Fig. 1. NO production rates from three sources: 1) Solid line—NO production per second from the IBPs, 2) Dashed line—NO production per day from oxidation of nitrous oxide, 3) Dash-dot line—NO production per day from galactic cosmic rays. For comparison purposes this NO production rate is shown with production due to galactic cosmic radiation and nitrous oxide destruction; the natural sources which are considered to account for most of the middle and lower atmosphere NO production. Galactic cosmic ray production follows that derived in Ref. (8). This source has its minimum production at the geomagnetic equator. Nitrous oxide is produced largely by biological activity and is transported to the stratosphere, where it interacts with excited atomic oxygen produced by photodissociation of ozone, water, and nitrous oxide. The governing reaction is The result of the calculations which are made for the region where the geomagnetic and geographic equators coincide is given in daily production rates in Figure 1. A critical factor in the problem is the duration of the proton precipitation. During SPS construction 90 days of ion propulsion are required to move from low to geosynchronous orbit. While it thus appears that proton precipitation would be a nearpermanent feature at equatorial latitudes, in fact the time is determined by the inner radiation belt flux and population. Protons in the inner belt are produced mostly from the decay of neutrons of cosmic ray origin. Secondary sources include nuclear reactions involving collisions between protons and atmospheric gas atoms. Typical times to produce the present proton population are hundreds of years (9).
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