NOAA's Gulfstream-IV Jet Takes Hurricane Track Predictions to New Heights
The airplanes and helicopters of NOAA's Aircraft Operations Center provide capable, mission-ready aircraft and professional crews to the scientific community, wherever and whenever they are required. NOAA aircraft operate throughout the United States and around the world—over open oceans, mountains, coastal wetlands, and Arctic pack ice. These versatile aircraft provide scientists with airborne platforms necessary to collect the environmental and geographic data essential to their research.
What better way to understand what makes a beast tick than entering its belly? Every year, NOAA does just that—flying aircraft directly into hurricanes to collect valuable data used to understand these potentially devastating storms. NOAA’s hurricane aircraft also support atmospheric and oceanographic research, enabling scientists to precisely observe, measure, and chart the dynamics of our coasts, oceans, and atmosphere.
The Aircraft Operations Center operates and manages most of NOAA’s 11 aircraft from its hangar at MacDill Air Force Base, Tampa, Florida. Click image for larger view.
The Aircraft Operations Center (AOC), part of NOAA’s Office of Marine and Aviation Operations, operates, modifies, and maintains NOAA’s fleet of 11 research aircraft. AOC personnel include men and women of the NOAA Commissioned Officer Corps and civilians.
Among NOAA’s aircraft are the famed NOAA WP-3D Orion “hurricane hunters,” which have been flying through turbulent storms since the 1970s. These aircraft have served NOAA well over the years. However, between 1982 and 2005, the acquisition and transformation of a Gulfstream-IV jet (or the “G-IV”) has added a new dimension to NOAA’s ability to track and forecast hurricanes.
NOAA’s hurricane hunter aircraft, two Lockheed WP-3D Orion aircraft (the “P-3s,” or also known affectionately as Kermit and Miss Piggy), were acquired in 1975 and 1976.
Data from the dropwindsondes are transmitted back to the aircraft. Click image for larger view.
While uniquely suited to fulfill the objectives of many of NOAA’s atmospheric and oceanographic research programs, the P-3s were primarily tasked for hurricane reconnaissance and research missions during the hurricane season. This meant flying into the eye wall of tropical cyclones and collecting low- and mid-altitude data using direct, in situ measurements and by instruments known as “dropwindsondes” deployed into the storm from the aircraft. Dropwindsondes are small, lightweight, self-contained, and expendable devices that measure and transmit vertical profiles of barometric pressure, ambient air temperature, relative humidity, and wind speed and direction.
However, about twice a year, the P-3s were also tasked with another mission for the National Hurricane Center: to fly around hurricanes and collect data on the steering currents thought to govern a hurricane’s path. These flights contributed vital data to the hurricane forecasting models from which projected track predictions were made. But because the P-3s could only reach a maximum altitude of 23,000 feet, they only captured data from 60 percent or less of the troposphere, which is the layer of the Earth’s atmosphere where weather happens.
A New Mission
Beginning in 1982 with Hurricane Debby, the P-3s began flying a new mission for NOAA’s Hurricane Research Division. The experiment required dropping Omega dropwindsondes—pre-global positioning system (GPS) sondes that employed the very low frequency Omega navigation signals to estimate the sonde’s motion relative to the aircraft—in the areas around the storm, gathering three-dimensional data from the synoptic environment and feeding it into models that created hurricane track forecasts. “Synoptic” surveillance involves watching meteorological conditions over a wide region at a given moment.
NOAA’s two P-3 “hurricane hunters” have been flying into hurricanes since the mid-1970s. Click image for larger view.
The P-3s were not optimal for this experiment; nevertheless, the flights added an extra dimension to the art and science of hurricane forecasting.
These additional data improved the forecast models substantially –up to a 15 percent improvement in the accuracy of the forecasted track. This was so significant that collecting these data quickly became an invaluable forecasting tool for meteorologists, and therefore warranted the acquisition of a better platform to support this new mission. Beginning in 1994, NOAA actively pursued the purchase of a Gulfstream-IV jet to support this new synoptic surveillance tool.
Jump forward to 2005, the busiest hurricane season on record, when NOAA’s newest hurricane hunter aircraft, a sleek Gulfstream-IV jet, flew in the steering currents around Hurricane Katrina at an altitude of 45,000 feet.
NOAA’s highest-flying meteorological platform—the Gulfstream-IV jet—takes hurricane measurements to a new level.
The G-IV was nicknamed Gonzo after the Muppet character because of the unique shape of its radar nose-cone. The G-IV deploys GPS dropwindsondes that collect in situ data on the steering currents that influence the storm’s movements. GPS dropwindsondes are instruments that measure temperature, humidity, pressure, and winds between the height where the aircraft deploys them and the ground, and use GPS technology to determine wind speed and velocity.
The G-IV jet, capable of deploying dropwindsondes through the steering currents of the hurricane, made a significant difference in the track forecast of Hurricane Katrina. Click image for larger view.
Importantly, this jet is able to collect data covering 80 to 88 percent of the troposphere, which is a dramatic increase over the capabilities of the P-3s in previous experiments. This marks the successful transition of synoptic surveillance from an experimental tool to an operational tool for hurricane forecasting.
G-IV Capability and Instrumentation
Traditionally used as corporate jets, the capabilities of the G-IV make it the best platform available to NOAA for the new synoptic surveillance hurricane mission.
The G-IV can fly higher than both NOAA’s P-3s and the Air Force Reserve’s C-130s, which are also tasked with hurricane reconnaissance missions. This allows the G-IV to drop GPS dropwindsondes through more of the troposphere, collecting more data and offering a more complete vertical snapshot of the environment around a tropical system than the P-3s and C-130s. In addition, its speed allows the G-IV to cover more area and travel to targeted locations faster than other aircraft.
Aboard a P-3, a crew member prepares to deploy a dropwindsonde through the aircraft’s chute into the atmosphere. Click image for larger view.
The key instrumentation aboard the G-IV is the Airborne Vertical Atmospheric Profiling System (AVAPS) data system. Developed by the National Center for Atmospheric Research, each AVAPS can receive and process data from as many as four dropwindsondes simultaneously. This is essential for obtaining a fine horizontal distribution of soundings.
Dropwindsondes are the primary data collection instruments aboard the G-IV and are deployed through a pressurized launch chute over specific locations identified as most critical by NOAA’s National Hurricane Center.
The GPS dropwindsondes are more capable than their predecessors, the Omega dropwindsondes, provide better accuracy in wind profiling, and can be deployed worldwide.
A Typical Hurricane Mission Today
The art and science of hurricane track forecasting has been, and will continue to be, dramatically affected by the data acquired by NOAA’s G-IV.
In 1985, predictions of tropical storm movement and intensity were reactive. The P-3s, working with the Air Force Reserve’s C-130s, collected data that were used to extract track and intensity trends to make predictions.
In 2005, using the data acquired from the G-IV’s synoptic surveillance flights, forecasters were able to offer more predictive forecasts. According to James Franklin, a forecaster with the National Hurricane Center, “the G-IV’s mission is a great example of a transition of research to operations. It is another piece in the process of making progress in forecast track accuracy.”
Although the coordinated hurricane missions of the P-3s and G-IV have taken on an almost routine rhythm, advancing technology promises to continue transforming NOAA’s hurricane surveillance, reconnaissance, and research mission. The integration of a Doppler radar on the G-IV in the near future will give scientists an unprecedented vertical profile of wind speed, direction, and precipitation. These data can then be fed into ever-improving intensity forecast models.
Data from the G-IV and the P-3, acquired from different heights during a hurricane, complement each other and provide a more complete picture of storm dynamics. Click image for larger view.
What was once an experimental tool using NOAA’s P-3s only a couple times a year has become a required tool any time a tropical system threatens landfall on the U.S. or its interests in the Atlantic Basin.
The G-IV has completed more than 175 hurricane synoptic surveillance flights since its incorporation into NOAA’s hurricane mission in 1997. That’s compared to only about 20 similar research missions between 1982 and 1996. With its undeniable contribution to the National Hurricane Center’s goal of increasing the accuracy of hurricane track forecasts, the G-IV has become a valuable asset to NOAA and the nation.
Contributed by Erika Brown, with thanks to Jack Parrish, James Franklin, Dr. Jim McFadden, CAPT Sean White, LCDR Eric Berkowitz, LCDR Randy TeBeest, CAPT Mark Finke, and Lori Bast, NOAA's Office of Marine and Aviation Operations