Investigating the sensitivity to resolving aerosol interactions in downscaling regional model experiments with WRFv3.8.1 over Europe

Abstract

Abstract. In this work we present downscaling experiments with the Weather Research and Forecasting model (WRF) to test the sensitivity to resolving aerosol–radiation and aerosol–cloud interactions on simulated regional climate for the EURO-CORDEX domain. The sensitivities mainly focus on the aerosol–radiation interactions (direct and semi-direct effects) with four different aerosol optical depth datasets (Tegen, MAC-v1, MACC, GOCART) being used and changes to the aerosol absorptivity (single scattering albedo) being examined. Moreover, part of the sensitivities also investigates aerosol–cloud interactions (indirect effect). Simulations have a resolution of 0.44∘ and are forced by the ERA-Interim reanalysis. A basic evaluation is performed in the context of seasonal-mean comparisons to ground-based (E-OBS) and satellite-based (CM SAF SARAH, CLARA) benchmark observational datasets. The impact of aerosols is calculated by comparing it against a simulation that has no aerosol effects. The implementation of aerosol–radiation interactions reduces the direct component of the incoming surface solar radiation by 20 %–30 % in all seasons, due to enhanced aerosol scattering and absorption. Moreover the aerosol–radiation interactions increase the diffuse component of surface solar radiation in both summer (30 %–40 %) and winter (5 %–8 %), whereas the overall downward solar radiation at the surface is attenuated by 3 %–8 %. The resulting aerosol radiative effect is negative and is comprised of the net effect from the combination of the highly negative direct aerosol effect (−17 to −5 W m−2) and the small positive changes in the cloud radiative effect (+5 W m−2), attributed to the semi-direct effect. The aerosol radiative effect is also stronger in summer (−12 W m−2) than in winter (−2 W m−2). We also show that modelling aerosol–radiation and aerosol–cloud interactions can lead to small changes in cloudiness, mainly regarding low-level clouds, and circulation anomalies in the lower and mid-troposphere, which in some cases, mainly close to the Black Sea in autumn, can be of statistical significance. Precipitation is not affected in a consistent pattern throughout the year by the aerosol implementation, and changes do not exceed ±5 % except for the case of unrealistically absorbing aerosol. Temperature, on the other hand, systematically decreases by −0.1 to −0.5 ∘C due to aerosol–radiation interactions with regional changes that can be up to −1.5 ∘C.

Investigating the WRF Temperature and Precipitation Performance Sensitivity to Spatial Resolution over Central Europe

“…An overestimation is found mainly over the north and northeast region of the domain and an underestimation over the southern part of the domain. This finding, i.e., the cold bias at the north and the warm bias at the south part of Europe has also been stated in other RCM studies [10,26]. The highest positive and negative differences are found in regions characterized by complex orographic features, e.g., the Alps and northern Italy (Figure 2).…”

“…It is a mesoscale numerical weather prediction system used for reproducing local weather and climate at high spatial resolutions. It has extensively been used for climate and meteorological applications over Europe (e.g., [25][26][27]).…”

“…The E-OBS data are based on the European Climate Assessment and Dataset (ECA&D) project station observation data (https://www.ecad.eu/download/ ensembles/download.php#datafiles (accessed on 5 February 2021)) that covers the entire European domain. The E-OBS dataset has extensively been used in the past for comparison studies over Europe (e.g., [10,26,[30][31][32][33][34][35]). To evaluate model performance, results were compared with the ensemble mean of the regular 0.25 • grid version of the E-OBS v20.0e observational dataset.…”

“…Performance sensitivity is examined for WRF downscaled simulated mean, maximum and minimum daily temperatures as well as precipitation and we compare the model's predictions against daily data from the E-OBS data base [23], in order to draw conclusions on the added value of their representation in higher grid size resolution scales. The grid size resolutions selected here, i.e., 36, 12, and 4 km, extend beyond the typical size of 0.11 • (~12 km) used in previous studies (e.g., [24][25][26]). The selected domain is extended over central Europe, due to the significant number of observational data, for assessing both annual and seasonal impact.…”

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

“…In the current context of climate crisis, the scientific challenge is twofold: (1) to gain a good understanding of the processes that occur in the atmosphere and of what will occur in the future because this is crucial (IPCC, 2013) in order (2) to advance effective measures at both global and regional scales (IPCC, 2014). In particular, climate change mitigation strategies require low-carbon energies to grow rapidly in the coming decades (Rohrig et al, 2019;IRENA, 2019). This rapid transition of the energy sector towards renewably powered decarbonized systems makes energy production, transmission and distribution increasingly sensitive to weather and climate variability (Bloomfield et al, 2016;Jerez et al, 2019).…”