ances produced changes in telecommunication systems performance that far exceeded any possible changes induced by intentional ionospheric heating. Figure 3 shows a record of the phase changes seen in the LORAN-C signals propagated from Fallon, Nevada, to Brush, Colorado (top curve), and from Dana, Indiana, to Boulder, Colorado (bottom curve), between 1700 and 1835 h (UT) on August 20, 1979. At 1731 h, a small solar flare was reported. This flare produced a phase shift of more than 1 /zs in the Fallon-Brush signal and 0.5 /zs in the Dana- Boulder signal. The small phase shifts of five minute duration commencing at 1710 and 1810 h were caused by interference from the 60 kHz time and frequency standard (WWVB) at Fort Collins, Colorado. The times during which the Platteville Facility was “ON” are also indicated by the hatching on the time scale beneath the Dana- Boulder trace. Figure 4 provides another example of changes in telecommunication system performance resulting from solar flare activity. Shown in the figure is a portion of the normal diurnal phase change of about 60 /zs for the OMEGA Hawaii-to-Boulder VLF signal for five consecutive days beginning on August 16, 1979. Two solar flares are reported on August 18, one commencing at 1356 h (UT) and the other at 1406 h (UT). These flares produced a shift in the phase of the OMEGA signal of more than 10 /zs compared to the average behavior observed on the other four days. This shift is above five times the changes in phase seen on a day-to-day basis. Even if these day-to-day changes were associated with intentional ionospheric heating, the effect of the solar flare far outweighed any heating-induced effect. Both OMEGA (VLF) and LORAN-C (LF) data show that naturally induced changes in the ionosphere, which occur on a routine basis, yield effects in propagation systems that are many times greater than any effects that could be associated with the ionospheric heating resulting from the ohmic interaction between the ionosphere and a 23 mW/cm2 SPS power beam.
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