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. Author manuscript; available in PMC: 2022 Feb 6.
Published in final edited form as: Geophys Res Lett. 2021 Aug 6;48(15):e2021GL094877. doi: 10.1029/2021gl094877

Evaluation of Atmospheric 3-Day Waves as a Source of Day-to-Day Variation of the Ionospheric Longitudinal Structure

Guiping Liu 1,2,3, Scott L England 4, Chin S Lin 5, Nicholas M Pedatella 6,7, Jeffrey H Klenzing 3, Christoph R Englert 8, Brian J Harding 1, Thomas J Immel 1, Douglas E Rowland 3
PMCID: PMC8528139  NIHMSID: NIHMS1746868  PMID: 34690382

Abstract

We report for the first time the day-to-day variation of the longitudinal structure in height of the F2 layer (hmF2) in the equatorial ionosphere using multi-satellite observations of electron density profiles by the Constellation Observing System for Meteorology, Ionosphere and Climate-2 (COSMIC-2). These observations reveal a ~3-day modulation of the hmF2 wavenumber-4 structure viewed in a fixed local time frame during January 30–February 14, 2021. Simultaneously, ~3-day planetary wave activity is discerned from zonal wind observations at ~100 km by the Ionospheric Connection Explorer (ICON) Michelson Interferometer for Global High-Resolution Thermospheric Imaging (MIGHTI). This signature is not observed at ~180–250 km altitudes, suggesting the dissipation of this wave below the F-region. We propose that the 3-day variation identified in h mF2 is likely caused by the planetary wave-tide interaction through the E-region dynamo.

Plain Language Summary

The F-region ionosphere at ~200–400 km altitudes often shows global-scale structures and variations that are attributed to neutral atmospheric tides and planetary waves propagating from the lower atmosphere. Previous observations have identified 3-day planetary waves at E-region altitudes (~100 km), but the vertical extent of these waves has not yet been determined due to lack of high altitude observations. For this study, we use newly obtained concurrent atmospheric and ionospheric observations that provide the necessary coverage. Our study provides the first observational evidence of the vertical propagation of a 3-day planetary wave across both E- and F-region altitudes. The results suggest that this wave causes the day-to-day variation of the four-peaked longitudinal structure in the equatorial ionosphere through modulating the E-region dynamo rather than direct propagation into the F-region.

1. Introduction

Understanding the variability of the ionosphere is critical for modeling and forecasting the near-Earth space environment. Ionospheric density is an important state variable, and the densest plasma is observed between ±30° magnetic latitude. Previous observations have shown remarkable spatial and temporal variations in this region (e.g., Chen, 1992; England et al., 2010; Forbes et al., 2018; Gan et al., 2020; Gu et al., 2018; Immel et al., 2009; Lin et al., 2007; Liu et al., 2010a, 2010b; Pancheva et al., 2008; Pedatella et al., 2012; Sagawa et al., 2005; Takahashi et al., 2007). At low latitudes, the plasma is relatively less impacted by magnetospheric and solar-wind drivers, at least during geomagnetically quiet times. Much of the ionospheric variability observed has thus been attributed to the forcing by the lower atmosphere.

Atmospheric waves are believed to be central in the vertical coupling of the ionosphere and atmosphere. These waves are mostly generated in the troposphere and stratosphere, and propagate upward. An important wave is the eastward propagating diurnal tide with zonal wavenumber-3 (DE3) excited by latent heat release from deep convection. DE3 can reach the lower ionospheric E-region altitudes (~100 km), where it modifies the wind-driven dynamo electric fields, leading to the four-peaked longitudinal structure in a fixed local time frame at higher altitudes (e.g., England et al., 2010; Hagan et al., 2009; Immel et al., 2006; Kil et al., 2008). The F-region ionosphere also exhibits variations corresponding to planetary waves with periods of ~2–20 days (e.g., Chen, 1992; Forbes & Leveroni, 1992; Forbes et al., 2018; Gan et al., 2020; Huang et al., 2011, 2012; Liu et al., 2012, 2013; 2015; Pancheva et al., 2008; Yamazaki et al., 2020). By modulating tides, the periodic signatures associated with these waves could be carried to high altitudes (e.g., England et al., 2012; Häusler et al., 2014; Liu et al., 2010a, 2010b; Pancheva et al., 2006). In addition, the 3-day waves may propagate up into the F-region causing direct variations in the density and height of the ionospheric F-layer peak (e.g., Takahashi et al., 2007). Tides and planetary waves can contribute significantly to the large variability in the equatorial ionosphere.

The 3-day planetary waves are also generated by latent heating in the tropical troposphere and these fast waves are expected to propagate to high altitudes as the damping and absorption at critical levels remove longer period waves most effectively (Salby & Garcia, 1987). Indeed, the 3-day waves have been observed in the lower thermosphere (e.g., England et al., 2012; Liu et al., 2019), and the ability of these waves to propagate into the F-region is supported by numerical studies (e.g., Chang et al., 2010) though mechanistic model results suggest that these waves should dissipate far below this region (e.g., Pogoreltsev et al., 2007). While these waves were modeled in the F-region, Chang et al. (2010) concluded that the influence of this wave type on the ionosphere was mainly through its modification of the E-region dynamo. Most observations of the atmosphere do not extend to ~200 km altitudes, and this implies that the pathway for the 3-day waves to drive the ionospheric variations has yet to be directly observed.

Here, we present for the first time the new observations by the Constellation Observing System for Meteorology, Ionosphere and Climate-2 (COSMIC-2) and the Michelson Interferometer for Global High-Resolution Thermospheric Imaging (MIGHTI) operated on the Ionospheric Connection Explorer (ICON) together with data from the Microwave Limb Sounder (MLS) on Aura during a ~15-day interval in January–February 2021. These data offer an opportunity to observe the 3-day wave activity in the atmosphere and simultaneously the response of the ionospheric longitudinal structure in the equatorial F-region. The neutral wind observations from MIGHTI span both E- and F-region altitudes, yielding reliable information on the vertical propagation of the observed wave.

2. Data and Analysis

2.1. COSMIC-2 Electron Density Profiles

COSMIC-2 employs a six-satellite constellation to monitor the state of the ionosphere through Global Navigation Satellite System (GNSS) radio occultation (RO) similarly to COSMIC (e.g., Schreiner et al., 2007). The satellites were launched into a 24° low-inclination orbit at an initial altitude of ~720 km on June 25, 2019, and by February 2021 they were evenly distributed into final orbits at ~550 km. Multiple satellites of this constellation make measurements simultaneously, covering many local times for a given latitude in one single day (see Figures 1a and 1b). Due to the low inclination of the orbits, these measurements are ideal for observing the equatorial ionosphere.

Figure 1.

Figure 1.

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(a) Coverage of Constellation Observing System for Meteorology, Ionosphere and Climate-2 (COSMIC-2) electron density profiles on January 30, 2021. Black curves mark ±12° magnetic latitudes. (b) Local times of the profiles between ±12° magnetic latitude on the day. Horizontal lines mark the range 16.5–18.5 hr. (c) Distribution of the selected profiles for each day during January 30–February 14, 2021 (day 30–45). The color-coded circles represent which satellite (E1 through E6) made these observations.

Vertical profiles of ionospheric electron densities have been retrieved from the RO measurements. Normally, ~3,000–4,000 profiles at ~1 km resolution are obtained per day. For COSMIC, the relative precision is only a few percent at 150–250 km altitude but larger at lower altitudes (Schreiner et al., 2007). The peak height of the F2 layer (hmF2) determined is also consistent with that from the incoherent scatter radar (e.g., Liu et al., 2010a). The root mean square error of the derived COSMIC-2 hmF2 is equal to ~23 and 14 km at low- and mid-latitudes, respectively (Cherniak et al., 2021).

For this study, we have fit the electron density profiles to a two-layer Chapman function (Fox, 1994; Lei et al., 2007) to calculate the hmF2 values. Profiles with more than 8 data points in the altitude range 150–500 km are fit using a least squares method. Only values derived from profiles with fitting errors (percentage difference between the fits and the data) lower than 10% are considered. The ~30% of profiles that have larger errors are discarded.

2.2. MIGHTI Atmospheric Wind Profiles

MIGHTI (Englert et al., 2017) was launched on the ICON mission (Immel et al., 2018) in its circular 575 km altitude, 27° inclination orbit on October 10, 2019, to measure vector wind profiles in the atmosphere from ~90 to ~300 km based upon the heritage of UARS/WINDII (e.g., Shepherd et al., 2012) and SHIMMER/STPSat-1 (Englert et al., 2010). Using Doppler shifts, the observations of the O (1S) and O (1D) airglow emissions at 557.7 and 630.0 nm wavelengths (green and red line) are used to retrieve the wind velocities at ~3 and 10 km altitude bins (e.g., Harding et al., 2017). The retrieved winds are consistent with the ground-based measurements with the correlation of ~0.8 (Harding et al., 2021; Makela et al., 2021).

The MIGHTI wind data are almost continuously available since late 2019, which is sufficiently long to identify planetary wave activities in coincidence with the ionospheric variations observed by COSMIC-2. The MIGHTI data cover low-to-mid latitudes from ~13°S to 42°N for each day, and in a given day approximately 15 different longitudes are sampled for the same latitude at two local times. Owing to the slow orbit precession, the local time difference between adjacent days of the observations over all longitudes is small (~30 min, Figure 4b). This type of sampling allows for the identification of short-period planetary waves using only a few days of data. However, ~45 days of data are needed to sample the full local time range at a given latitude, and the combination of multiple days reduces the sensitivity to short-term tidal variations.

Figure 4.

Figure 4.

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(a) Periodograms of the zonal winds by Michelson Interferometer for Global High-Resolution Thermospheric Imaging (MIGHTI) for daytimes at ~94, 97, and 100 km altitude, presented versus latitude during January 30–February 14, 2021. White contour lines mark the 80% statistical significance level. (b) 3–4 days bandpass filtered zonal winds at 94 km over 0–10°N latitude. Dashed lines correspond to the 3-day eastward propagation. The numbers on the y-axis on the right mark the dayside local times observed on individual days. (c) Periodogram of the zonal winds over 0–10°N latitude across 180–250 km altitude during January 30–February 14, 2021. (d) DE3 amplitudes from the Aura/Microwave Limb Sounder (MLS) temperatures at ~97 km altitude. (e) Periodograms of the DE3 amplitudes at various latitudes over January 30–February 14, 2021.

2.3. MLS Atmospheric Temperatures

Aura/MLS has measured the temperatures at altitudes ranging from the surface to ~97 km since July 2004, and the vertical resolution of the data is about 15 km in the mesosphere and lower thermosphere with a precision of ~2.5 K (Schwartz et al., 2008). The coarse resolution should not significantly affect the observations of day-to-day variations (Forbes & Wu, 2006) and the tidal analysis. We have used the highest level centered at ~97 km near the mesopause, where the DE3 tide attains large amplitudes (e.g., Forbes et al., 2008). As the satellite is in a near-polar and Sun-synchronous orbit, the local times observed from the descending and ascending orbit nodes differ by 12 h over the equator (slightly changing at mid- and high-latitudes). This allows for determining the day-to-day variations of diurnal tides.

We have binned the daily data at every 5° latitude and 24° longitude. For each bin, the temperature differences between the descending and ascending orbit nodes are calculated and divided by 2. A least squares fit to zonal wavenumbers from 0 to 4 is then applied to calculate the amplitudes of various components. The temperatures are measured 12 h apart in local time, so the differences cancel out the contributions from 12-h tides and zonal means (they are measured at the same phases). The wave-4 obtained represents mostly DE3 (e.g., Oberheide & Gusev, 2002), although the westward propagating wavenumber-5 may also contribute, at a much smaller amplitude (e.g., Forbes et al., 2008).

3. Results and Discussion

3.1. 3-Day Variation of hmF2 Longitudinal Structure

Figure 1c shows the distribution of the COSMIC-2 electron density profiles used for this study. These are chosen for the equatorial region within ±12° magnetic latitude and between 16.5–18.5 h LT throughout January 30–February 14, 2021. The hmF2 maximizes at these latitudes (Figure 2a), and during this interval the satellites are in their final orbits. Figures 1a and 1b show that 50–90 samples are obtained at the selected LTs for each day. This allows for studying the equatorial longitudinal structure and its day-to-day variation at a fixed local time during daytime when the ionosphere is dense. These data are also in an interval when DE3 has a large amplitude as it often maximizes around February/March (e.g., Oberheide & Forbes, 2008; Figure 4d).

Figure 2.

Figure 2.

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(a) Height of the F2 layer (hmF2) at 16.5–18.5 h LTs as averaged from January 30 to February 14, 2021. Black curves mark ±12° magnetic latitudes. (b) Longitudinal structures of hmF2 averaged between ±12° magnetic latitude and 16.5–18.5 h LT (circles) on individual days. Colored curve is from least squares fit to longitudinal wave numbers from 0 to 4.

The longitudinal dependence of hmF2 is evident in Figure 2a, for which the hmF2 values are averaged over all days and binned every 24° longitude and 5° latitude. As shown, hmF2 reaches the largest values within ±12° magnetic latitude and shows a wave-like structure with distinguishable peaks in different sectors.

The day-to-day variation of the hmF2 longitudinal structure is demonstrated in Figure 2b. The equatorial hmF2 data at the given local times are presented as a function of longitude for individual days from January 30 to February 14, 2021. The hmF2 peak and the longitude of greatest hmF2 differ greatly on different days. The wave structure appears each day, but the amplitude of the structure varies. The amplitude appears to be enhanced during days 33–42.

To quantify the day-to-day variation, the amplitudes of the hmF2 structure with wavenumbers from 0 to 4 are calculated through a least squares fit. Figure 3a displays the calculated amplitudes of the wavenumber-4 component. As shown, the wave-4 amplitude exhibits a ~3–4 day periodic signature. The periodogram in Figure 3c verifies that the dominant signature of the wave-4 variation has a period of ~3 days.

Figure 3.

Figure 3.

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(a) Amplitudes of the height of the F2 layer (hmF2) wave-4 longitudinal structure from January 30 to February 14, 2021. Superimposed are the Aura/MLS derived DE3 amplitudes (blue) at ~97 km altitude over 10°N latitude and the solar f10.7 cm fluxes (orange). (b) The 3-hourly Kp index during the time interval. (c) Periodograms of the hmF2 wave-4 amplitude (black), Kp and solar flux (colored) over January 30–February 14, 2021. The dashed line marks the 80% confidence level.

The Kp values during the time interval presented are mostly small, except for days 33/34, 38, and 44 (Figure 3b). This interval is not subject to large geomagnetic disturbances. The slightly enhanced geomagnetic activity occurs ~5–6 days apart, and the ~3-day periodicity is not seen in the periodogram of Kp (Figure 3c). The observed 3-day variation in the hmF2 structure is thus not likely to be related to geomagnetic driving.

The ionosphere is known to respond to the solar forcing at sub-harmonics of the solar rotation period, but the period that corresponds to solar wind streams and coronal holes (e.g., Pedatella et al., 2010) would not drive the longitudinal structure. Figure 3c shows the same 3-day signature in the f107, suggesting a possible solar influence as the solar irradiance could modify the tidal amplitude and affect the conductivity of the ionospheric dynamo. However, Figure 3a shows that the solar activity at this time is low with the mean flux of ~71 sfu and the standard deviation of ~1 sfu. This small change is not in phase with both the hmF2 and tidal variations, and the solar flux change appears to lag for ~1–2 days. On the contrary, the hmF2 wave-4 variation follows the DE3 amplitude (further discussed in Section 3.3), showing a correspondence between them.

3.2. Atmospheric 3-Day Wave Activity

Figure 4a shows the periodogram of the MIGHTI zonal winds observed for daytime at 94, 97, and 100 km altitude from the O (1S) green line emission as a function of latitude (at 5° bin) during January 30–February 14, 2021. These altitudes are close to the E-region at the lower limit of the MIGHTI wind observations. At each altitude and latitude, the data have been averaged for every 1.6 h UT. Data are missing for some hours, but more than 200 data points (80%) are available. A ~3-day wave signature is observed at all altitudes, showing the coherence of this wave signature across a range of altitudes. In the fixed local time frame, periods at and below 24 h represent diurnal tides and the longitudinal variations. The 3-day wave signature is prominent at low-latitudes at all three altitudes, having the maximum amplitude at ~25°N. The wave amplitude decreases near the equator especially at 97 and 100 km altitudes, but the signature is still visible at equatorial latitudes. The relative signature of this wave appears to be the strongest at 94 km but weaker at 100 km, which could be related to the dissipation of this wave at these altitudes. The wave amplitude decreases from 97 to 100 km, being consistent with the dissipation of this wave at the bottom of the E-region. This is not surprising as the 3-day wave has been observed to propagate to only ~105 km for the case reported by England et al. (2012).

Figure 4b presents the zonal winds at 94 km altitude over equatorial latitudes (0–10°N), where strong 3-day signature is observed, as a function of longitude and time. The values presented at each longitude bin (24°) have been band-pass filtered for periods between 3 and 4 days. A ~3-day wave with the amplitude of 20 m s−1 occurs on days 35–45, following the phase progression of eastward propagating 3-day wave with zonal wavenumber of 1. This feature is consistent with the 3-day planetary wave that has been frequently observed at low-latitudes in the lower thermosphere (e.g., England et al., 2012; Liu et al., 2015, 2019).

The vertical extent of this 3-day wave is examined using the zonal winds at higher altitudes from the O (1D) red line emission. The same analysis as for the lower E-region winds is repeated and shown in Figure 4c as a function of altitude from ~180 to 250 km. Similarly, the coherence of the periodograms between adjacent levels (each of which is performed separately) provides an indication of the confidence in the identified signatures. A ~5-day signature is observed at these altitudes, peaking at ~230 km near the F-peak. This signature is not evident at E-region altitudes (Figure 4a), so it may be driven internally in the F-region. The ~3-day signature is barely noticeable across this vertical range, verifying that this wave does not propagate into the F-region with significant amplitude. Given that the wave amplitude is detected decreasing at 97 km (Figure 4a), this 3-day wave should be dissipated in the E-region.

3.3. 3-Day Wave Modulation of DE3 Tide

The large variability of the equatorial F-region ionosphere at geomagnetic quiet conditions has been linked to the forcing by global-scale waves propagating from the lower atmosphere. Specifically, the four-peaked longitudinal structure at a fixed local time is thought to arise from the DE3 tidal forcing through its modification of the E-region dynamo electric field (e.g., England et al., 2010; Hagan et al., 2009; Immel et al., 2006; Kil et al., 2008). Multi-day periodic signatures have been determined to correspond to planetary waves (e.g., Chen, 1992; Gan et al., 2020; Forbes & Leveroni, 1992; Forbes et al., 2018; Liu et al., 2012, 2013, 2015 Pancheva et al., 2008; Yamazaki et al., 2020). This study identifies a 3-day variation of the wavenumber-4 structure in hmF2 around the equator, and the wave-4 amplitude varies following the DE3. This variation is most likely the result of the forcing by both the DE3 tide and 3-day planetary wave.

The presence of the 3-day planetary wave is observed in the neutral wind at 94–100 km altitude for this study, but there is no evidence of this wave activity at higher altitudes across 180–250 km. This indicates that this wave does not propagate directly to F-region altitudes. The wave amplitude decreases above 94 km, suggesting the wave dissipation at lower altitudes. It is thus possible that this wave modulates the DE3 and causes the 3-day variation of the hmF2 longitudinal structure. An examination is shown in Figures 4d and 4e, for which the diurnal wavenumber-4 amplitudes, which serve as an approximation of the DE3, are computed using the Aura/MLS temperature observations near the mesopause. Figure 4d demonstrates that the DE3 approaches large amplitudes peaking over equatorial latitudes below 20°. Shown in Figure 4e, the tidal amplitude also shows a ~3-day periodicity centered around 10° and 20°N latitude, which is consistent with the DE3 modulation by the 3-day wave. This falls within the latitudinal range of the hmF2 variation. Because the 3-day wave activity is not observed in the neutral wind at F-region altitudes, the modulation should occur at lower altitudes and the resulting effect is carried into high altitudes through the E-region dynamo mechanism.

4. Summary and Conclusions

The origin of the 3-day variation of the longitudinal wavenumber-4 structure in hmF2 in the equatorial ionosphere viewed in a fixed local time frame is investigated in this study using the recently obtained coordinated observations of COSMIC-2 electron density profiles and ICON/MIGHTI atmospheric wind profiles during January 30–February 14, 2021. These combined observations offer the opportunity to identify the day-to-day variation of the ionospheric longitudinal structure and to simultaneously observe the multi-day planetary wave activities in the neutral atmosphere. This study reports the 3-day modulation of the F-region ionospheric structure in coincidence with a 3-day planetary wave observed in the atmospheric wind at E-region altitudes. For the first time the vertical propagation of the 3-day wave is examined across a broad altitude range, including both E- and F-region.

The 3-day planetary wave is observed at 94–100 km altitudes, but for the case studied here, this wave shows no detectable signature in the neutral wind at higher altitude ~180–250 km. This 3-day wave thus does not propagate into the F-region. The wave amplitude decreases above 94 km and the DE3 amplitude at ~97 km shows a ~3-day modulation, which suggest that this wave dissipates at lower E-region altitudes. The 3-day variation of the hmF2 wavenumber-4 structure identified is most likely the result of the combined effect of both the DE3 tide and the 3-day planetary wave. It is expected that this 3-day wave modulates the DE3 and through the E-region dynamo action the effect is carried into the F-region ionosphere.

Previous results have shown 3-day periodicity observed in ionospheric scintillation resulting from Equatorial Spread-F (ESF) consistent with the periodicities observed in the neutral atmosphere (e.g., Liu et al., 2013). The work presented above illuminates the mechanism connecting these two. In general, ESF plasma density structures grow under a Rayleigh-Taylor Instability (RTI) acting on the bottomside ionosphere (e.g., Tsunoda, 2010). From a climatology perspective, the growth of ESF is well-understood, however, the day-to-day prediction is still highly limited (Makela & Otsuka, 2012). This is a critical gap in Space Weather, as ESF impacts communication and navigation signals (e.g., Carter et al., 2020 and references therein). The frequency of seeding (Retterer & Roddy, 2014) suggests that modulation of the ionospheric background can act as a filter for whether ESF grows for a given seed. This modulation can occur through atmospheric planetary waves or geomagnetic activity (Carter et al., 2014).

In the context of this work, the neutral wind changes resulting from the planetary waves modify the polarization electric fields through the E-region dynamo. These altered fields then change the height and distribution of the F-layer plasma (e.g., Klenzing et al., 2013), as shown here by the change in hmF2. This redistribution of the plasma can alter the growth rates, acting to either enhance or suppress the likelihood of ESF growing from a given seed (e.g., Abdu, 2019). Future work will investigate the full impact of planetary waves on the RTI growth rate.

Key Points:

  • First examination of 3-day wave activity across ~100–250 km altitudes and the ionospheric peak height change using coordinated satellites

  • Ionospheric longitudinal structure shows a ~3-day variation coinciding the planetary wave observed in atmospheric winds at ~100 km altitude

  • The neutral atmospheric 3-day wave signature is not observed at ~180–250 km altitudes, suggesting the modulation of tides in the E-region

Acknowledgments

COSMIC-2 is led by NOAA and USAF in partner with National Space Organization in Taiwan and UCAR. ICON is supported by NASA’s Explorers Program through contracts NNG12FA45C and NNG12FA42I. G. Liu acknowledges partial support by 80NSSC18K0649 and 80NSSC20K1323. S. L. England was supported by NASA contract NNG12FA45C. These results are partly based upon work supported by the National Center for Atmospheric Research, which is a major facility sponsored by the National Science Foundation under Cooperative Agreement No. 1852977. J. H. Klenzing acknowledges partial support from NNH20ZDA001N-LWS.

Footnotes

References

  1. Abdu MA (2019). Day-to-day and short-term variabilities in the equatorial plasma bubble/spread F irregularity seeding and development. Progress in Earth and Planetary Science, 6(1), 1–22. 10.1186/s40645-019-0258-1 [DOI] [Google Scholar]
  2. Carter BA, Currier JL, Dao T, Yizengaw E, Retter J, Terkildsen M, et al. (2020). On the assessment of daily equatorial plasma bubble occurrent modeling and forecasting. Space Weather, 18, e2020SW002555. 10.1029/2020SW002555 [DOI] [Google Scholar]
  3. Carter BA, Retterer JM, Yizengaw E, Groves K, Caton R, McNamara L, et al. (2014). Geomagnetic control of equatorial plasma bubble activity modeled by the TIEGCM with Kp. Geophysical Research Letters, 41(15), 5331–5339. 10.1002/2014GL060953 [DOI] [Google Scholar]
  4. Chang LC, Palo SE, Liu H-L, Fang T-W, & Lin CS (2010). Response of the thermosphere and ionosphere to an ultra fast Kelvin wave. Journal of Geophysical Research, 115, A00G04. 10.1029/2010JA015453 [DOI] [Google Scholar]
  5. Chen P-R (1992). Two day oscillation of the equatorial ionization anomaly. Journal of Geophysical Research, 97(A5), 6343–6357. 10.1029/91JA02445 [DOI] [Google Scholar]
  6. Cherniak I, Zakharenkova I, Braun J, Wu Q, Pedatella N, Schreiner W, et al. (2021). Accuracy assessment of the quiet-time ionospheric F2 peak parameters as derived form COSMIC-2 multi-GNSS radio occultation measurements. Journal of Space Weather and Space Climate, 11, 18. 10.1051/swsc/2020080 [DOI] [Google Scholar]
  7. England SL, Immel TJ, Huba JD, Hagan ME, Maute A, & DeMajistre R. (2010). Modeling of multiple effects of atmospheric tides on the ionosphere: An examination of possible coupling mechanisms responsible for the longitudinal structure of the equatorial ionosphere. Journal of Geophysical Research, 115, A05308. 10.1029/2009JA014894 [DOI] [Google Scholar]
  8. England SL, Liu G, Zhou Q, Immel TJ, Kumar KK, & Ramkumar G. (2012). On the signature of the quasi-3-day wave in the thermosphere during the January 2010 URSI World Day Campaign. Journal of Geophysical Research, 117, A06304. 10.1029/2012JA017558 [DOI] [Google Scholar]
  9. Englert CR, Harlander JM, Brown CM, Marr KD, Miller IJ, Stump JE, et al. (2017). Michelson interferometer for global high-resolution thermospheric imaging (MIGHTI): Instrument design and calibration. Space Science Reviews, 212(1–2), 553–584. 10.1007/s11214-017-0358-4 [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Englert CR, Stevens MH, Siskind DE, Harlander JM, & Roesler FL (2010). Spatial heterodyne imager for mesospheric radicals on STPSat-1. Journal of Geophysical Research, 115, D20306. 10.1029/2010JD014398 [DOI] [Google Scholar]
  11. Forbes JM, & Leveroni S. (1992). Quasi 16-day oscillation in the ionosphere. Geophysical Research Letters, 19(10), 981–984. 10.1029/92gl00399 [DOI] [Google Scholar]
  12. Forbes JM, Maute A, Zhang X, & Hagan ME (2018). Oscillation of the ionosphere at planetary-wave periods. Journal of Geophysical Research, 123, 7634–7649. 10.1029/2018JA025720 [DOI] [Google Scholar]
  13. Forbes JM, & Wu D. (2006). Solar tides as revealed by measurements of mesosphere temperature by the MLS experiment on UARS. Journal of the Atmospheric Sciences, 63, 1776–1797. 10.1175/jas3724.1 [DOI] [Google Scholar]
  14. Forbes JM, Zhang X, Palo S, Russell J, Mertens CJ, & Mlynczak M. (2008). Tidal variability in the ionospheric dynamo region. Journal of Geophysical Research, 113, A02310. 10.1029/2007JA012737 [DOI] [Google Scholar]
  15. Fox MW (1994). A simple, convenient formalism for electron density profiles. Radio Science, 29, 1473–1491. 10.1029/94rs01666 [DOI] [Google Scholar]
  16. Gan Q, Eastes RW, Burns AG, Wang W, Qian L, Solomon SC, et al. (2020). New observations of large-scale waves coupling with the ionosphere made by the GOLD Mission: Quasi-16-day wave signatures in the F-region OI 135.6-nm nightglow during sudden stratospheric warmings. Journal of Geophysical Research, 125, e2020JA027880. 10.1029/2020ja027880 [DOI] [Google Scholar]
  17. Gu S-Y, Liu H-L, Dou X, & Jia M. (2018). Ionospheric variability due to tides and quasi-two day wave interactions. Journal of Geophysical Research, 123, 1554–1565. 10.1002/2017JA025105 [DOI] [Google Scholar]
  18. Hagan ME, Maute A, & Roble RG (2009). Tropospheric tidal effects on the middle and upper atmosphere. Journal of Geophysical Research, 114, A01302. 10.1029/2008JA013637 [DOI] [Google Scholar]
  19. Harding BJ, Chau JL, He M, Englert CR, Harlander JM, Marr KD, et al. (2021). Validation of ICON-MIGHTI thermospheric wind observations: 2. Green-line comparisons to specular meteor radars. Journal of Geophysical Research, 126, 2020JA028947. 10.1029/2020JA028947 [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Harding BJ, Makela JJ, Englert CR, Marr KD, Harlander JM, England SL, & Immel TJ (2017). The MIGHTI wind retrieval algorithm: Description and verification. Space Science Reviews, 212, 585–600. 10.1007/s11214-017-0359-3 [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Häusler K, Hagan ME, Baumgaertner AJG, Maute A, Lu G, Doornbos E, et al. (2014). Improved short-term variability in the thermosphere-ionosphere-mesosphere-electrodynamics general circulation model. Journal of Geophysical Research, 119, 6623–6630. 10.1002/2014JA020006 [DOI] [Google Scholar]
  22. Huang CY, Delay SH, Roddy PA, & Sutton EK (2011). Periodic structures in the equatorial ionosphere. Radio Science, 46(4), 1–8. 10.1029/2010RS004569 [DOI] [Google Scholar]
  23. Huang CY, Delay SH, Roddy PA, Sutton EK, & Stoneback R. (2012). Longitudinal structures in the equatorial ionosphere during deep solar minimum. Journal of Atmospheric and Solar-Terrestrial Physics, 90–91, 156–163. 10.1016/j.jastp.2012.04.012 [DOI] [Google Scholar]
  24. Immel TJ, England SL, Mende SB, Heelis RA, Englert CR, Edelstein J, et al. (2018). The ionospheric connection explorer mission: Mission goals and design. Space Science Reviews, 214, 13. 10.1007/s11214-017-0449-2 [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Immel TJ, England SL, Zhang X, Forbes JM, & DeMajistre R. (2009). Upward propagating tidal effects across the E- and F-regions of the ionosphere. Earth Planets and Space, 61, 1–11. 10.1186/bf03353167 [DOI] [Google Scholar]
  26. Immel TJ, Sagawa E, England SL, Henderson SB, Hagan ME, Mende SB, et al. (2006). Control of equatorial ionospheric morphology by atmospheric tides. Geophysical Research Letters, 33, L15108. 10.1029/2006GL026161 [DOI] [Google Scholar]
  27. Kil H, Talaat ER, Oh S-J, Paxton LJ, England S-L, & Su S-Y (2008). Wave structures of the plasma density and vertical ExB drift in low-latitude F region. Journal of Geophysical Research, 113, A09312. 10.1029/2008JA013106 [DOI] [Google Scholar]
  28. Klenzing J, Burrell AG, Heelis RA, Huba JD, Pfaff R, & Simões F. (2013). Exploring the role of ionospheric drivers during the extreme solar minimum of 2008. Annales Geophysicae, 31(12), 2147–2156. 10.5194/angeo-31-2147-2013 [DOI] [Google Scholar]
  29. Lei J, Syndergaard S, Burns AG, Solomon SC, Wang W, Zeng Z, et al. (2007). Comparison of COSMIC ionospheric measurements with ground-based observations and model predictions: Preliminary results. Journal of Geophysical Research, 112, A07308. 10.1029/2006JA012240 [DOI] [Google Scholar]
  30. Lin CH, Wang W, Hagan ME, Hsiao CC, Immel TJ, Hsu ML, et al. (2007). Plausible effect of atmospheric tides on the equatorial ionosphere observed by the FORMOSAT3/COSMIC: Three-dimensional electron density structure. Geophysical Research Letters, 34, L11112. 10.1029/2007GL029265 [DOI] [Google Scholar]
  31. Liu G, England SL, Immel TJ, Frey HU, Mannucci AJ, & Mitchell NJ (2015). A comprehensive survey of atmospheric quasi 3 day planetary-scale waves and their impacts on the day-to-day variations of the equatorial ionosphere. Journal of Geophysical Research, 120, 2979–2992. 10.1002/2014JA020805 [DOI] [Google Scholar]
  32. Liu G, England SL, Immel TJ, Kumar KK, Ramkumar G, & Goncharenko LP (2012). Signatures of the 3-day wave in the low-latitude and midlatitude ionosphere during the January 2010 URSI World Day campaign. Journal of Geophysical Research, 117, A06305. 10.1029/2012JA017588 [DOI] [Google Scholar]
  33. Liu G, England SL, & Janches D. (2019). Quasi two-, three-, and six-day planetary-scale wave oscillations in the upper atmosphere observed by TIMED/SABER over ~17 years during 2002–2018. Journal of Geophysical Research, 124, 9462–9474. 10.1029/2019JA026918 [DOI] [Google Scholar]
  34. Liu G, Immel TJ, England SL, Frey HU, Mende SB, Kumar KK, & Ramkumar G. (2013). Impacts of atmospheric ultrafast Kelvin waves on radio scintillations in the equatorial ionosphere. Journal of Geophysical Research, 118, 885–891. 10.1002/jgra.50139 [DOI] [Google Scholar]
  35. Liu G, Immel TJ, England SL, Kumar KK, & Ramkumar G. (2010a). Temporal modulations of the longitudinal structure in F2 peak height in the equatorial ionosphere as observed by COSMIC. Journal of Geophysical Research, 115, A04303. 10.1029/2009JA014829 [DOI] [Google Scholar]
  36. Liu G, Immel TJ, England SL, Kumar KK, & Ramkumar G. (2010b). Temporal modulation of the four-peaked longitudinal structure of the equatorial ionosphere by the 2 day planetary wave. Journal of Geophysical Research, 115, A12338. 10.1029/2010JA016071 [DOI] [Google Scholar]
  37. Makela JJ, Baughman M, Navarro LA, Harding BJ, Englert CR, Harlander JM, et al. (2021). Validation of ICON-MIGHTI thermospheric wind observations: 1. Night-time red-line ground-based Fabry-Perot interferometers. Journal of Geophysical Research, 126, e2020JA028726. 10.1029/2020JA028726 [DOI] [PMC free article] [PubMed] [Google Scholar]
  38. Makela JJ, & Otsuka Y. (2012). Overview of night-time ionospheric instabilities at low- and mid-latitudes: Coupling aspects resulting in structuring at the mesoscale. Space Science Reviews, 168(1–4), 419–440. 10.1007/s11214-011-9816-6 [DOI] [Google Scholar]
  39. Oberheide J, & Forbes JM (2008). Tidal propagation of deep tropical cloud signatures into the thermosphere from TIMED observations. Geophysical Research Letters, 35, L04816. 10.1029/2007GL032397 [DOI] [Google Scholar]
  40. Oberheide J, & Gusev OA (2002). Observation of migrating and nonmigrating diurnal tides in the equatorial lower thermosphere. Geophysical Research Letters, 29(24), 2167. 10.1029/2002GL016213 [DOI] [Google Scholar]
  41. Pancheva DV, Mukhtarov PJ, Mitchell NJ, Fritts DC, Riggin DM, Takahashi H, et al. (2008). Planetary wave coupling (5–6 day waves) in the low-latitude atmosphere-ionosphere system. Journal of Atmospheric and Solar-Terrestrial Physics, 70, 101–122. 10.1016/j.jastp.2007.10.003 [DOI] [Google Scholar]
  42. Pancheva DV, Mukhtarov PJ, Shepherd MG, Mitchell NJ, Fritts DC, Riggin DM, et al. (2006). Two day wave coupling of the low-latitude atmosphere-ionosphere system. Journal of Geophysical Research, 111, A07313. 10.1029/2005JA011562 [DOI] [Google Scholar]
  43. Pedatella NM, Lei J, Thayer JP, & Forbes JM (2010). Ionosphere response to recurrent geomagnetic activity: Local time dependency. Journal of Geophysical Research, 115, 2301. 10.1029/2009ja014712 [DOI] [Google Scholar]
  44. Pedatella NM, Liu H-L, Richmond AD, Maute A, & Fang T-W (2012). Simulations of solar and lunar tidal variability in the mesosphere and lower thermosphere during sudden stratosphere warmings and their influence on the low-latitude ionosphere. Journal of Geophysical Research, 117, A08326. 10.1029/2012JA017858 [DOI] [Google Scholar]
  45. Pogoreltsev AI, Vlasov AA, Fröhlich K, & Jacobi C. (2007). Planetary waves in coupling the lower and upper atmosphere. Journal of Atmospheric and Solar-Terrestrial Physics, 69, 2083–2101. 10.1016/j.jastp.2007.05.014 [DOI] [Google Scholar]
  46. Retterer JM, & Roddy P. (2014). Faith in a seed: On the origins of equatorial plasma bubbles. Annales Geophysicae, 32(5), 485–498. 10.5194/angeo-32-485-2014 [DOI] [Google Scholar]
  47. Sagawa E, Immel TJ, Frey HU, & Mende SB (2005). Longitudinal structure of the equatorial anomaly in the night-time ionosphere observed by IMAGE/FUV. Journal of Geophysical Research, 110, A11302. 10.1029/2004JA010848 [DOI] [Google Scholar]
  48. Salby ML, & Garcia RR (1987). Transient response to localized episodic heating in the tropics, Part I: Excitation and short-time near-field behavior. Journal of the Atmospheric Sciences, 44, 458–498. [DOI] [Google Scholar]
  49. Schreiner W, Rochen C, Sokolovskiy S, Syndergaard S, & Hunt D. (2007). Estimates of the precision of GPS radio occultations from the COSMIC/FORMOSAT-3 mission. Geophysical Research Letters, 34, L04808. 10.1029/2006GL027557 [DOI] [Google Scholar]
  50. Schwartz MJ, Lambert A, Manney GL, Read WG, Livesey NJ, Froidevaux L, et al. (2008). Validation of the aura microwave limb sounder temperature and geopotential height measurements. Journal of Geophysical Research, 113, D15S11. 10.1029/2007JD008783 [DOI] [Google Scholar]
  51. Shepherd GG, Thuillier G, Cho Y-M, Duboin M-L, Evans WFJ, Gault WA, et al. (2012). The wind imaging interferometer (WINDII) on the upper atmosphere research satellite: A 20 year perspective. Reviews of Geophysics, 50, RG2007. 10.1029/2012RG000390 [DOI] [Google Scholar]
  52. Takahashi H, Wrasse CM, Fechine J, Pancheva D, Abdu MA, Batista IS, et al. (2007). Signatures of ultra fast Kelvin waves in the equatorial middle atmosphere and ionosphere. Geophysical Research Letters, 34, L11108. 10.1029/2007GL029612 [DOI] [Google Scholar]
  53. Tsunoda RT (2010). On equatorial spread F: Establishing a seeding hypothesis. Journal of Geophysical Research, 115(12), A12303. 10.1029/2010JA015564 [DOI] [Google Scholar]
  54. Yamazaki Y, Matthias V, Miyoshi Y, Stolle C, Siddiqui T, Kervalishvili G, et al. (2020). September 2019 Antarctic sudden stratospheric warming: Quasi-6-day wave burst and ionospheric effects. Geophysical Research Letters, 47, e2019GL086577. 10.1029/2019GL086577 [DOI] [Google Scholar]

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