Third international challenge to model the medium- to long-range transport of radioxenon to four Comprehensive Nuclear-Test-Ban Treaty monitoring stations

Maurer, C.*; Galmarini, S.*; Solazzo, E.*; Kumierczyk-Michulec, J.*; Bar, J.*; Kalinowski, M.*; Schoeppner, M.*; Bourgouin, P.*; Crawford, A.*; Stein, A.*; Chai, T.*; Ngan, F.*; Malo, A.*; Seibert, P.*; Axelsson, A.*; Ringbom, A.*; Britton, R.*; Davies, A.*; Goodwin, M.*; Eslinger, P. W.*; Bowyer, T. W.*; Glascoe, L. G.*; Lucas, D. D.*; Cicchi, S.*; Vogt, P.*; Kijima, Yuichi ; Furuno, Akiko   ; Long, P. K.*; Orr, B.*; Wain, A.*; Park, K.*; Suh, K.-S.*; Qurel, A.*; Saunier, O.*; Qulo, D.*

After performing multi-model exercises in 2015 and 2016, a comprehensive Xe-133 atmospheric transport modeling challenge was organized in 2019. For evaluation measured samples for the same time frame were gathered from four International Monitoring System stations located in Europe and North America with overall considerable influence of IRE and/or CNL emissions. As a lesion learnt from the 2nd ATM-Challenge participants were prompted to work with controlled and harmonized model set ups to make runs more comparable, but also to increase diversity. Effects of transport errors, not properly characterized remaining emitters and long IMS sampling times (12 to 24 hours) undoubtedly interfere with the effect of high-quality IRE and CNL stack data. An ensemble based on a few arbitrary submissions is good enough to forecast the Xe-133 background at the stations investigated. The effective ensemble size is below five.