peak was the culmination of a 57-knot increase in about 10 seconds.

Overall, Barron said the team did not encounter any unexpected weather phenomena - which was good, considering this was the third season of observations and studies of Juneau winds. Teams were here in 1998 and 2000.

"At this point, surprises are bad," Barron said.

The research team included five members from the University of Wyoming, three from the National Center for Atmospheric Research and two from the University of Oklahoma. The researchers will now focus on analyzing the data and developing the wind hazard indices.

Andrew Krueger can be reached at akrueger@juneauempire.com. Send questions or comments for What's Up With That to whatsup@juneauempire.com.

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