Sporadic-E as a tracer for atmospheric waves

doi:10.1016/0032-0633(91)90021-2

Planetary and Space Science

Volume 39, Issue 10, October 1991, Pages 1421-1434

https://doi.org/10.1016/0032-0633(91)90021-2 Get rights and content

Abstract

During three days of quiet geomagnetic conditions in August 1988, both the EISCAT UHF radar and the NOAA digital ionospheric sounder (Dynasonde) were operated from 12:00 to 22:00 U.T. Sporadic-E layers were observed on all three days, controlled by the action of the semi-diurnal tide. Gravity wave activity was very evident in both data sets, and particularly visible in the changes in intensity and position of the layers. By combining the two sets of measurements it is possible to build up a spatial picture of the phase fronts passing over Tromsø, with sporadic-E layers acting as tracers for them in the E-region. It is observed that structures in the electron density associated with gravity waves descend from the F-region through the E-region to merge with the increases in the layer intensity. The enhancements in the layers, which we suggest are produced by horizontal convergence, are ribbon-like and aligned along the gravity wave phase fronts in the E-W direction, travelling southwards at 60 km h⁻¹ and about 50 km apart.

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Cited by (20)

Auto-detection of sporadic E and spread F events from the digital ionograms
2022, Advances in Space Research
Citation Excerpt :
Ordinary sporadic E (Es) layers are commonly detected in the E region at heights of 90 km to 130 km, with very narrow ionisation increases of 2–10 km (Denardini et al., 2016). Whitehead (1989) studied ionisation enhancements in the E area at middle and low latitudes and found that they are induced by vertical shear caused by opposite horizontal neutral winds, which are driven by gravity waves (Hooke, 1970; Lanchester et al., 1991; Jayachandran et al., 1999) or tidal motions (Chimonas, 1971). The features of the several varieties of Es layer identified in different latitudinal sectors were summarised by Resende et al. (2013), with type “q” being the most often seen Es type layer in the equatorial region (Esq).
To evaluate huge ionogram datasets and detect ionosphere variabilities, automatic identification of Sporadic E (Es) and Spread F (SF) events in digital ionograms is required. This work presents an auto-detection technique to identify the ionograms' Es and SF signatures. Es and SF events are detected automatically by de-noising the ionogram, segmentation, and quantifying the frequency and height points in each layer segmented part. The technique's performance is assessed using ionograms acquired by the Canadian Advanced Digital Ionosonde (CADI) at a low latitude station in Hyderabad, India, in 2015. With a detection efficiency of 96.71%, 89.71%, and 93.39%, the suggested technique successfully detected the Es, Range Spread F (RSF), and Strong Spread F (SSF) events from ionograms. To demonstrate the correlation between SSF and S4, the occurrence rate of SSF is compared to the amplitude scintillation (S4) rate of the Global Positioning System (GPS). The recommended technique is useful for launching ionospheric alert systems for high-frequency communications and GPS users.
Case study of simultaneous observations of sporadic sodium layer, E-region field-aligned irregularities and sporadic E layer at low latitude of China
2017, Advances in Space Research
Citation Excerpt :
Oscillations in the height of Na layer imply the presence of GW, since the Na layer can be regarded as a passive tracer in the short-time scales atmospheric dynamics (Bills and Gardner, 1993; Dou et al., 2009). It has been confirmed that the interaction of GW with DT can cause perturbations in height and intensity of Es (Lanchester et al., 1991). This also can cause variations in SSL and FAI echoing layer.
Using the Na lidar at Haikou (20.0°N, 110.3°E), the VHF coherent radar and the digital ionosonde both at Sanya (18.4°N, 109.6°E), cases of simultaneous observations of sporadic sodium layer (SSL), E-region field-aligned irregularities (FAI) and sporadic E layer (Es) in the mesosphere and lower thermosphere (MLT) region at low latitude of China are studied. It is found that SSL occurs simultaneously or follows the enhancement of Es and FAI. The Es, FAI and SSL descend slowly with time which is mostly controlled by the diurnal tide (DT). Besides, the interaction of gravity wave (GW) with tides can cause oscillations in FAI and SSL. Our observations support the neutralization of ions for SSL formation: when the metallic ions layer descents to the altitudes where models predict, the sodium ions convert rapidly to atomic Na that may form an SSL event. Moreover, the SSL peak density will increase (decrease) in the convergence (divergence) vertical shear region of zonal wind.
Forcing of the ionosphere by waves from below
2006, Journal of Atmospheric and Solar-Terrestrial Physics
Meteorological processes in the lower-lying layers, particularly in the troposphere, affect the ionosphere predominantly through the upward propagating waves and their modifications and modulations. Those waves are planetary waves, tidal waves, gravity waves, and almost forgotten infrasonic waves. A part of wave activity can be created in situ at ionospheric heights as primary (e.g., diurnal tide, gravity waves) or secondary waves (e.g., some gravity or planetary waves), but this paper is focused on the upward propagating waves from below the ionosphere. They propagate into the ionosphere mostly directly but the planetary waves can propagate upwards to the F region heights only indirectly, via various potential ways like modulation of the upward propagating tides. The waves may be altered during upward propagation via non-linear interactions, particularly in the MLT region. A brief overview of effects on the ionosphere of upward propagating waves from lower-lying regions is given, separately for the lower ionosphere, for the E-region ionosphere, and for the F-region ionosphere. The upward propagating waves of the neutral atmosphere origin are important both from the point of view of vertical coupling in the atmosphere–ionosphere system, and for applications in radio propagation/telecommunications, as they are responsible for a significant part of uncertainty of the radio wave propagation condition predictions.
Middle atmosphere and lower thermosphere processes at high latitudes studied with the EISCAT radars
1994, Journal of Atmospheric and Terrestrial Physics
The middle and upper atmosphere and the ionosphere at high latitudes are studied with the EISCAT incoherent scatter radars in northern Scandinavia. We describe here the investigations of the lower thermosphere and the E-region, and the mesosphere and the D-region. In the auroral zone both these altitude regions are influenced by magnetospheric processes, such as charged particle precipitation and electric fields, which are measured with the incoherent scatter technique. Electron density, neutral density, temperature and composition are determined from the EISCAT data. By measuring the ion drifts, electric fields, mean winds, tides and gravity waves are deduced. Sporadic E-layers and their relation to gravity waves, electric fields and sudden sodium layers are also investigated with EISCAT. In the mesosphere coherent scatter occurs from unique ionization irregularities. This scatter causes the polar mesosphere summer echoes (PMSE), which are examined in detail with the EISCAT radars. We describe the dynamics of the PMSE, as well as the combination with aeronomical processes, which could give rise to the irregularities. We finally outline the future direction which is to construct the EISCAT Svalbard Radar for studying the ionosphere and the upper, middle and lower atmosphere in the polar cap region.
Quasi-periodic scintillation events at southern auroral latitudes
1994, Journal of Atmospheric and Terrestrial Physics
Quasi-periodic (QP) radio scintillations were observed during (1987) on 244 MHz and 1.5 GHz geostationary satellite transmissions in the southern auroral zone from Davis station (68.6°S, 78.0°E geographic, 74.6°S Aλ) in Antarctica. Three distinct types of OP events were identified, with occurrence times mainly restricted to the period 18-00 MLT. The substantial loss of signal associated with these events appears to be an important factor in determining the reliability of satellite links on 1.5 GHz in auroral regions. Previous observations at mid-latitudes of QP scintillations have noted a preference for large zenith angles and equatorward azimuths. It is demonstrated that a height transition in a densely ionized layer can produce QP scintillations in a manner analogous to a dense column of ionization but at lower ionization densities, as well as demonstrating a zenith angle and azimuthal dependence that is more consistent with observations than a column of ionization. At the occurrence times noted, the raypath may be intersecting the poleward edge of the trough where sporadic-E is a regular feature. QP scintillation events may result when the E_s-layer is height modulated by the passage of acoustic-gravity waves originating in the auroral zone.
EISCAT: early history and the first ten years of operation
1993, Journal of Atmospheric and Terrestrial Physics

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Sporadic-E as a tracer for atmospheric waves

Abstract

J. atmos. terr. Phys.

J. atmos. terr. Phys.

J. atmos. terr. Phys.

J. atmos. terr. Phys.

J. atmos. terr. Phys.

J. atmos. terr. Phys.

Planet. Space Sci.

Adv. Space Res.

J. atmos. terr. Phys.

Enhancements of sporadic E by horizontal transport within the layer

J. geophys. Res.

EISCAT: an updated description of technical characteristics and operational capabilities

Radio Sci.

Atmospheric tides, 1. Model description and results for the solar diurnal component

J. geophys. Res.

Atmospheric tides, 2. The solar and lunar semi-diurnal components

J. geophys. Res.