Vardavas Ilias
Environmental Studies Research Topics
Evolution of Planetary Atmospheres
A greenhouse-land weathering model has been developed to predict the variation in atmospheric temperature and CO2 arising from the evolution of: the earth's atmosphere; continent land area; early biosphere; solar flux. The model predicts the two major glaciation periods; one between 2.5 and 2.0 Gyr ago; one between 1.0 and 0.5 Gyr ago. The evolution of the XUV and Lyman-alpha flux from solar-like G-type stars has been related to stellar properties such as the Rossby number. This with the radiative/convective-photochemistry-microphysical model developed for Titan’s atmosphere is being used to examine the evolution of planetary atmospheres. |
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Radiation Transfer and Climatic Change
Parameterizations based on laboratory infrared, visible and uv absorption cross-sections were developed for rapidly computing the atmospheric transmission of molecules important to the thermal structure of the atmosphere. Analytical expressions were developed for generating the photodissociation rate of atmospheric water vapour. A radiative convective model was developed for computing the mean vertical atmospheric temperature structure from the ground up to 70 km. It also generates the outgoing infrared flux spectrum. The model incorporated both solar and terrestrial flux transfer and the thermodynamics of atmospheric water vapour. The method has been used to simulate climatic evolution arising from variations in the solar flux, planetary albedo and atmospheric chemistry. | |
Meteorology and Hydrology
A meteorological cycles-radiation model was developed to simulate the seasonal variation of net all-wave radiation flux and evaporation rate at any geographical location. The evaporation model was used to develop a daily rainfall-runoff model for catchment and a daily water budget model for a flood plain. A simple model for estimating lake evaporation from standard meteorological data has been developed and applied to four Australian lakes in four climatic regions; tropical, temperate, mediterranean and alpine. A rainfall-runoff model has been developed for the semi-arid Mediterranean Messara Valley of Crete. Models and measurements have been used to estimate potential evapotranspiration in the desertification-threatened Messara Valley of Crete. |
Conceptional Rainfall-Runoff Model |
The Earth’s Radiation Budget and Aerosols
Spectral longwave and shortwave radiation models have been developed for computing atmospheric solar and terrestrial radiation fluxes and global mean surface temperature. The models have been used to estimate the surface and Top-of-Atmosphere solar and terrestrial radiation budget for the Earth using satellite climatological data. The models are now used to compute the radiative forcing of atmospheric aerosols. Applications include the Heat Budget of the Mediterranean, Red and Black seas, and the radiative forcing associated with the ENSO phenomenon. |
Global distribution of the downward shortwave flux (Wm-2) at the surface for January 1988 |
The FORTH AERONET site for monitoring aerosol loads in the Eastern Mediterranean |
Global distribution of the aerosol direct radiative effect (Wm-2) on the outgoing shortwave radiation at top-of-atmosphere |
Atmospheric Photochemistry
A photochemical radiation model to investigate the physico-chemical processes that control atmospheric oxygen and ozone levels has been developed. The model involves the transfer of terrestrial and solar visible and uv radiation through the atmosphere and the transport of chemical species by eddy and molecular diffusion. The uv flux transfer involves multiple scattering by air, clouds and surface. This is used to compute the photodissociation rates of molecular species with altitude. The model is able to simulate the important coupling between the atmospheric radiation field, temperature and chemical composition. The model has been used to study prebiotic planetary atmospheres and the chemical and thermodynamic structure of Titan based on Cassini/Huygens Mission data. | |
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