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Observing Prince William Sound conditions Two-week ‘Sound Predictions 2009’ exercise tests weather and sea condition data gathering and forecasting for ocean observation Alan Bailey Petroleum News
Encircled by jagged mountain ranges, bordered by glacier-carved fiords and battered by storms sweeping in from the Gulf of Alaska, Prince William Sound would seem to offer some unique challenges to those who wish to perfect the science of forecasting ocean and weather conditions. But, as a relatively self-contained region of manageable size on Alaska’s vast 44,000 miles of remote and rugged coastline, and with some ocean observing already in place as a consequence of the neighboring Valdez Marine Terminal and its associated tanker traffic, the sound has become the initial focus of research for the Alaska Ocean Observing System.
“It’s a small enough area. It’s close by. So we chose that as our focal point,” Molly McCammon, AOOS executive director, told a media briefing July 16.
McCammon was introducing a project called “Sound Predictions 2009,” in which between July 19 and Aug. 3 a team of scientists from the University of Alaska Fairbanks, the Cordova-based Oil Spill Recovery Institute and some other research groups is working in the sound, making weather and ocean observations both to test various methods of data acquisition and to test computer-based forecasting models that can help predict the changing weather and sea conditions.
More accurate predictions This fieldwork represents the culmination of six years of effort, setting up meteorological stations and observation platforms, and developing the computer models, to help people such as fishermen, search-and-rescue personnel and oil spill responders by providing more accurate predictions of winds, weather, ocean currents and ocean conditions, McCammon said.
“We have a strong interest in being able to improve oil spill response capabilities, and the ocean observing network is definitely one of the components that we see as being able to improve our capabilities,” said Scott Pegau, research program manager for the Oil Spill Recovery Institute.
And a prime purpose of the field testing is to gain an understanding of which observation techniques add value to the forecasting models, thus enabling decisions about what minimum, cost-effective observation package might be deployed in other Alaska coastal regions, such as in the Gulf of Alaska or Cook Inlet, McCammon said.
The field exercise will also test the practicalities of delivering and displaying data from the sound, making the data available to both researchers and the general public, Pegau said.
Complex in detail But those pesky mountains and fiords around Prince William Sound play havoc with winds and currents, pushing the capabilities of forecasting models and requiring specialized model development.
“It’s a real interesting place to start this type of effort because of the complexity,” Pegau said.
For example, the National Weather Service’s weather forecasting model’s data, arranged on a 12-kilometer grid, cannot deal adequately with the impact on local weather systems of small-scale geographic features.
“At 12 kilometers most of those little fiords disappear,” Pegau said. “A lot of the mountains disappear.”
But, with the amount of necessary computer processing escalating as the level of detail in a model increases, the models developed for Prince William Sound only include fine detail within the area where the forecasts are required, expanding to a more broad-brush level of detail over a wide region around the area of interest.
“So by scaling it down we’re able to provide the boundary conditions that we need and a computational efficiency that’s reasonable,” Pegau said.
And the Regional Ocean Modeling System model that the AOOS team is using to simulate ocean conditions in Prince William Sound works in three dimensions, to project currents and other ocean parameters over a range of depths.
Drifter buoys One of the prime observational techniques being used on the water to test the ocean model is the placement of drifter buoys, equipped with GPS radios and Iridium phones to transmit their locations, and carrying subsurface drogues that cause each drifter to move with the sea current at a specific ocean depth. The currents traced by the drifters can be compared with currents predicted by the computer model.
And, to test improvements in the modeling techniques in recent years, these observations are taking place in the same area as that of a similar exercise in 2004 — initial model runs in 2004 predicted a clockwise current around the sound, in contradiction to the counter-clockwise flow that was actually observed, Pegau said.
The team has also established high-frequency radar sites around the sound, to map surface currents by measuring the Doppler shift in radar signals bounced off sea waves.
The AOOS team wants to see whether the observations and the modeling results will prove of practical value in support of oil spill models operated by the National Oceanic and Atmopheric Administration and by Alyeska Pipeline Service Co., the operator of the Valdez Marine Terminal, and in support of U.S. Coast Guard search and rescue models. In addition, the team is developing a biological model to simulate and predict the movement of nutrients in the waters of the Sound.
Fixed buoys, boats and robots As well as deploying the drifters, the AOOS team has arranged the measurement of currents, water temperatures and salinities through fixed buoys, one of these operated by the National Data Buoy Center and others attached to oil response mooring buoys operated by Alyeska’s Ship Escort-Response Vessel System. These latter buoys can also determine plant life levels in the water by measuring the water chlorophyll content. Large buoy moorings at the two main entrances to the sound measure water flow in and out of the sound.
And for weather observations the AOOS team has placed eight new weather stations around the sound.
Boat surveys conducted during the two-week field exercise are measuring various parameters over a range of water depths at various locations — the boats will also deploy a couple of autonomous underwater vehicles, underwater robots that can be programmed to follow specific underwater trajectories, collecting data, Pegau said.
One of these robots, looking like a small torpedo, is propeller driven and can cruise at about three knots for six to eight hours, measuring the temperature, salinity and chlorophyll levels. The other robot has wings that enable it to operate as an underwater glider, causing the device to move forward as it rises or falls as a consequence of programmed alterations in the amount of ballast it contains. The glider-like device could operate continuously for the entire two weeks of the field tests. Both devices rise to the surface periodically, to automatically verify their locations and accept any new instructions, Pegau said.
Observation balloon In addition to deploying devices with instruments for collecting data, the team is testing an observation balloon, equipped with a video camera and tethered to the back of a vessel, to enable visual surveillance from a height of about 500 feet. If this system works, oil spill responders could use it to see what is around them in the water and possibly home in on oil slicks — the camera can capture both visible light and infrared, leading to the possibility of spotting oil on the water at night and perhaps in weather conditions that prohibit conventional aerial surveillance.
Information about the Sound Predictions 2009 program can be found on the AOOS Web site at www.aoos.org. AOOS is a federal, state and private partnership that forms part of a U.S. ocean observing system, itself part of an international ocean observing network.
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