Computer models aid Japanese nuclear response

U-Md. research team wants more data made public

As the Japanese nuclear crisis continues to unfold, the airborne spread of radioactive materials from the stricken reactors at the Fukushima Daiichi power station continues to be a key concern of Japanese and American officials. To help determine the path that any hazardous emissions are likely to take, scientists are employing specialized computer models, known as “trajectory models,” which can take into account factors such as winds and temperatures aloft to determine how high a parcel of air is likely to climb, how far it may go, and where it may be within certain timeframes.

In the local area, a team from the University of Maryland at College Park has been providing publicly viewable trajectory model projections for emissions of radionucleides from the Fukushima facility, in an effort to address a need they say was created in part by the lack of information being put out by U.S. and Japanese authorities.

Using the HYSPLIT model developed by the National Oceanic and Atmospheric Administration (NOAA) in partnership with Australia’s Bureau of Meteorology, scientists at the University of Maryland at College Park have been able to provide evidence to back up recent statements by American officials playing down the public health risks to the West Coast from the radioactive plume emanating from the Fukushima facility.

HYSPLIT model for March 23. Courtesy University of Maryland.

“We had heard everyone saying this stuff is going to be too dilute to get to America, but we wanted to check ourselves,” said Ross J. Salawitch, an atmospheric scientist at the University of Maryland, noting the importance of putting the information in the public domain. “Basically we think this is quite benign for North America, and unless the situation on the ground changes dramatically there is no reason to change that.”

According to Salawitch, one of the key factors determining the destination of any radioactivity from the Fukushima facility is the height to which the emissions are lofted. Since very little is publicly known about the precise quantities, loft heights, and other technical details about the emissions, he says there are significant uncertainties involved with his group’s plots, as well as those from other entities.

”The notion that you can track an air parcel precisely as it travels across the Pacific is fanciful,” he said. “The difficulty in doing that is we really don’t know what is being emitted.” That information, if known at all, is being closely held by Japanese authorities and the U.S. government, which has a team of about 40 nuclear energy experts on the ground in Japan equipped with sophisticated monitoring gear.

Department of Energy (DOE) experts are feeding their monitoring data into trajectory models, such as HYSPLIT, to arrive at more realistic simulations of just how much radioactive materials are likely to be transported away from the plant, along with the critical questions of the distance and timing of that transport. Those model results are being shared with the Japanese government, but are not publicly available in the U.S.

By keeping the detailed information regarding emissions amounts close to the vest, however, the University of Maryland team says the Energy Department is making it difficult for outside researchers to come to more robust conclusions and communicate them with the public. Rather than utilizing official trajectory forecasts, American officials are relying more heavily on information gleaned from monitoring stations on the West Coast that are detecting trace amounts of radiation from Japan, levels that so far have been far below thresholds for harming human health.

Still, the University of Maryland researchers say the American public could benefit from knowing more about the path any additional radioactive materials are likely to take, which depends on knowing how much and what kinds of materials are being lofted into the skies above Fukushima. “It’s unfortunate,” said Jeff Stehr, who has been producing the trajectory models along with Salawitch and other colleagues. “Why not release some of these numbers?”

(1:25 p.m. update: Yesterday, DOE released measurements of the cumulative amounts of radiological materials that have settled on the ground in Japan, noting that “nearly all elevated readings are within 25 miles of Fukushima Daiichi.” DOE has not, however, released its trajectory modeling or real-time information from any continued aerial monitoring missions that could shed light on the ongoing emissions from the nuclear plant, which would aid researchers such as Salawitch and his colleagues.)


The HYSPLIT model, which is short for “HYbrid Single-Particle Lagrangian Integrated Trajectory model,” was designed for just this type of emergency situation, although it is usually called into action for more common incidents, such as chemical spills, large fires, and even volcanic eruptions that can send ash plumes into the paths of jet airliners.

The model is designed to hone in on how small-scale, difficult-to-detect particles are likely to flow through the atmosphere. HYSPLIT is not unlike a police dog at an airport, using its sense of smell to sniff out potentially dangerous packages from the piles of innocuous luggage, except the HYSPLIT model actually predicts where those “packages” are likely to go while traveling the atmospheric conveyer belt.

The HYSPLIT model takes in weather observations and forecasts from NOAA, and allows researchers to choose where and when particles are put into the model. For example, modelers could choose to add hazardous radioactive materials between ground level and 2,000 feet in height over the Fukushima Daiichi plant. From that point, using weather forecast information, HYSPLIT would look at the forecasted winds in that column of air, move the particles, take a step forward in time, and repeat the process until a trajectory forecast is generated.

Researchers can request access to HYSPLIT and run it from their own computers, making it extremely adaptable to a wide variety of research needs, “We have to just commend NOAA for making this available... This is an extremely valuable tool,” Salawitch said.

The University of Maryland team does not normally study radioactive plumes, instead focusing on somewhat more mundane matters such as air quality, the depletion of the ozone layer, and the global carbon cycle, but Salawitch says they decided to put their expertise and HYSPLIT to use in response to a clear need for more information about the possible public health consequences of the nuclear emergency.


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