Microwave Limb Sounder
Stratospheric Ozone (Global)
SummaryThe stratospheric ozone (O3) layer (near 20 km altitude) is an absorber of ultraviolet light from the sun; this absorption protects humans from the potentially deadly effects of skin cancer, and can also shield animals and the marine food chain, as well as plants, from undesirable UV-related consequences. Health effects tied to excessive UV exposure include skin cancer, cataracts, and a decline of the immune response system; while there are significant changes in average UV exposure from low to high latitudes, additional exposure (at any latitude) represents some increase in the risks. Decreases in the ozone layer have therefore been a cornerstone of atmospheric research for the past several decades, motivated by the realisation that industrial release of chlorofluorocarbon (CFC) gases at the Earth's surface were linked to a gradual depletion of the ozone layer, as well as the seasonal "ozone hole" phenomenon over Antarctica caused by enhancements in the ozone-destroying forms of chlorine and bromine in the northern hemisphere during the cold winter and spring periods. The different variations in ozone between the northern and southern hemispheres are related to the interplay of dynamical and chemical effects. A circling whirlpool of winds isolates the so-called polar vortex region at high latitudes in winter. More vigorous wave activity in the North leads to a shorter-lived winter polar vortex than in the South, and this reduces the net ozone loss in the northern hemisphere. On a global scale, ozone depletion is typically measured with respect to pre-1980 abundances; values of overhead (column) ozone abundances in the past few years have been lower than the pre-1980 levels by 3 to 6% (for mid- to high latitudes in the North and South, respectively). Thanks to internationally-agreed reductions in CFC emissions after the 1987 Montreal Protocol on Subtances that Deplete the Ozone Layer (with its many subsequent amendments), global ozone is expected to recover to pre-1980 levels in the 2nd half of the 21st century. The slow recovery process arises because of the very long lifetime of the main CFC gases in the upper atmosphere (sunlight destroys these compounds very slowly). There is mounting evidence that a slow path towards such a recovery is being achieved, although continued attention to unexpected chemistry and the variations in ozone is still a very useful endeavor.NASA's ozonewatch website provides up-to-date information on the status of the ozone layer and the ozone hole over the South Pole. A summary of the history of ozone research and the relationship between UV radiation and ozone can be found here: http://www.skincancer.org/ozone-and-uv-where-are-we-now.html. Research and results regarding environmental effects of ozone depletion can be found, for example, in the following location: http://www.gcrio.org/ozone/toc.html. Based on accumulated research of the Earth's atmospheric composition, scientific consensus reports are published every four years about the state of the ozone layer and the chemical and dynamical effects surrounding the variations in stratospheric ozone. See the following link for access to the 2006 Scientific Assessment of ozone depletion, with "Twenty questions and answers" and an Executive Summary, in addition to the more extensive and detailed research and results: http://www.wmo.int/pages/prog/arep/gaw/ozone_2006/ozone_asst_report.html. Besides health-related concerns, the study of ozone and the distribution of other gases in the Earth's atmosphere is an important process to help understand atmospheric behavior and to help predict future global change. The Aura satellite is continuing its measurements of ozone and many other gases on a global scale, using both the MLS and OMI instruments (since August, 2004). MLS provides a vertically-resolved view of changes in ozone, with profiles being measured on a roughly 3 km vertical grid, every 170 km around the orbit (for about 3500 profiles every 24 hours). Ozone and related datasets are also being connected to previous global satellite measurements, so that data records can be constructed and preserved for studies of long-term changes in atmospheric composition. More detailed MLS-derived information and scientific publications relating to ozone can be found on the MLS website (http://mls.jpl.nasa.gov under "Publications"); this includes the use of MLS data for investigations of polar ozone loss, and the inference of changes in tropospheric ozone through the combined usage of OMI (total column ozone) and MLS (stratospheric column) measurements. |
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MLS-related publications concerning global stratospheric ozone2011
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