EXPANDED VIEWS OF THE ATMOSPHERE :
A new satellite network will capture more information than ever about the atmosphere.
Researchers working on COSMIC include (left to right): Chris Rocken and Bill Kuo of UCAR and Chio Zong Cheng, Tie-Yue Liu, and Tsai-Hao Fu of Taiwan’s National Space Organization. (Photo by Jonathan Spangler, UCAR.)
One of the basic challenges confronting scientists is the need for observing the atmosphere in ever-increasing detail. Even though various instruments provide views, each has its limits. Satellites cannot see through thick clouds, balloon-mounted radiosondes are launched only at select times and in limited locations, and radars do not provide useful observations of the upper atmosphere.
But dramatic changes are in store. A consortium of U.S. and Taiwanese agencies, using a system designed by UCAR, is set to launch a revolutionary satellite network in 2006. By deploying technology that measures the density of the atmosphere with radio signals, the satellites will provide a consistent, global picture of the atmosphere regardless of weather conditions.
Called COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) in the United States and FORMOSAT-3 in Taiwan, the $100 million project is the largest scientific collaboration ever between the United States and Taiwan.
“COSMIC is an important step in gathering the data scientists need to better understand the atmosphere,” explains NCAR scientist Ying-Hwa “Bill” Kuo, director of the UCAR COSMIC program. “It has the potential to lead to major advances in climate and space weather research, while significantly improving global and regional weather prediction.”
An array of six satellites will collect approximately 2,500 profiles of atmospheric density every 24 hours. The profiles will enable scientists to deduce information on atmospheric temperature, moisture, and pressure. These sounding profiles will be gathered nearly uniformly around the globe, including over vast stretches of ocean inadequately monitored by current satellites and other tools. The COSMIC data, which will be made available to meteorological centers around the world within a few hours of being obtained, will help forecasters to better predict storm patterns, including the tracks of hurricanes and typhoons as well as winter storm systems.
The stability and accuracy of the measurements should be a boon to scientists quantifying long-term climate change trends. In addition, COSMIC’s measurements of electron density in the ionosphere are expected to improve analysis and forecasting of space weather, particularly geomagnetic storms that can increase drag on satellites, play havoc with communications systems, and disrupt power grids on the ground.
Radio occultation on a large scale
COSMIC relies on the Global Positioning System and a technology known as radio occultation. A satellite in low-Earth orbit receives radio signals from GPS satellites. As the receiving satellites rise or set behind the Earth relative to the GPS satellite (a process known as occultation), the radio waves pass through the atmosphere and are slowed and bent by molecules. By measuring these subtle signal changes scientists can determine underlying atmospheric conditions such as air density, electron density, temperature, and moisture.
“This is the first time the technique of radio occultation has been used on a large scale in near real time to provide a continuous monitoring of worldwide atmospheric conditions,” Kuo says.
UCAR and its collaborators began exploring the use of GPS-based observing systems in 1995 with the successful launch of a proof-of-concept mission, known as GPS Meteorology. The COSMIC partnership had its genesis two years later, when Taiwan’s National Space Program Office (now the National Space Organization) began planning a satellite mission.
For Taiwan, the benefits are twofold: the island nation will gain better predictions of potentially destructive typhoons while also advancing its aeronautics industry. UCAR, for its part, will gain important scientific insights while helping to refine global weather forecasting, climate monitoring, and space weather forecasting.
The six satellites will be launched together on a Minotaur rocket from Vandenberg Air Force Base in southern California. Each one weighs about 70 kilograms (155 pounds) and will carry three instruments: a GPS radio occultation receiver to capture information on atmospheric conditions, a tiny ionospheric photometer to measure the horizontal distribution of electron density in the upper atmosphere, and a tri-band beacon to transmit radio signals to ground stations worldwide.
Taiwan’s National Science Council, its National Space Organization, and the U.S. National Science Foundation (NSF) are providing primary support for COSMIC. The Taiwanese agencies, with their industry partners, are overseeing the construction of the satellites. UCAR is responsible for the onboard instruments, and it will also process and disseminate the satellite data. Other U.S. collaborators include NASA, NOAA, the Air Force, and the Office of Naval Research.
An artist’s impression of a COSMIC satellite in orbit. (Image ©UCAR, courtesy COSMIC)
Flying in and out of Taiwan can be challenging because the island’s mountains and the surrounding ocean often contribute to adverse weather conditions. To bolster air safety, the Taiwan Civil Aeronautics Administration selected NCAR in the late 1990s to create a new weather information and warning system for the island.
The resulting Advanced Operational Aviation Weather System (AOAWS) is helping to safeguard aircraft against weather threats such as tropical cyclones, major thunderstorms, in-flight icing, and turbulence. Pilots, controllers, forecasters, and other users can chart a flight route within Taiwan’s airspace, obtain hazardous weather information, and gather routine data and forecasts along that route.
Taiwan experts study NCAR's weather information and warning system. (Photo ©UCAR.)
“This is a true technology transfer success story,” says NCAR scientist William Mahoney, who helped oversee the project. “Taiwan now has state-of-the-art aviation weather technology that far surpasses international safety standards.”
The system relies on a powerful computer forecasting model, as well as such instruments as Doppler weather radars, Low Level Wind Shear Alert System sensors, satellites, aircraft reports, and the Taiwan lightning detection network. NCAR will expand the system in 2006: new capabilities will include thunderstorm nowcasting and the addition of an NCAR computer model that provides an exceptionally detailed picture of the atmosphere.
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