Characterization of traveling ionospheric disturbances over low latitude brazilian region associated to Perkins plasma instability generated at medium latitudes / Caracterização de distúrbios ionosféricos propagantes na região de baixas latitudes no setor brasileiro associados à instabilidade de plasma Perkins gerada em médias latitudes

AUTOR(ES)

Danielle Cristina de Morais Amorim

DATA DE PUBLICAÇÃO

2010

RESUMO

With ground based measurements of OI 630 nm emission, by using all-sky imaging system installed at Cachoeira Paulista, we investigated the occurrence of specific events of Medium Scale Traveling Ionospheric Disturbances (MSTIDs), which occurred during nights geomagnetically quiet. Probably, these disturbances are associated with Perkins plasma instability generated at medium latitudes. Airglow images show dark band structures aligned from southwest to northeast propagating towards northwest with azimuth range of 280° to 320°, and average speed of 50-200 m/s at an altitude of 220-300 km, which is the typical altitude region where OI 630 nm emission occurs. We made a statistical study by using all-sky images, in which we verified that the frequency of occurrence of MSTIDs is anti-correlated with the solar cycle, that is, most of occurrence is during low solar activity, followed by descending and ascending solar activities. During high maximum solar activity period, no clear occurrences were recorded in all-sky images. Observations made by using ionosonde show that the ionospheric F layer plasma displaces abruptly into higher altitudes when these dark patches passes over Cachoeira Paulista, and thus, causes decreases on the OI 630 nm emission intensity. The Perkins plasma instability has a growth rate inversely proportional to the ion-neutral collision frequency. Since the collision frequency is higher during high solar activity period, thus the growth rate is lower and the displacement of F-layer is not so abrupt in order to diminish the intensity of OI 630 nm emission. For this reason, we made a study by using only ionosonde data, regarding maximum (2000) and minimum (2008) solar activity periods. We observed that such phenomenon also occurs during maximum solar period; however, the rise of the F-layer is not so abrupt in order to diminish the airglow intensity as provided. This specific type of MSTID produces spread-F on ionosonde signals, and during some events, weak scintillation on GPS signals. In this work, we present the methodology and results we obtained from the analysis of imager, ionosonde and GPS data.

ASSUNTO(S)

perkins instability luminescência atmosférica airglow sondagem ionosférica instabilidade de plasma ionospheric sounding instabilidade perkins traveling ionospheric disturbances distúrbios ionosféricos propagantes plasma instability

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