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Published December 20, 1989 | Published
Journal Article Open

Sensitivity Study of Advection and Diffusion Coefficients in a Two-Dimensional Stratospheric Model Using Excess Carbon 14 Data


Using the California Institute of Technology/Jet Propulsion Laboratory two-dimensional transport model, with transport coefficients taken from Yang and Tung (1989), we study the time evolution of excess carbon 14 in the stratosphere and the troposphere from October 1963 to December 1966. The model provides a satisfactory simulation of the observed data. Due to the impulsive nature of its source, initial distributions of excess carbon 14 exhibit large spatial gradients. This permits important constraints on the range of transport coefficients in the lower stratosphere to be derived. The standard model uses the circulation and eddy diffusivity of the year 1980. Large deviations (by factor of 2) from this standard transport are ruled out by our model. A self-consistently derived K_(yy) which is small (∼10^9 cm^2 s^(−1)) in tropical regions, but is larger (∼10^(10) cm^2 s^(−1)) at higher latitudes is preferred. A Kzz as large as 1×10^4 cm^2 s^(−1) would be inconsistent with the data. Excess carbon 14 is removed from the atmosphere with surface deposition velocities v_S = 3 × 10^(−3) cm s^(−1) and v_N = 5 × 10^(−3) cm s^(−1) in the southern and northern hemispheres, respectively. The last result is contrary to the current understanding that the oceans are the dominant sink for excess ^(14)C.

Additional Information

© 1989 by the American Geophysical Union. Received December 14, 1988; revised April 19, 1989; accepted April 19, 1989. Paper number 89JD00796. We thank K. K. Tung and H. Yang for sending us the detailed transport coefficients of their two-dimensional model and for many discussions and comments which resulted in a great improvement of this paper. We are indebted to H. S. Johnston and F. S. Rowland for useful discussions. An anonymous referee was helpful in sharpening the conclusions of our paper. This work is supported by NASA grant NAGW-413 to the California Institute of Technology. Contribution 4724 from the Division of Geological and Planetary Sciences, California Institute of Technology.

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