25 research outputs found
Backtracking radioxenon in Europe using Ensemble transport and dispersion modelling
The Comprehensive nuclear Test-Ban-Treaty bans nuclear explosions by everyone, everywhere. Radioxenon monitoring by the International Monitoring System is a key component of the verification of the Treaty. Atmospheric transport modelling can be used to determine the sources of radioxenon plumes. The Flexpart model is used to backtrack radioxenon observations in Europe to determine their source. An ensemble is used to quantify uncertainty
Predicting small-scale, short-lived downbursts : case study with the NWP limited-area ALARO model for the Pukkelpop thunderstorm
The authors consider a thunderstorm event in 2011 during a music festival in Belgium that produced a short-lived downburst of a diameter of less than 100 m. This is far too small to be resolved by the kilometric resolutions of today's operational numerical weather prediction models. Operational forecast models will not run at hectometric resolutions in the foreseeable future. The storm caused five casualties and raised strong societal questions regarding the predictability of such a traumatic weather event.In this paper it is investigated whether the downdrafts of a parameterization scheme of deep convection can be used as proxies for the unresolved downbursts. To this end the operational model ALARO [a version of the Action de Recherche Petite Echelle Grande Echelle-Aire Limitee Adaptation Dynamique Developpement International (ARPEGE-ALADIN) operational limited area model with a revised and modular structure of the physical parameterizations] of the Royal Meteorological Institute of Belgium is used. While the model in its operational configuration at the time of the event did not give a clear hint of a downburst event, it has been found that (i) the use of unsaturated downdrafts and (ii) some adaptations of the features of this downdraft parameterization scheme, specifically the sensitivity to the entrainment and friction, can make the downdrafts sensitive enough to the surrounding resolved-scale conditions to make them useful as indicators of the possibility of such downbursts
Source localisation and its uncertainty quantification after the third DPRK nuclear test
The International Monitoring System is being set up aiming to detect violations of the Comprehensive Nuclear-Test-Ban Treaty. Suspicious radioxenon detections were made by the International Monitoring System after the third announced nuclear test conducted by the Democratic People's Republic of Korea (DPRK). In this paper, inverse atmospheric transport and dispersion modelling was applied to these detections, to determine the source location, the release term and its associated uncertainties. The DPRK nuclear test site was found to be a likely source location, though a second likely source region in East Asia was found by the inverse modelling, partly due to the radioxenon background from civilian sources. Therefore, techniques to indirectly assess the influence of the radioxenon background are suggested. In case of suspicious radioxenon detections after a man-made explosion, atmospheric transport and dispersion modelling is a powerful tool for assessing whether the explosion could have been nuclear or not
Assessment of the announced North Korean nuclear test using long-range atmospheric transport and dispersion modelling
On 6 January 2016, the Democratic People's Republic of Korea announced to have conducted its fourth nuclear test. Analysis of the corresponding seismic waves from the Punggye-ri nuclear test site showed indeed that an underground man-made explosion took place, although the nuclear origin of the explosion needs confirmation. Seven weeks after the announced nuclear test, radioactive xenon was observed in Japan by a noble gas measurement station of the International Monitoring System. In this paper, atmospheric transport modelling is used to show that the measured radioactive xenon is compatible with a delayed release from the Punggye-ri nuclear test site. An uncertainty quantification on the modelling results is given by using the ensemble method. The latter is important for policy makers and helps advance data fusion, where different nuclear Test-Ban-Treaty monitoring techniques are combined
Time resolution requirements for civilian radioxenon emission data for the CTBT verification regime
The capability of the noble gas component of the International Monitoring System as a verification tool for the Comprehensive Nuclear-Test-Ban Treaty is deteriorated by a background of radioxenon emitted by civilian sources. One of the possible approaches to deal with this issue, is to simulate the daily radioxenon concentrations from these civilian sources at noble gas stations by using atmospheric transport models. In order to accurately quantify the contribution from these civilian sources, knowledge on the releases is required. However, such data are often not available and furthermore it is not clear what temporal resolution such data should have. In this paper, we assess which temporal resolution is required to best model the Xe-133 contribution from civilian sources at noble gas stations in an operational context. We consider different sampling times of the noble gas stations and discriminate between nearby and distant sources. We find that for atmospheric transport and dispersion problems on a scale of 1000 km or more, emission data with subdaily temporal resolution is generally not necessary. However, when the source-receptor distance decreases, time-resolved emission data become more important. The required temporal resolution of emission data thus depends on the transport scale of the problem. In the context of the Comprehensive Nuclear-Test-Ban Treaty, where forty noble gas stations will monitor the whole globe, daily emission data are generally sufficient, but for certain meteorological conditions, better temporally resolved emission data are required
Preliminary signs of the initiation of deep convection by GNSS
This study reports on the exploitation of GNSS (Global Navigation Satellite System) and a new potential application for weather forecasts and nowcasting. We focus on GPS observations (post-processing with a time resolution of 5 and 15 min and fast calculations with a time resolution of 5 min) and try to establish typical configurations of the water vapour field which characterise convective systems and particularly which supply precursors of their initiation are associated with deep convection. We show the critical role of GNSS horizontal gradients of the water vapour content to detect small scale structures of the troposphere (i. e. convective cells), and then we present our strategy to obtain typical water vapour configurations by GNSS called "H2O alert". These alerts are based on a dry/wet contrast taking place during a 30 min time window before the initiation of a convective system. GNSS observations have been assessed for the rainfall event of 28-29 June 2005 using data from the Belgian dense network (baseline from 5 to 30 km). To validate our GNSS H2O alerts, we use the detection of precipitation by C-band weather radar and thermal infrared radiance (cloud top temperature) of the 10.8-micrometers channel [Ch09] of SEVIRI instrument on Meteosat Second Generation. Using post-processed measurements, our H2O alerts obtain a score of about 80 %. Final and ultra-rapid IGS (International GNSS Service) orbits have been tested and show equivalent results. Fast calculations (less than 10 min) have been processed for 29 June 2005 with a time resolution of 5 min. The mean bias (and standard deviation) between fast and reference post-processed ZTD (zenith total delay) and gradients are, respectively, 0.002 (+/- 0.008) m and 0.001 (+/- 0.004) m. The score obtained for the H2O alerts generated by fast calculations is 65 %
Uncertainty quantification in long-range Lagrangian atmospheric transport and dispersion modelling
Quantification of uncertainty in Lagrangian dispersion modelling, using ECMWF’s new ERA5 ensemble
FLEXPART is a Lagrangian particle dispersion transport model which is originally designed for calculating the long-range and mesoscale dispersion of air pollutants from point sources. Through the years, these type of models have proven to be a very useful tool in an operational context for the protection of the population in case of accidents in a nuclear power plant. In the meantime, FLEXPART has evolved into a more comprehensive tool for atmospheric transport modelling and analysis, and it can be used for a wide range of applications. The model can be used in a forward or backward mode, making it possible to trace back the source pollution contribution of a certain pollutant. To perform the FLEXPART dispersion simulations under consideration, we will use meteorological data from the European Centre for Medium Range Forecasts (ECMWF), more specifically the new ERA5 10-member climate data reanalysis at a 63 km resolution. We will explore how good we can access the model uncertainty in an objective way by taking advantage of ensemble weather forecasts
Source localization of ruthenium-106 detections in autumn 2017 using inverse modelling
In late September and October 2017, Ru-103 and Ru-106 have been detected throughout the northern hemisphere by national environmental radioactivity monitoring networks and by the International Monitoring System that is being established to verify compliance with the Comprehensive Nuclear-Test-Ban Treaty. Ru-103 (half-life: 39.26 d) and Ru-106 (half-life: 373.6 d) are radioactive particulates that have no natural sources and for which there is no measurable global background