Increased solar ultraviolet‐B associated with record low ozone over Texas

Abstract

A report (Kerr and McElroy, 1993) about record high solar UV‐B irradiance at 300 nm at Toronto in 1993 suggests that global ozone decline may have caused increased UV‐B elsewhere. This suggestion is consistent with observations of increased UV‐B associated with record low ozone near and around Seguin, Texas, during the summer of 1993. A sharp drop in ozone occurred during late June, and on 23 June total ozone fell to 230 Dobson units, which is 25.7% below the Nimbus‐7/TOMS observed mean for June 20–24 from 1979 to 1991 (310 DU). Direct UV‐B at 300 nm was the highest since ground observations were begun in February 1990. During July and August 1993, the mean total ozone was, respectively, 13% and 10.7% lower than during July and August 1990. When the Sun was not obscured by clouds or haze during July and August 1993, the mean direct irradiance at 300 nm was, respectively, 18.1% and 13.4% higher than during July and August 1990.