After studying aviation icing for over a decade, NCAR is taking
a look at how winter weather affects highway travel. (Photo ©
The Denver Post.)
Thousands of men and women face off with this glassy enemy each year.
They spray deicing fluid on aircraft, steer planes around risky areas,
and blanket roadways with tons of salt and sand. Their efforts pay off,
but too often their attack is an uncoordinated one, based largely on
rules of thumb rather than state-of-the-art detection and decision support.
NCARs Research Applications Program stepped into this fray more
than a decade ago. At the behest of the Federal Aviation Administration,
RAP worked with partners in industry and academia to develop systems
for detecting icing on the runway and in the sky. Some of these products
have made their way to the Internet, and a new generation of tools is
taking shape. NCAR has also set its sights on the road, where icing
threatens millions of drivers. A fine-grained system that promises to
revolutionize how roads are treated for snow and ice is being tested
this winter in the Midwest.
Flight tools take off
The FAA has been very good to us, says Marcia Politovich.
She and her NCAR colleagues, in turn, have been very good for the nations
aviation infrastructure. The project scientist, who leads the in-flight
icing team of the FAA Aviation Weather Research Program, has been involved
since the program began in 1990. Once the domain of subjective decisions
made by human forecasters, in-flight icing diagnosis is now produced
through a human-machine mix.
Current Icing Potential, a set of maps available on the Internet (see
On the Web), shows where two types of icing might be expected
across the country at multiple flight levels. The product updates hourly,
drawing on surface observations, satellite and radar data, pilot reports,
and the Rapid Update Cycle numerical model. CIP gained FAA approval
in 2001 as a tool for dispatchers to make fly/no-fly decisions and for
flight planning and route changes.
CIP complements forecast and intensity information available from
AIRMETs, the traditional National Weather Service alerts issued at six-hour
intervals. Its especially helpful for commuter planes and other
propeller-driven aircraft, says Politovich. These planes cruise at lower,
ice-prone altitudes, and some of them lack the mechanisms commonly found
on jets that prevent ice buildup by heating the front edges of wings.
A companion tool, Forecast Icing Potential (FIP), projects potential
icing up to 12 hours ahead. It goes up for FAA approval in 2003.
Both CIP and FIP can be found on an experimental Web site created
through another RAP-based, FAA-funded project, the Aviation Digital
Data Service (see On the Web, p. 8). ADDS pools information
from a variety of sources to give pilots at-a-glance guidance on icing
and other hazards. The old system, based on AIRMET text, requires multiple
pages of computer printout or speaking by phone with an FAA specialist,
explains codeveloper Greg Thompson. To know where the icing, turbulence,
or convection is expected that day, pilots have to read or listen to
a series of cryptic airport identifiers and connect the dots to construct
an imaginary polygon. With ADDS, pilots can check out the CIP
and FIP outlooks and view maps built from AIRMETs with the outline of
predicted hazardous areas clearly marked, or they can view the AIRMETs
in text form. Users can also plot a vertical cross section of conditions
along a proposed route.
Politovich and her colleagues have embarked on a new, even more challenging
step: trying to depict not just the existence of icing but its intensity.
Only AIRMETs now provide that information, but different planes
respond to icing differently, says Politovich, and an aircraft-normalized
view of icing cant be easily gleaned from the AIRMETs reports.
Its still a big problem.
Other NCAR scientists are exploring ways to capture icing data from
By next year, the centers S-Pol radar will include a
second wavelength for transmitting and receiving. This should allow
for greatly improved detection of liquid water, including the supercooled
variety that leads to icing.
Guifu Zhang is working on a technique to infer regions of icing
in vertical temperature and moisture profiles obtained from ground-based
Satellite-based algorithms are being developed by Merritt Deeter
and Julie Haggerty that relate ice crystal and droplet sizes within
a cloud to measurements obtained at the cloud top.
A new version of the Rapid Update Cycle model, introduced last
spring, includes an improved microphysics package from Roy Rasmussen,
Thompson, and Kevin Manning (see On the Web), with another
upgrade now in the works. Online users can see what type of precipitation
to expect (snow, rain, freezing rain, sleet, or a mix) at intervals
from 1 to 12 hours ahead.
Reducing the tab for
When winter weather cant be avoided, deicing fluida brew
of propylene or ethylene glycol, water, and thickenerscan be a
lifesaver. Airlines spend millions of dollars each year spraying planes
before takeoff. A system unveiled in 1995 to help determine when and
how to deice planes is now entering a new phase.
Project leader Rasmussen has been involved from the start, when the
Weather Support to Deicing Decision Making system was deployed at Denvers
former airport, Stapleton International.
It was subsequently demonstrated at Chicagos OHare International
Airport and New Yorks LaGuardia Airport, where it produced an
estimated $1 million per year in savings at the two sites. After being
transferred to a private vendor, WSDDM was picked up for deployment
at the three major New York airports from 1999 into 2002. Despite the
systems proven value, its price tag of $200,000 per airport seemed
too much after the September 11 attacks. Every purchase is being
scrutinized with a fine-toothed comb after 9/11, notes Rasmussen.
Its had a devastating effect on aviation.
This snow-making device was developed by NCAR scientists Alan
Hills, Roy Rasmussen, Charles Knight, and (pictured at left) Scott
Landolt over the last six years in order to test aircraft deicing
fluids in a controlled setting. The machine is housed in an NCAR cloud
physics lab, with a clone at APS Aviation in Canada. Its raw material
is purified water frozen into ice cores, each about 8 centimeters
(3 inches) wide by 120 cm (48 in) long. Using a computer-controlled
process, the machine shaves the cores to produce snowfall at virtually
any desired rate. Although many ski resorts have giant snowmakers,
this one is different in that the snowflakes it generates have
a density, size, and velocity close to that of natural snow,
says Hills, who has led many of the machines refinements after
initial work by Rasmussen and Knight. The closest analog to the NCAR
device may be in Hollywood, where similar ice-shaving technology helps
create many of the snowfalls seen on camera. (Photo at left by Carlye
Calvin; instrument photo by Alan Hills.)
The city of Denver is slated to pick up the tab for a new version
of WSDDM being tested this winter at Denver International Airport. Thanks
to the city sponsorship, a wide range of airport users will be able
to access the system, and costs will be lowered by using internal airport
data networks rather than the dedicated phone lines in place at the
New York airports. Future versions of the system will be Web-based,
reducing costs even further, says Rasmussen.
In Denvers version of WSDDM, real-time observations are being
updated once a minute, and the start and stop times of snowfall are
being predicted an hour in advance. NCARs Mei Xu and Andrew Crook
are devising techniques to assimilate radar data into the Penn State/NCAR
Mesoscale Model (MM5) in order to extend WSDDMs snowfall forecasts
out to 12 hours.
Simply providing a real-time estimate of snowfall as it falls is a
nontrivial exercise. In the mid-1990s, Rasmussen and colleagues discovered
that icing at ground level is more closely related to the amount of
liquid water in snow than to the visibility criteria long used to gauge
snowfall intensity (light/moderate/ heavy). Based on this work, the
United States and Canada now take the time of day, temperature, and
other factors into account when reporting snowfall intensity. A new
sensor (see sidebar) may further change the landscape of snow measurement.
A cold room at NCARs Foothills Laboratory is a convenient
year-round venue for testing snowfall and its impact on deicing. Project
scientist Alan Hills and associate scientists Scott Landolt and Matt
Tryhane use the laband, when weather permits, an outdoor site
just south of Boulderto see how snowfall and temperature affect
the performance of deicing fluids for aircraft. The data help the FAA
to certify specific brands of fluid with confidence.
The next frontier: highways
Next to the sleek setups at airports, the process that deploys trucks
along roadways to tackle snow and ice seems positively low-tech. With
the right information at hand, though, far more could be accomplished.
Such is the philosophy driving the Winter Road Maintenance Decision
Support System (MDSS).
The idea is to help agencies that maintain roads to better gauge
where and when to use deicing techniques, says NCARs William
Mahoney, who heads up the project. This means providing much more than
a generic outlook such as snow likely tonight, Mahoney points
out. We need forecasts that are more specific, more timely, and
tailored for decision makers who are not meteorologists.
To develop a prototype, NCAR teamed with four other labs associated
with the U. S. Army, NOAA, and the Massachusetts Institute of Technology.
The end result pulls together existing road and weather data to create
an easy-to-decipher picture of current conditions. The system uses numerical
modeling to project hour-by-hour roadway conditions up to two days in
advance, with an update furnished every three hours.
Users can pick a route, look at conditions, see what would happen
if they didnt take any action, and ask the system for a recommended
treatment, says Mahoney.
William Mahoney, Roy Rasmussen, and Marcia Politovich are among
the leaders of icing-related studies in NCARs Research Applications
Program. (Photo by Carlye Calvin.)
From February into April, MDSS will be put through its paces by three
state-run maintenance groups serving highways across central Iowa. Each
plowing routes predominant characteristics, such as pavement type,
will be specified in advance. With such detail in hand, the system can
assess how temperature and precipitation will affect the road surface.
Ultimately, users will be able to ask the system to track features as
specific as a single bridge paved in concrete along an asphalt road.
A lot of the folks with experience in highway maintenance are
starting to retire, says Mahoney. The new guy may not know
that when you hit a certain bridge you should do something different.
Those are things you learn from experience. The MDSS is designed to
help make that process more uniform. Its a blend of scienceweather
and road-condition predictionand art, the state of practice for
winter icing and deicing.
Only a few drivers will be affected by this winters tests, but
millions more could benefit in the next few years. About half of the
nations state transportation departments have already signed on
as stakeholders, along with some 25 private-sector companies.
Were cutting our teeth in this area, says Mahoney,
whos been crisscrossing the country pulling together support for
the program. Nothing like this has been done before. Its