A simultaneous observation of large-scale periodic TIDs in both hemispheres following an onset of auroral disturbances

Hajkowicz, L.A.; Hunsucker, R. D.

doi:10.1016/0032-0633(87)90038-9

Cited by 65 publications

(69 citation statements)

References 7 publications

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“…Francis, (1973) and the more complex coupled model used here predicts additional slower modes of smaller amplitude. These are in agreement with observations by Thome (1968) and Hajkowicz and Hunsucker (1987).…”

Section: Discussionsupporting

confidence: 94%

“…NmF2 or hmF2) presents an incomplete picture of the family of TIDs. The conjugate AGWs originating in both north and south auroral zones interfere constructively at the equator and the magnitude of the TID is slightly increased, con®rming the suggestion of Hajkowicz and Hunsucker (1987) and the statistical survey of Hajkowicz (1991). The TIDs interfere to produce a stationary and decaying perturbation both above and below the F2 peak; the increase in magnitude of the perturbation in the upper F-region at the equator compared to that at mid-latitudes is of greater magnitude than the similar increase in magnitude of the perturbation in the lower F-region.…”

Section: Discussionsupporting

confidence: 59%

“…These e ects have been previously explained as AGW`seeding' of equatorial spread-F (Kelley, 1989). Hocke and Schlegel (1996) review the results of several observational campaigns, including those observing near, at or across the equator (Thome, 1968;Sterling et al, 1971;Hajkowicz and Hunsucker 1987) and Hajkowicz and Hunsucker (1987) suggest that, in the case of AGWs and associated TIDs approaching the equator from both hemispheres,``it is likely that both TIDs produce a constructive interference e ect at the points of their encounter near the equator''. Large-scale ionospheric disturbances propagating equatorwards and associated with low-latitude aurorae have been studied by Igarashi et al (1991).…”

Section: Introductionmentioning

confidence: 99%

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A study of atmospheric gravity waves and travelling ionospheric disturbances at equatorial latitudes

Moffett

1997

Ann Geophysicae

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Abstract.A global coupled thermosphere-ionosphereplasmasphere model is used to simulate a family of large-scale imperfectly ducted atmospheric gravity waves (AGWs) and associated travelling ionospheric disturbances (TIDs) originating at conjugate magnetic latitudes in the north and south auroral zones and subsequently propagating meridionally to equatorial latitudes. A`fast' dominant mode and two slower modes are identi®ed. We ®nd that, at the magnetic equator, all the clearly identi®ed modes of AGW interfere constructively and pass through to the opposite hemisphere with unchanged velocity. At F-region altitudes the`fast' AGW has the largest amplitude, and when northward propagating and southward propagating modes interfere at the equator, the TID (as parameterised by the fractional change in the electron density at the F2 peak) increases in magnitude at the equator. The amplitude of the TID at the magnetic equator is increased compared to mid-latitudes in both upper and lower F-regions with a larger increase in the upper F-region. The ionospheric disturbance at the equator persists in the upper F-region for about 1 hour and in the lower F-region for 2.5 hours after the AGWs ®rst interfere, and it is suggested that this is due to enhancements of the TID by slower AGW modes arriving later at the magnetic equator. The complex e ects of the interplays of the TIDs generated in the equatorial plasmasphere are analysed by examining neutral and ion winds predicted by the model, and are demonstrated to be consequences of the forcing of the plasmasphere along the magnetic ®eld lines by the neutral air pressure wave.

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Section: Discussionsupporting

confidence: 94%

Section: Discussionsupporting

confidence: 59%

Section: Introductionmentioning

confidence: 99%

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A study of atmospheric gravity waves and travelling ionospheric disturbances at equatorial latitudes

Moffett

1997

Ann Geophysicae

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“…More precisely, studies based on meridionally spaced "chains" of ionosondes give high velocity values. For example, Hajkowicz and Hunsucker (1987) found an equatorward propagation velocity of about 800 m/s and a constant period of about 135 min. Similar results were reported by Yeh et al (1994) in a study based on spaced TEC measurement from geostationary satellite signals, and from ionosonde chains.…”

Section: Auroral Activity and Height Enhancementsmentioning

confidence: 99%

On the nature of nighttime ionisation enhancements observed with the Athens Digisonde

Tsagouri

Belehaki

2002

Ann. Geophys.

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Abstract. True height electron density profiles observed with the Athens Digisonde were analyzed together with geomagnetic data indices for six magnetic storms in September and October 2000 in an effort to define the ionospheric structure during events of nighttime ionisation enhancements and to discuss the physical processes that may cause them. An upwelling of the F2-layer, limited to the dark hemisphere, was evident in all storm events as the ionospheric response to enhanced geomagnetic activity, but nighttime positive effects and nighttime height enhancements are attributed to two distinct mechanisms, according to our findings. Height enhancements are wave-like disturbances and the time delay of their occurrence at middle latitudes depends on the increase rate of the AE index, and consequently, on the rate that the solar wind input energy dissipates in the auroral ionosphere. Thus, they most probably originated in the auroral oval region and propagated toward the equator-like TID disturbances, with a periodicity that depends on the ionisation density. On the other hand, foF2 increases do not share the same wavy appearance, which could mean that they are not connected to TIDs and are not of auroral oval origin. The increased nighttime density can only be speculated to be due to increased downward fluxes from the plasmasphere.

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“…Hedin and Mayr, 1987;Taylor and Edwards, 1991;Hines, 1993;Forbes et al, 1995) and on observations of plasma oscillations with incoherent scatter (IS) radars, HF and MF radars, ionosondes, and total electron contents when it was assumed that the plasma acts a passive tracer to display motions of the neutral atmosphere (e.g. Titheridge, 1968;Hajkowicz and Hunsucker, 1987;Rice et al, 1988;Hajkowicz, 1991;Williams et al, 1993;Manson et al, 1997). The observations also indicated that the propagation of traveling ionospheric disturbances is associated with atmospheric gravity waves (AGWs).…”

Section: Introductionmentioning

confidence: 99%

Effects of atmospheric oscillations on the field-aligned ion motions in the polar F-region

Oyama¹,

Nozawa²,

Buchert³

et al. 2000

Ann. Geophys.

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Abstract. The ®eld-aligned neutral oscillations in the F-region (altitudes between 165 and 275 km) were compared using data obtained simultaneously with two independent instruments: the European Incoherent Scatter (EISCAT) UHF radar and a scanning FabryPerot interferometer (FPI). During the night of February 8, 1997, simultaneous observations with these instruments were conducted at Troms , Norway. Theoretically, the ®eld-aligned neutral wind velocity can be obtained from the ®eld-aligned ion velocity and by di usion and ambipolar di usion velocities. We thus derived ®eld-aligned neutral wind velocities from the plasma velocities in EISCAT radar data. They were compared with those observed with the FPI (k 630:0 nm), which are assumed to be weighted height averages of the actual neutral wind. The weighting function is the normalized height dependent emission rate. We used two model weighting functions to derive the neutral wind from EISCAT data. One was that the neutral wind velocity observed with the FPI is velocity integrated over the entire emission layer and multiplied by the theoretical normalized emission rate. The other was that the neutral wind velocity observed with the FPI corresponds to the velocity only around an altitude where the emission rate has a peak. Di erences between the two methods were identi®ed, but not completely clari®ed. However, the neutral wind velocities from both instruments had peak-to-peak correspondences at oscillation periods of about 10±40 min, shorter than that for the momentum transfer from ions to neutrals, but longer than from neutrals to ions. The synchronizing motions in the neutral wind velocities suggest that the momentum transfer from neutrals to ions was thought to be dominant for the observed ®eld-aligned oscillations rather than the transfer from ions to neutrals. It is concluded that during the observation, the plasma oscillations observed with the EISCAT radar at di erent altitudes in the F-region are thought to be due to the motion of neutrals.

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A simultaneous observation of large-scale periodic TIDs in both hemispheres following an onset of auroral disturbances

Cited by 65 publications

References 7 publications

A study of atmospheric gravity waves and travelling ionospheric disturbances at equatorial latitudes

A study of atmospheric gravity waves and travelling ionospheric disturbances at equatorial latitudes

On the nature of nighttime ionisation enhancements observed with the Athens Digisonde

Effects of atmospheric oscillations on the field-aligned ion motions in the polar F-region

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