Directional Frequency Correction for the Star Meteorological Joint Frequency Computer Program
Atmospheric dispersion computer programs are widely used to simulate air and surface exposures from airborne and deposited radionuclides. For longer-term emissions (i.e., occurring for a year or longer), many of these models use joint frequency tables, which summarize the frequency of occurrence wind speed groups and direction as a function of different stability categories to define the atmospheric dispersion conditions. This paper addresses directional limitations of a computer code, STAR (STAbility ARray) that has been historically used to generate these joint frequency tables. As part of an effort to provide an updated version of the STAR code, directional limitations were found stemming from the manner in which the reported direction data are stored in joint frequency data tables. The STAR code provides tabular frequency summaries based on 16 22.5-degree wind direction sectors. Direction data in United States is currently reported in 10-degree increments. However, the STAR code puts each wind direction occurrence into the 22.5-degree sector containing that wind direction, introducing a consistent positive bias for some of the cardinal direction sectors (north, south, east, and west) and a consistent negative bias for all the other sectors. Individual entries in the joint frequencies summaries with high wind frequencies tend to be overestimated by up to about 30% or underestimated down to about -10%. A larger range of changes is seen for entries with lower wind frequencies. To avoid these errors, it is recommended that joint frequencies generated by the STAR program be checked for this directional bias. If the source observational data is for 1969 or later years and generated by the original EPA STAR program it is likely that the bias will be in the dataset. To be certain, it is best to regenerate the STAR data summary using a revised version of the STAR program (STARR) or an alterative program that better handles the binning of wind directions.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 915296
- Report Number(s):
- PNNL-SA-53231; HLTPAO; 400403209; TRN: US200817%%307
- Journal Information:
- Health Physics, 93(2):151-156, Vol. 93, Issue 2; ISSN 0017-9078
- Country of Publication:
- United States
- Language:
- English
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