NASA has been monitoring the status of the ozone layer through satellite observations since the 1970s, beginning with the TOMS sensors on the Nimbus satellites. The latest-generation ozone-monitoring technology, the Ozone Monitoring Instrument (OMI), is flying onboard NASA's Aura satellite. The ozone hole is not technically a 'hole' where no ozone is present, but is actually a region of exceptionally depleted ozone in the stratosphere over the Antarctic. The ozone hole begins to grow in August and reaches its largest area in depth in the middle of September to early October period. In the early years (before 1984) the hole was small because chlorine and bromine levels over Antarctica were low. Year-to-year variations in area and depth are caused by year-to-year variations in temperature. Colder conditions result in a larger area and lower ozone values in the center of the hole. This animation shows total ozone in the Antarctic region along with the maximum ozone depth and size since the earliest measurements of Earth Probe instrument on the TOMS satellite. This animation was created for an exhibit at the Smithsonium Museum. Data dropouts have been removed for the following times: 1998/12/14-31, 2002/08/03-11, 2003/11/28-2003/12/02. The minimum ozone recorded is 82.0 du on September 26, 2003. The maximum area of 29 million square kilometers (11.4 million square miles) occurred on September 9, 2000.
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 22.214.171.124.0