Improvement of source and wind field input of atmospheric dispersion model by assimilation of concentration measurements: Method and applications in idealized settings

AbstractThe problem of correcting the pollutant source emission rate and the wind velocity field inputs in a puff atmospheric dispersion model by data assimilation of concentration measurements has been considered. Variational approach to data assimilation has been used, in which the specified cost function is minimized with respect to source strength and/or wind field. The analyzed wind field satisfied the constraints derived from the conditions of mass conservation and linearized flow equations for perturbations from the first guess wind field. ‘Identical twin’ numerical experiments have been performed for the validation of the method. The first guess estimation errors of source emission rate and wind field were set to a factor of up to 10 and up to 6m/s respectively. The calculations results showed that in most studied cases an improvement of vector wind difference (VWD) error by about 0.7–1m/s could be achieved. The resulting normalized mean square error (NMSE) of concentration field was also reduced significantly

Verification of a One-Dimensional Model of CO2 Atmospheric Transport Inside and Above a Forest Canopy Using Observations at the Norunda Research Station

A model of (Formula presented.) atmospheric transport in vegetated canopies is tested against measurements of the flow, as well as (Formula presented.) concentrations at the Norunda research station located inside a mixed pine–spruce forest. We present the results of simulations of wind-speed profiles and (Formula presented.) concentrations inside and above the forest canopy with a one-dimensional model of profiles of the turbulent diffusion coefficient above the canopy accounting for the influence of the roughness sub-layer on turbulent mixing according to Harman and Finnigan (Boundary-Layer Meteorol 129:323–351, 2008; hereafter HF08). Different modelling approaches are used to define the turbulent exchange coefficients for momentum and concentration inside the canopy: (1) the modified HF08 theory—numerical solution of the momentum and concentration equations with a non-constant distribution of leaf area per unit volume; (2) empirical parametrization of the turbulent diffusion coefficient using empirical data concerning the vertical profiles of the Lagrangian time scale and root-mean-square deviation of the vertical velocity component. For neutral, daytime conditions, the second-order turbulence model is also used. The flexibility of the empirical model enables the best fit of the simulated (Formula presented.) concentrations inside the canopy to the observations, with the results of simulations for daytime conditions inside the canopy layer only successful provided the respiration fluxes are properly considered. The application of the developed model for radiocarbon atmospheric transport released in the form of (Formula presented.) is presented and discussed

The Wildfire Problem in Areas Contaminated by the Chernobyl Disaster

This paper examines the issue of radionuclide resuspension from wildland fires in areas contaminated by the Chernobyl Nuclear Power Plant explosion in 1986. This work originated from a scientific exchange among scientists from the USDA Forest Service, Ukraine and Belarus that was organized to assess science and technology gaps related to wildfire risk management. A wildfire risk modeling system was developed to predict likely hotspots for large fires and where wildfire ignitions will most likely result in significant radionuclide (Cesium, 137Cs) resuspension. The system was also designed to examine the effect of fuel breaks in terms of reducing both burn probability and resuspension. Results showed substantial spatial variation in fire likelihood, size, intensity, and potential resuspension within the contaminated areas. The potential for a large wildfire and resuspension was highest in the Belorussian Polesie Reserve, but the likelihood of such an event was higher in the Ukrainian Chernobyl Exclusion Zone due to a higher predicted probability of ignition. Fuel breaks were most effective in terms of reducing potential resuspension when located near areas that had both high ignition probability and high levels of 137Cs contamination. Simulation outputs highlighted how human activities shape the fire regime and likelihood of a large fire in the contaminated areas. We discuss how the results can be used to develop a fire management strategy that integrates ignition prevention, detection, effective suppression response, and fuel breaks. Specifically, the modeling system can now be used to explore a wide range of fire management scenarios for the contaminated areas and contribute to a comprehensive fire management strategy that targets specific drivers of fire by leveraging multiple tools including fire prevention and long-term fuel management. Wildfire-caused emissions of radionuclides in Belarus, Ukraine, and Russia are a socio-ecological problem that will require defragmenting existing risk management systems and leveraging multiple short- and long-term mitigation measures