This thesis presents new estimates of the components of the longwave radiation (LW) part of the Earth's global annual mean energy budget. The study is motivated by a schematic diagram of the Earth's Energy Budget widely used by the sci.entific community since its publication in the late 1990's. Nevertheless, estimates presented in this diagram were produced using a single standard temperatur e and gaseous vertical profile to represent the whole global atmosphere and a radiative code that can no longer be considered state-of-the-art. This thesis evaluates the reference diagram by calculating the geographical distribution ofLW components using an 12-year climatological dataset and outputs from a state-of-the-art line-by-line radiation code as input to a discrete ordinate scattering model. The direct radiative effect of mineral dust aerosol and the scat- . tering impact by cloud particles on the LW radiation budget are also studied. The global annual mean Outgoing Longwave Radiation (OLR), downward irradiance at the surface for cloudy sky and cloud LW forcing are found to be 235,341 and 27 Wm-2, respectively and are in good agreement with satellite and surface observations. Comparison between the present and reference diagram estimates shows differences up to 20 Wm-2 for some coqiponents. Natural and anthropogenic mineral dust aerosols globally reduce OLR by around 0.20 Wm-2 and regionall~ reduce OLR up to 10 Wm-2 under high dust concentration conditiolilS. The effect of multiple scattering by clouds particles on LW is found to decrease OLR by 3 Wm-2 with a hitherto unrecognised contribution from low clouds. AJthough this effect of 3 Wm-2 appears small compared to the global mean OLR value of 235 Wm-2 , neglecting scattering will lead to 10%biases in the global mean LW cloud forcing. Given the current observational and computational knowledge of radiative transfer, this thesis provides one of the most elaborate estimates of LW irradiances, which are an update of the reference diagram of the Earth's energy budget.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:485501 |
| Date | January 2006 |
| Creators | Sievert da Costa Coelho, Simone Marilene |
| Publisher | University of Reading |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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