2 EFFECTS OF INJECTANTS IN THE 70-120-km ALTITUDE RANGE 2.1 INTRODUCTION The injectants are discussed in Section 2.2. The ambient levels of water vapor and of noctilucent clouds are reviewed in Sections 2.3 and 2.4, respectively, since the predicted enhancement as described by PF = 0.07 (see Table 4) is so large that possible changes in both water vapor and clouds must be evaluated. We must know both the mean levels of these quantities and also their fluctuations, so as to be able to evaluate potential impacts. Condensation has been observed in rocket exhausts in this altitude range (see Benech and Dessens, 1974) as well as at high altitudes, which could give rise to a significant enhancement in mesospheric cloudiness, as discussed in Section 2.5. The whole issue of condensation and re-evaporation in rocket exhausts is important from the standpoint of the absorption and, in particular, scattering of sunlight and earth shine, which affects the global climatology as well as optical remote sensing. Additionally, the issue is also critical for the overall effect of water injections, especially at the higher altitudes, near LEO; reference to Table 4 shows that water sediments out of Domain B much more rapidly if deposited in the atmosphere as an aerosol than as a gas, giving rise to a very much smaller perturbation factor or PF. The problem of condensation and re-evaporation was addressed by two groups (see items 2.5 and 3.4.1 of Table 5). A discussion also was given by P. Bernhardt after the workshop. These three discussions are presented verbatim as Section 2.5. Section 2.6 treats the spreading of rocket exhausts, on various scales, which could be very important both as far as the impact and the experimental simulation of an injection are concerned. Rocket exhausts deposit a large amount of energy in the atmosphere: Would this activity be expected to produce any observable effects? This question is raised in Section 2.7. Photochemical effects, including enhancement or reduction in ionization, possible changes in ozone and other neutral species, and changes in airglow, are reviewed in Section 2.8, and changes in atmospheric conductivity related to these changes in ionization are treated in Section 2.9. One very important effect of H2 injections from the HLLV second stage burn is the ionospheric depletion associated with the formation of H20+ and OH ions in the F-region as a consequence of the upward diffusion of hydrogen from the 70-120-km altitude region. This problem is discussed in Sections 3.1 and, especially, 3.2. The topics discussed above relate to phenomenology. The overall significance of these possible changes is reviewed in Section 2.10, and in the light of the phenomenology and of the significance of the effects a listing of atmospheric experiments that merit consideration is given in Section 2.11.
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