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Identifier 000382225
Title A study of the impact of aerosols on the energy budget of the atmosphere using satellite measurements of climatic parameters and computer models
Alternative Title Μελέτη της επίδρασης των αερολυμάτων στο ενεργειακό ισοζύγιο της ατμόσφαιρας με χρήση δορυφορικών μετρήσεων κλιματολογικών παραμέτρων και υπολογιστικών μοντέλων
Author Μπενάς, Νικόλαος
Thesis advisor Βαρδαβάς, Ηλίας
Reviewer Χατζηαναστασίου, Ν.
Ματσούκας, Χ.
Abstract A deterministic spectral shortwave radiative transfer model was used for the computation of the Earth's atmospheric radiation budget, based on high temporal and spatial resolution satellite data of aerosols and atmospheric climatic parameters from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor. The study focused on the evaluation of the aerosol direct radiative effect (DRE) on the radiation budget components. Due to the high spatial and temporal variability of aerosols, the DRE, which constitutes a crucial component of the overall effect of aerosols on climate, is thus also highly variable. The aerosol direct effect on the tropospheric ozone photolysis rate, J(O1D), was also examined, being a dominant sink of tropospheric ozone. We note that tropospheric ozone contributes to the global greenhouse effect. Thus, J(O1D) is an important climatic parameter, which needs to be studied using modelling approaches, due to the scarcity of measuring stations, and because it takes place primarily below 330 nm, a spectral region where the aerosol effect is a key operating factor. The aerosol direct effect on potential evaporation was also assessed. Potential evaporation equals actual evaporation in shallow lakes, and constitutes a crucial parameter of the hydrological cycle. The aerosol DRE decreases potential evaporation by decreasing the solar radiation reaching the Earth's surface. The model runs were performed for the period 2000-2010 over several sites in Greece, which are characterised by high aerosol loads, with unique characteristics in terms of seasonal variation and origin. Two research stations in Crete (HCMR/AERONET and Finokalia), were selected due to the appropriateness of the island for studying Saharan dust episodes, which are frequent in the wider Eastern Mediterranean, and the availability of ground-based data for both model supplementary input and validation. The model was also run over four lakes in Central Greece, which constitute the main water supply reservoirs of the city of Athens, for the evaluation of the aerosol effect on potential evaporation. MODIS Level 2 data of aerosols, clouds and atmospheric parameters were analyzed and processed, and used as input to the model. These data are available since 2000, on a daily basis and at 10kmx10km and 5kmx5km spatial resolution. The model takes into account all physical parameters and processes that affect significantly the solar radiation transfer. The aerosol DRE is determined at the Earth's surface, within the atmosphere and at the top of the atmosphere. The model output downwelling shortwave radiation was successfully validated against ground{based measurements at the HCMR and Finokalia stations and at the four lakes in Central Greece. The model output J(O1D) was successfully validated against Finokalia station measurements. The analysis of the aerosol DRE on the model radiation budget, J(O1D) and potential evaporation was performed on an instantaneous/daily mean, seasonal and inter{annual basis. Dust event effects were also quantified, and trends during the period examined were assessed and evaluated in terms of corresponding trends and effects of operating factors, including aerosols, clouds and total ozone. Results show a decreasing trend in aerosols and the corresponding DRE over all sites examined. Changes in the radiation budget components, however, are also controlled by other factors; an increase in cloud fraction over HCMR station counterbalanced the effect that the DRE reduction would have caused. Similarly, although the DRE on J(O1D) has decreased, J(O1D) has not increased as was expected, due to an increase in total atmospheric ozone. The presence of aerosols reduces potential evaporation by about 0.5 mm on a mean daily basis, reaching up to 2 mm in summer. However, a decreasing trend in the aerosol load and DRE was found over all lakes during the period 2001-2010. Depending on the availability of model input data, the methodology developed in this study is applicable to any region of specific interest over the globe.
Language English
Subject Atmospheric aerosols
Climate change
Evaporation
Radiation transfer
Tropospheric ozone photolysis
Αερολύματα
Διάδοση ακτινοβολίας
Εξάτμιση
Κλιματική αλλαγή
Φωτόλυση τροποσφαιρικού όζοντος
Issue date 2014-02-10
Collection   School/Department--School of Sciences and Engineering--Department of Physics--Doctoral theses
  Type of Work--Doctoral theses
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