Added Value of Aerosol-Cloud Interactions for Representing Aerosol Optical Depth in an Online Coupled Climate-Chemistry Model over Europe

Abstract

Aerosol-cloud interactions (ACI) represent one of the most important sources of uncertainties in climate modelling. In this sense, realistic simulations of ACI are needed for a better understanding of the complex interactions between air pollution and the climate system. This work quantifies the added value of including ACI in an online coupled climate/chemistry model (WRF-Chem, 0.44 ∘ horizontal resolution, years 2003 to 2010) in order to assess whether there is an improvement in the representation of aerosol optical depth (AOD). Modelling results for each species have been evaluated against the Copernicus Atmosphere Monitoring Service (CAMS) reanalysis, and AOD at 675 nm has been compared to AERONET data. Results indicate that the improvements of the monthly biases are around 8% for total AOD550 when including ACI, reaching 20% for the monthly bias in AOD550 coming from dust. Moreover, the temporal representation of AOD550 largely improves (increase in the Pearson time correlation coefficients), ranging from 6% to 20% depending on the chemical species considered. The benefits from this improvement overcome the problems derived from the high computational time required in ACI simulations (eight times higher with respect to simulations not including aerosol-cloud interactions).

Sensitivity of surface solar radiation to aerosol–radiation and aerosol–cloud interactions over Europe in WRFv3.6.1 climatic runs with fully interactive aerosols

“…1c and S3c) depicts mostly positive values (by ∼ 5 W m −2 ) over the central and southern regions. This result indicates that indirect aerosol effects tend to counteract the joint direct and semi-direct effects seen in the ARI minus BASE pattern, reducing them by up to half over most of the domain, which is in agreement with previously reported findings (Pavlidis et al, 2020).…”

“…This approach permits us to better isolate the signals from aerosol-radiation-cloud interactions due to the climate variability alone and the so-called climate change penalty alone, but at the expense of the reliability of the simulated patterns. Anthropogenic emissions have been dramatically reduced since the 1980s and are expected to continue in that pathway to the future (IPCC, 2013(IPCC, , 2014, so keeping 2010 values (as we did) could lead to an underestimation of AOD in the historical period (in fact, it does; reference AOD cli-matologies can be found in Pavlidis et al, 2020) and to its overestimation in the future period. Under these constraints, we draw the following conclusions.…”

“…We focus on the summer season (JJA) when solar energy is at its maximum, AOD typically reaches high values and the aerosol radiative effect has been proven to be strongest (Pavlidis et al, 2020).…”

“…In contrast, in-cloud aerosol scavenging processes lead to outof-cloud cleaner atmospheres (Croft et al, 2012). All these processes can potentially alter local and regional circulations, therefore having an impact beyond the radiative balance (Kloster et al, 2010;Wilcox et al, 2013;Nabat et al, 2014;Wang et al, 2016;Pavlidis et al, 2020).…”

“…The first is the increas-ing use of RCMs to evaluate renewable energy resources and their supply potential (e.g., Jerez et al, 2013Jerez et al, , 2015Jerez et al, , 2019Gil et al, 2019;Soares et al, 2019;van der Wiel et al, 2019). The second is the key role of aerosols regarding the accuracy of the simulated solar resource by climate models (Gaetani et al, 2014;Nabat et al, 2015b;Pavlidis et al, 2020), particularly attributed to their direct and semi-direct effects, which would help to explain the aforementioned discrepancy between GCM and RCM future projections (Boé et al, 2020;Gutiérrez et al, 2020). Third, none of the previous studies have so far dealt with the non-evident RCM sensitivity to interactively modeled atmospheric aerosol concentrations and the resulting aerosol-radiation and aerosol-cloud interactions in order to simulate the solar resource under historical and future climate scenarios.…”