Unit:
Τομέας Φυσικής ΕφαρμογώνLibrary of the School of Science
Dissertation committee:
Γεώργιος Κάλλος Καθηγητής (επιβλέπων), Δημοσθένης Ασημακόπουλος Καθηγητής, Μαρία Τόμπρου Αναπλ. Καθηγήτρια
Original Title:
An integrated atmospheric modelling system for the simulation of coupled physical and chemical processes
Translated title:
Eνα ολοκληρωμένο ατμοσφαιρικό μοντέλο για τη προσομοίωση φυσικών και χημικών διεργασιών
Summary:
This doctoral work aims at an enhanced understanding of the complex links and
feedbacks between natural and anthropogenic pollutants and the
radiation-cloud-precipitation cycle in the atmosphere, through direct,
semi-direct and indirect interactions. For this scope the development of a
proper modelling tool was necessary in order to use it for the coupled
simulation of these physical and chemical processes. For this purpose the
Regional Atmospheric Modeling System (RAMS) has been extended with gas, aqueous
and aerosol phase chemical mechanisms, online photolysis component, biogenic
and anthropogenic emissions and a new radiation scheme. The aerosols from the
natural and anthropogenic activities have been linked with the radiation and
microphysical processes in order to address issues related to their interaction
with the radiation budget, cloud properties, precipitation and, consequently,
photolytic reaction and chemical processes. The new integrated model is named
RAMS/ICLAMS (Regional Atmospheric Modeling System/Integrated Community Limited
Area Modeling System). The main results from the application of the model
revealed the complex nature of the paths of interaction between the different
atmospheric processes. The simulations with and without aerosol impacts showed
the contribution of the direct and indirect mechanisms in the atmosphere.
Through these mechanisms the alteration of radiation fluxes influences
meteorology (temperature, surface fluxes, clouds etc.) and chemistry
(photochemical processes, temperature dependent reactions, pollutant advection
and diffusion). The effect of aerosols was projected in a linear way on
shortwave radiation and a non-linear way on long-wave radiation. Terrestrial
upwelling longwave radiation showed a complex daytime behavior, showing both
enhancement and attenuation areas. The results indicated that the vertical
structure of the dust layer governs the magnitude of feedback on radiation. Sea
salt particles also reduce surface shortwave radiation and increase downwelling
longwave radiation. The activation of natural particles as CCN causes small
changes in radiation fluxes and temperature, however, precipitation is
influenced more by the indirect than by the direct and semi-direct effects. The
total precipitation of a cloud system is not affected by the presence of the
additional CCN but its spatiotemporal characteristics are altered when taking
or not taking into account the feedback mechanisms. The inclusion of aerosol
radiative effects leads to improved performance of the model regarding both
meteorological and air quality parameters. The simulations with the online
model gave more accurate results, for ozone and sulphate aerosols, compared to
the offline approach (represented by an offline chemical transport model).
These results indicate that coupled simulation can add to the accuracy of the
model. Apart from the avoidance of interpolation between models (since in the
online approach all processes are simulated in the same spatiotemporal
configuration), the improvement can be attributed to the online calculation of
the photolysis rates. Additionally, the detailed analysis of a characteristic
case in the Eastern Mediterranean where both anthropogenic and natural aerosol
sources were considered resulted in a model precipitation bias that is half the
bias of the non-interactive model. Moreover, the bias is improved in the
“natural and anthropogenic” compared to “only natural” simulations. The
continuous improvement of the results with the inclusion of the additional
information is an indication that a number of physical processes related to the
indirect effect are now covered on a more satisfactory way.
Keywords:
Integrated model, Aerosol-cloud-radiation interactions, Atmospheric chemistry
Number of references:
266
Number of pages:
[8], 235, [32]
File:
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document.pdf
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