June 2, 2009
Alaska Radar System Aids Research On Space Weather, Solar Storms
SRI International, an independent nonprofit research institute, announced today that early scientific results are now available from the Advanced Modular Incoherent Scatter Radar (AMISR), a modular, transportable radar system funded by the National Science Foundation (NSF) that has recently completed the first two years of operation.
Scientists are using the novel system to investigate the interaction of upper atmospheric phenomena, which are driven by energetic particles and the solar wind that cause spectacular displays of the aurora borealis, with lower atmospheric phenomena such as tropospheric storms and weather patterns. Remote operation and electronic beam steering allows researchers to operate and position the radar beam instantaneously to accurately measure rapidly changing space weather events.
"The AMISR system is unique among upper atmospheric radars in that it is capable of observing small-scale and temporally dynamic phenomena such as the aurora and space weather storms. Scientists need to understand how the upper atmosphere behaves on these scales to adequately study climate change and other processes linked to the transfer of energy and momentum from the surface of the sun to Earth's atmosphere," said Robert Robinson, AMISR program manager at NSF.
New Research Investigates Auroral Arcs and High-Altitude Clouds
A recent issue of the Journal of Atmospheric and Solar-Terrestrial Physics (JASTP) is dedicated to early research results from the Poker Flat, Alaska deployment of AMISR (known as PFISR).
The article, "Coordinated Optical and Radar Image Measurements of Noctilucent Clouds and Polar Mesospheric Summer Echoes," by Michael Taylor, Ph.D., professor at Utah State University, describes the first detailed investigation of the common horizontal and vertical structures of radar and optical mesospheric clouds. These are the highest altitude clouds, which form in the mesopause, the coldest part of the Earth's atmosphere. These high-altitude clouds may be an indicator for global climate change since their increasing occurrence rate implies a cooling mesopause.
A second article, "Volumetric Imaging of the Ionosphere: Initial Results from the PFISR," by Joshua Semeter, Ph.D., associate professor at Boston University, presents the first three-dimensional images of the aurora borealis seen from PFISR. Volumetric imaging allows scientists to observe in three dimensions where and how magnetospheric energy is deposited into the system that couples the Earth's ionosphere and upper atmosphere. Without this kind of detailed understanding, space weather models can not reproduce or predict future behavior.
Novel Radar is Dedicated Solely to the Research Community
NSF operates other large incoherent scatter radars, including ones located in Greenland, Peru, Puerto Rico, and Massachusetts. The SRI-designed AMISR is the first NSF-funded radar system that was developed and built specifically for scientific research.
NASA has used the array to determine the most optimal space weather conditions for launching scientific rockets. Since AMISR is capable of simultaneous monitoring in multiple directions, measurements can provide a multi-dimensional view of Earth's upper atmosphere and ionosphere in real-time, providing a unique perspective for scientific rocket and satellite missions. AMISR is a significant technical advance from systems that provide one-dimensional measurements along a single trajectory.
AMISR also supported the International Polar Year (IPY), an international research program focusing on the polar regions of the world. Jan Sojka, Ph.D., professor at Utah State University, is one of many scientists who have requested experiment time on the new radar. His objective is to study how the ionosphere changes in response to energy input from above and below. He scheduled AMISR observations every 10 minutes for the entire IPY.
Sojka explained, "The year-long AMISR data set contained the information we needed to resolve long-standing questions about how the ionosphere responds to energy input associated with such phenomena as the aurora borealis and atmospheric waves and tides. Only AMISR has the necessary temporal and spatial resolution to study this very dynamic region of Earth's atmosphere."
Initial results from Sojka's work are detailed in the article, "The PFISR IPY Observations of Ionospheric Climate and Weather," also in the PFISR special issue.
AMISR began operating in January 2007. The AMISR system at Poker Flat was the first of three radars constructed by SRI. The next two radars are being constructed in Arctic Canada, at Resolute Bay in the territory of Nunavut. The first of the two radars will become operational later in 2009. These incoherent scatter radars are the closest in the world to the magnetic north pole (an important distinction when it comes to ionospheric and magnetospheric research) and provide unprecedented views of the complex physical processes that couple the sun, magnetosphere, and ionosphere.
"Because the very large AMISR system is configured in modules, the facility can be relocated for studying upper atmospheric activity around the globe," said John Kelly, Ph.D., director of SRI's Center for GeoSpace Studies. "In addition, each of the three antennae faces of the system can operate together or can be independently deployed in up to three separate locations. This facilitates comprehensive data gathering to increase our scientific understanding of upper atmospheric phenomena, which ultimately will help prevent the potentially large economic losses that can result from severe space weather events."
In addition to funding from NSF, several companies supported the SRI-led project. These include subcontractor Sanmina-SCI, which manufactured the Antenna Element Units, the basic building blocks of the radar panels. The Massachusetts Institute of Technology (MIT) served as the co-investigator on the project.
Silicon Valley-based SRI International is one of the world's leading independent research and technology development organizations. Founded as Stanford Research Institute in 1946, SRI has been meeting the strategic needs of clients for more than 60 years. The nonprofit research institute performs client-sponsored research and development for government agencies, commercial businesses, and private foundations. In addition to conducting contract R&D, SRI licenses its technologies, forms strategic partnerships, and creates spin-off companies.
SRI's Center for GeoSpace Studies researches the fundamental processes governing the nature of the upper atmosphere and space environment. Experimental studies use incoherent scatter radar, satellite and optical instruments, and radiowave diagnostics. Under the auspices of the National Science Foundation, SRI's Center operates, manages, and conducts research at a facility in Sondrestrom, Greenland, and at the Resolute Bay Early Polar Cap Observatory in Canada.
NSF-Funded Radar Array Provides First Comprehensive View of the Upper Atmosphere
Advanced Modular Incoherent Scatter Radar (AMISR) is the first system to provide scientists with the technology necessary to collect critical data and study global climate trends from year to year. Scientists can now investigate the energy and momentum transfer among all layers of the Earth's upper atmosphere, accessing critical data on the complex physical processes that comprise the sun, magnetosphere, and ionosphere. Data collected from the high-latitude atmosphere and ionosphere provide an opportunity for early detection of climate-change phenomena. Space weather events, which can potentially damage and interrupt power grids and satellite and electronic communication, are also monitored.
AMISR measures 30 meters on a side and is made up of 4,096 antennas, giving a combined power of up to two megawatts. By phasing the signal coming from the individual antennas, the radar beam can be steered almost instantaneously from one position in the sky to another. This unique feature of AMISR is especially important for studying rapidly moving features of the atmosphere.
Collecting Incoherent Scatter Radar from an Array of Antennas
The term "incoherent scatter" refers to the way in which transmitted radio waves are reflected by ambient electrons in the atmosphere. Using high-powered transmitters and sensitive receivers, scientists can analyze the backscattered signals to determine the density, temperature, and velocity of electrons in the ionosphere over several hundreds of kilometers of altitude. Where other incoherent scatter radars use a single high-powered transmitter, AMISR uses an array of antennas, each of which is driven by a specially designed, solid-state, 500-watt transmitter.
AMISR can be operated remotely and also collect data from several directions at the same time. Currently, the radar is being used to study the aurora borealis and other dynamic features of the high-latitude ionosphere. By measuring the electric fields and particles at high latitudes, scientists can study how the magnetosphere, an immense comet-shaped structure around the Earth that extends tens of thousands of kilometers into space, changes in response to solar storms. This is important for predicting space weather, which can disrupt technical systems such as electric power distribution, navigation, communication, and aviation.
3D Views Provide Accurate and Comprehensive Space Weather Analysis
AMISR has enabled researchers to better understand how the magnetosphere and solar winds deposit energy into the Earth's atmosphere. By studying radar clouds and aurorae in three dimensions (two horizontal, one vertical), scientists can determine whether a change in the upper atmosphere at one location is caused by a real change in the overall system or simply the movement of a plasma cloud that already existed. (Did the plasma cloud form here or move from another location?)
This is crucial for truly understanding this coupled system and to make predictions about future behavior.
On the Net:
- Advanced Modular Incoherent Scatter Radar
- National Science Foundation
- Journal of Atmospheric and Solar-Terrestrial Physics
- Article: Volumetric Imaging of the Ionosphere: Initial Results from the PFISR
- International Polar Year
- SRI International
- SRI's Center for GeoSpace Studies