Meteorologists have been studying the suddenly changing tracks, rapid changes in structure and intensity, as well as sudden changes in rainfall of tropical cyclones. While great improvement in tracking these storms has been made over the past several years, more can be learned.
Progress in understanding the processes related to rapid intensification and secondary eyewall formation in hurricanes has been slow but with the use of NASA’s Global Hawk unmanned aircraft, scientists with NOAA’s Hurricane Research Division will be able to get a better understanding of why some hurricanes fluctuate, jumping from one category to another on the Saffir-Simpson hurricane wind scale in only a few hours.
NASAs Global Hawk unmanned aircraft
In December 2007, two Northrop Grumman RQ-4 Global Hawk aircraft were transferred from the U.S. Air Force to the National Aeronautics and Space Administration’s (NASA) Dryden Flight Research Center at Edwards Air Force Base in California, for use in high-altitude, long-duration science missions.
Each aircraft has a range of 11,000 nautical miles and can stay airborne for up to 26 hours. The first real use of Global Hawks was in 2010, with the Genesis and Rapid Intensification Processes (GRIP) project. Using a combination of onboard, manned and unmanned remote sensing instruments, scientists were able to observe and characterize the lifecycle of hurricanes.
These studies went on during the peak of the Atlantic hurricane season from August 15 through September 30 in 2010, with the GRIP deployment taking off in Ft. Lauderdale, Florida. Below is a photo taken by Global Hawk of Hurricane Earl. Earl was a Cape Verde hurricane that caused damage in the northern Leeward Islands and made landfall as a Category 1 hurricane (on the Saffir-Simpson Hurricane Wind Scale) in Nova Scotia, Canada. It reached its peak intensity as a Category 4 hurricane over the western Atlantic.
Using Global Hawk in the 2015 Atlantic Hurricane Season
Strangely enough, with all the different tools scientists have at their disposal, including some that have been retooled for the mission, the one thing lacking has been a major hurricane. Rick Knabb, the director of the National Hurricane Center, gave a press briefing to reporters just a few weeks ago on the scientific gains made since Hurricane Katrina.
Knabb said the lack of major hurricanes the past three years has meant scientists have been unable to take full advantage of the Global Hawk, as well as satellites, underwater sleds, buoys, and even floating monitors dropped in front of tropical storms before they reach coastal areas.
“We don’t see a measurable improvement in our intensity forecast yet, especially over two or three years. We need to see a longer trend,” Knabb said. He added that, right now, scientists measure the accuracy of their storm intensity data by comparing their forecasts with the actual storm intensity, but after the fact. Knabb said that the average errors “have only come down a little bit.”
With Hurricane Danny, the Global Hawk will use 88 dropsonde packages. These are cylindrical monitoring equipment packages that are dropped into a storm or in the atmosphere around the storm. The equipment measures and samples wind, humidity, temperature, and other indices that are then uploaded into computer models.
Scientists can then predict a hurricane’s movement and intensity. Interestingly, scientists also measure the height of the ocean, determining where there is warm water, like the loop current. The loop current is a current that flows north between Cuba and the Yucatán Peninsula. It then loops north into the Gulf of Mexico, loops east and south before again moving east through the Florida Straits and joining the Gulf Stream. The Global Hawk is scheduled for 10 flights in late August and early September this year.
