The offline Lagrangian particle model FLEXPART–NorESM/CAM (v1): model description and comparisons with the online NorESM transport scheme and with the reference FLEXPART model

Abstract

Abstract. The offline FLEXible PARTicle (FLEXPART) stochastic dispersion model is currently a community model used by many scientists. Here, an alternative FLEXPART model version has been developed and tailored to use with the meteorological output data generated by the CMIP5-version of the Norwegian Earth System Model (NorESM1-M). The atmospheric component of the NorESM1-M is based on the Community Atmosphere Model (CAM4); hence, this FLEXPART version could be widely applicable and it provides a new advanced tool to directly analyse and diagnose atmospheric transport properties of the state-of-theart climate model NorESM in a reliable way. The adaptation of FLEXPART to NorESM required new routines to read meteorological fields, new post-processing routines to obtain the vertical velocity in the FLEXPART coordinate system, and other changes. These are described in detail in this paper. To validate the model, several tests were performed that offered the possibility to investigate some aspects of offline global dispersion modelling. First, a comprehensive comparison was made between the tracer transport from several point sources around the globe calculated online by the transport scheme embedded in CAM4 and the FLEXPART model applied offline on output data. The comparison allowed investigating several aspects of the transport schemes including the approximation introduced by using an offline dispersion model with the need to transform the vertical coordinate system, the influence on the model results of the sub-grid-scale parameterisations of convection and boundary layer height and the possible advantage entailed in using a numerically non-diffusive Lagrangian particle solver. Subsequently, a comparison between the reference FLEX-PART model and the FLEXPART-NorESM/CAM version was performed to compare the well-mixed state of the atmosphere in a 1-year global simulation. The two model versions use different methods to obtain the vertical velocity but no significant difference in the results was found. However, for both model versions there was some degradation in the well-mixed state after 1 year of simulation with the buildup of a bias and an increased scatter. Finally, the capability of the new combined modelling system in producing realistic, backward-in-time transport statistics was evaluated calculating the average footprint over a 5-year period for several measurement locations and by comparing the results with those obtained with the reference FLEXPART model driven by re-analysis fields. This comparison confirmed the effectiveness of the combined modelling system FLEXPART with NorESM in producing realistic transport statistics.

Methodology to obtain highly resolved SO<sub>2</sub> vertical profiles for representation of volcanic emissions in climate models

“…to track volcanic clouds (Eckhardt et al, 2008;Kristiansen et al, 2010). Transport with FLEXPART produces results in good agreement with both transport simulated by the Norwegian Earth System Model (Cassiani et al, 2016), and to observational data (Groot Zwaaftink et al, 2018;Langford et al, 2018).…”

Water Pathways for the Hindu-Kush-Himalaya and an Analysis of Three Flood Events

“…Furthermore, this is a useful tool in testing the skill of climate models to be able to replicate moisture pathways in regions during problematic periods, where models are known to perform poorly, such as in the case here of the HKH region during the monsoon. This can help validate whether climate models which appear to perform coherently with observations are doing so for the right reasons and help to diagnose why poorly performing models are in fact doing so; see, for example, the offline implementation of FLEXPART for studying transport in the CMIP5-version of the Norwegian Earth System Model [60]. This may, thus, prove to be a useful tool for the improvement of the performance of models over some key regions of interest.…”

Source–receptor matrix calculation for deposited mass with the Lagrangian particle dispersion model FLEXPART v10.2 in backward mode

“…For this study, we used 3-hourly ERA-Interim re-analysis data from ECMWF with a resolution of 1 • latitude × 1 • longitude and 61 vertical levels. There exist other versions of FLEX-PART, such as for the Weather Research and Forecasting (WRF) model (Brioude et al, 2013) or the Norwegian Earth System Model (NorESM)/Community Atmosphere Model (CAM) (Cassiani et al, 2016), in which our changes are not yet implemented. Of some importance for this paper is the fact that FLEXPART uses an internal terrain-following coordinate system that is automatically adjusted to the vertical resolution at which meteorological input data in native model coordinates are provided.…”