3. Measurements of natural impulsive NO perturbations, such as aurorae, large solar flares, and winter anomalies, to investigate the consequences and fate of NO injected into the mesosphere. 4. Execution of a nitric oxide chemical release in the D- and Eregions. The experimental techniques that might be used to carry out these experiments include: 1. Nitric oxide detection based on y-band resonant fluorescence of sunlight, from rockets or satellites (in place or planned). 2. Observation of nitric oxide infrared and chemiluminescent emissions using ground- or rocket-based photometry. 3. Electron concentration measurements from rockets (using probes of radio propagation) or from the ground (using radar backscatter on partial reflection)• 4. Ion concentration measurements by mass spectrometry. 5. Radiowave propagation changes at HF and VLF using ground-to-ground or ground-to-air communication links. There are serious technical problems associated with all of the suggested experiments. An example is the problem of tracking a rocket reentry plume, as already mentioned. With regard to the study of NO produced by auroral events, as a simulation of SPS rocket-reentry, one would need to reconcile several fundamental differences between mesospheric conditions at middle and high latitudes, such as the sunlight intensity, temperature, and background composition and ionization levels. Similarly, winter anomalies are, at best, only poorly understood (on a physical basis) at this time. To our knowledge, only one NO chemical release has been made in the upper atmosphere (18.5 pounds of NO at 106 km over New Mexico; Pressman et al., 1956). On that occasion, the airglow emissions were observed from the ground for about 10 minutes. In some ways, an NO release is simpler than an ^0 release: NO will not condense upon release as may ^0, background mesospheric NO concentrations are much lower than H2O concentrations, and NO may produce more distinct emissions by which to trace its dispersion. Nevertheless, it is not clear that rocket reentry effects can be properly studied through NO releases. 2.11.8 Conductivity Experiments (Vondrak) The most useful requirement for the evaluation of SPS effects on conductivity is improved modeling and theoretical understanding of the present global distribution of ionization in the middle atmosphere and lower ionosphere. Such modeling is needed in order to make a sensible evaluation of the significance of perturbations to the natural distribution of ionization. A three-dimensional specification of electron concentration can be used to compute the two-dimensional distribution of height-integrated conductivity. Although derived from and compared with experimental data, such a model is
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