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[wind]

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[rain]
As the Hurricane and Severe

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Storm Sentinel campaign takes off, the Global Hawk aircraft

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will serve as a long-distance airborne laboratory designed to study the factors

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that can create and drastically change tropical cyclones.

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This airborne mission--

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HS3 for short--is studying those storms, and one of the

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targets of study is the Saharan Air Layer.

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This warm, dusty mass of air originates from the Sahara and

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drifts west into the Atlantic. The exact impact of the

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Saharan Air Layer is unclear. Research has shown that the SAL

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can weaken a storm by promoting downdrafts, and its

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strong winds can increase vertical wind shear in and around the storm.

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During the HS3 campaign, scientists will analyze the Saharan Air

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Layer using a suite of instruments on board the unmanned Global Hawk

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aircraft. One instrument, the Cloud Physics Lidar,

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will gather data straight through storms and dusty air layers.

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Braun: The Cloud Physics Lidar, or CPL, gives us the vertical profile

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of the dust. So we can see not only where within the atmosphere it is, but

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get a relative sense at least of how much dust there is

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and the extent to which it's getting wrapped into the storm circulation.

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The lidar works by sending 5,000 rapid light pulses a second

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that bounce and scatter off any particles they encounter. The light

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that bounces back to the instrument can help distinguish the type of particle,

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which then gives us a better look at the anatomy of the storm.

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Data from the Cloud Physics Lidar will not only improve models

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of the Saharan Air Layer, but also expand the understanding of how

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the dust interacts with the storms.
Braun: That's really the measurement challenge

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is to be able to collect the needed observations

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of where the Saharan Air is, what its characteristics are, how

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much does it penetrate into a storm, and when it does, what

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is it actually doing to the storm? How is it inhibiting development? And those

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are things that we're trying to answer.

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[beeping, thunder]

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