Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsm23b..01l&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #SM23B-01
Physics
2407 Auroral Ionosphere (2704), 2487 Wave Propagation (0689, 3285, 4275, 4455, 6934), 2704 Auroral Phenomena (2407), 6934 Ionospheric Propagation (0689, 2487, 3285, 4275, 4455)
Scientific paper
Despite their remote location, radio receivers at South Pole Station regularly detect AM broadcast band signals propagating from transmitters thousands of kilometers away. Statistical analysis of received radiowave power at South Pole during 2004 and 2005, integrated over the frequency range of AM broadcast stations, reveals a distinctive time-of-day (UT) dependence: a broad maximum in received power centered at 1500 UT corresponds to magnetic daytime; signal levels are lower during magnetic nighttime except for a <0.5 dB local maximum near 0210 UT. (For reference, midnight magnetic local time occurs at 0330 UT at South Pole.) The observed UT dependence of the integrated power must be attributed to magnetic geometry since solar illumination has no time-of-day dependence at South Pole (90° S geographic latitude). To understand the observed UT dependence, we performed Monte Carlo simulations of signals propagating to South Pole along a large sample of great circle paths. For each path the signal absorption was calculated based on two contributions: daytime D-region absorption and auroral absorption. The latter varies with day of year and magnetic local time in a complex fashion due to the asymmetric shape and varying size of the auroral oval and the offset of South Pole from the geomagnetic pole. The Monte Carlo simulations confirm that the enhanced absorption of AM broadcast signals during magnetic nighttime results from auroral absorption. Furthermore, the simulations predict that a weak (<0.5 dB) peak near magnetic midnight, similar to that observed in the data, arises from including in the statistical data base intervals when the auroral oval is contracted. These results suggest that ground based radio observations at a sufficiently remote high-latitude site such as South Pole may effectively monitor auroral oval characteristics on a statistical basis at least.
LaBelle James
Noonan K.
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