Features of 3–7-day planetary-wave-type oscillations in F-layer vertical drift and equatorial spread F observed over two low-latitude stations in China

摘要

Recent studies on the equatorial atmosphere–ionosphere couplingsystem have shown that planetary-wave-type oscillations, as an importantseeding mechanism for equatorial spread F (ESF), play an important role inESF irregularity development and its day-to-day variability in theequatorial latitudes. In this study, ionosonde virtual height and ESFmeasurements over Sanya (18.4° N, 109.6° E;12.8° N dip latitude) and meteor radar neutral-wind measurementsover Fuke (19.5° N, 109.1° E; 14° N dip latitude)during 2013 are used to investigate the features of planetary-wave-typeoscillations in both the lower atmosphere and the ionosphere and theirpossible influences on ESF occurrence under the weak solar maximum year. The∼ 3-day and ∼ 7-day planetary-wave-type oscillations have beenobserved in the neutral zonal winds and the time rate of change inF-layer virtual heights. According to the propagation characteristics, the3-day and 7-day planetary-wave-type oscillations are basically recognized asultrafast and fast Kelvin waves, respectively. With increasing heights, the3-day wave oscillations are gradually amplified, while the 7-day waveoscillations are generally constant. By performing across-wavelet transform on the onsets of ESF and the vertical drifts of the Flayer, we found that there are simultaneously occurring 7-day and 3-day commonwave oscillations between them. The 7-day waves are mainly in the inversionphase,while the 3-day waves are mostly in an in-phase state, indicating that the 7-daywaves may play a main role in ESF initiation. Approximate delays of 6 days forthe 7-day waves and 5 days for the 3-day waves in their propagationupward from the lower atmosphere to the ionosphere areevaluated with wavelet power spectrum analysis. The estimated upward velocitiesfrom these time delays provide consistent evidence that the 7-day and 3-daywaves propagate vertically upward with typical Kelvin wavecharacteristics. The results highlight the role of planetary-wave-typeoscillations in the initiation and development of ESF in the Chinese low-latitude region.