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Meteorological Research at the Idaho National Laboratory Site: Improved Atmospheric Dispersion Modeling for the Idaho National Laboratory Site

Background

The Field Research Division of the National Oceanic and Atmospheric Administration Air Resources Laboratory (NOAA ARL-FRD) provides meteorological support to the INL Site. This includes maintaining the INL Site meteorological tower network (the INL Site Mesonet) and running atmospheric dispersion models for emergency response applications. For many years NOAA ARL¬FRD has used a locally developed dispersion model called MDIFF to simulate potential hazardous releases from INL Site facilities. However, MDIFF has not been significantly upgraded in many years and is showing its age. Both INL Site and NOAA staff have requested new modeling capabilities that are not present in MDIFF. While MDIFF could in principal be upgraded, it is more cost effective to adopt a newer model that already has many of the requested capabilities.

The NOAA Air Resources Laboratory already has an advanced dispersion model called HYSPLIT that contains many of the features that have been requested for future INL Site applications. HYSPLIT is used operationally within NOAA for various applications including smoke forecasting from wildfires and forecasting the movement of ash plumes from volcanic eruptions. It is also used by the National Weather Service to produce plume forecasts for toxic releases.

NOAA ARL-FRD recommended several years ago that HYSPLIT be adopted for INL Site use, but funding restraints did not allow any efforts along these lines until 2007. Adoption of HYSPLIT benefits both INL Site and NOAA as a whole. INL Site benefits because HYSPLIT is a more modern model with new modeling and display capabilities. Unlike MDIFF, HYSPLIT also has broad support within NOAA, so the limited resources available locally can be leveraged through interactions with the broader HYSPLIT community within NOAA. The benefit to NOAA is that any improvements to HYSPLIT made for INL Site applications can feed back to the wider HYSPLIT community.

Objectives

The objectives of this work are to:

  • Transition INL Site dispersion modeling from MDIFF to HYSPLIT
  • Develop more realistic wind fields that account for the local topography and changes in the wind with height
  • Improve the dispersion model output so it is more useful to decision makers in the INL Site Emergency Operations Center
  • Provide capability to forecast future plume movements using gridded atmospheric models
  • Develop release scenarios for INL Site facilities that are compatible with the HYSPLIT model inputs

Accomplishments Through 2007

Many of the capabilities required for using HYSPLIT at INL Site actually coincide with the needs of other HYSPLIT users within NOAA. NOAA ARL-FRD has therefore collaborated with these other groups in adding many features. These include improving the model output so that it more useful for decision makers and adding a chemical database within HYSPLIT that is used in generating contours. Output from the model can be provided in a GIS format that allows it to be layered with other geographical data. A basic radiological dose calculation algorithm has also been added, although it is still undergoing testing.

NOAA ARL-FRD is running a version of the WRF gridded atmospheric weather prediction system with a horizontal grid spacing of 4 km over the INL Site region. The forecast winds from WRF can be used in HYSPLIT to create forecasts of future plume movements.

Results

HYSPLIT now has many of the capabilities that are needed for INL Site dispersion modeling. The main obstacle remaining is the development of a realistic three-dimensional wind field based on the INL Site Mesonet data, and this is discussed below.

Plans for Continuation

Unlike MDIFF, HYSPLIT requires a three-dimensional wind field that accounts for vertical changes in the winds and for terrain effects. This can already be done using the output from gridded models such as WRF, but it must be remembered that these gridded models are only producing forecast winds and not actual winds. These forecasts can fail just like the models used by the National Weather Service in producing general weather forecasts. For this reason, it is not advisable to rely solely on forecast model winds when generating plume plots in an emergency-response environment.

NOAA ARL-FRD therefore plans to develop a capability to generate a three-dimensional HYSPLIT wind field based directly on the INL Site Mesonet data. Such a wind field is a “nowcast” rather than a forecast, since it involves current conditions rather than future conditions. MDIFF currently creates two-dimensional nowcasts simply by horizontally interpolating between Mesonet towers. The situation is more complicated with HYSPLIT because of the need to deal with vertical variations in the wind. In addition, it is highly desirable to have the HYSPLIT winds flow realistically over or around terrain obstacles and to obey mass continuity. Simple interpolation does not produce such results. NOAA ARL-FRD is therefore looking at either adopting or developing a so-called diagnostic wind-field model that matches the Mesonet observations as closely as possible while still obeying physical constraints such as terrain blockage and mass continuity. Once such a wind-field model is in place, the transition from MDIFF to HYSPLIT can be initiated.


Investigators and Affiliations

Richard M. Eckman, Meteorologist, National Oceanic and Atmospheric Administration, Air Resources Laboratory, Field Research Division, Idaho Falls, Idaho Funding Sources

Funding Sources

U.S. Department of Energy Idaho Operations Office

National Oceanic and Atmospheric Administration, Air Resources Laboratory

 


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