ENHANCED GLOBAL NUCLEAR EVENT LOCATION AND ITS UNCERTAINTY ANALYSIS BASED ON VARIOUS ADJOINT ENSEMBLE DISPERSION MODELLING TECHNIQUES

After the detection of treaty-relevant radionuclides in filters or air samples, atmospheric backtracking techniques are employed by the Provisional Technical Secretariat (PTS) of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) to trace back the measured substances to their potential areas of origin. In the case of an underground nuclear test, potential sources are co-located with the epicentres of seismic events that may have been triggered by the explosions. Previous studies have shown that predictions or analyses of atmospheric transport can be significantly improved by ensemble techniques. Within the CTBT environment it is important to build confidence in the source-receptor sensitivity (SRS) field based backtracking products issued by the PTS in the case of the occurrence of treaty relevant radionuclides. Therefore the PTS has set up a highly automated response system together with the Regional Specialized Meteorological Centres of the World Meteorological Organization in the field of dispersion modelling. These Centres have committed themselves to provide the PTS with the same standard SRS fields as calculated by their systems for CTBT relevant cases. The SRS field data standard allows for ensemble dispersion modelling. The parametric inter-comparison among ensemble members has been integrated into the decision making software tool WEB-GRAPE (CTBTO Newsletter Spectrum, 7, page 19). In sensitivity studies we varied the choice of LPDM, and the kind and source of wind field utilized to demonstrate the potential of the following two ensemble dispersion modelling (EDM) methods: a) Multi-model EDM in order to improve the accuracy of a global scale source attribution based on joint CTBTO-WMO experiments in January 2005 (Becker et al., 2007) and December 2007 (Wotawa and Becker, 2008). b) Single-model EDM with different lead times of the wind fields utilized in order to estimate the relative error of forecasted source attribution results in comparison to the analyzed ones c) Single-model EDM with different choices of wind field resolutions for the source receptor sensitivity fields of the same station at Schauinsland in order to assess quality of the PTS standard backtracking results based on the rather coarse 1º×1º horizontal resolution