Detection of stratospheric ozone intrusions by windprofiler radars

Stratospheric ozone attenuates harmful ultraviolet radiation and protects the Earth's biosphere. Ozone is also of fundamental importance for the chemistry of the lowermost part of the atmosphere, the troposphere. At ground level, ozone is an important by-product of anthropogenic pollution, damaging forests and crops, and negatively affecting human health. Ozone is critical to the chemical and thermal balance of the troposphere because, via the formation of hydroxyl radicals, it controls the capacity of tropospheric air to oxidize and remove other pollutants. Moreover, ozone is an important greenhouse gas, particularly in the upper troposphere. Although photochemistry in the lower troposphere is the major source of tropospheric ozone, the stratosphere-troposphere transport of ozone is important to the overall climatology, budget and long-term trends of tropospheric ozone. Stratospheric intrusion events, however, are still poorly understood. Here we introduce the use of modern windprofiler radars to assist in such transport investigations. By hourly monitoring the radar-derived tropopause height in combination with a series of frequent ozonesonde balloon launches, we find numerous intrusions of ozone from the stratosphere into the troposphere in southeastern Canada. On some occasions, ozone is dispersed at altitudes of two to four kilometres, but on other occasions it reaches the ground, where it can dominate the ozone density variability. We observe rapid changes in radar tropopause height immediately preceding these intrusion events. Such changes therefore serve as a valuable diagnostic for the occurrence of ozone intrusion events. Our studies emphasize the impact that stratospheric ozone can have on tropospheric ozone, and show that windprofiler data can be used to infer the possibility of ozone intrusions, as well as better represent tropopause motions in association with stratosphere-troposphere transport.     

Unprecedented Arctic ozone loss in 2011

Chemical ozone destruction occurs over both polar regions in local winter-spring. In the Antarctic, essentially complete removal of lower-stratospheric ozone currently results in an ozone hole every year, whereas in the Arctic, ozone loss is highly variable and has until now been much more limited. Here we demonstrate that chemical ozone destruction over the Arctic in early 2011 was--for the first time in the observational record--comparable to that in the Antarctic ozone hole. Unusually long-lasting cold conditions in the Arctic lower stratosphere led to persistent enhancement in ozone-destroying forms of chlorine and to unprecedented ozone loss, which exceeded 80 per cent over 18-20 kilometres altitude. Our results show that Arctic ozone holes are possible even with temperatures much milder than those in the Antarctic. We cannot at present predict when such severe Arctic ozone depletion may be matched or exceeded.