Ultraviolet (UV) Radiation and its physical Modulating Factors in Africa Based on TOMS and NOAA Polar Orbiting Satellites
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Date
2007-07
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Addis Ababa University
Abstract
Ultraviolet radiation is the main source of energy for the photochemical reaction and
dynamics in the stratosphere and ionosphere. It is also one of the main sources of energy
required for the evolution of animals and plants.
The method used to make people aware the risks related to UV is using a calculation
of the amount of daily irradiance, which is called dose rate. This dose rate then is
changed to UV index (UVI). Erythermal UV radiation (UVery) is the integrated solar
spectrum over the effective biological response to UV wavelengths on the ground
between 295-400 nm. This effective biological response is called action spectrum. The
action spectrum is the normalized UV amount, which affects the health of animals and
plants or biosphere in general. The value of UVI in Africa is 4 to 9, moderate to high
overall. This is due to the tropical nature of most parts of Africa. The trend of UV
radiation in Africa shows significant decrease in the year from 1980 to 1992 and a slight
increase in recent years from 1997 to 2002. The ozone amount on the other hand is
increasing in Africa. The variability of ozone in tropical Africa is relatively stable. The
aerosol index in Africa is generally decreasing. UV, aerosols and ozone do not show
high seasonal variability in this part of the continent.
The study and understanding of UV and its determining factors in Africa hardly
exists. Here attempts are made to associate UV with these determining factors. UV and
ozone established 41% of the total variability in the surface UV in Africa. Clouds show
31% variability in the surface UV and aerosols established only 7% total surface UV
determination
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Africa Based on TOMS and NOAA Polar Orbiting Satellites