Summary UV Bulletin

Summary of the 2006 ozone hole season, issued 1/8/07

Synopsis:
The ozone hole of 2006 was one of the largest and deepest on record. Low stratospheric ozone concentrations generally promote increased UV intensities. However, other factors such as solar elevation, clouds, and the position of the ground station with respect to the ozone hole’s center also play an important role. These parameters are crucial for understanding UV intensities measured at NSF network sites during the austral fall of 2006.

The ozone hole was approximately centered at the South Pole during October and much of November 2006. This led to elevated UV intensities at the South Pole during the entire season. McMurdo Station is relatively close to the South Pole, and UV levels were also increased during much of September, October and November. A record UV Index of 7.5 was observed on 2 December 2006. Palmer Station, located 2800 km away from the South Pole, was affected several times by the ozone hole, but there were also extended periods when total ozone was above 300 DU. This led to a large variability in UV intensities. Ushuaia was affected by the ozone hole only in early October (when solar elevations were still small), and mid-November. UV levels at Ushuaia were close the long-term mean, with the exception of a distinct peak on 15 November 2006.

McMurdo Station, Antarctica:
Total ozone observations at McMurdo Station between 10 September and 4 December ranged from 124 to 315 DU, according to the Ozone Monitoring Instrument (OMI). Total ozone was frequently below 220 DU until mid-November. Notable exceptions were 3 October and 20 October, when McMurdo was located close to the edge of the ozone hole, and ozone values were above 240 DU.

UV intensities frequently exceeded the climatological mean, particularly between 7 October and 14 October, and between 1 November and 21 November. Observations during these periods were close to the upper limit of the range defined by measurements from the last 16 years. UV intensities below the long-term mean were observed for short periods only (i.e. 17 October – 21 October and 23 November – 25 November). As the Sun rose, the daily maximum UV Index increased from about 1 on 1 October to 6 on 1 December. The UV Index was above the long-term mean by about 40% on 13 October and by about 75% on 6 November. On 2 December, when the 2006 ozone hole started to disintegrate, total ozone dropped to 190 DU and record UV intensities were observed. The noontime UV Index of this day was 7.5, equaling the old record from late November 1998. After 4 December 2006, total ozone was above 300 DU, and UV intensities remained moderate.

Palmer Station, Antarctica:
Total ozone measurements at Palmer Station between October and December 2006 varied from 129 DU to 380 DU. Following the dynamics of the ozone hole, low and high ozone values alternated every 5-7 days. This led to a pronounced variability in UV intensity. For example, the maximum daily UV Index on 9 October (141 DU) was 7.3, which exceeded the long-term mean for this day by 75%. On 12 October (313 DU), the UV Index was only 1.9. Other notable spikes in UV occurred on 31 October (UV Index 6.3), 15 November (UV Index 9.8), 27 November (UV Index 8.1), and 8 December (UV Index 8.7). UV Indices as high as 14 have been observed historically during the first week of December when depleted air masses moved over Palmer Station. Measurements in 2006 remained below historic records.

South Pole, Antarctica:
Total ozone at the South Pole remained below 220 DU until 3 December, according to OMI. Total ozone ranged between 100 and 165 DU in October, and between 125 and 220 DU in November. UV intensities exceeded the long-term mean between late September and late November, with only few exceptions. The UV Index increased almost monotonically from 0.2 on 1 October to 3 on 19 November. Measurements during this period were at the upper limit of the range defined by data from the last 16 years. Between 19 November and 2 December, the UV Index varied between 2 and 3, but stayed below the all-time record of 3.8, which was observed on 30 November 1998.

Due to low solar elevations at the South Pole, UV levels are generally smaller than at the Antarctic coast. However, human exposure to UV radiation is significant even for UV Indices below 3, due to radiation reflected off snow.

Ushuaia, Argentina:
Total ozone measurements at Ushuaia between October and December varied from 199 to 415 DU. Ushuaia became affected by the ozone hole between 4 October (199 DU) and 9 October (250 DU), and between 13 November and 16 November. When the ozone hole started to break up in early December, ozone depleted airmasses moved over Ushuaia. On 9 December, 240 DU were observed by OMI.

UV intensities varied about the long-term mean of measurements from the last 18 years, with few exceptions. Most notable was a spike in UV on 15 November, coinciding with a sharp drop in total ozone. The maximum UV Index of this day was 10. A marked increase was also observed on 10 December (UV Index 9.7). Typical UV Indices for November and December are 5 and 6, respectively, but UV Indices as high as 11 have been observed historically.

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