AOC-transformations

NOAA’s Gulfstream-IV Jet Takes Hurricane Track Predictions to New Heights

The Aircraft Operations Center (AOC), part of NOAA’s Office of Marine and Aviation Operations, operates, modifies, and maintains NOAA’s fleet of research aircraft. AOC personnel include NOAA Corps pilots and navigators, and civilian meteorologists and flight and electronic engineers and technicians. Among the aircraft AOC operates are the famed NOAA WP-3D Orion “hurricane hunters,” which have been flying through turbulent storms since the 1970s. In 1996, NOAA acquired a Gulfstream-IV jet and transformed it into a flying meteorological laboratory. Data from the G-IV added a new dimension to hurricane forecasting and has improved landfall prediction accuracy by more than 20 percent.

It is November 1995, the end of what was then the second busiest hurricane season in recorded history. There have been 19 named storms in the Atlantic basin, 11 of which reached hurricane strength. Hurricane Marilyn devastated the US Virgin Islands, and Hurricane Opal blasted her way across the Florida panhandle.

During that year, NOAA’s hurricane hunters, two Lockheed WP-3D Orion aircraft (known affectionately as Miss Piggy and Kermit) acquired by NOAA in 1975/1976, took off from NOAA’s Aircraft Operations Center and, fully laden with fuel, reached a maximum altitude of 23,000 feet. They were primarily tasked for hurricane reconnaissance missions, which meant flying into the eyewalls of tropical storms and collecting low- and mid-altitude data, including wind speed, barometric pressure, and wind direction, through direct measurements and by dropping instruments known as Omega dropwindsondes into the storm.

However, on average twice a year, the P-3s were tasked with a research mission for the National Hurricane Center: to fly in the environment around the hurricanes and collect data on the steering currents thought to govern a hurricane’s path. These flights, while contributing vital data to the computerized hurricane forecasting models that develop projected track predictions, only had the capability to capture 50% or less of the tropospheric data because of the altitude limitations of the P-3s.

Jump forward to 2005, the busiest hurricane season on record, when NOAA’s newest hurricane hunter aircraft, a sleek Gulfstream IV jet acquired in 1996, flies in the steering currents around Hurricane Katrina at an altitude of 45,000 feet. The G-IV, nicknamed Gonzo after the unique-shaped nose radar on the aircraft, deploys GPS dropwindsondes that collect in situ data about the steering currents influencing the storm’s movements. Importantly, the new jet is able to collect data covering 80-88% of the troposphere, the lowest layer of the earth’s atmosphere where weather happens. This is a dramatic increase over P-3-collected data from previous experiments, and represents the successful transition of synoptic surveillance (watching meteorological conditions over a wide region at a given moment) from research to operations for hurricane forecasting

From research to operations – the path to the G-IV

Beginning in 1982 with Hurricane Debby, the P-3s began flying a new research mission for the Hurricane Research Division. The experiment required dropping Omega dropwindsondes into the environment surrounding the storm, gathering data from the synoptic environment and feeding it into models that created potential track forecasts. While P-3s were not the optimal platform for this experiment as their altitude and speed capabilities limited the investigation of the environment surrounding a storm, they nevertheless added an extra dimension to the art and science of hurricane forecasting.

The impact of this additional data on the forecast models was substantial – the data demonstrated up to a 15 percent improvement in forecasted track accuracy. This improvement was significant enough to transition the research project into operations and warrant the acquisition of a more capable platform to support this new mission. Beginning in 1994, NOAA actively pursued the purchase of a Gulfstream-IV jet to support the transition of the synoptic surveillance research project into operations.

G-IV Capability and Instrumentation

Traditionally used as corporate jets, the speed and altitude capabilities of the G-IV make it the best platform available to NOAA for this new 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 higher altitude capability allows the jet to drop its GPS dropwindsondes through more of the troposphere, collecting more data and offering a more complete vertical snapshot of the environment around a tropical system. Its speed allows the G-IV to cover more area and get to targeted locations faster than other platforms.

The key instrumentation aboard the G-IV is the AVAPS data system. Developed by the National Center for Atmospheric Research (NCAR), this system can receive and process data from as many as four dropwindsondes simultaneously. Dropwindsondes are the primary data collection instruments aboard the G-IV, and are deployed through launch chutes in the aircraft at specific locations identified by the National Hurricane Center. The GPS dropwindsondes used by the G-IV are much more capable than their predecessor, the Omega dropwindsondes, providing better accuracy in wind profiling and the ability to be deployed worldwide.

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, would collect data that were used to extract the track and intensity trends from which predictions were made. In 2005, using the data acquired from the G-IV’s synoptic surveillance flights, forecasters were now 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 missions. The integration of a Doppler radar on the G-IV in the near future will give scientists an unprecedented vertical profile of data on wind speed, direction, and precipitation, to feed into ever-improving intensity and track forecast models.

What was once an experimental research project using one or both NOAA P-3s a couple of times a year has expanded into a routine mission requirement any time a tropical system threatens landfall on the US or its interests in the Atlantic Basin. The G-IV has completed more than 175 hurricane flights since its incorporation into NOAA’s hurricane mission in 1997; compared to only about 20 similar research missions carried out between 1982 and 1996. With its undeniable contribution to the National Hurricane Center’s goals of increasing the accuracy of hurricane track forecasts, the G-IV has proven to be a valuable asset for NOAA and the Nation.

On the Web: www.aoc.noaa.gov

Submitted by Erika Brown, with thanks to Jack Parrish, James Franklin, Eric Berkowitz, Randy TeBeest, and Sean White for their contributions.