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

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.

On the Nature of the Intraseasonal Variability of Nighttime Ionospheric Irregularities Over Taiwan

“…Unlike the fast Fourier transform (FFT), it can be used even when the data has gaps and the sampling is aperiodic. LS technique of frequency transformation is used effectively in the geo‐scientific applications to derive dominant time periods even if the time series is shorter than the periodicities of interest [Zhu et al, ]. Frequency resolution of LS technique is better than the FFT and is utilized in the applications where exact time period is required to be extracted from a time series not significantly longer than the period of interest.…”

“…Planetary waves, like Kelvin waves, propagate to mesospheric heights and above, modifying the dynamically controlled component of the E region conductivity in form of the Es density, which in turn influences the F region dynamo and RT instability growth rate (Abdu and Brum, 2009). Recently, Zhu et al (2017) proposed a similar mechanism for planetary wave effects. While most of the investigations have so far highlighted 3-to 7-day wave activity in the ionospheric irregularities, longer periodicities have mostly been reported in the background ionospheric parameters.…”

“…The impact of Kelvin waves in the variability of ionospheric scintillations and total electron content has recently been investigated (Chang et al, ). Investigations have revealed that planetary‐scale waves influence F region irregularities by modulating the height of the F layer (Abdu et al, ; de Abreu et al, ; Takahashi et al, ) and the conductivity of the E region (Abdu & Brum, ; Zhu et al, ). Such variations have also been found in the postsunset vertical drift of the F layer, which plays an important role in F region stability.…”

Linkage of Equatorial Ionization Anomaly With the Day‐To‐Day Occurrence of Postsunset Irregularities and Scintillation in Low‐Latitude Region Around 110°E

“…On 27 March 2014 (DOY86), CTR was very large (CTR = 16.6) and ASY was small (ASY = 0.034), scintillation was also absent. These imply that there would be other key factors controlling the occurrence of post-sunset irregularities and scintillation, besides zonal electric field and neutral wind, such as gravity waves (e.g., Aswathy & Manju, 2017), planetary waves (e.g., Manju & Aswathy, 2020;Zhu et al, 2017) or wave-like structures (Li et al, 2012;Narayanan et al, 2012). As Li et al (2012) and Narayanan et al (2012) indicated that the presence of Large-Scale Wave Structure (LSWS) alone was not sufficient to initiate the development of R-T instability, and the strong zonal electric field (E × B) alone may also not sufficient to trigger the occurrence of irregularities, both the strong zonal electric field and meridional wind cannot trigger the occurrence of irregular ities and scintillation under the absent of seed perturbation or wave-like structures.…”

Semimonthly oscillation observed in the start time of equatorial Spread-F

“…Actually, observations have shown that there is a strong day-to-day variability of the EPB occurrence and development (e.g., Carter et al, 2014;Abdu, 2019) and it is a topic of current research. There is evidence of planetary waves acting in the neutral 10 winds and consequently changing the background condition of the atmosphere (e.g., Forbes, 1996;Takahashi et al, 2006;Abdu and Brum, 2009;Chang et al, 2010;Zhu et al, 2017). Stening and Fejer (2001) published the first work proposing the influence of lunar tides in the probability of occurrence of EPBs.…”