Narration: Rob Gutro


As the Hurricane and Severe Storm Sentinel campaign takes off, the Global Hawk aircraft will serve as a long-distance airborne laboratory designed to study the factors that can create and drastically change tropical cyclones. This airborne mission-- HS3 for short--is studying those storms, and one of the targets of study is the Saharan Air Layer. This warm, dusty mass of air originates from the Sahara and drifts west into the Atlantic. The exact impact of the Saharan Air Layer is unclear. Research has shown that the SAL can weaken a storm by promoting downdrafts, and its strong winds can increase vertical wind shear in and around the storm. During the HS3 campaign, scientists will analyze the Saharan Air Layer using a suite of instruments on board the unmanned Global Hawk aircraft. One instrument, the Cloud Physics Lidar, will gather data straight through storms and dusty air layers.

Braun: The Cloud Physics Lidar, or CPL, gives us the vertical profile of the dust. So we can see not only where within the atmosphere it is, but get a relative sense at least of how much dust there is and the extent to which it's getting wrapped into the storm circulation.

The lidar works by sending 5,000 rapid light pulses a second that bounce and scatter off any particles they encounter. The light that bounces back to the instrument can help distinguish the type of particle, which then gives us a better look at the anatomy of the storm. Data from the Cloud Physics Lidar will not only improve models of the Saharan Air Layer, but also expand the understanding of how the dust interacts with the storms.

Braun: That's really the measurement challenge is to be able to collect the needed observations of where the Saharan Air is, what its characteristics are, how much does it penetrate into a storm, and when it does, what is it actually doing to the storm? How is it inhibiting development? And those are things that we're trying to answer.