The effect of aerosols on long wave radiation and global warming

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dc.contributor Helsingin yliopisto, Matemaattis-luonnontieteellinen tiedekunta, Fysiikan laitos fi
dc.contributor University of Helsinki, Faculty of Science, Department of Physics en
dc.contributor Helsingfors universitet, Matematisk-naturvetenskapliga fakulteten, Institutionen för fysik sv Zhou, You 2015
dc.identifier.uri URN:NBN:fi:hulib-201711155702
dc.description.abstract Long wave (LW) radiation in the Earth's atmosphere is defined as the radiation at wavelengths longer than 4 µm (infrared). The short wave (SW) radiation wavelengths are less than 4 µm (visible light, ultraviolet). SW radiation is usually from solar origin. The absorbed solar SW radiation is closely balanced by the outgoing LW radiation in the atmosphere. This radiation balance keeps the global average temperature stable. The main cause of the current global warming trend is human expansion of the 'greenhouse effect'. Atmospheric greenhouse gases absorb the thermal LW radiation from a planetary surface. The absorbed radiation is re-emitted to all directions. Some of the energy is transferred back to the surface and the lower atmosphere since part of the re-radiation is directed towards the surface, resulting in increased surface temperature. The local radiation balance is also affected by clouds and aerosols in the atmosphere since they too can absorb and scatter radiation. The effects of clouds and greenhouse gases on the global radiative balance and surface temperature are well known. The aerosols, however, are one of the greatest sources of uncertainty in the interpretation and projection of the climate change. Natural aerosols such as those due to large eruptions of volcanoes and wind-blown mineral dust are recognised as significant sources of climate forcing. In addition, there are several ways in which humans are altering atmospheric aerosols. These include industrial emissions to the lower atmosphere as well as emissions to as high as lower stratosphere by aircraft. In this thesis the effect of aerosols on LW radiation was studied based on narrowband LW calculations in a reference mid-latitude summer atmosphere with and without aerosols. Aerosols were added to the narrowband LW scheme based on their typical schematic observed spectral and vertical behaviour over European land areas. This was found to agree also with spectral aerosol data from the Lan Zhou University Semi-Arid Climate Observatory and Laboratory measurement stations in north-western China. A volcanic stratospheric aerosol load was found to induce local LW warming with a stronger column “greenhouse effect” than a doubled CO2 concentration. A heavy near-surface aerosol load was found to increase the downwelling LW radiation to the surface and to reduce the outgoing LW radiation, acting very much like a thin low cloud in increasing the LW greenhouse effect of the atmosphere. The short wave reflection of white aerosol has, however, stronger impact in general, but the aerosol LW greenhouse effect is non-negligible under heavy aerosol loads. en
dc.language.iso eng
dc.publisher Helsingfors universitet sv
dc.publisher University of Helsinki en
dc.publisher Helsingin yliopisto fi
dc.subject aerosols en
dc.subject long wave radiation en
dc.subject radiative forcing en
dc.subject long wave heating rate en
dc.subject long wave radiation scheme en
dc.subject Lan Zhou city en
dc.subject climate change en
dc.title The effect of aerosols on long wave radiation and global warming en
dc.type.ontasot pro gradu-avhandlingar sv
dc.type.ontasot pro gradu -tutkielmat fi
dc.type.ontasot master's thesis en
dct.identifier.urn URN:NBN:fi:hulib-201711155702

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