Evaluating the representation of aerosol optical properties using an online coupled model over the Iberian Peninsula

Abstract

Abstract. The effects of atmospheric aerosol particles on the Earth's climate mainly depend on their optical, microphysical and chemical properties, which modify the Earth's radiative budget. The aerosol radiative effects can be divided into direct and semi-direct effects, produced by the aerosol–radiation interactions (ARIs), and indirect effects, produced by aerosol–cloud interactions (ACIs). In this sense the objective of this work is to assess whether the inclusion of aerosol radiative feedbacks in the online coupled WRF-Chem model improves the modelling outputs over the Iberian Peninsula (IP) and surrounding water areas. For this purpose, the methodology is based on the evaluation of modelled aerosol optical properties under different simulation scenarios. The evaluated data come from two WRF-Chem simulations for the IP differing in the inclusion/no-inclusion of ARIs and ACIs (RF/NRF simulations). The case studies cover two episodes with different aerosol types over the IP in 2010, namely a Saharan dust outbreak and a forest fire episode. The evaluation uses observational data from AERONET (Aerosol Robotic Network) stations and MODIS (Moderate Resolution Imaging Spectroradiometer) sensor, including aerosol optical depth (AOD) and Ångström exponent (AE). Experimental data of aerosol vertical distribution from the EARLINET (European Aerosol Research Lidar Network) Granada station are used for checking the models. The results indicate that for the spatial distribution the best-represented variable is AOD and the largest improvements when including the aerosol radiative feedbacks are found for the vertical distribution. In the case of the dust outbreak, a slight improvement (worsening) is produced over the areas with medium (high/low) levels of AOD(−9 % / +12 % of improvement) when including the aerosol radiative feedbacks. For the wildfire episode, improvements of AOD representation (up to 11 %) over areas further away from emission sources are estimated, which compensates for the computational effort of including aerosol feedbacks in the simulations. No clear improvement is observed for the AE representation, the variability of which is largely underpredicted by both simulations.

An assessment of aerosol optical properties from remote-sensing observations and regional chemistry–climate coupled models over Europe

“…Therefore, the droplet number affected both the calculated droplet mean radius and the cloud optical depth when using the short-wave radiation scheme. One limitation of WRF-Chem in the treatment of aerosol-cloud interactions was that these couplings were not computed in the convective clouds simulated by the cumulus parameterisation Yang et al, 2011;Archer-Nicholls et al, 2016;Palacios-Peña et al, 2017).…”

“…As indicated by Palacios-Peña et al (2017), the AOD discrepancies between simulations and observations can be attributed to the errors in the model estimations of the aerosol dry mass, the fraction of particles for a given mass or water associated with aerosols. According to the aerosol dry mass estimation, found an overestimation in the simulated PM 2.5 levels for the AQMEII Phase 2 simulations which are comparable to EuMetChem simulations, and Soares et al (2015) established a rough overestimation at about 50 % of the total biomass burning emissions used here.…”

“…According to Palacios-Peña et al (2017), AOD discrepancies between simulations and observations can be attributed to errors in the model estimation of the aerosol dry mass, the fraction of particles for a given mass or the water associated with aerosols. A model underestimation of the aerosol dry mass of dust can explain the AOD underestimation during the Saharan desert dust episode because of the underestimation in the PM 10 levels found by .…”

“…Major efforts have been made to create networks of ground-based measurements of aerosol optical properties around the world, e.g. as the AErosol RObotic NETwork (AERONET; Holben et al, 1998), the European Aerosol Research Lidar Network (EARLINET; Pappalardo et al, 2014) or the Latin American Lidar Network (LALINET; Antuña-Marrero et al, 2016). There are instruments aboard satellites that provide information about aerosol optical properties with a wide spatial coverage, e.g.…”

An assessment of aerosol optical properties from remote sensing observations and regional chemistry-climate coupled models over Europe

“…Therefore, the droplet number affected both the calculated droplet mean radius and the cloud optical 30 depth when using the short-wave radiation scheme. One limitation of WRF-Chem in the treatment of aerosol-cloud interactions was that these couplings were not computed in the convective clouds simulated by the cumulus parametrisation (Chapman et al, 2009;Yang et al, 2011;Schultz, 2016;Palacios-Peña et al, 2017 …”