another paper (30). As for the troposphere, changes in water vapor will be less than 0.1%, hardly important relevant to climatic changes. Moreover, very little sulfur or particulate materials are expected from HLLVs, and condensation or nucleation processes are not likely to be affected significantly. Dynamical interactions between the troposphere and upper atmosphere have traditionally been thought of as a “one-way street,'' that is, the troposphere performs work on the stratosphere, but does not respond in turn to stratospheric motions. This is because stratospheric motions contain much less energy than tropospheric motions, a result of the much lower mass of the stratosphere. The mean meridional circulation of the stratosphere, for example, would not have much effect on the troposphere since meridoneal wind speeds are comparable in magnitude to tropospheric wind speeds and thus much less energetic because of lower air density in the stratosphere. However, eddy motions, such as large-scale planetary waves, generally amplify as they propagate upward, maintaining a nearly constant energy per unit volume. If one allows for these waves to be reflected in the stratosphere by some mechanism, with the amplitude and the phase of the reflected waves being governed by stratospheric conditions, it is possible for the stratosphere to have a feedback effect on tropospheric planetary waves. In fact, as Charney and Drazin (53) pointed out, the westerly jet of the winter upper stratosphere does act as just such a reflection mechanism. The implications of this for climatic changes are significant, for if changes in the zonal jet could be reduced by compositional changes at high altitudes, planetary wave reflection characteristics would also be affected, thus affecting the phase or amplitude of planetary waves in the troposphere (54). A number of investigators have explored this mechanism, including Avery and Geller (55) and Geller and Alpert (56). Their studies focused on the linear planetary wave response of a number of zonally averaged atmospheres to topographic and adiabatic forcing. Comparison of results for different cases could then show whether different types of changes in the stratospheric zonal wind had significant effects on tropospheric climate. The major result of the studies is as follows: below 35 km (22 mi), zonal wind changes of 20% or more must occur before planetary wave phase or amplitude changes at the surface approach the interannual variability (56). Of course, this result does not take into account the highly nonlinear nature of stratospheric motions; still, it is a good indication of the magnitudes necessary to cause significant dynamically induced climate changes. The implications of this result for SPS operations can be crudely assessed by making some estimates of the effects of HLLV water vapor emission. The radiative- convective model of Manabe and Wetherald (52) suggests a 10 °K decrease in stratospheric temperatures associated with quintupling the water vapor content. Scaling this down to an expected 10% maximum H2O increase if HLLV water vapor remains at low latitudes, we obtain temperature decreases of —0.2 °K. When these decreases are compared with the equator-pole temperature gradient of about 40 °K (which is proportional to the zonal wind strength), it can be seen that the maximum expected change in the zonal wind is only 0.5%, well below the threshold for significant effects on reflected planetary waves. As before, HLLV-induced ozone changes would have even less effect, since they are confined to levels above 40 km (25 mi). Based on these estimates, we conclude that no significant effects on Earth's climate should result from the projected launch schedule of HLLVs (400 yr-1). That is, we expect no temperature changes, locally or globally averaged, in excess of 0.1 °K and no dynamical variations exceeding 5% of the interannual variability in planetary wave activity.
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