PLANETARY WAVE AND SOLAR EMISSION SIGNATURES IN THE EQUATORIAL ELECTROJET

Recent analyses of observational data reveal the presence of perturbat ions in the E and F regions of the equatorial ionosphere with periods ranging from 2 to 45 days. The characteristic periods of many of these perturbations suggest an association with free Rossby (resonant mode) oscillations, perhaps excited either in the lower atmosphere or in si tu. Zn the present work we analyze hourly magnetic observations from H uancayo Observatory, Peru (12.00 degrees S, 75.30 degrees W geographic ; 0.72 degrees S, 4.78 degrees W geomagnetic), for the presence and pe rsistence of these oscillations during the whole year of 1979. The mea sured variations can be interpreted in terms of oscillations of the wi nd field in the E region (approximately 100-160 km), which in turn cau se perturbations in the electric fields generated by the wind-driven a tmospheric dynamo and in the magnetic field intensity measured at the ground. The observations suggest that the effects of planetary wave os cillations with periods close to 2.5, 3, 6, 7, 9, 10.5, and 16 days ma y regularly propagate into the thermosphere and ionosphere, causing os cillations which are significant in magnitude. On the basis of an aver aged periodogram analysis, we estimate that planetary wave effects may account for up to 75% of the total energy in Delta H values in the 2 to 35 day period range, suggesting that planetary waves may provide an important contribution to the dynamics and electrodynamics of the low er ionosphere and thermosphere. EUV fluxes during 1979 are noted to ha ve a predominant 13.5-day periodicity during the first half of the yea r and the more typical 27-day oscillation during the latter half of 19 79. These features can in principle affect the Delta H variations thro ugh their influence on the E region conductivity. We examine such infl uences here, especially those that affect the interpretation of the qu asi 16-day oscillation.