The ozone layer, which protects humans, plants, and animals from potentially damaging ultraviolet (UV) light from the Sun, develops a hole above Antarctica in September that typically lasts until early December. However, in November 2009, that hole shifted its position, leaving the southern tip of South America exposed to UV light at levels much greater than normal.

To characterize this event and to evaluate satellite monitoring capabilities, de Laat et al. analyze satellite and ground-based measurements of ozone levels and the UV index (UVI). They find that the ozone column over southern South America was especially thin from 11 to 30 November 2009, and significantly higher UVI values were measured.

Such abnormally low ozone levels sustained during a continuous period of three weeks had not been observed above southern South American at any time in the past 30 years, the researchers say. The high UVI values occurred over populated regions, meaning that humans had been exposed to increased levels of UV light. The scientists also note that the satellite-based measurements agreed well with the ground-based measurements, suggesting that satellite measurements can be valuable for monitoring ozone and UV radiation levels.

Authors of the study include: A. T. J. de Laat, R. J. van der A, M. A. F. Allaart, and M. van Weele: Royal Netherlands Meteorological Institute, de Bilt, Netherlands; G. C. Benitez: Observatorio Central de Buenos Aires, Servicio Meteorológico Nacional, Buenos Aires, Argentina and PEPACG, Pontificia Universidad Católica Argentina, Buenos Aires, Argentina; C. Casiccia: Laboratorio de Monitoreo de Ozono y Radiación Ultravioleta, University of Magallanes, Magallanes, Chile; N. M. Paes Leme: Ozone Laboratory, National Institute for Space Research, São José dos Campos, Brazil; E. Quel, J. Salvador, and E. Wolfram: División Lidar, CEILAP, CITEFA, CONICET, Río Gallegos, Argentina.