Abstract
Abstract. Recent studies on the equatorial atmosphere–ionosphere coupling system have shown that planetary-wave-type oscillations, as an important seeding mechanism for equatorial spread F (ESF), play an important role in ESF irregularity development and its day-to-day variability in the equatorial latitudes. In this study, ionosonde virtual height and ESF measurements over Sanya (18.4° N, 109.6° E; 12.8° N dip latitude) and meteor radar neutral-wind measurements over Fuke (19.5° N, 109.1° E; 14° N dip latitude) during 2013 are used to investigate the features of planetary-wave-type oscillations in both the lower atmosphere and the ionosphere and their possible influences on ESF occurrence under the weak solar maximum year. The ∼ 3-day and ∼ 7-day planetary-wave-type oscillations have been observed in the neutral zonal winds and the time rate of change in F-layer virtual heights. According to the propagation characteristics, the 3-day and 7-day planetary-wave-type oscillations are basically recognized as ultrafast and fast Kelvin waves, respectively. With increasing heights, the 3-day wave oscillations are gradually amplified, while the 7-day wave oscillations are generally constant. By performing a cross-wavelet transform on the onsets of ESF and the vertical drifts of the F layer, we found that there are simultaneously occurring 7-day and 3-day common wave oscillations between them. The 7-day waves are mainly in the inversion phase, while the 3-day waves are mostly in an in-phase state, indicating that the 7-day waves may play a main role in ESF initiation. Approximate delays of 6 days for the 7-day waves and 5 days for the 3-day waves in their propagation upward from the lower atmosphere to the ionosphere are evaluated with wavelet power spectrum analysis. The estimated upward velocities from these time delays provide consistent evidence that the 7-day and 3-day waves propagate vertically upward with typical Kelvin wave characteristics. The results highlight the role of planetary-wave-type oscillations in the initiation and development of ESF in the Chinese low-latitude region.
Highlights
The equatorial spread-F (ESF) plasma irregularities mainly occurring in the equatorial and low-latitude ionosphere have been the theme of many studies since the late 1930s (Booker and Wells, 1938)
Gravity waves generated in the troposphere by meteorological activity with periods ranging from minutes to hours generally propagate upward into the mesosphere and the lower thermosphere (MLT) and could play an important role in seeding the ESF
It is relevant to mention that the observed spread-F events in equinoctial months in the low latitudes of Southeast Asia are mainly ESF, and their generation is closely related to prereversal vertical drift enhancement (PRE)
Summary
The equatorial spread-F (ESF) plasma irregularities mainly occurring in the equatorial and low-latitude ionosphere have been the theme of many studies since the late 1930s (Booker and Wells, 1938). They are becoming an important subject in space weather research due to their impacts on satellite navigation and communication application systems. Gravity waves generated in the troposphere by meteorological activity with periods ranging from minutes to hours generally propagate upward into the mesosphere and the lower thermosphere (MLT) and could play an important role in seeding the ESF.
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