Image Caption: NASA's unmanned Global Hawk No. 872 on a runway at the agency's Wallops Flight Facility in Virginia. Credit: NASA's Wallops Flight Facility

Ellen Gray, NASAs Goddard Space Flight Center

Looking out the window of a commercial plane during takeoff is like taking the nickel tour of the profile of the atmosphere. As the plane ascends, what may start as a gloomy day on the ground, can turn into rain streaking across the window as you pass through the white-gray cloud, and then sunny skies above once the plane reaches cruising altitude.

NASAs Cloud Physics Lidar (CPL) instrument, flying aboard an unmanned Global Hawk aircraft in this summers Hurricane and Severe Storm Sentinel, or HS3, mission, is studying the changing profile of the atmosphere in detail to learn more about how hurricanes form and strengthen.

CPL profiles the atmosphere to get a two-dimensional picture of cloud and aerosols, from the top down, said Matt McGill of NASAs Goddard Space Flight Center in Greenbelt, Maryland, who led the instrument team that designed and built the CPL. Its data, presented as if it were a curtain hanging from the sky, shows whats in the atmospheres different layers.

From about 60,000 feet on the Global Hawk, twice the altitude of a commercial plane, 94 percent of the atmosphere lies below the instrument. The lidar works by sending rapid pulses of light that, like a radar beam, bounce and scatter off any particles they encounter, such as cloud droplets or dust particles. Some of the scattered light returns to the instrument where it records how long it took for the photons to leave and return giving the altitude of the particles.

[ Watch the Video: Making Saharan Air Apparent ]

CPL sends out 5,000 pulses of light per second in three different wavelengths, allowing the science team to discriminate between different types of particles, McGill said. Is it a cloud made of water? Is it a cloud made of ice or mixed [water and ice]? And we can say something about what type of airborne particle we are seeing. Is it dust or smoke or pollution?

For the scientists studying hurricanes, those distinctions are important. One of the major areas of study is how Saharan dust off of Africa travels across the Atlantic and affects hurricane formation and intensification. CPL data have been used to verify model projections of Saharan dust in the tropics. The CPL data showed dust layers had a vertical distribution different than models predicted. Instead dust layers occupied narrower altitude ranges. The finding led to an improvement in the dust models, which then feed into hurricane models.

Situated in the nose of the Global Hawk flying over the storm environment, CPL also has a role in on-the-fly mission planning. While in flight, the CPL sends its data back to the team on the ground. The mission scientists involved in the flight planning can sit there and watch the data with us in real time and say, Oh, were not getting what we want. Then they can go work with the flight planners and pilots to reroute the aircraft into different areas, said McGill. They love that.

The rest is here:

NASA HS3 Instrument Views 2 Dimensions Of Clouds