Marit Finne
Editor-in-Chief
Vaisala News
Vaisala Helsinki
Finland
NOAA’s WP-3 Orion Hurricane Research Aircraft are among the most
advanced airborne environmental research platforms for the study of severe
storms and global climate change.
NOAA
‘Hurricane Hunters’
Flying in the Storm
Specially equipped NOAA aircraft
play an integral role in hurricane
forecasting. NOAA’s Hurricane
Research Scientists fly a Gulfstream
G-IV Jet beyond hurricanes at high
altitudes (40,000–45,000 feet) and
two WP-3 Orion turboprops into
hurricanes at low altitudes
(1,500–10,000 feet), to collect
research data. During their
missions, these aircraft release
Vaisala RD93 GPS dropwindsondes
used for weather reconnaissance,
hurricane and weather research.
G
roundbreaking research and improved forecasts have already emerged from
the data gathered by RD93
GPS dropwindsondes in hurricanes and winter storms. The
dropsonde data have improved
the mean hurricane track forecasts from the Geophysical
Fluid Dynamics Laboratory’s
(GFDL) hurricane model by as
much as 32 per cent and the
intensity forecasts by as much
as 20 per cent.*)
Pilots trained to
fly hurricanes
NOAA Corps pilots, who support the civilian scientists and
engineering staff of the Aircraft
Operations Center (AOC), are
among an elite group of pilots
who are trained to fly into hurricanes, sometimes at danger-
14 150/1999
ously low altitudes. The ‘NOAA
Hurricane Hunters’ Captain
David Tennesen and Lieutenant Commander Sean White
are NOAA Corps officers stationed at the Aircraft Operations Center at MacDill Air
Force Base in Tampa, Florida.
Captain Tennesen, a pilot since
1968, is the senior aviator at
AOC while Lieutenant Commander White, a meteorologist, has been Project Manager
for the NOAA Gulfstream IV
since its acquisition.
Specially equipped NOAA
aircraft play an integral role in
hurricane forecasting. Data collected during hurricanes by
these high-flying meteorological stations and from a variety
of other sources are fed into
numerical computer models, to
help forecasters predict how
intense a hurricane can be, and
where it will make landfall.
Hurricanes Have a Mind of Their Own
Satellite images of hurricanes show a unique and characteristic cloud formation, signaling an intense tropical weather system. The powerful storms spawned in the tightly coiled systems produce heavy rain and winds with maximum sustained
speeds of 74 mph/64 knots (33 m/s).
The United States has a significant hurricane problem.
There are already some 45 million permanent residents along
the hurricane-prone coastlines – and the population is still
growing.
A hurricane is a type of tropical cyclone – a general term
for all weather systems circulating (counterclockwise in the
Northern Hemisphere) over tropical waters.
Hurricanes are products of the tropical ocean and atmosphere. Powered by heat from the sea, they are steered by the
easterly trade winds and the temperate westerlies, as well as
by their own ferocious energy. Around their core, winds grow
to a great velocity, generating violent seas. Moving ashore,
they sweep the ocean inward while spawning tornadoes and
producing torrential rains and floods. Each year an average
of ten tropical storms (of which six become hurricanes), develop over the Atlantic Ocean, Caribbean Sea, or Gulf of
Mexico. Every three years, about five hurricanes strike the
United States coastline. Two of the five will be major hurricanes (category 3 or greater, on the Saffir-Simpson Hurricane
Scale. The scale from minimum to maximum is 1 to 5).
Lieutenant Commander Sean
White is Project Manager of the
NOAA Gulfstream G-IV Jet, seen
in the background with the Muppets
character logo.
NOAA’s Corps pilots fly the
Gulfstream G-IV Jet at high
altitudes (41,000–45,000 feet)
and two WP-3 Orion turboprops
at lower altitudes (1,500–25,000
feet), to collect research-mission data. Lieutenant Commander White explains that he
coordinates field operations
and crew activities (pilots,
meteorologists, engineers and
technicians) in all the phases required to accomplish each mission.
DR93 GPS dropsonde
measures critical
atmospheric conditions
Lieutenant Commander Sean White, with Vaisala’s DR93 GPS
Dropsonde, coordinates field operations and crew activities in all the
phases required to accomplish each mission in the NOAA aircraft.
The Airborne Vertical Atmospheric Profiling System (AVAPS)
was developed by the U.S.
National Center for Atmospheric Research (NCAR), in
cooperation with the German
Aerospace Research Establishment (DLR) and the NOAA
Corps. NCAR has licensed the
production of the RD93 GPS
dropsonde, which is a key component of the AVAPS, to Vaisala. The Airborne Vertical Atmospheric Profiling System,
which incorporates a Vaisala
RD93 GPS dropwindsonde, is
an advanced tool for weather
reconnaissance, hurricane and
weather research.
The NOAA G-IV plane flies
high-altitude tracks, between
41,000 to 45,000 feet (12,497
–13,716 m), to release the GPS
dropsonde at predetermined
locations. Using the specific
mission systems onboard the
aircraft, the information measured by the GPS dropsonde is
collected, analyzed, processed,
formatted into a message and
transmitted via Satellite Communications (SATCOM) to
the ground, almost in real time.
These atmospheric vertical profiles are used to initialize
numerical models providing
data otherwise not available in
the ’data void’ regions over the
oceans.
Captain Tennesen says, “Since
the 1997 hurricane season, the
G-IV jet complements the work
of the WP-3s. Data from dropsondes measuring barometric
pressure, temperature, humidity, and wind flow are transmitted to a satellite, which then
transmits the data to the National Hurricane Center in Miami, and the National Environmental Satellite, Data and Information Service outside Washington, DC.”
Air missions
relay storm data
During hurricane synoptic surveillance missions, the NOAA
G-IV flies in the environment
of the hurricane. The tracks usually target specific areas around
the hurricane, concentrating on
P HO TO CO U RT ES Y OF NO A A, U SA .
Captain David Tennesen, the Senior
Aviator, with his favorite aircraft,
NOAA WP-3 Orion.
150/1999 15
synoptic features that influence
its track. For winter storm reconnaissance, the aircraft flies in
sensitive areas over the North
Pacific two to five days upstream
of the weather development areas
affecting the United States. These
predetermined sensitive areas
are chosen to provide the numerical models with crucial
data that otherwise would be
unavailable.
During the acquisition process and instrumentation of the
NOAA G-IV, the Atmospheric
Technology Division (ATD) of
the National Centers for Atmospheric Research was chosen to
design and develop the new
GPS dropsonde. The NCAR/
ATD chose Vaisala’s PTU sensor and GPS components for
their design of the new GPS
dropsonde.
“Though I was only indirectly involved in the enhancement
process that further improved
the GPS dropsonde, I have
nothing but high praise for
Vaisala’s efforts to respond to
our needs and the tight delivery
schedule. Along with individuals within NOAA, NCAR and
the Air Force’s Weather
Reconnaissance Squadron, Vaisala’s commitment to quality
has provided the GPS dropsonde that will enable the
NOAA G-IV to enter the 21st
Century as the premier highaltitude platform,” Sean White
says.
Research flying is
a team effort
The Aircraft Operations Center
(AOC) was created in 1983 to
consolidate the aviation assets
of the National Oceanic and
Atmospheric Administration.
Its versatile aircraft collect the
environmental and geographic
data essential to NOAA hurricane research. “Our aircraft
operate in some of the world’s
most remote and demanding
flight regimes – over open ocean,
mountains and coastal wetlands, in and around hurricanes
or other severe weather,” Captain Tennesen points out.
David Tennesen stresses that
the research flying they do is
very much a team effort. “Every
crew member and the research
instruments they operate must
work together for each flight to
16 150/1999
This picture shows the lightning rod protruding from the front of the aircraft.
*) References
[1] Hock, Terrence F., and
James L. Franklin, 1999:
The GPS Dropsonde, The
Bulletin of the American
Meteorological Society,
Volume 80, No.3,
March 1999.
[2] Aberson, Sim D. and James
L. Franklin, 1999:
Impact on Hurricane Track
and Intensity Forecasts of
GPS Dropwindsonde
Observations from the
First-Season Flights of the
NOAA Gulfstream-IV Jet
Aircraft, The Bulletin of
the American
Meteorological Society,
Volume 80, No.3,
March 1999.
Hurricane Hugo making landfall, September 22, 1989. Charleston radar
image. Photo courtesy of NOAA, Hurricane Research Division, USA.
The graph shows the vertical motion the NOAA Hurricane Hunters fly
through on one of their research flights. As can be seen, this is not a smooth
airline ride.
be a success. This includes the
dropsondes. The accuracy of
the Vaisala instrument and the
information it collects directly
affects the weather forecasts for
the entire Northern Hemisphere.”
Lieutenant Commander White
says his most memorable experience was a flight into Hurricane Hugo as the navigator
on a WP-3 aircraft in September 1989, during a mission
originating from Barbados.
“During this low-level research
mission, the aircraft experienced extreme turbulence upon
entering the eyewall of Hurricane Hugo, at an altitude of
1,500 feet (452 m). After a precautionary shutdown of one of
the engines during the eye-wall
penetration and the subsequent entry of the calm eye at
about 800 feet (243 m), the 3engine, 1-hour climb to a safer
altitude in the small eye of
Hugo, together with the penetration of the eyewall to exit
and the subsequent ferry back
to Barbados formed the most
sobering experience of my life.”
The center, or eye, of a hurricane is relatively calm. The most
violent activity takes place in the
area immediately around the
eye, called the eyewall. At the
top of the eyewall, (about
50,000 feet /15,240 m), most of
the air is propelled outward, increasing the air’s upward motion.
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