High resolution atmospheric transport modelling in support of radionuclide detections at CTBTO network

Abstract:

In order to support its mission of monitoring compliance with the treaty banning nuclear explosions, the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) operates four global networks of seismic, infrasound, hydroacoustic, referred to as waveform, sensors and air samplers accompanied with radionuclide detectors. The role of the International Data Centre (IDC) of CTBTO is to associate the signals detected in the monitoring networks with the physical phenomena which emitted these signals, by forming events.

While the process of event building for the waveform technologies is well-established, the task of event building using the radionuclide detections remains a challenge. One of the reasons is the complexity of the process of atmospheric transport of airborne radionuclides from their sources to the detecting stations and subsequent difficulties in representing this process in models. An atmospheric transport model is driven by meteorological fields generated by numerical models coupled to observations. In addition, it is equipped with parameterisations of sub-grid scale processes to account for incompleteness of the representation of meteorological processes in the meteorological fields.

In this presentation we will discuss possibilities of improving the accuracy of the atmospheric transport modelling simulations in support of radionuclide detections at CTBTO. Some of these improvements can be implemented operationally, while others, due to their computational cost, could only be performed on request. We will present the influence an increase of resolution of global meteorological fields, provided by the EMCWF (European Centre of Medium-Range Weather Forecasts), has on the quality of the simulations. We will address possible benefits of using high resolution regional meteorological fields generated with the mesoscale model WRF (Weather research and Forecasting). We will illustrate the impact of parameterisations, namely those linked to the atmospheric boundary layer physics. In order to focus full attention on atmospheric processes we will present analyses of case studies based on a trustworthy source of radionuclides which can be connected to detections in the CTBTO network. Finally, we will discuss modelling limitations due to the turbulent nature of the atmospheric processes.