Estudo das irregularidades ionosféricas equatoriais utilizando sinais GPS / Global positioning system studies of equatorial ionospheric irregularities

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

Signals transmitted by the Global Positioning System (GPS) satellites were used to study equatorial ionospheric irregularities over Brazil. GPS (L1=1.575 GHz) scintillation data were used to infer the occurrence of ~400m scale-size irregularities and compared with equatorial Spread F (ESF) observations carried out by several other instruments like VHF coherent backscatter radar, digisonde and airglow photometer. GPS scintillation was also used to infer the characteristics of the intermediate scale-size ionospheric irregularities occurrence over São José dos Campos (-18o dip latitude) located close to the Equatorial Anomaly crest. Local time and seasonal variations of the irregularities were inferred by using GPS scintillation data. Results agree quite well with the well-known seasonal pattern of ESF in Brazil determined from ionosonde observations. However, the time decay of GPS scintillation irregularities was much shorter due to their smaller scale-sizes. Stronger scintillations were observed during equinoctial months when the ionospheric background density is much higher. Solar cycle effects on GPS scintillation occurrence and magnitude were also determined. Scintillation magnitude and occurrence tend to increase with solar cycle. Latitudinal dependence of GPS scintillation occurrence and magnitude was estimated from several stations distributed over the Brazilian Territory. Dual - frequency GPS receivers were also used to estimate the Total Electron Content (TEC) that accounts contributions from ionosphere and plasmasphere electron densities. TEC measurements at São Luís (-1.73o dip latitude) were used to study the ionospheric irregularity effects on the day-to-day variability of the vertical TEC (VTEC) over the magnetic equatorial region. The occurrence of ionospheric irregularities was also estimated from the RMS (Root-Mean- Square Deviation) of VTEC. Finally, latitudinal distributions of VTEC, from about 30o to about +10o dip latitude were estimated from simultaneous VTEC measurements performed at São Luís and São José dos Campos. VTEC latitudinal distributions were successfully used to study the behavior of the ionosphere during ESF and non-ESF conditions. The Equatorial Anomaly occurrence may partially explain the observed latitudinal variation of scintillation magnitudes since they also depend on the height and thickness of the irregularities layer, besides the background electron density.

ASSUNTO(S)

ionosphere ionosfera global positioning system spread f propagação de ondas space geophysics geofÍsica espacial spread f ionospheric electron density wave propagation sistema de posicionamento global densidade eletrônica ionosférica

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