Analysis of the aerosol-radiation -cloud interactions through the use of regional climate/chemistry coupled models

Resumen

The response of the climate systems to aerosols and their effect on the radiative budget of the Earth is the most uncertain climate feedback and one of the key topics in climate change mitigation. Air quality-climate studies (AQCI) are a key, but uncertain contributor to the anthropogenic forcing that remains poorly understood. To build confidence in the AQCI studies, regional-scale integrated meteorology-atmospheric chemistry models are in demand. The main objective of the present Thesis is the characterization of the uncertainties in the climate-chemistry-aerosol-cloud-radiation system associated to the aerosol direct and indirect radiative effects caused by aerosols over Europe, employing an ensemble of fully-coupled climate and chemistry model simulations. The first topic covered deals with the microphysics parameterization configuration of an online-coupled model. The differences when using two microphysics schemes within the Weather Research and Forecasting coupled with Chemistry (WRF-Chem) model are analyzed. The evaluated simulations come from the Air quality Model Evaluation International Initiative (AQMEII) Phase 2. The impact on several variables is estimated when selecting Morrison vs. Lin microphysics. The results showed smaller and more numerous cloud droplets simulated with the Morrison and therefore this scheme is more effective in scattering shortwave radiation. Also, the impact of biomass burning (BB) aerosols on surface winds during the Russian heat wave and wildfires episode is studied. The methodology consists of three WRF-Chem simulations over Europe, run under the context of EuMetChem COST Action ES1004, differing in the inclusion (or not) of aerosol-radiation (ARI) and aerosol-cloud interactions (ACI). These aerosols can affect surface winds where emission sources are located and further from the release areas. Local winds decrease due to a reduction of shortwave radiation at the ground, which leads to decreases in 2-m temperature. Atmospheric stability increases when considering aerosol feedbacks, inducing a lower planetary boundary layer height. This Dissertation also investigates the ability of an ensemble of simulations to elucidate the aerosol-radiation-cloud interactions. An assessment of whether the inclusion of atmospheric aerosol radiative feedbacks during two aerosol case studies of an ensemble of on-line coupled models improves the simulation results for maximum, mean and minimum 2-m temperature is done. The simulations (COST Action ES1004) are evaluated against observational data from E-OBS database. In both episodes, a general underestimation of the studied variables is found, being most noticeable in maximum temperature. The biases are improved when including ARI or ARI+ACI in the dust case. Although the ensemble does not outperform the individual models (in general), its improvements when including ARI+ARI are more remarkable. Last, an improvement of the spatio-temporal variability and correlation coefficients when aerosol radiative effects are included is found. Finally, the representation of the ACI in regional-scale integrated models when simulating the climate-chemistry-cloud-radiation system is analyzed. It complements the temperature analyses. The evaluated simulations are run in the context of AQMEII Phase 2 and include the ARI+ACI interactions. Simulations are evaluated against the (ESA) Cloud_cci data. Results show an underestimation(overestimation) of cloud fraction (CFR) over land(ocean) areas, which could be related to satellite retrieval missing thin clouds. Lower bias and mean absolute error (MAE) are found in the ensemble Cloud optical depth (COD) and cloud liquid ice path (CIP) are generally underestimated. The differences are related to microphysics. The development of this Thesis has contributed to the state of the art in AQCI studies. Although including aerosol feedbacks does not modify the bias, the spatio-temporal variability and correlation coefficients are improved.