Ensemble Dispersion Simulation of a Point-Source Radioactive Aerosol Using Perturbed Meteorological Fields over Eastern Japan

Tsuyoshi Thomas Sekiyama,Masaru Kunii,Mizuo Kajino

doi:10.3390/atmos12060662

Tsuyoshi Thomas Sekiyama, Masaru Kunii + Show 1 more

Open Access

https://doi.org/10.3390/atmos12060662

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Journal: Atmosphere	Publication Date: May 22, 2021
Citations: 3	License type: CC BY 4.0

Affiliation: Japan Meteorological Agency, University of Tsukuba

Abstract

We conducted single-model initial-perturbed ensemble simulations to quantify uncertainty in aerosol dispersion modeling, focusing on a point-source radioactive aerosol emitted from the Fukushima Daiichi Nuclear Power Plant (FDNPP) in March 2011. The ensembles of the meteorological variables were prepared using a data assimilation system that consisted of a non-hydrostatic weather-forecast model with a 3-km horizontal resolution and a four-dimensional local ensemble transform Kalman filter (4D-LETKF) with 20 ensemble members. The emission of radioactive aerosol was not perturbed. The weather and aerosol simulations were validated with in-situ measurements at Hitachi and Tokai, respectively, approximately 100 km south of the FDNPP. The ensemble simulations provided probabilistic information and multiple case scenarios for the radioactive aerosol plumes. Some of the ensemble members successfully reproduced the arrival time and intensity of the radioactive aerosol plumes, even when the deterministic simulation failed to reproduce them. We found that a small ensemble spread of wind speed produced large uncertainties in aerosol concentrations.

Highlights

Ensemble simulation is a set of multiple numerical simulations that have slightly different initial conditions, boundary conditions, parameters, or models that are all geophysically plausible
The error growth and propagation in the model simulation depend on the chaotic advection, diffusion, precipitation, thermodynamics, and chemistry, which all should be explored in detail
The dispersion model uncertainty has not been well explored with ensemble simulations because (1) it is difficult to prepare meteorological perturbations with sophisticated methods like the singular vector (SV) and ensemble Kalman filter (EnKF) methods and (2) even if ensemble simulations are performed, it is difficult to examine the probabilistic results in detail when tracer concentration observations and emission inventories are not sufficiently available

Summary

Introduction

Ensemble simulation is a set of multiple numerical simulations that have slightly different initial conditions, boundary conditions, parameters, or models that are all geophysically plausible. Ensemble prediction systems (EPSs) have been developed worldwide by operational weather forecast centers These systems have adopted initial-condition ensemble simulations that are suitable for error growth evaluation. We have investigated the model uncertainty of a regional aerosol dispersion simulation with the meteorological initial perturbation generated by the EnKF. The dispersion model uncertainty has not been well explored with ensemble simulations because (1) it is difficult to prepare meteorological perturbations with sophisticated methods like the SV and EnKF methods and (2) even if ensemble simulations are performed, it is difficult to examine the probabilistic results in detail when tracer concentration observations and emission inventories are not sufficiently available. The emission term was unperturbed and not investigated in this study

Methodology

Conclusions