Numerical simulations of windblown dust over complex terrain: the Fiambalá Basin episode in June 2015

Abstract

On the 13 June 2015, the London Volcanic Ash Advisory Centre (VAAC) warned the Buenos Aires VAAC abouta possible volcanic eruption from the Nevados Ojos del Salado volcano (6,879m), located in the Andes mountain range onthe border between Chile and Argentina. A volcanic ash cloud was detected by the SEVIRI instrument on board the MeteosatSecond Generation (MSG) satellites from 14:00 UTC on 13 June. Further studies concluded that the phenomenon was causedby 5 remobilization of ancient pyroclastic deposits (circa 4.5Ka Cerro Blanco eruption) from the Bolsón de Fiambalá (FiambaláBasin) in northwestern Argentina.In this paper, we provide the first comprehensive description of the dust episode through observations and numerical simulations.We have investigated the spatio-temporal distribution of aerosols and the emission process over complex terrain to gaininsight into the key role played by the orography and the condition that triggered the long-range transport episode.10 Numerical simulations of windblown dust were performed using the WRF-ARW/FALL3D modeling system with meteorologicalfields downscaled to a spatial resolution of 2km in order to resolve the complex orography of the area. Resultsindicated that favourable conditions to generate dust uplifting occurred in northern Fiambalá Basin, where orographic effectscaused strong surface winds. According to short-range numerical simulations, dust particles were confined to near-ground layersaround the emission areas. On the other hand, dust aerosols were injected up to 5-6km high in central and southern regions15 of the Fiambalá Basin, where intense ascending airflows are driven by horizontal convergence.Long-range transport numerical simulations were also performed to model dust cloud spreading over northern Argentina.Results of simulated vertical particle column mass were compared with the MSG-SEVIRI retrieval product. We tested twonumerical schemes: with the default configuration of the FALL3D model, we found difficulties to simulate transport throughorographic barriers, whereas an alternative configuration, using a numerical scheme to more accurately compute the horizontal20 advection in abrupt terrains, substantially improved the model performance.