Long-term ozone decline over the Canadian Arctic to early 1997 from ground-based and balloon observations

Column ozone measurements in the Canadian High Arctic (north of 70 degrees N) started in 1957 and there have been regular ozone sonde flights there since 1966. Column ozone values over the High Arctic were as much as 45% below normal for some days in March 1997. During March 1996 arctic ozone values were also very low. In both years, temperatures in the arctic stratosphere were extremely cold and, especially in 1997, the vortex wind pattern was unusual for the arctic and quite similar to the antarctic spring vortex. Similar cold stratospheric temperatures were present in 1967, but ozone deviations were much smaller. Despite the very low values in the High Arctic during March 1997, the average column ozone from three Canadian sites in the 50-60 degrees N latitude range was only 3.5% below normal.