Atmosphere‐Ionosphere (A‐I) Coupling as Viewed by ICON: Day‐to‐Day Variability Due to Planetary Wave (PW)‐Tide Interactions

Abstract

It is now widely accepted that tides, planetary waves (PWs) and ultra-fast Kelvin waves (UFKW) propagating upward from the lower atmosphere play an important role in determining the longitudinal and day-to-day variability of the ionosphere. Insofar as PWs and the low-latitude ionosphere is concerned, this realization has its early roots in the work of Ito et al. (1986) and Chen et al. (1992; see also their references to the earlier Chinese literature), who first recognized the connection between quasi-2-days wave (Q2DW) variations in winds, and Q2DW variations in electric fields generated by neutral-plasma interactions in the E-region (i.e., the wind dynamo), ground magnetic perturbations (Ito et al.) and the critical frequency of the F-region, f 0 F 2 (Chen et al.). (The E-region electric fields E map along magnetic field lines to the F-region, where they are manifested as E × B drifts that transport plasma from equatorial to tropical latitudes to produce the "equatorial ionization anomaly (EIA).") These authors moreover confirmed their hypotheses through numerical modeling. Chen et al. (1992; (see also later work by Pancheva et al., 2006) furthermore postulated that the Q2DW exerted its influence through modulation of tidal winds, rather than directly through the Q2DW wind field. This point of view is at the heart of the neutral wind-driven ionospheric variability examined in the present work.Between about 1990 and 2010, many additional analyses that documented PW variations with periods of order 2-20 days in the ionosphere were published (e.g., see review by Lastovicka et al., 2006). Most of these were conducted with ionosonde data, and emphasized middle latitudes. The origins of ionospheric Abstract Coincident Ionospheric Connections Explorer (ICON) measurements of neutral winds, plasma drifts and total ion densities (:=Ne, electron density) are analyzed during January 1-21, 2020 to reveal the relationship between neutral winds and ionospheric variability on a day-to-day basis. Atmosphere-ionosphere (A-I) connectivity inevitably involves a spectrum of planetary waves (PWs), tides and secondary waves due to wave-wave nonlinear interactions. To provide a definitive attribution of dynamical origins, the current study focuses on a time interval when the longitudinal wave-4 component of the E-region winds is dominated by the eastward-propagating diurnal tide with zonal wavenumber s = −3 (DE3). DE3 is identified in winds and ionospheric parameters through its characteristic dependence on local solar time and longitude as ICON's orbit precesses. Superimposed on this trend are large variations in low-latitude DE3 wave-4 zonal winds (±40 ms −1 ) and topside F-region equatorial vertical drifts at periods consistent with 2-days and 6-days PWs, and a ∼3-day ultra-fast Kelvin wave (UFKW), coexisting during this time interval; the DE3 winds, dynamo electric fields, and drifts are modulated by these waves. Wave-4 variability in Ne is of order 25%-35%, but the origins are more complex, likely additionally reflecting trans...

Vertical Coupling by Solar Semidiurnal Tides in the Thermosphere From ICON/MIGHTI Measurements

“…, as demonstrated through general circulation modeling by Hagan et al (2009) and Pedatella et al (2012). Forbes et al (2021) demonstrated the presence of SPW4 and SE2 in ICON/MIGHTI winds at 106 and 295 km, the potential for SE2 to propagate to F-region altitudes, and noted connections with contemporaneous topside F-region electron density variability observed by ICON. He et al (2011) emphasized the importance of SE2 trans-equatorial winds to latitudinal asymmetries of ionospheric observations.…”

“…Forbes et al. (2021) demonstrated the presence of SPW4 and SE2 in ICON/MIGHTI winds at 106 and 295 km, the potential for SE2 to propagate to F‐region altitudes, and noted connections with contemporaneous topside F‐region electron density variability observed by ICON. He et al.…”

Characterization of the Thermospheric Mean Winds and Circulation During Solstice Using ICON/MIGHTI Observations

“…Forbes et al. (2021) analyzed coincident ICON measurements of neutral horizontal winds, ion drifts, and densities and demonstrated a direct link between the day‐to‐day variability of the wave‐4 structure in the E‐region and drifts and densities of ions in the F‐region ionosphere. More recently, England et al.…”

Hough Mode Extensions (HMEs) and Solar Tide Behavior in the Dissipative Thermosphere

“…(2012), and Forbes et al. (2021, 2022) demonstrate how HMEs can facilitate the interpretation of tidal winds in the 100–300 km height regime based on ICON/MIGHTI measurements.…”