EOL

EOL Seminar: The Design, Development, and Deployment of the HIAPER Cloud Radar (HCR)

The Design, Development, and Deployment of the HIAPER Cloud Radar (HCR)

J. (Vivek) Vivekanandan

Earth Observing Laboratory National Center for Atmospheric Research

Cloud droplets in 3D

October 1, 2015 | It seems like a simple question: When a wet cloud mixes with dry air, do the cloud's droplets evaporate completely one by one? Or do all the droplets shrink simultaneously, each giving up a tiny bit of its water at the same time? The two theories of what might happen to water droplets when clouds begin to dissipate were proposed more than 30 years ago. But evidence as to which one might be correct—information that could improve how clouds are represented in weather and climate models—has been hard to come by. The instruments traditionally used to measure droplets in clouds cannot view individual droplets in three dimensions while simultaneously recording the sizes of each droplet. The Holographic Detector for Clouds (HOLODEC) mounted on the wing of a research aircraft.  (Photo by Scott Spuler, ©UCAR. This image is freely available for media & nonprofit use.) That just changed. An experimental instrument built at the National Center for Atmospheric Research (NCAR) in collaboration with Michigan Technological University has given scientists a detailed look inside clouds using holography, the technique used to make holograms. What they learned, detailed in a new study published in the journal Science, is that droplets tend to either evaporate entirely or remain untouched. (Read more about the new study.) The Holographic Detector for Clouds (HOLODEC) uses laser light to take a 3D "image" of the droplets inside the cloud.  "It's a combination of camera technology and computing technology," said NCAR scientist Jeff Stith, a cloud physicist who heads NCAR's Research Aviation Facility. "The instrument basically takes a hologram of a thousand or so particles and the computer reconstructs each droplet. It's a huge computational effort that wouldn’t have been possible years ago." Profile of the ultraviolet laser beam used to generate the holograms. (Image by Scott Spuler, ©UCAR. This image is freely available for media & nonprofit use.) Stith is a co-author of the new study in Science along with NCAR research engineer Scott Spuler, who designed the optics for HOLODEC. Spuler worked on the instrument with study co-author Jacob Fugal when Fugal was a postdoctoral fellow through NCAR's Advanced Study Program. Fugal, who earned his doctoral degree at Michigan Tech, is now at the Johannes Gutenberg University of Mainz and the Max Planck Institute for Chemistry. Stith and Spuler worked with researchers from Michigan Tech to install HOLODEC on the wing of the National Science Foundation/NCAR C-130 and to fly the airborne laboratory into an appropriate cloud. Now that the results of the flight are published, Stith expects to hear from more scientists who believe HOLODEC could be useful in their own work. "The instrument is still somewhat experimental," he said. "But we anticipate it will be highly requested in the future." About the Article Matthew J. Beals, Jacob P. Fugal, Raymond A. Shaw, Jiang Lu, Scott M. Spuler, Jeffrey L. Stith. Holographic measurements of inhomogeneous cloud mixing at the centimeter scale, Science, doi: 10.1126/science.aab0751 Writer/ContactLaura Snider FundersNational Science FoundationU.S. Department of Energy      

EOL Seminar - Summer Undergraduate Program for Engineering Research Intern Project Presentations

Please join us for a seminar given by our four SUPER interns as they present the projects they have been working on this summer. 

Katie McMenamin 

EOL Seminar - Observations of Atmospheric Composition from Geostationary Satellite Constellation for Air Quality and Climate

Observations of Atmospheric Composition from the Geostationary Satellite Constellation for Air Quality and Climate

David EdwardsDirector, Atmospheric Chemistry Observations & Modeling (ACOM) LaboratoryNational Center for Atmospheric Research

Scientists tackle mystery of thunderstorms that strike at night

BOULDER – Thunderstorms that form at night, without a prod from the Sun's heat, are a mysterious phenomenon. This summer scientists will be staying up late in search of some answers. From June 1 through July 15, researchers from across North America will fan out each evening across the Great Plains, where storms are more common at night than during the day. The research effort, co-organized by the National Center for Atmospheric Research (NCAR) and several collaborating institutions, will use lab-equipped aircraft, ground-based instruments, and weather balloons to better understand the atmospheric conditions that lead to storm formation and evolution after sunset. Their results may ultimately help improve forecasts of these sometimes damaging storms. The Plains Elevated Convection at Night (PECAN) field campaign will involve scientists, students, and support staff from eight research laboratories and 14 universities. The $13.5 million project is largely funded by the National Science Foundation (NSF), NCAR's sponsor, which contributed $10.6 million. Additional support is provided by NASA, the National Oceanic and Atmospheric Administration (NOAA), and the U.S. Department of Energy. Aloft in the night Thunderstorms that form during the day are less puzzling than nighttime storms. The Sun heats the Earth’s surface, which in turn, warms the air directly above the ground. When that warm air is forced to rise, it causes convection—a circulation of warm updrafts and cool downdrafts—and sometimes creates a storm. The formation of thunderstorms at night, however, when the Sun is not baking the land, is less well understood. "At night, the entire storm circulation is elevated higher off the ground," said NCAR scientist Tammy Weckwerth, a PECAN principal investigator. "This makes observations of the conditions leading to nighttime thunderstorms much more challenging because that part of the atmosphere is not well covered by the network of instruments we normally rely on. The vast array of instruments available to PECAN researchers will allow them to collect data higher in the atmosphere. This data will help scientists characterize the conditions that lead both to individual storm formation as well as to the clustering and organizing of these storms into large-scale systems, which can drop significant precipitation. "Nighttime thunderstorms are an essential source of summer rain for crops but are also a potential hazard through excessive rainfall, flash flooding, and dangerous cloud-to-ground lightning," says Ed Bensman, program director in NSF’s Division of Atmospheric and Geospace Sciences.  "Weather forecast models often struggle to accurately account for this critical element of summer rainfall on the Great Plains.  The PECAN field campaign will provide researchers and operational forecasters with valuable insights into thunderstorms at night—and improve our ability to model them more accurately." Deploying in the dark The campaign, based in Hays, Kansas, will begin each day at 8 a.m., when a crew of forecasters starts developing a nightly forecast. At 3 p.m. the scientists will use the forecast to determine where across northern Oklahoma, central Kansas, or south-central Nebraska to deploy their mobile resources. Moving dozens of people around the Great Plains each night will be a challenge for PECAN, but it's also what distinguishes it from past field projects.  "Previous severe weather campaigns have focused mostly on daytime storms, for largely practical reasons, as it is more difficult to set up instruments in the dark," said Bart Geerts, a professor of atmospheric science at the University of Wyoming and a PECAN principal investigator. "But the large thunderstorm complexes travelling across the Great Plains at night really are a different beast." NCAR's portable S-Pol radar is one of the many instruments that will be deployed during the PECAN field campaign to help scientists better understand nighttime thunderstorms. (©UCAR. This image is freely available for media & nonprofit use.) Scientists believe that several interacting factors may contribute to nocturnal storm formation and maintenance: a stable layer of air at the surface; a strong wind current above that layer, known as a low-level jet; and atmospheric waves, some of which are called "bores," that ripple out from the storms themselves.  "But we just don't really know how they interact," Geerts said. "That's what PECAN is about." A better understanding of these storms will have relevance for areas beyond the Great Plains. Clustered nighttime thunderstorms are common in various regions scattered across the globe. A fleet of instruments PECAN will use three research aircraft, two of which—a University of Wyoming King Air and a NASA DC-8—will fly in the clear air away from the storms. Only the third, a NOAA P-3, which is widely used in hurricane research and reconnaissance, will be able to fly into the trailing region of storms.   The researchers will also rely on a number of ground-based instrument suites, known as PECAN Integrated Sounding Arrays, or PISAs. Six of the PISAs will operate from fixed locations around the study area, and four will be mobile, allowing them to be repositioned each night depending on where storms are expected to form. The instruments within each PISA vary, but collectively they will give each array the ability to measure temperature, moisture, and wind profiles, as well as launch weather balloons. Among the instruments are several newly developed at NCAR's Earth Observing Laboratory (EOL), including one that uses an innovative laser-based technique to remotely measure water vapor and an advanced wind profiler. Finally, the scientists will have a fleet of mobile and fixed radars, including the NCAR S-Pol. In all, PECAN researchers will have access to more than 100 instruments brought to the effort by partner institutions from across North America. "The sheer number of instruments being coordinated is unprecedented," said Weckwerth, who has participated in more than 15 other field expeditions. The planning necessary to manage this large collection of instruments—from finding property suitable for a fixed radar to making sure the mobile instruments are out of harm's way while tracking a storm—is being taken on by EOL's Project Management Office. That team is also responsible for housing, food and other logistics for the scientists and students who are participating in the campaign.

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