Low-N2O air masses after the breakdown of the Arctic polar vortex in 1997 simulated by the CCSR/NIES nudging CTM

Low-concentration N2O regions in high latitudes of the lower stratosphere were observed by the Improved Limb Atmospheric Spectrometer (ILAS) for one and half months after the Arctic vortex breakdown in May 1997. A new Chemical Transport Model (CTM), referred to as the CCSR/NIES nudging CTM, has been developed, and used to simulate these low-N2O air masses. The simulation shows that one of the air masses had a horizontal scale of 1,000-1,500 km, and remained at high latitudes for 1.5-2.5 months after the polar vortex breakdown. The simulation also shows that the contrast between the N2O concentration of the low-N2O air mass and that of the ambient air was diminished when the air mass was stretched, which had a considerable influence on the duration of the air mass. From the duration, and the horizontal scale simulated by the CTM, an estimate was made of the horizontal eddy diffusivity after the polar vortex breakdown.