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Recent studies on the equatorial atmosphere–ionosphere coupling\udsystem have shown that planetary-wave-type oscillations, as an important\udseeding mechanism for equatorial spread F (ESF), play an important role in\udESF irregularity development and its day-to-day variability in the\udequatorial latitudes. In this study, ionosonde virtual height and ESF\udmeasurements over Sanya (18.4° N, 109.6° E;\ud12.8° N dip latitude) and meteor radar neutral-wind measurements\udover Fuke (19.5° N, 109.1° E; 14° N dip latitude)\udduring 2013 are used to investigate the features of planetary-wave-type\udoscillations in both the lower atmosphere and the ionosphere and their\udpossible influences on ESF occurrence under the weak solar maximum year. The\ud∼ 3-day and ∼ 7-day planetary-wave-type oscillations have been\udobserved in the neutral zonal winds and the time rate of change in\udF-layer virtual heights. According to the propagation characteristics, the\ud3-day and 7-day planetary-wave-type oscillations are basically recognized as\udultrafast and fast Kelvin waves, respectively. With increasing heights, the\ud3-day wave oscillations are gradually amplified, while the 7-day wave\udoscillations are generally constant. By performing a\udcross-wavelet transform on the onsets of ESF and the vertical drifts of the F\udlayer, we found that there are simultaneously occurring 7-day and 3-day common\udwave oscillations between them. The 7-day waves are mainly in the inversion\udphase,\udwhile the 3-day waves are mostly in an in-phase state, indicating that the 7-day\udwaves may play a main role in ESF initiation. Approximate delays of 6 days for\udthe 7-day waves and 5 days for the 3-day waves in their propagation\udupward from the lower atmosphere to the ionosphere are\udevaluated with wavelet power spectrum analysis. The estimated upward velocities\udfrom these time delays provide consistent evidence that the 7-day and 3-day\udwaves propagate vertically upward with typical Kelvin wave\udcharacteristics. The results highlight the role of planetary-wave-type\udoscillations in the initiation and development of ESF in the Chinese low-latitude region

annales geophysicae

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