The sun is a powerful thing. As we know, it provides the Earth with light and heat to make it possible for us humans to live. The surface temperature of the Earth and structure of our atmosphere depend specifically on the solar irradiance, which is the numerical value of solar energy. This energy radiates from the sun in the form of waves. Being very difficult to measure these waves from the surface of the Earth as the atmosphere absorbs much of the radiation, Joanna Haigh and her team performed their research using the SORCE satellite (solar radiation and climate experiment). Radiation observed consisted of infrared, visible light and ultraviolet waves. Visible and near-infrared energy are those that heat the troposphere; the section of our atmosphere closest to Earth’s surface. Ultraviolet rays on the other hand were looked at more closely. They are responsible for starting chemical reactions that produce ozone in the next section of the atmosphere, the stratosphere. When ozone is created, heat is produced, therefore warming up the stratosphere.
The sun is currently nearing the end of its twenty-third solar cycle, and it was observed from 2004 to 2007 using the SORCE satellite that in this phase of the cycle, there is a significant increase in visible radiation and a decrease in ultraviolet waves. This results in a net warming on the surface of the Earth since there is more visible energy, which also have long wavelengths. The declining UV rays have shorter wavelengths, so there seems to be less ozone content present and cooler temperatures in the lower stratosphere, while the upper stratosphere was seen to have higher temperatures and more ozone.
Haigh and her research team from Imperial College London understand that the instruments used and their given time period do not present them with enough evidence to have realistic results, but they use what they can. The SIM instrument (spectral irradiance monitor) used onboard the SORCE measured daily wavelengths being radiated from the sun. A detailed chemical model of the atmosphere was also developed and used in experimentation. This measured accurate results for altitudes above twenty-five kilometers, and was therefore only used to test effects in the stratosphere. Although more time would be required to extract precise results, they noticed that the radiative forcing in this declining twenty-third sun cycle has different effects on the atmosphere than earlier in the cycle.
Radiative forcing is defined as the change in net irradiance from the sun, specifically in the thin layer between the troposphere and stratosphere, the tropopause. When this value is positive, the surface of the Earth is warmer and with a negative value, the surface is cooler. Forcing is constantly being maintained by ultraviolet radiation, keeping the ozone content at the right level. SIM provided the researchers with some interesting information. The solar cycle had peaked from 2000 to 2002, then from which the radiation started to decrease. The decline in ultraviolet rays monitored by SIM gave the impression that radiative forcing had also been decreasing from 2002. This consequently led the research group to believe that this is why the ozone levels were decreasing in the stratosphere, along with temperature. The atmosphere had also been seen to adapt to these low ozone levels and produce a healing effect. More UV waves are sent to the lower stratosphere where oxygen photolysis occurs and ozone is therefore produced.
An increase in ozone benefits the Earth and atmosphere is a variety of ways. It is able to prevent harmful radiation from entering the troposphere and have a negative effect on the Earth’s surface. The ozone allows for the stratosphere to heat up rather than the powerful rays reaching us humans. There is also an increase in infrared radiation, contributing to the inclined temperatures in the stratosphere. We will still be unaware of the many processes occurring in our atmosphere for quite some time, but until the skies are clear, keep that sunscreen handy.
Works Cited
Haigh, J. D., et al. (October 2010). An influence of solar spectral variations on radiative forcing of climate. Nature. Retrieved from
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