Dissertation committee:
Μαρία Χατζάκη, Επίκουρη Καθηγήτρια, Τμήμα Γεωλογίας και Γεωπεριβάλλοντος, Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών
Στυλιανός Καζαντζής, Κύριος Ερευνητής, World Optical Depth Research & Calibration Center, Physikalisch-Meteorologisches Observatorium Davos/World Radiation Center
Παναγιώτης Νάστος, Καθηγητής, Τμήμα Γεωλογίας και Γεωπεριβάλλοντος, Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών
Αλκιβιάδης Μπάης, Καθηγητής, Τμήμα Φυσικής, Αριστοτέλειο Πανεπιστήμιο Θεσσαλονίκης
Philippe Blanc, Καθηγητής, MINES ParisTech, Paris Sciences & Lettres research university (PSL)
Κωνσταντίνος Ελευθεράτος, Αναπληρωτής Καθηγητής, Τμήμα Γεωλογίας και Γεωπεριβάλλοντος, Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών
Γεωργία Σωτηροπούλου, Επίκουρη Καθηγήτρια, Τμήμα Φυσικής, Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών
Summary:
Aerosols and clouds play a dominant role for solar radiation attenuation with great implication in climate and energy related applications. The scope of this dissertation is to investigate the role of aerosols and clouds to this attenuation, aiming to improve surface solar radiation forecasting and related applications. In addition, atmospheric aerosols, being also of particular concern for human health, have both natural and anthropogenic origin, and it is more than necessary to understand and analyze their variability at different spatial scales.
Cities are one of the major sources of anthropogenic aerosols. The increased urbanization (70% of world’s population by 2050) raises several environmental challenges, including air quality degradation. The spatial and temporal variability of urban aerosol state of 81 cities with a population over 5 million was investigated, relying on daily satellite-based aerosol optical depth (AOD) retrievals of fine spatial resolution, over an 18-year period (2003 to 2020). The population changes of those cities were also examined. According to the results the European and American cities have lower aerosol loads compared to African and Asian cities. For European, North American, and East Asian cities, aerosols are decreasing over time while their population is increasing. Especially for Chinese cities the greatest reduction in aerosols was found, despite their population growth, in response to the rigorous environmental measure implemented the last decade. For the rest of Asian, African, and South American cities, an increase in their aerosol load was found along with an increase of their population. For Indian cities the greatest increase in aerosol loads was found, a change that was correlated with the population growth. The agreement of the satellite-derived AOD trends against those obtained from ground-based AERONET measurements was also examined. Most of the trends agreed in sign for ground-based stations within the geographical limits of the contiguous urban area of the examined cities. This study highlights the vital and essential contribution of spaceborne products to monitor aerosol burden over megacities.
To analyze both anthropogenic and nature aerosols, including their direct radiative effects, focus was put on the regional scale and especially to the broader Mediterranean basin. The natural aerosol component that has significant contribution to the aerosol mixture over Mediterranean is dust. The continuous satellite monitoring of atmospheric aerosols provides long term satellite datasets of AOD, dust optical depth (DOD) and their vertical distribution in the atmosphere which contribute to understanding their direct radiative effects. The quantification of total and dust aerosols direct effects on global horizontal irradiance (GHI; important for photovoltaic installations) and direct normal irradiance (DNI; important for concentrating solar power systems) was attained for the broader Mediterranean basin, over the period 2003-2017, using the satellite based ModIs Dust AeroSol (MIDAS) AOD/DOD datasets and radiative transfer modeling (RTM), under clear-sky conditions. The Mediterranean basin is a region of high interest for such a research effort since it combines high solar energy potential with an increasing capacity in solar energy installations. Aerosol attenuation of annual GHI and DNI were 1–13% and 5–47%, respectively. Over North Africa and the Middle East, attenuation by dust was found to contribute 45–90% to the overall attenuation by aerosols. After 2008, attenuation of surface solar radiation by aerosols became weaker mainly because of changes in the amount of dust. Sensitivity analysis using different AOD/DOD inputs from Copernicus Atmosphere Monitoring Service (CAMS) reanalysis dataset revealed that using CAMS products leads to underestimation of the aerosol and dust radiative effects compared to MIDAS, mainly because the former underestimates DOD. The results of this analysis are important for understanding of the role of aerosols and especially of dust on GHI and DNI over the Mediterranean Basin and planning of future solar installations.
As solar energy nowcasting and short-term forecasting are essential for the optimization of solar renewable energy use in the energy mix, accurate clouds and aerosol datasets are the key factors to achieve optimum results. SENSE2 is the upgraded version of an existing solar energy nowcasting system that produces real-time estimates of surface GHI based on earth observation data (satellite and model based) at high spatial and temporal resolution (~5 km, 15 min) for a domain including Europe and the Middle East–North Africa (MENA). The improvements that have been introduced to SENSE2 are a new model configuration and the upgrade of cloud and aerosol inputs. The improved SENSE2 has been validated for 1 year (2017) using ground-based measurements from 10 stations. The limitations of evaluating such a model were investigated using surface-based sensors due to cloud effects. Results for instantaneous (every 15 min) comparisons show that the GHI estimates are within ±50 W m-2 (or ±10%) of the measured GHI for 61% of the cases after the implementation of the new model configuration and a proposed bias correction. The bias ranges from -12 to 23 W m-2 (or from -2 to 6.1%) with a mean value 11.3 W m-2 (2.3%). It was demonstrated that the main overestimation of the SENSE2 GHI is linked with the uncertainties of the cloud-related information within the satellite pixel, while relatively low underestimation, linked with AOD forecasts (derived from CAMS), is reported for cloudless-sky GHI. The highest deviations for instantaneous comparisons are associated with cloudy atmospheric conditions when clouds obscure the sun over the ground-based station. Thus, they are much more closely linked with satellite vs. ground-based comparison limitations than the actual model performance. The NextSENSE2 short term forecasting system (up to 3 h ahead) based on a cloud motion vector technique, was also validated. It was found that it outperforms the persistence forecasting method, which assumes the same cloud conditions for the future time steps, especially for periods with increased cloudiness and changes in cloudiness.
Keywords:
solar radiation, aerosol, clouds, solar radiation forecasting, radiative transfer modeling
