3 EFFECTS ON THE ATMOSPHERE (INCLUDING CLIMATOLOGY) The natural atmosphere contains both electrically neutral and ionized constituents. Whereas the neutral species are distributed throughout the entire atmosphere, significant populations of ionized species are found only at altitudes greater than about 60 km. The characteristic physical and chemical properties of the natural atmosphere and atmospheric processes provide a convenient means for separating it into a series of layers beginning with the troposphere, in which weather phenomena occur, and ending with the exosphere, which reaches out to the region where terrestrial space and outer space merge (see Fig. 3.1). Overlapping these general atmospheric layers are a series of layers containing ionized atomic and molecular species electrically balanced by an equal number of free electrons. Superimposed on the upper layers is a region referred to as the magnetosphere. While it is true that the earth's magnetic field extends from the surface out, the magnetosphere is that portion of the outer magnetic field (above about 150 km) in which the motion of charged particles is dominated by magnetic forces instead of by the particle collisions characteristic of molecular diffusion. The investigation of atmospheric effects associated with the SPS has been divided into task areas that take advantage of the naturally occurring atmospheric layering. Of course, it is important to realize that while the various atmospheric layers are to some extent isolated from one another, mechanisms do exist that naturally couple adjacent layers. Hence, whereas the SPS may influence specific layers of the atmosphere directly, for example by the discharge of rocket propellants, such layer-specific influences may be subsequently propagated to adjacent layers either by naturally-occurring or inadvertantly-formed coupling processes. Figure 3.2 shows a few of the general types of atmospheric effects expected to result from rocket launches. Whereas all of the processes illustrated in the figure are expected to occur, the magnitudes of the effects and their consequences for climate and weather, radio wave propagation, and other phenomena of importance to public health and welfare or the ecology remains uncertain. Not illustrated in Fig. 3.2 but also of potential importance are effects associated with rectenna operations, including effects of the transmission of microwave energy through the troposphere.
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