Riders of the storms

PARAPUBLIC NOAA HURRICANE HUNTERS

National Oceanic and Atmospheric Administration Air Operations Center WP-3D Orions fly into hurricanes to help provide warnings to authorities. Mark Broadbent reports

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The WP-3Ds can fly for more than nine hours and range out to more than 2,500 nautical miles in their storm- chasing flying activities.
Lt Kevin Doremus/NOAA

At Lakeland Linder Regional Airport in Florida there’s a small group of aircraft operated by the National Oceanic and Atmospheric Administration (NOAA) Aircraft Operations Center (AOC) with a very niche role.

Nine aircraft, comprising two Lockheed WP-3D Orions, one Gulfstream IV-SP, one Beechcraft King Air 350ER, one Turbo Commander and four DHC Twin Otters, are tasked with protecting lives and property in the United States, contributing to scientiic research and conserving and managing coastal and marine resources.

The AOC is part of the NOAA Oice of Marine and Aviation Operations and its aircraft operate nationwide. The King Air, Turbo Commander and Twin Otters study marine life populations, assess shoreline change, survey water resources and snow, undertake air chemistry studies and remote sensing projects, and support emergency responses to natural disasters.

Hurricane hunters

The WP-3Ds and GIV-SP undertake the unit’s most high-proile work. One of the NOAA’s primary functions is weather forecasting and warning of dangerous weather. The agency has diferent tools for forecasting tropical storms and hurricanes, including groundbased remote sensing stations and satellites.

These methods have obvious limitations, however; sensing stations are static and the laws of orbital mechanics mean passes by satellite over a storm system are inevitably limited to speciic times. Aircraft can play a key role in illing the gaps by lying directly into and above storm systems, gathering quality data to improve the accuracy of forecasts and warnings and therefore aid public agencies in coping with major storms.

This is where the AOC at Lakeland comes in. Three of the centre’s nine aircraft are used for this data collection role: two Lockheed WP-3D Orions, also known as the ‘hurricane hunters’, and a Gulfstream IV-SP. The WP-3Ds, N42RF (c/n 5622), nicknamed ‘Kermit’, and N43RF (c/n 5633) ‘Miss Piggy’, were both obtained new from Lockheed back in the 1970s and GIV-SP N49RF (c/n 1246) ‘Gonzo’ was acquired in 1996.

Over the years, these aircraft have operated above the Arctic and Alaska, most regions of the United States and into the Caribbean, supporting hurricane and tropical storm research in the Atlantic, Caribbean, Gulf of Mexico and the eastern Paciic.

Fuselage and tail radars

The three aircraft are equipped with an array of scientiic instruments and recording systems. Key instruments on the WP-3Ds are a 360o C-band lower fuselage radar and an X-band tail Doppler radar (TDR); these aircraft are the only ones in the United States’ nationwide ‘hurricane hunter’ fleet equipped with both fuselage-mounted and tailmounted radars.

Lieutenant Commander Adam Abitbol, a WP-3D pilot with the NOAA, explained to AIR International that the lower-fuselage radar scans the storm horizontally and the TDR scans vertically. By sweeping together, the radars produce a cross-sectional view of the storm that looks similar to an MRI scan, proiling the storm’s layers and internal structure.

Publicly available information about the radars from the NOAA’s Hurricane Research Division (HRD) explains further: “The major drawback of the lower-fuselage radar is the large vertical beam width [4.1o] which causes inadequate illumination of the targets in the beam …At close range there is little loss because the radar beam is narrow enough to be totally within the strong relectivity region at lower altitudes in the storm. As range increases, the height of the centre of the beam increases and more of the beam is unilled or illed with the less relective portion of the storm. This problem can be solved by compositing a number of radar sweeps in time over a ixed domain.

“The major drawback of the tail radar is …X-band radars sufer from intervening rain attenuation which limits the maximum range at which Doppler estimates are obtained. This problem is remedied by lying close to the area of interest.”

Sensors and dropsondes

The WP-3Ds also have fuselage-mounted analogue and digital light-level data sensors. There are cloud physics instruments in the form of 2-D and 1-D particle measuring probes mounted near the wing trailing edges, which sample the sizes of raindrops and ice crystals, and an aerosol sampling system.

Mounted on the lower fuselage is a downwards-pointing stepped frequency microwave radiometer (SFMR) and a C-band scatterometer (C-SCAT).

The SFMR antenna passively reads the microwave radiation coming from the ocean surface, while the C-SCAT antenna is a microstrip phased array whose main lobe can be pointed at 20°, 30°, 40° and 50° of nadir to produce conical scans of the ocean surface every two seconds. There is an air temperature radiometer and solar and infrared radiometers.

Four generators (three engine driven, one driven by the auxiliary power unit) provide electrical support for all these systems, with each generator supplying 120V three-phase, 400Hz power and 90KVA maximum power. The WP-3D crews also drop expendable sensors through a launch tube including GPS dropsondes that, Lt Cdr Abitbol said, “fall into the column of air and report back all the state variables, the temperature, pressure, humidity, speed, wind direction”.

Bathythermographs are dropped to measure ocean temperature and expendable SFMRs are released to sense wind speed at the ocean surface by measuring and computing radiation emitted by the sea foam created by the high winds at the surface.

The Orions are also able to drop a small expendable unmanned system called Coyote, which is controlled remotely, either from the crew aboard the WP-3D or from a ground control station.

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NOAA Lockheed WP-3D Orion N42RF ‘Kermit’ photographed in October 2016 following a major overhaul and upgrades.
Mike Mascaro/NOAA
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Close cooperation between the crew is necessary in the challenging environment lying into hurricanes. Here is the light deck of WP-3D N42RF during an August 2017 light into Hurricane Harvey.
Lt Kevin Doremus/NOAA
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The Orions will typically make four passes through a hurricane on one light from diferent directions. This was the eyewall of Hurricane Katrina viewed from the WP-3D.
NOAA

The GIV-SP has a TDR system, a flightlevel data sensor and the ability to drop GPS dropsondes.

Using the data

Lt Cdr Abitbol explained how the Orions and Gulfstream work together to collect data. The WP-3Ds fly directly into the storm, typically at altitudes of between 8,000ft and 10,000ft, with the GIV-SP keeping station at higher altitude, about 45,000ft.

He said: “They’re able to get a very accurate vertical profile of the atmosphere by releasing dropsondes from 45,000ft. The WP-3D does the exact same thing with the exact same instruments, but we’ll drop from 8,000ft.”

The result is a complete vertical profile of the storm from high to low altitude, with the data from the GIV-SP complementing that acquired by the WP-3Ds from lower down.

All the information gathered by the sensors is initially assessed by scientists on board. Aircraft-satellite data links transmit data to the NOAA’s National Hurricane Center and National Centers for Environmental Prediction every 15–30 minutes where it is analysed by sctientists using bespoke software developed by the HRD. The data, together with information from other collection sources, including ground units and satellites, enables forecasters to visualise the storm’s structure. The results feed the models used to produce storm forecasts.

Lt Cdr Abitbol highlighted the value of the information collected by the WP-3Ds and GIV-SP: “Our data is directly responsible for some of the real-time updates tracking a storm’s intensity. It provides a lot more precision, a lot more resolution to the fidelity of the track, which helps to give some additional warning.”

Flying missions

What the NOAA aircraft do during each mission is dependent on the specific tasking received by the AOC at Lakeland. Lt Cdr Abitbol said the end ‘customer’ will provide the centre with an outline of its requirements and an updated fix on the storm’s location and details of its expected track.

The NOAA AOC will in turn notify the end user about the WP-3D’s radius and how many passes of the storm the aircraft can undertake given the storm’s location relative to the operating base, and the aircraft’s range based on fuel and crew duty requirements.

Lt Cdr Abitbol explained: “Generally, we’ll get four passes through the hurricane on one flight, although that can change depending on the mission and on how far away [the hurricane] is and on how far the transit is.

“Each pass through the storm is about 210 miles [337km] from start to finish. We’ll start on the west side of the storm and fly about 105 miles [169km] into the eye and then another 105 miles out to the eastern side. We’ll then reposition and do a pass from north to south, a pass from southeast to northwest, then a pass from southwest to northeast, basically cutting up the storm like a pizza.”

Demanding lying

The WP-3Ds are well liked by their crews. This is not surprising given their payload capability, endurance and range, but Lt Cdr Abitbol, a former US Navy EP-3E pilot, says the aircraft’s most impressive quality is its handling in the intense stormy conditions the ‘hurricane hunters’ of the AOC fly into, conditions that most aviators routinely avoid rather than intentionally fly into.

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The view from inside Hurricane Matthew in 2016, as seen from WP-3D N43RF ‘Miss Piggy’.
Terry Lynch/NOAA
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A flight director on N43RF during the ocean winds project, one of the climate research projects in which the WP-3Ds are involved outside of hurricane season.
Terry Lynch/NOAA
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Gulfstream IV-SP N49RF (c/n 1246) ‘Gonzo’, used for obtaining measurements from high altitude, departs Lakeland Linder Regional Airport in August 2017.
Lt Kevin Doremus/NOAA
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He said: “The WP-3D is built like a tank. It’s a turboprop, so there’s instantaneous thrust; there’s no spool time like you ind with a turbofan. It was built to be an all-weather aircraft and so its ability to ly through large volumes of water makes it ideally suited to ly in a storm. It’s a beautiful plane to ly; it continues to surprise me as to how well built and resilient it is in that environment.”

The WP-3D’s rugged qualities do not mean lying around and within tropical storms is any less diicult, of course. Lt Cdr Abitbol said: “Mature tropical cyclones can be challenging to ly; we’re lying right through the centre of the storm,” so crew coordination is clearly hugely important.

On the WP-3D there are two pilots, a light engineer, a navigator, the light director, two or three engineering and electronic specialists, a radio/avionics specialist and up to 12 scientists. Lt Cdr Abitbol emphasised the level of teamwork required on data-gathering lights: “This is especially evident during the penetration passes through the storm. We delegate the authority to use the power levers to our light engineer. The pilot is in the left seat lying the mission; he’ll have both hands on the yoke.

“The light engineer will be controlling the throttles and the right-seat pilot will be backing up the controls and coordinating the communications with the light director in the back, as well as ensuring our altitude, airspeed and track are all accurate and where they need to be.

“There’s a lot of talking back and forth. We all know each other well and can anticipate each other’s motions. All of that combined helps us set up the aircraft and maintain altitude, airspeed and track as closely as possible to that intended, even during periods of extreme turbulence.”

The NOAA AOC currently has seven WP-3D pilots, four light engineers, four navigators and four light directors, which stafs two crews (each crew has three pilots, two engineers, one navigator and one light director). The GIV-SP is currently stafed by three pilots and one light director, but there are no navigators and light engineers on that aircraft.

Research platform

The AOC’s aircraft are used for more than just hurricane research. The instrumentation on the WP-3Ds makes them versatile and highly capable aircraft for gathering data, too, so ‘Kermit’ and ‘Miss Piggy’ are frequently used outside the hurricane season to support atmospheric and air chemistry studies and research into climate trends.

The AOC recently supported NASA’s ongoing Operation IceBridge project to observe, measure and image changes in polar ice, with N43RF ‘Miss Piggy’ deploying to Kangerlussuaq in Greenland for the research lights. Each winter, the WP-3Ds study ocean winds, typically lying from Halifax in Nova Scotia or, in the last couple of years, Ireland. The Orions have also operated over Kansas to support ongoing studies into ‘supercell’ thunderstorms (speciically, mesoscale convective systems that can spread across an entire state, last more than 12 hours and reach an altitude of up to 50,000ft). Lt Cdr Abitbol said the WP-3Ds will return to this project next year.

Meanwhile, the GIV-SP is supporting the NOAA’s GRAV-D (Gravity for the Redeinition of the American Vertical Datum) project to redeine the gravitational baseline for the United States.

The equipment aboard the aircraft can be changed to ensure the aircraft are configured appropriately for each mission. Lt Cdr Abitbol said: “We have roll-on/roll-of capability; we have a capability here at the AOC on engineering and fabrication where we can put operational instrumentation on the WP-3D within anywhere from six hours to four days.”

The NOAA’s aircraft are therefore kept busy with other work out of the storm season, which lasts from June 1 to November 30 each year in the Atlantic and from May to November 30 in the eastern Paciic.

Next year, though, the Orions will once again return to their primary task: lying directly into hurricanes, their crews quite literally riding on the storm.