* integrated global NO source strengths are roughly: 3 tg/yr in the stratosphere from N2O decomposition; 2 tg/yr transported from the thermosphere to the mesosphere; 1-8 tg/yr between 70 and 90 km due to aurora; and 0.05 tg/yr between 70 and 100 km from meteors. The global morphology and variability of thermospheric nitric oxide (above 100 km) have been defined in detail by extensive satellite observations (Rusch and Barth, 1975; Stewart and Cravens, 1978; Cravens and Stewart, 1978). Thermospheric morphology should be reflected, to some degree, in mesospheric NO concentrations. In the case of mesospheric nitric oxide at mid and low altitudes, Rusch (1973) found typically less than 25% variability in NO concentrations at all altitudes between 65 and 105 km over a wide latitude range (from 40°N to 40°S) for the months of his observations (December, March, and July). By contrast, nitric oxide below 105 km in the polar region is found to be significantly more abundant and highly variable (Rusch and Barth, 1975). Large local variations may occur in mesospheric nitric oxide even at mid-latitudes. For example, the winter anomaly in D-region radiowave absorption at mid-latitudes is probably related to the transport of large quantities of NO from the auroral zone (Sechrist, 1977). Rusch (1973) reports one occasion of a sudden threefold increase in mesospheric NO between 10°N and 40°N observed by satellite. Basically, however, we expect SPS rocket-generated NO to be super-imposed on a background mid-latitude concentration profile similar to that in Fig. 4. Nitric Oxide Experiments. Nitric oxide generated in rocket reentry plumes can affect D- and E-region ionization and, as a result, high frequency (HF) communication links and dynamo region conductances. Hence, it is important to evaluate the potential impact on the lower ionosphere of heavy SPS rocket activity. Nitric oxide produced by reentering spacecraft may be detected in several ways: by enhanced resonant scattering of ultraviolet sunlight; by enhanced infrared emission at 5.3 pm; by induced chemiluminescence (NO + 0, NO2 +0, NO + 03); by changes caused in D-region electron concentrations and ion composition; or, least directly, by alterations in radiowave propagation characteristics. All of the above measurements are difficult enough to carry out in the ambient atmosphere, and would be more difficult in the wake of a rentering rocket. Major problems could involve the identification and tracking of the reentry plume and the deployment of instruments to favorable viewing sites. Nevertheless, several atmospheric experiments relevant to SPS activities could be proposed: 1. Studies of ambient mesospheric NO to determine more carefully its sources, sink, and variability. 2. Monitoring of space shuttle reentry tests beginning in 1979/1980 for effects on the lower ionosphere.
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