Two-scale multi-model ensemble: is a hybrid ensemble of opportunity telling us more?

In this study we introduce a hybrid ensemble consisting of air quality models operating at both the global and regional scale. The work is motivated by the fact that these different types of models treat specific portions of the atmospheric spectrum with different levels of detail and it is hypothesized that their combination can generate an ensemble that performs better than mono-scale ensembles. A detailed analysis of the hybrid ensemble is carried out in the attempt to investigate this hypothesis and determine the real benefit it produces compared to ensembles constructed from only global scale or only regional scale models. The study utilizes 13 regional and 7 global models participating in the HTAP2/AQMEII3 activity and focuses on surface ozone concentrations over Europe for the year 2010. Observations from 405 monitoring stations are used for the evaluation of the ensemble performance. The analysis first compares the modelled and measured spectra and then assesses the properties of the mono-scale ensembles, particularly their level of redundancy, in order to inform the process of constructing the hybrid ensemble. The main conclusion of this study is that the improvements obtained by the hybrid ensemble relative to the mono-scale ensembles can be attributed to its hybrid nature. Moreover, the optimal set is constructed from an equal number of global and regional models at only 15% of the stations. Finally, the study reaffirms the importance of an in-depth inspection of any ensemble of opportunity in order to extract the maximum amount of information and to have full control over the data used in the construction of the ensemble.

GALMARINI Stefano;  KIOUTSIOUKIS Ioannis;  SOLAZZO Efisio;  ALYUZ Ummungulsum;  BALZARINI A.;  BELLASIO R.;  BENEDIKTOW Anna;  BIANCONI Roberto;  BIESER J.;  BRANDT J.;  CHRISTENSEN J.;  COLETTE Augustin;  CURCI Gabriele;  DAVILA Yanko;  DONG Xuzhu;  FLEMMING Johannes;  FRANCIS X.V.;  FRASER Andrea;  FU Joshua;  HENZE Daven;  HOGREFE Christian;  IM Ulas;  VIVANCO M. G.;  JIMENEZ-GUERRERO Jose A;  JONSON Jan Eiof;  KITWIROON Nutthida;  MANDERS-GROOT A;  MATHUR Rohit;  PALACIOS-PEÑA Laura;  PIROVANO G.;  POZZOLI Luca;  PRANK M.;  SCHULTZ Michael;  SOKHI Ranjeet S.;  SUDO K.;  TUCCELLA Paolo;  TAKEMURA T.;  SEKIYA T.;  UNAL Alper; 

2018-06-27

COPERNICUS GESELLSCHAFT MBH

JRC110862

1680-7316,   

https://www.atmos-chem-phys.net/18/8727/2018/,    https://publications.jrc.ec.europa.eu/repository/handle/JRC110862,   

10.5194/acp-18-8727-2018,