A Preliminary Report on the Numerical Simulation of the Three-dimensional Structure and Variability of Atmospheric Nzo

1 "SINK" = C[ 34 + n(O( D» .K5] RN20 (1) Abstract. A numerical simulation of atmospheric NZO using the GFDL 3-D tracer model with a small uniform surface source (15 Mton yr-1) and stratospheric destruction (150 yr lifetime) has been run to a state near transport and chemical statistical equilibrium. The resulting NZO tropospheric distribution is relatively uniform with a slight excess in the Southern Hemisphere. In the model stratosphere there is a sharp poleward decrease in NZO mixing ratio away from high values in the tropics with pronounced winter minimums at 500S and GOoN. Even with the small uniform surface source, relative standard deviations of NZO in the surface layer range from 0.1% to 0.8%, well within the range of recentmeasurements. Additional experiments suggest that motions acting upon NZO accumulation in the source region boundary layer and upon the mixing ratio gradient between the troposphere and lower stratosphere are the major sources of tropospheric NZO variability. whereJ4. the daily average N20 dissociation rate coefficient and n(O(lD». the daily average metastable atomic oxygen number density. are evaluated at the upper two sigma surfaces. The rate coefficient for O(lD)-oxidation of N20. K5. is taken from the compilation of Hampson and Garvin (1975). J4 is calculated using the temperature-independent absorption coefficients measured by Johnston and SelwYn (1975). the solar flux data from the compilations of Ackerman (1971) and Simon (1974). the 02 and 03 absorption coefficie~rom Ackerman (1971). and observed annual zonal mean ozone profiles. The daily average number density of O(lD) was calculated from Introduction and Model Description