Observations of day-to-day variability in precursor signatures to equatorial F-region plasma depletionsReportar como inadecuado

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1 Laboratório de Fisica Atmosférica e Aeronomia 2 INPE - Instituto Nacional de Pesquisas Espaciais

Abstract : In December 1995, a campaign was carried out to study the day-to-day variability in precursor signatures to large-scale ionospheric F-region plasma irregularities, using optical diagnostic techniques, near the magnetic equator in the Brazilian sector. Three instruments were operated simultaneously: a an all-sky 180° field of view imaging system for observing the OI 630 nm nightglow emission at Alcântara 2.5°S, 44.4°W; b a digisonde 256-Lowell at São Luis 2.6°S, 44.2°W; and c a multi-channel tilting filter-type zenith photometer for observing the OI 630 nm and mesospheric nightglow emissions at Fortaleza 3.9°S, 38.4°W. During the period December 14-18, 1995 summer in the southern hemisphere, a good sequence of the OI 630 nm imaging observations on five consecutive nights were obtained, which are presented and discussed in this study. The observing period was geomagnetically quiet to moderate Kp = 0+ to 5+; Dst = 18 nT to -37 nT. On four nights, out of the five observation nights, the OI 630 nm imaging pictures showed formations of transequatorial north-south aligned intensity depletions, which are the optical signatures of large-scale ionospheric F-region plasma bubbles. However, considerable day-to-day variability in the onset and development of the plasma depleted bands was observed. On one of the nights it appears that the rapid uplifting of the F-layer in the post-sunset period, in conjunction with gravity wave activity at mesospheric heights, resulted in generation of very strong plasma bubble irregularities. One of the nights showed an unusual formation of north-south depleted band in the western sector of the imaging system field of view, but the structure did not show any eastward movement, which is a normal characteristic of plasma bubbles. This type of irregularity structure, which probably can be observed only by wide-angle imaging system, needs more investigations for a better understanding of its behaviour.

Autor: P. R. Fagundes - Y. Sahai - I. S. Batista - M. A. Abdu - J. A. Bittencourt - H. Takahashi -

Fuente: https://hal.archives-ouvertes.fr/


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