Record low ozone at the South Pole in the spring of 1993

Abstract

On October 12, 1993, a balloon‐borne ozone detector recorded a total ozone value of 91±5 Dobson Units (DU) at the U.S. Amundsen‐Scott Station at the south pole. This is the lowest value of total ozone ever recorded anywhere, 13% below the previous low of 105 DU at the south pole in October of 1992 [Hofmann and Oltmans, 1993]. A region with a thickness of 5 km, from 14 to 19 km, was totally devoid of ozone as compared to only about half this thickness for the ozone void in 1992. Sub‐100 DU total ozone values were observed on several soundings during 1993 whereas the 105 DU value was observed on only one occasion in 1992. The vertical profile of ozone indicates that the main reason for the record low ozone values in 1993 was an approximately 1 km upward extension of the ozone hole caused by unusual ozone loss in the 18–23 km region. Temperatures in this region were unusually low in September and October. Thus, the extension of the ozone hole may have been the result of the prolonged presence of polar stratospheric clouds at 18–23 km combined with the continued presence of sulfate aerosol from the Pinatubo eruption and, finally, increased chlorine levels. This scenario resulted in elevated ozone loss in a region where the ozone loss process is normally not saturated.