HIRDLS observations and simulation of a lower stratospheric intrusion of tropical air to high latitudes

On 26 January 2006, the High Resolution Dynamic Limb Sounder (HIRDLS) observed low mixing ratios of ozone and nitric acid in a ~2 km layer near 100 hPa extending from the subtropics to 55°N over North America. The subsequent evolution of the layer is simulated with the Global Modeling Initiative model and substantiated with HIRDLS observations. Air with low mixing ratios of ozone is transported poleward to 80°N. Although there is evidence of mixing with extratropical air, much of the tropical intrusion returns to the subtropics. This study demonstrates that HIRDLS and the GMI model resolve thin intrusion events. The observations combined with simulation are a first step towards development of a quantitative understanding of the lower stratospheric ozone budget.