Stratosphere the stratosphere temperatures increase with altitude "(see temperature inversion)"; the top of the stratosphere has a temperature of about 270 K (−3°C or 26.6°F). This vertical stratification, with warmer layers above and cooler layers below, makes the stratosphere dynamically stable: there is no regular convection and associated turbulence in this part of the atmosphere. However, exceptionally energetic convection processes, such as volcanic eruption columns and overshooting tops in severe supercell thunderstorms, may carry convection into the stratosphere on a very local and temporary basis. Overall the attenuation of solar UV at wavelengths that damage DNA by the ozone layer allows
Sun tanning tanning and UV radiation exposure, either from the sun or from indoor tanning. Production of vitamin D is essential for human health. Moderate exposure (avoiding sunburn) to UV radiation provides benefits such as increased vitamin D, as well as other possible benefits that are still being studied. Several tanning activators have used different forms of psoralen, which are known to be photocarcinogenic. Health authorities have banned psoralen since July 1996. Tanning has gone in and out of fashion. In the United States and Western Europe before about the 1920s, tanned skin was associated with the lower classes, because they worked