NOAA’s HURRICANE AIRCRAFT GET BREATHER AFTER GRUELING
BACK-TO-BACK FLIGHTS

October 18, 2002 — Hurricane season, which began June 1 and ends November 30, began with a whisper and worked up to a roar by mid-September. NOAA’s three hurricane aircraft—two WP-3D Orion hurricane research turbo-prop aircraft and a Gulfstream-IV surveillance jet—conducted flights during Edouard, Fay, Gustav and Hanna. However, it wasn’t until Isidore and Lili struck that the three aircraft got really cranked up. (Click NOAA photo for larger view of NOAA "hurricane hunting" aircraft standing ready in NOAA's Aircraft Operations Center in Tampa, Fla., before flying into then Tropical Storm Isidore on September 24, 2002. Click here for high resolution version of this image, which is a large file. Please credit "NOAA.")

Hurricane Isidore and Hurricane Lili brought severe winds and rain, storm surge and flooding to the Gulf coast areas unfortunate enough to be in their destructive paths at landfall. These storm systems also yielded up a wealth of data during back-to-back flights for three long, grueling weeks in missions ultimately meant to increase scientific knowledge, improve forecast models and save lives.

One P-3 flew as low as 600 feet above the ocean in howling winds for NOAA Research to study the interaction between the upper layers of ocean and the atmospheric conditions within the storm. The other P-3 also flew back and forth through each storm’s dangerous eyewall to help NOAA Satellite Service scientists verify and validate, through use of remote sensing instruments mounted aboard the aircraft, the ocean surface wind data collected by satellite-borne instruments during severe weather. The Gulfstream-IV jet flew upstream, downstream and to the sides of the storms in their steering currents at altitudes reaching 45,000 feet to help NOAA National Weather Service forecasters pinpoint where Hurricane Isidore and Hurricane Lili would make landfall. (Click NOAA photo for larger view of NOAA P-3 "hurricane hunting" aircraft before flying into then Tropical Storm Isidore on September 24, 2002. Click here for high resolution version of this image, which is a large file.)

These are just simplified examples of NOAA science conducted during these very complex missions—missions that require cooperation, coordination and flexibility between personnel of the NOAA Aircraft Operations Center, who operate, manage, equip and maintain the NOAA aircraft, and the NOAA scientists who use these specially equipped, high-tech airborne meteorological platforms to further their understanding and knowledge of severe storm systems.

“It was a very productive month for researchers, and everything worked splendidly in all three aircraft,” said Jim McFadden of AOC, who is program manager for NOAA’s heavy aircraft. “It was like a well-oiled machine. It just flowed, and all the expendables that were dropped from the aircraft—dropwindsondes, ABTXs [instruments which measure ocean temperature], and ocean probes—worked flawlessly. We didn’t miss a beat during any of these flights.”

Much of the data gathered during the P-3 and G-IV flights are transmitted from expendable instruments that are deployed through chutes in the aircraft. Dropwindsondes (for drop wind sounding) provide a profile of weather information in the atmosphere over the ocean, directly measuring temperature, humidity and pressure as well as relaying information from global positioning satellites that is used to compute wind speed and direction. All of this information is radioed back to the aircraft twice every second as the sonde falls through the atmosphere at a speed of about 3,000 feet per minute. The sonde data are processed aboard the aircraft and transmitted via satellite to the NOAA National Centers for Environmental Prediction in Camp Springs, Md. NCEP sends the data to the NOAA National Hurricane Center and the NOAA Hurricane Research Division in Miami, Fla.

During Isidore and Lili, other expendable instruments were deployed for the P-3 air-sea interaction studies as well—AXBTs (Airborne Expendable BathyThermographs) and ocean probes, which sink a thousand feet below the water’s surface and relay back information on ocean currents and vertical profiles of temperature and salinity.

According to McFadden, the level of activity of the P-3s was higher than in the past because of the sheer number of expendables dropped. About 1,025 instruments were dropped from the P-3s during the 18 missions and 166.5 flight hours in and around Isidore and Lili.

All this flight activity required the participation of every crew member at AOC.

Each P-3 has one crew, with an extra pilot, to staff it. “Nobody gets sick; that’s our motto,” McFadden said. “Practically everyone at AOC, except people in administration or management, was flying. I’d come in and there wouldn’t be anyone here because they were either flying or home resting for the next flight. We only have enough people to fly, no backup, except an extra pilot per plane who is in training.”

Each mission lasts nine to ten hours, and safety regulations require crew to rest at least 12 hours between flights.

Jack Parrish, project manager for the G-IV, said, “The G-IV crews tackled six named tropical cyclones in 30 days, two of them nearly daily from September 17 past the end of the month. A record-breaking period by anyone’s count.” Between Isidore and Lili, the G-IV flew 15 tasked missions, spent nearly 115 hours in flight, dropped 386 dropwindsondes and covered more than 53,000 nautical miles. Parrish said that the G-IV’s flights into Lili provided by far its longest continuous stretch of aircraft-supplemented dropwindsonde coverage on a tropical cyclone. With the continuous coverage missions in Isidore, the data will add greatly to the forecasting database. (Click NOAA photo for larger view of NOAA Gulfstream-IV "hurricane hunting" aircraft before flying into then Tropical Storm Isidore on September 24, 2002. Click here for high resolution version of this image, which is a large file.)

During Isidore, the G-IV flew two missions in one day for two separate forecast model periods—the first time this had ever been done. Parrish said this was possible because as of this year the G-IV has two full crews that can alternate with each other, thanks to Congressional funding for the second crew.

Conducting daytime and nighttime flights in one 24-hour period is a significant accomplishment because it enables forecasters to better verify their models, according to Paul Flaherty, G-IV flight director and meteorologist. “When we can collect data for adjacent model runs, we can determine which forecast models will be more accurate over the next two- to three-day period,” he said. “The more data we have, the more accurate the forecasts.”

So who tasks the aircraft? Who gets the data and how are they used? Why does NOAA need two types of aircraft to collect hurricane data?

The NOAA National Hurricane Center tasks the G-IV to fly, and provides a flight track to AOC. Pilots check it out to make sure it is within the jet’s range for fuel. Once approved, AOC documents the plans and sends them to the FAA center responsible for the airspace in which the jet will be flying. AOC also sends a “Notice to Airmen” to warn other pilots that instruments will be dropped from the aircraft. If the flight area is to be heavily trafficked, FAA may advise against the drops. This is more a problem for the G-IV than the P-3s, as the G-IV flies so high. Tasking for the G-IV is fairly straightforward and follows the same routine each time.

Not so for the P-3s. The NOAA Hurricane Research Division usually tasks these aircraft, and the process requires a lot more coordination. The weight of equipment, expendables and people to be carried must be figured to the nth degree to ensure the aircraft is not overloaded. More scientists with differing experiments and needs are involved, and research plans must be worked out prior to the flights. Consequently, flight plans may change up to the last minute and FAA notification and the Notice to Airmen are also last minute. Often the P-3 flights have to be coordinated with the military as well, as the P-3 flies much lower and may need to go through restricted airspace. The P-3 sometimes flies in Cuban airspace, which requires coordination with Cuban authorities.

“It’s not a straightforward process, but once you get the logistics worked out and are on the airplane, the trip usually goes very smoothly,” said McFadden. “It can be very hectic up to that point. That’s what science is all about.”

According to Flaherty, on any given flight information is sent to both NHC and HRD. When the NHC tasks an aircraft to fly a storm, HRD will be there to gather research information. When HRD wants an aircraft to fly a research mission, NHC may request that information be sent to them as well. Gathered P-3 and G-IV data from each flight is used both operationally and for research purposes.

Though the G-IV primarily flies surveillance missions, it also gathers operational data. Its real-time data are used by the forecasters to forecast the track. The data the P-3 get in real time are used by forecasters to verify such things as storm strengthening and recent movement. The real-time data are used operationally but are also available for research by HRD.

Flaherty likened the difference between the P-3s and G-IV to a leaf falling into a stream. “The P-3s gather data about the leaf, while the G-IV gathers data about the stream,” he said.

The G-IV flies around the storm at altitudes reaching 45,000 feet, where steering currents direct the path of the storm. The data from G-IV flights give a 3-D picture of what the storm is doing, and help forecasters predict its track. The G-IV jet cannot handle severe turbulence and must avoid the worst weather. The sturdier P-3 airplanes fly directly into the guts of the storm, through the severe winds and rain of the eyewall, into the calm eye, and back through the eyewall at altitudes usually ranging from 1,500 to 15,000 feet. The data help forecasters determine hurricane intensity and movement. Low-altitude flights can be extremely dangerous, as there is little margin for error in controlling the aircraft.

Indeed, maintaining control of the aircraft within the eyewall is the biggest challenge facing P-3 pilots.

“The biggest risk that all flight crews face is catastrophic loss of control because the storm is stronger than the aircraft,” said Capt. Dave Tennesen, NOAA Corps, who is one of the senior P-3 pilots. “We’ve learned from experience that there are clues to conditions too dangerous to fly in. Using a team approach with our flight meteorologists, we look for those clues and simply avoid those parts of the storm. We search ahead with our huge belly radar, and identify where not to go.” (Click NOAA photo for larger view of NOAA P-3 Orion "hurricane hunting" aircraft with belly radar. Click here for high resolution version of this image, which is a large file.)

Oddly enough, small birds can pose nearly as much risk to an aircraft as severe weather.

“Just before we got into the eye of Isidore, the P-3 got hit by a small bird, probably no bigger than a sparrow. It felt like someone hit the plane with a baseball bat, and there was damage to the outside structure. At 220 knots, hitting a bird is tremendously dangerous to any aircraft, because it can drill a hole into the structure. We are especially vulnerable because we fly so low,” Tennesen said.

Tennesen flew mostly at night during Isidore. The rain was so heavy, he said, that it piled up on the windshield and slowed the P-3 down. At higher altitudes he saw quarter-sized pieces of icewater particles that, because of electrification, looked like balls of light hitting the windshield. “Like the many camera flashes you see at a rock concert,” he said.

Flaherty said that the G-IV flies upstream, downstream and on each side of the storm. If it’s a strong storm, the crew can’t see much through the haze. They attempt to go through the turbulent rain bands, which can be dangerous for the jet. “If our track brings us too close to something too dangerous, we won’t follow it—we’ll go around. We try to get a feel for where the thunderstorm tops are. We look at where rain bands are and where they are developing, and try to pick our way through the lines. If we can’t do that safely, we’ll divert around the storm,” he said.

“Lili was especially interesting,” Flaherty said. “It was a Category 4 storm, and we were really expecting the flight to be rough. It was the easiest flight this year. It was a very calm flight, which surprised me.” NHC was surprised when the G-IV found 65 knot winds off the coast of the Florida Keys, Flaherty said, because it showed the storm’s effects were being felt further away and strengthening more than expected.

Max Mayfield, director of the NOAA National Hurricane Center, said that the G-IV data for both storms were extremely helpful. He wrote to Capt. Bob Maxson, director of AOC, that, “I want to be sure you know how grateful I am for all of the excellent support the National Hurricane Center received from AOC the past couple of weeks. Your staff has flown numerous hours and it has paid off in helping save lives during Isidore and Lili. I have received thanks from FEMA, Texas and Louisiana emergency management directors, the Navy and several citizens for outstanding track forecasts. There is no denying that the jet data helped improve the track forecasts. This was a real team effort and your staff is to be commended. Please pass along my thanks to all at AOC who had a hand in helping us the past few weeks. It is still amazing to me that there was no direct loss of life in Lili. Our nation's Hurricane Warning Program is as good as it is in part because of the commitment of the folks at AOC.”

The P-3 research missions received similar praise from Michael Black, field program director for the NOAA Hurricane Research Division. “Overall, the set of missions into Isidore and Lili were an outstanding success and will allow researchers from around the globe to gain insight and understanding in helping to solve the mystery of how hurricanes evolve and interact with the ocean below them. AOC performed admirably during these hectic two weeks of flying; not a single mission was scrubbed and almost all of them were executed as planned and without a hitch. Without the dedication, hard work, and professionalism of the management, aircrew and support personnel at AOC, the tremendous science that was accomplished would not be possible.” (Click NOAA photo for larger view of NOAA "hurricane hunting" aircraft before flying into then Tropical Storm Isidore on September 24, 2002. Click here for high resolution version of this image, which is a large file.)

Paul Chang, senior scientist at NOAA’s Office of Research and Application was pleased with the result of the satellite-instrument calibration flights as well.

“The remote-sensing and in-situ data we collected from our P-3 flights through Lili will go a long way in improving our understanding of what we should expect in terms of wind retrieval performance in adverse weather from space-based microwave scatterometers such as QuikSCAT,” Chang said.

Since the last flight into Lili on October 4, aircraft operations have gotten a much-needed break. Though Hurricane Kyle hovered over the Atlantic for several weeks, the aircraft were not tasked to fly into it. NHC and HRD have funding for a finite number of flight hours, and must thus carefully pick and choose the storm systems to fly into for the greatest return in advancing research objectives and public safety. (Click NOAA photo for larger view of maintenance being performed on NOAA "hurricane hunting" aircraft before flying into then Tropical Storm Isidore on September 24, 2002. Click here for high resolution version of this image, which is a large file.)

One P-3 has gone into a six-month period of extensive maintenance to extend its service life. In addition to conducting training and test flights as well undergoing routine maintenance, the other P-3 and the G-IV stand ready to serve should another tropical storm system swirl a deadly path in USA’s direction.

Relevant Web Sites
NOAA Office of Marine and Aviation Operations

NOAA Aircraft Operations Center

NOAA Hurricane Research Division

NOAA National Hurricane Center

NOAA Research

NOAA National Centers for Environmental Prediction

NOAA Satellite Service

NOAA’s Office of Research and Application

Media Contact:
Jeanne Kouhestani, NOAA Office of Marine and Aviation Operations, (301) 713-3431 ext. 220
(Photos courtesy of Kent Laborde, NOAA public affairs.)