Numerical diffusion on vertical advection due to gravitational settling in WRF: 2D simulations

One of the deficiencies of atmospheric dust models is that they struggle to accurately reproduce the transport of coarse and giant dust particles, according to observational evidence. Among the reasons behind that model incapacity that have been proposed in the literature, is the issue of numerical diffusion inside the advection codes of the models. In this study, we examine the importance of that issue in the WRF-L model. To do so, we update the default numerical scheme (UPWIND) which is used for the vertical advection of dust due to gravitational settling. The diffusive UPWIND scheme is replaced with a non-diffusive one, named UNO3 (third-order Upstream Non-Oscillatory scheme). To test the code performance, we perform simulations reproducing the 2D transport of a dust plume which is released at 4 km height above Cabo Verde towards Barbados. The model is initialized on 13/06/2014 at 12 UTC (which coincides with the day of the SALTRACE flight above Cabo Verde) using meteorological conditions of radiosonde from Tenerife airport and wind profile based on ECMWF model climatology. The results suggest that, in the UNO3 simulation, dust particles with a diameter 26 μm can be transported more than 500 km longer than in the BASE simulation and the dust in the atmosphere can be 10% more in the UNO3 simulation compared to the BASE simulation. In future studies, the UNO3 scheme will be tested in other aerosol types also (e.g. volcanic ash, smoke from fires).

Acknowledgements: Authors acknowledge support by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the “2nd Call for H.F.R.I. Research Projects to support Post-Doctoral Researchers” (Project Acronym: StratoFIRE, Project number:  3995) and the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (Project Acronym: D-TECT, Grant Agreement: 725698).