Spread<i>F</i>and ionospheric currents

Perkins, F. W.

doi:10.1029/ja078i001p00218

Cited by 430 publications

(533 citation statements)

References 19 publications

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“…It is known that the main source of spread-F echoes is the modulation of the F layer by medium-scale gravity waves (Fejer and Kelley, 1980;Bowman, 1990). The initiation of mid-latitude F-region instability by gravity waves was studied theoretically by Huang et al (1994), who extended the instability mechanism ®rst proposed by Perkins (1973). Some correlation between spread-F and Es scattering seems to be observed in our data.…”

Section: Discussion and Concluding Remarkssupporting

confidence: 68%

Decameter mid-latitude sporadic-E irregularities in relation with gravity waves

Bourdillon¹,

Lefur²,

Haldoupis

et al. 1997

Ann Geophysicae

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Abstract. HF radar observations of mid-latitude sporadic-E irregularities carried out with the Valensole radar in South France are compared with simultaneous ionosonde measurements underneath the irregularity zones. In a previous study of Valensole radar data, it has been shown that HF backscatter from the night-time mid-latitude E region is usually associated with largescale wave-like modulations. To obtain more information on the geophysical conditions prevailing during backscatter events, a new experiment was performed which also included a vertical ionosonde beneath the scattering region. The data to be presented here are from two periods when radar scattering appeared simultaneously with large variations in the virtual height and the Doppler velocity of F-layer re¯ected echoes measured with the vertical ionosonde, indicating very clearly the passage of atmospheric gravity waves (AGWs). The e ect of the atmospheric waves on the sporadic-E layer is not always as marked as it is in the F region. In the ®rst event, the passage of the AGWs is accompanied by an upward followed by a downward movement of the Es-layer. The apparent descending movement of the Es-layer from 135 to 110 km in less than 10 min corresponded to a positive (downward) Doppler velocity of 35 m/s measured by the vertical ionosonde, and was accompanied by a range variation in the radar scattering region with a negative rate of about 90±110 m/s. In the second event, the Es-layer is not as strongly disturbed as in the previous one, but, nevertheless, the range variations of the scattering region can still be associated with height¯uctuations of the Es-layer.

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Section: Discussion and Concluding Remarkssupporting

confidence: 68%

Decameter mid-latitude sporadic-E irregularities in relation with gravity waves

Bourdillon¹,

Lefur²,

Haldoupis

et al. 1997

Ann Geophysicae

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“…In this paper, we show that this equilibrium is in fact unstable, at night, to electrodynamical forces that arise when plane wave perturbations in altitude or density are imposed on the E s layer. We show that the growth rate of the instability depends on the azimuthal alignment of the phase fronts of the plane-wave distortion, a feature that is reminiscient of the Perkins instability [Perkins, 1973]. The dependence on azimuth is consistent with observations of structure in E s layers that show the same preferred alignment.…”

supporting

confidence: 79%

A direction‐dependent instability of sporadic‐E layers in the nighttime midlatitude ionosphere

Cosgrove

Tsunoda

2002

Geophysical Research Letters

144

214

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[1] The configuration of a midlatitude sporadic-E (E s ) layer at a zonal wind-shear node has been assumed to be a stable equilibrium, as long as the wind shear is hydrodynamically stable. In this paper, we show that this equilibrium is in fact unstable, at night, to electrodynamical forces that arise when plane wave perturbations in altitude or density are imposed on the E s layer. We show that the growth rate of the instability depends on the azimuthal alignment of the phase fronts of the plane-wave distortion, a feature that is reminiscient of the Perkins instability [Perkins, 1973]. The dependence on azimuth is consistent with observations of structure in E s layers that show the same preferred alignment.INDEX TERMS: 2471 Ionosphere: Plasma waves and instabilities. Citation: Cosgrove, R. B., and R. T. Tsunoda, A direction-dependent instability of sporadic-E layers in the nighttime midlatitude ionosphere, Geophys. Res.

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“…The evening vertical drift, or the pre-reversal electric field increases with solar flux (Abdu et al, 1983;Fejer et al, 1999), which could lead to greater rate of occurrence of ESF and EPB during the periods of higher solar activity (Sahai et al, 2000;Sobral et al, 2002). Growth rate for Perkins instability (Perkins, 1973), which is used to explain the generation of MSTID (Kelley and Fukao, 1991), is inversely proportional to ion-neutral collision frequency. When the solar activity is low, the smaller ion-neutral collision frequency could give a significantly higher growth rate for the Perkins instability (Kelley and Fukao, 1991), thus favoring more occurrence of MSTID than high solar activity period.…”

Section: Discussionmentioning

confidence: 99%

Airglow observations over the equatorial ionization anomaly zone in Taiwan

et al. 2011

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Abstract. Airglow imaging at mid-latitude stations often show intensity modulations associated with medium scale travelling ionospheric disturbances (MSTID), while those carried out near the equatorial regions reveal depletions caused by equatorial plasma bubbles (EPB). Two all sky cameras are used to observe plasma depletions in the 630.0 nm emission over the equatorial ionization anomaly (EIA) region, Taiwan (23 • N, 121 • E; 13.5 • N Magnetic) during 1998-2002 and 2006-2007. The results show EPB and MSTID depletions in different solar activity conditions. Several new features of the EPB depletions such as bifurcation, secondary structure on the walls, westward tilt, etc., are discussed in this paper. Evidence of tilted depletions with secondary structures developing on the eastern wall that later evolve to appear as bifurcations, are presented for the first time. Moreover, detail investigations are carried out using International Reference Ionosphere (IRI) model as well as the electron density from Ionosonde and Global Positioning System (GPS) Occultation Experiment (GOX) onboard FORMOSAT-3/COSMIC satellite, to understand the conditions that favor the propagation of MSTID to the latitude of Taiwan.

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SpreadFand ionospheric currents

Cited by 430 publications

References 19 publications

Decameter mid-latitude sporadic-E irregularities in relation with gravity waves

Decameter mid-latitude sporadic-E irregularities in relation with gravity waves

A direction‐dependent instability of sporadic‐E layers in the nighttime midlatitude ionosphere

Airglow observations over the equatorial ionization anomaly zone in Taiwan

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