A study on year-to-year variation in Arctic and mid-latitude atmosphere mixing using the distribution of nitrous oxide concentration

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For better simulations of ozone destruction in the polar regions, a radiation transfer scheme of CCSR/NIES chemical transport model is modified from a plane parallel approximation to a pseudo-spherical approximation. This leads to an improvement of the onset time of Antarctic ozone hole, which become 10 days earlier than that in the plane parallel model. The modification also leads to a 20 DU smaller total ozone amount in the ozone hole development phase. These changes make the model more realistic.An effect of ozone destruction inside the Arctic polar vortex on the ozone concentration outside is examined using the chemical transport model. A model calculation for the year 1997 shows that the decrease in ozone concentration outside the Arctic polar vortex in February and March is limited to the equivalent latitude belt of 5-10 degrees outside the vortex boundary.The distribution of nitrous oxide (N_2O) at mid-and high-latitudes in the northern hemisphere lower stratosphere is investigated for 25 years from 1978 to 2002 using the output of the chemical transport model and Probability Distribution Function (PDF) technique. A distinct difference in the N_2O distribution between in the early polar vortex breakup years and in the late years is found. Analyses show that in a whole region north 45°N the difference is caused by a stronger downward motion in the polar lower stratosphere in the early breakup years than that in the late breakup years. Inside the polar vortex, however, the difference is caused rather by the horizontal mixing across the large horizontal gradient region of N_2O concentration at the vortex boundary than by the vertical advection.All these results show that there is a clear relationship between N_2O concentration field and the dynamics in the atmosphere (meridional circulation and wave activity) and suggest a relationship between a year-to-year variation of N_2O distribution and that of ozone.