UAH's Apke uses satellite scans to study thunderstorms

Can you tell much about a thunderstorm by starting at the top?

Jason Apke, a doctoral student in atmospheric science at The University of Alabama in Huntsville (UAH), thinks he might one day be able to use images of cloud tops taken every minute by a National Oceanic and Atmospheric Administration (NOAA) weather satellite to predict hail and strong rain, maybe even conditions that might lead to tornadoes.

"Currently, the meteorology community thinks of Super Rapid Scan satellite images as a series of pretty pictures," Apke said. "The question is whether we can take something that is a pretty picture and make science out of it."

Stringing together images from the Super Rapid Scan imager on the NOAA Geostationary Operational Environmental Satellite-14 (GOES-14) satellite into short movies, Apke found motion related to strong storms can be seen in structures on top of the storm clouds.

"Vorticity (rotation) with supercells, for instance, extends all the way to the cloud top, and you can see it with the Super Rapid Scan, which we've never been able to do before," Apke said.

Using the movies along with computer photogrammetry algorithms, he is able to identify flow fields that move around the storm top. He looks for the wind direction and speed, finding where cloud fields are rotating or moving in opposite directions.

"Mainly we're focused on what we can do with these flow fields, and how we can use them in a meteorological sense," he said. "Cloud top divergence gives us another way to determine the strength of the updraft in a storm."

Cloud top divergence, or motion away from a point, is related to how fast an updraft is moving when it reaches the storm top. And divergence is a more constant feature of the cloud top sequences, Apke said. "Not all strong storms produce the cloud top vorticity we've been seeing, but we do see constant, long-lived divergence signals associated with supercells."

That data about spin and growth inside a storm, combined with the shear between air masses moving in opposite directions, might one day provide useful information about which storms are about to produce violent weather and when. Apke and his faculty advisor, associate professor of atmospheric science Dr. John Mecikalski, are going to start by trying to forecast hail.

"Hail size is closely related to updraft strength," Apke said. "Larger updrafts can hold larger hail stones, but existing weather observing systems can't easily measure a storm's updraft strength."

While cloud top divergence might be used to improve forecasts in regions where weather radar is present, it might be especially useful in those parts of the world where weather radar isn't available.

"If you don't have radar information, such as for marine areas and countries without advanced radar networks, you have to use satellite data alone to find strong storms and produce warnings," Apke said. "We might potentially use cloud top divergence and vorticity to better inform that forecasting community."

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