Estudo Comparativo dos Efeitos de Tempestades Magneticas Em VLF na Anomalia Magnetica Do Atlantico Sul (Comparative Study of the Effects of Magnetic Storms within VLF (Very Low Frequencies) on the Magnetic Anomalies of the South A

摘要

Effects produced in the lower ionosphere by forty magnetic storms were analyzed in the period of 1976 to 1981. Using VLF propagation path omega-Argentina/Atibaia, which is located in the Brazilian Geomagnetic Anomaly. Some storm effects which occurred in 1981 were also analyzed by means of a VLF/LF Oblique Ionosonde operated by CTA/IAE, with the transmitter located in Paula Freitas and the receiver in Gaspar. Comparison between frequencies of 13.6 and 10.2 KHz showed well-defined propagation characteristics. For the frequencies of 10.2 and 13.6 KHz, the height near 80 and 83 km night propagation was obtained, respectively. Differences in electron density and ionization time for each region was verified. Reflectivity data for the Oblique Ionosonde indicated the occurrence of more than one reflection layer of the signal in near heights. The results confirmed the increase of electron density in about 8 to 48 hours after the sudden commencement (sc) onset, and lasting from one to several days. Electron flux calculations revealed the existence of particles with energy ranging from 10 to 200 KeV and flux ranging from J = 1000-1,000,000 electrons/sq cm s for energy between 50 is equal to or less than E sub 0 is equal to or less than 150 KeV for the largest observed phase deviation. The electron density in the region considered changed from 1000 to 10,000 electrons/cu cm during the periods of maximum activity. On the other hand, some magnetic storms have shown a decrease in the electron density near the sc, effect not observed in this region.