Beaver Valley, PA nuclear power plant. Image by U.S. NRC
HYSPLIT Transfer Coefficient Matrix
A procedure has been implemented to provide semi-operational plume forecasts in real-time
by continuously updating the previous day's transport and dispersion as new meteorological data become available.
Simulations are divided into smaller time segments and each segment is continued as an independent
calculation using a unit source emission. The unit source calculations give the dispersion factors
from the release point for every emission period to each downwind grid location, defining how much
of the emissions are transferred to each location varying as a function of time, which is defined
as the Transfer Coefficient Matrix
(TCM). The TCM is computed for inert and depositing species and
when quantitative air concentration results are required, the final air concentration is computed in
a simple post-processing step by multiplying the TCM by the appropriate emission rate and radioactive
decay constant. Results for multiple emission scenarios can easily be created and used to optimize
model results as more measurement data become available.
In this online version, up to three simultaneous, independent source locations can be tracked by NOAA in
a non-operational environment. The TCM results are downloaded to the READY web server and
made available to the user to estimate the source term (emissions) and resulting concentrations. The user can
adjust the emissions during any 3 hour release
period in an attempt to improve the HYSPLIT model results of concentrations compared to measured
concentrations for any user-selected measurement location. The user can select one of four generic species that were
tracked as surrogates for the radionuclides: a gas with no wet or dry scavenging (non-depositing gas),
a gas with a relatively large dry deposition velocity (0.01 m/s) and wet removal (Henry's constant = 0.08)
to represent gaseous I-131 (depositing gas), a particle with a small deposition velocity (0.001 m/s, light
particle), and a particle with a large deposition velocity (0.01 m/s, heavy particle).
Produce concentration and/or deposition maps using the default source term as defined by NOAA or estimate emissions using the Inverse Modeling Technique from measurements provided by EPA (in a real event).
HYSPLIT has been configured to automatically produce atmospheric dispersion forecasts for several locations four times daily. These locations may change based on the needs of NOAA and its partners. The model assumes a unit of mass emission over 60 hours and produces graphics for two concentration grids: a fine grid (~ 1km horizontal resolution) and a coarse grid (~10 km horizontal resolution). Output on the fine grid extends from hour 1 to hour 12 each hour, while the coarse extends from hour 2 to hour 60 every 2 hours.