Sensitivity experiments with regional climate modelsforcings and spin-up time

Abstract

The main objective of the thesis is to study the sensitivity of the regional climate model, WRF, at the time of spin-up, to radiative forcing due to the concentration of greenhouse gases and the interaction processes of aerosols. There are also specific objectives that can be summarized as follows: " Study the importance of including the variation in the atmospheric concentration of greenhouse gases in regional climate models as an external forcing. " Determine an optimal relaxation time or spin-up for our regional simulations. That is, the time the model needs for the atmospheric and soil variables to reach a physical balance. " Quantify the sensitivity of the inclusion of dynamic simulation of aerosols and their direct and indirect interaction with radiation. " Generate a large database of high-resolution regional simulations (~50 km) with the Euro-CORDEX domain. These simulations are published. The results of Chapter 2 show that temperature trends are significantly affected by 1-2K century$^{-1}$. Taking into account global warming of 1.5ºC would be a non-negligible impact of up to 1K of the temperature at 2 meters in future projections. Maximum and minimum temperatures are also affected in a similar way. Even, in some cases, these differences double. It is necessary to carefully reconsider the configurations of the RCMs regarding the inclusion of the evolution of greenhouse gas concentrations as an external forcing. In addition, it must be clearly documented in the literature in order to reproduce and improve confidence in published research. In Chapter 3, we base our analysis on simulations with WRF on a Euro-CORDEX domain and discover that the optimal duration is approximately 6 months. It is important to start the simulations on a date away from winter, as it guarantees a more realistic representation of the snow cover. Soil variables require longer spin-up periods than atmospheric variables. This lack of balance can be neglected unless the objective of the study has to do with feedback from the atmosphere and deep soil. The results of Chapter 4 show that the average precipitation does not vary much although a spatial redistribution occurs when introducing the ACI and ARI interactions. Mainly, in Central Europe we find a decrease in precipitation and in the Eastern Mediterranean an increase. The introduction of these interactions improves our model estimates in ERA5 with respect to the over estimate existing in the BASE scenario. This decrease in precipitation in Central Europe seems to coincide when there are PMratio events with great intensity and large size. Studying different rainfall regimes and different zones, it is found that aerosols contribute positively or negatively to precipitation depending on the place and intensity of precipitation. In the Northern, Central and Eastern parts of Europe, they reduce precipitation in our experiments but for the Mediterranean, precipitation increases. This is because in this last zone, it is the PM10 that has the greatest influence and is what is used as condensation nuclei in the ACI+ARI experiment unlike the other two experiments where these condensation nuclei are prescribed. In this thesis several sensitivity studies are presented in simulation of the regional climate with regional climate models. The value of this thesis, in addition to the analysis of the different physical processes involved, is given by the different recommendations that can be given to other researchers who are going to carry out climatic experiments of this type. Since the importance that different elements in the design of the experiments may have on the uncertainty associated with the generation of climates at the regional level has been quantified, as well as the importance of documenting certain details of the simulations that are carried out.