Instead of chasing storms, NASA researchers are using new weather forecasting methods to see storms ahead of time.
By studying lightning, a team of scientists is working to develop new ways to predict the intensity of incoming hurricanes. In general, an increase in thunderstorms in a storm indicates that the storm is likely to be stronger.
However, even weaker hurricanes sometimes have large outbreaks of thunderstorms, so forecasters must carefully analyze additional data to determine what an outbreak of lightning actually is in order to predict the intensity of a hurricane.
A team of scientists led by NASA researcher Patrick Duran recently released a study on the evolution of lightning flash density, flash size and flash power during Hurricane Dorian. Duran and his team support NASA’s research and analysis program, the Weather Focus Area, as part of a short-term forecasting research and relocation center at NASA’s Marshall Space Flight Center Huntsville,in Alabama.
Duran and colleagues used a new tool from the National Ocean and Atmospheric Administration, the latest series of geostationary operational environmental satellites called Geostationary Lightning Mapper (GLM), to capture information about hurricane lightning. GLM continuously detects the size and strength of lightning even above open sea.
“In this study,” Duran said, “we were able to prove that the thunderstorms in Hurricane Dorian were larger and more energetic when the storm was intensifying than when it was weakening.”
Using GLM, the team analyzed the two most distinct lightning outbreaks in the innermost part – or inner-core – of Hurricane Dorian.The first outbreak occurred during intensification, with periods of rapid intensification (defined as an increase of 30 kt (35 miles) in sustained winds over 24 hours).
During rapid intensification, the number of internal-lightning flashes increased as the maximum wind concentrated within the radius, or with the distance between the center of the cyclone and its intense wind band. The second outbreak occurred while weakening.
As the weakening continued, there were still numerous flashing within the maximum wind radius of a flash rate more than three times during the intensification – a signal usually related to the strengthening. These flashes were much shorter and less powerful than the intensification periods.
The GLM sensor provides continuous monitoring of lightning in most of the western hemisphere, including the Atlantic and Eastern Pacific basins. The GLM sensor, effectively an optical event detector, measures changes in the illumination of the cloud top radiance produced by lightning.
GLM not only has the ability to detect the position of the flash but also the average flash area and total optical power enables lightning testing from a variety of new perspectives.
“We further argued that changes in the location of lightning could help identify mechanisms that affect storm intensity.” “This information can help explain how the structure of the storm changes to peak intensity and can potentially help forecasters interpret whether a lightning outbreak signifies storm intensification or weakening.”
“In the future,” Duran said, “we will analyze a large number of storms to discover how lightning patterns differ between storms that intensify and those that weaken. We think these patterns could be particularly effective in quickly identifying density, which is very difficult to predict.”
“We are still learning how to interpret and use GLM in operational tropical cyclone analysis and forecasting,” said Stephanie Stevenson, a meteorologist and programmer at the National Hurricane Center. “This study pushes us to understand how the unique regions and energy fields of GLM can be used in conjunction with lightning density to observe storm evolution.”