396 NEWELL AND MILLER eddies play a relatively important role in the lower stratosphere, as noted earlier by Murakami.” This point will be mentioned again later in the paper. The zone of forced motion in the lower stratosphere has been investigated in detail from IGY data by Barnes”! and Oort,‘® and both find that zonal available potential energy is created in this region. MASS TRANSFER How is mass transported in this system? We may write an equation for the poleward transport in a (hypothetical) meridional plane:”* [QV] = [Q][V] + [Q*V*] + [Q’V’] where Q represents a particular property such as the concentration of a trace substance and V represents the north to south componentof the wind. Primes denote deviations from a time average, and asterisks, a deviation from a zonal average; bars denote time averages, and brackets, averages around a latitude circle. The left-hand side of the equation represents the average poleward flux of a property over a given period, say one month. The first term on the right-hand side represents the portion of the total transport due to mean meridional motions, the second is that due to transient eddies, and the third is that due to so-called “standing eddies,” which are in reality the quasi- stationary large-scale flow pattern evident on mean maps. A similar equation with the vertical velocity, W,inplace of V may also be written, but the terms are difficult to evaluate because of the uncertainties regarding estimates of W. When Q represents heat or momentum, it has been found that for the lowest 25 km of the atmosphere in extratropical regions the transient and standing eddy terms are sufficient to balance the appropriate budgets. Are they also sufficient to balance the mass budget? The paper presented at the previous AEC fallout conference” based upon ozone data suggested that they are in the region of the lower stratosphere. Prior to 1960 it was generally considered that mean meridional motions were of prime importance in the lower stratosphere. One of the major difficulties of such ideas is that they are not consistent with the findings concerning the momentum and the energy budgets. The equatorward and upward motion of U.S.S.R. debris is also difficult to reconcile with a poleward meridional motion throughout. However, this is not to imply that the meridional motions are unimportant as Barnes”? emphasized at the previous AEC fallout conference. Since that time three of our colleagues have given thought to the problem. Oort*4 collected all our IGY data (230 stations) on the mean meridional motion and constructed a coherent picture of the results at 100, 50,