WRF-Chem model simulations of a dust outbreak over the central Mediterranean and comparison with multi-sensor desert dust observations

Abstract

Abstract. In this study, the Weather Research and Forecasting model with online coupled chemistry (WRF-Chem) is applied to simulate an intense Saharan dust outbreak event that took place over the Mediterranean in May 2014. Comparison of a simulation using a physics-based desert dust emission scheme with a numerical experiment using a simplified (minimal) emission scheme is included to highlight the advantages of the former. The model was found to reproduce well the synoptic meteorological conditions driving the dust outbreak: an omega-like pressure configuration associated with a cyclogenesis in the Atlantic coasts of Spain. The model performances in reproducing the atmospheric desert dust load were evaluated using a multi-platform observational dataset of aerosol and desert dust properties, including optical properties from satellite and ground-based sun photometers and lidars, plus in situ particulate matter mass concentration (PM) data. This comparison allowed us to investigate the model ability in reproducing both the horizontal and the vertical displacement of the dust plume, as well as its evolution in time.The comparison with satellite (MODIS-Terra) and sun photometers (AERONET) showed that the model is able to reproduce well the horizontal field of the aerosol optical depth (AOD) and its evolution in time (temporal correlation coefficient with AERONET of 0.85). On the vertical scale, the comparison with lidar data at a single site (Rome, Italy) confirms that the desert dust advection occurs in several, superimposed "pulses" as simulated by the model. Crossanalysis of the modeled AOD and desert dust emission fluxes further allowed for the source regions of the observed plumes to be inferred. The vertical displacement of the modeled dust plume was in rather good agreement with the lidar soundings, with correlation coefficients among aerosol extinction profiles up to 1 and mean discrepancy of about 50 %.The model-measurement comparison for PM 10 and PM 2.5 showed a good temporal matching, although it revealed a marked overestimation of PM 10 and PM 2.5 (of the order of 70 % during the dust peak). For PM 10 , it was also possible to investigate the accordance between the model-and the measurement-based dust PM 10 , this confirming the model PM 10 overestimation to be related to over-predicted dust mass up to a factor of 140 %. In all the model-measurement comparisons performed, the enhanced capabilities of the physics-based emission scheme with respect to its simplified, minimal version were evident and are documented.

Dust Storm Event of February 2019 in Central and East Coast of Australia and Evidence of Long-Range Transport to New Zealand and Antarctica

“…To obtain outputs for the aerosol optical properties (extinction coefficient, extcof55, at 550 nm wavelength), we chose the aerosol chemistry GOCART (chem_opt = 300) and the output of the aerosol extinction coefficient calculated based on the Maxwell-Garnett approximation (aer_opt_opt = 2). As the interactive feedback of radiative aerosols in meteorology can affect dust emissions, as shown by Wang et al 2018 [48], and similarly by Rizza et al 2017 [30], who considered the aerosol chemistry GOCART scheme in their study of a dust outbreak from the Sahara Desert in 2004 as well as the Maxwell-Garnett rule for deriving aerosol properties, this WRF-Chem simulation study of the dust event on the east coast of Australia also considers the direct radiative effect of aerosol using Rapid Radiative Transfer Model (RRTMG) for both short-wave and long-wave radiation (ra_sw_physics = 4, ra_lw_physics = 4). The direct radiative effect of aerosol on meteorology determined by RRTMG was also used by Zhao et al 2011 [49] and Chen et al 2014 [28] in their studies of the effect of aerosols on precipitation in West Africa and dust mass balance from Asian desert dust sources.…”

Dust Storm Event of February 2019 in Central and East Coast of Australia and Evidence of Long-Range Transport to New Zealand and Antarctica

“…To have aerosol optical properties output (extinction coefficient, extcof55, at 550 nm wavelength), the aerosols chemistry GOCART (chem_opt=300) and output of aerosol extinction coefficient calculated based on Maxwell-Garnett approximation (aer_opt_opt=2) are chosen. As radiative aerosols interactive feedback on meteorology can effect the dust emission as was shown by Wang et al 2018 [48] and similar to Rizza et al 2017 [30] who considered the aerosol chemistry GOCART scheme in their study of dust outbreak from Sahara Desert in 2004 and the Maxwell-Garnett rule to derive aerosol properties, this WRF-Chem simulation study of dust event in east coast of Australia also considers the aerosol direct radiative effect using Rapid Radiative Transfer Model (RRTMG) for both short-wave and long wave radiation (ra_sw_physics=4, ra_lw_physics=4). Direct aerosol radiative effect on meteorology using RRTMG were also used by Zhao et al 2011 [49] and Chen et al 2014 [28] in their studies of aerosols effect on precipitation in West Africa and dust mass balance from Asian desert dust sources.…”

The Implementation of a Mineral Dust Wet Deposition Scheme in the GOCART-AFWA Module of the WRF Model

“…However, "DUST-GOCART/AFWA" produces an important over-prediction of dust concentration [64]. This may be explained in part by the fact that the AFWA scheme only considers vertical dust flux which is related to clay content [60], and it does not support a dust wet deposition scheme, in contrast to the "DUST-UOC", which considers a more realistic soil texture type. Furthermore, the "DUST-UOC" supports a dust wet deposition scheme based on the study of Jung [65], only for below cloud scavenging of aerosols.…”

“…The WRF/Chem model includes three alternative packages for mineral dust emission: two (namely, "DUST-GOCART", "DUST-GOCART/AFWA") from the GOCART module, and the third (namely, "DUST-UOC") from the University of Cologne [60]. In "DUST-GOCART", the dust emissions are scaled with the soil erodibility fields, as described by Ref.…”