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gfdl's home page > gfdl on-line bibliography > 1982: Journal of Geophysical Research, 87(C4), 3061-3080
Tropospheric N2O variability
| Levy, H., II, J. D. Mahlman, and W. J. Moxim, 1982: Tropospheric N2O variability. Journal of Geophysical Research, 87(C4), 3061-3080. |
| Abstract: Tropospheric N2O climatologies are simulated with the GFDL general circulation/tracer model for three idealized source specifications: (1) a constant surface flux of 1.44 x 109 molecules cm-2 s-1 distributed uniformly over the earth's surface, with a global source strength of 17 tg N2O yr-1 and an atmospheric lifetime of 131 yr; (2) a 13 month integration of the stable N2O field from experiment 1 with its N2O source removed; (3) a constant surface flux of 2.24 x 1010 molecules cm-2 s-1 over only those land areas with precipitation in excess of an arbitrary limit of 127 cm yr-1, but with the same global strength (17 tg N2O yr-1) and atmospheric lifetime (131 yr) as in experiment 1. In the boundary layer, the model produces an interhemispheric gradient with a minimum in the northern hemisphere (NH). This is due to the greater downward transport in the NH which results in more dilution of NH boundary layer N2O mixing ratios by the N2O-poor air from the lower stratosphere. The boundary layer distribution of N2O is also influenced by the distribution of the surface source. The lack of an N2O maximum in the model's NH boundary layer suggests that, unlike the model's idealized source, the true source has a large excess in the Northern Hemisphere. Above the boundary layer, the N-S gradient is controlled by the large-scale vertical transport that produces a NH minimum in N2O mixing ratio. The impact of the surface source distribution is small. Current measurements at 500 mb have too low a precision to confirm or disprove the model prediction of an interhemispheric gradient with a NH minimum in the middle troposphere. The sources of temporal variability in the model's N2O fields are transient motions of all scales acting on mixing ratio gradients, both vertcal and horizontal. The model finds that a small surface source of 17 tg N2O yr-1, sufficient to balance stratospheric destruction, is more than able to maintain the observed variability in the boundary layer. |