Disturbances at F2-region heights of equatorial anomaly during geomagnetic storms

Mansilla, Gustavo Adolfo

doi:10.1016/s1364-6826(03)00119-6

Cited by 10 publications

(10 citation statements)

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“…In fact, changes in the gaseous composition of the thermosphere (increase in the molecular nitrogen density and a concurrent depletion in atomic oxygen density) can expand from high to low latitudes during intense storms and this affect the ionization production and loss balance (e.g., Prö lss, 1995;Mansilla, 2003). Such is the case of the delayed negative storm effects observed during the recovery phases of the storms of August and October 2003, which have associated no variation in the height of the F2-layer.…”

Section: Discussionmentioning

confidence: 99%

Some ionospheric storm effects at equatorial and low latitudes

Mansilla¹

2014

Advances in Space Research

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Section: Discussionmentioning

confidence: 99%

Some ionospheric storm effects at equatorial and low latitudes

Mansilla¹

2014

Advances in Space Research

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“…Satellite measurements of such a reduction associated with negative ionospheric storms have been given by Strickland et al (2001) based on far ultraviolet imaging, though not at low latitudes. Mansilla (2003) has reported direct satellite measurements of compositional change in the neutral atmosphere at equatorial latitudes associated with geomagnetic storms but were unable to determine their origin or ionospheric effect. GPS measurements of TEC were recently used by Fedrizzi et al (2001) to identify a north-south asymmetry in negative ionospheric storm effect.…”

Section: Discussionmentioning

confidence: 99%

Combined TOPEX/Poseidon TEC and ionosonde observations of negative low-latitude ionospheric storms

et al. 2004

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Abstract. Ionospheric storms showing a strong depression in daytime foF2 values were sought which penetrated to lowlatitudes, as identified by vertical ionosondes operating at Darwin and Townsville over the period [1992][1993][1994][1995][1996][1997][1998]. The 32 storms thus identified showed a seasonal occurrence peaking near the equinoxes with a bias to the summer side. Of these storms, three (27 March 1995, 25 October 1997, 8 November 1997 combined Australian and South East Asian ionosonde observations with local afternoon TOPEX/Poseidon measurements of TEC. The equatorial anomaly is usually well developed at this time of day and consequently these storms were chosen for detailed study. The TOPEX/Poseidon satellite provided vertical profiles of the ionosphere across both hemispheres, thus allowing the totality of storm behaviour to be observed for the first time at low-latitudes and related directly to the ionosonde observations. The three storms were remarkably consistent in their behaviour, the negative ionospheric storm day followed some 24-36 h after the beginning of a magnetic storm and the development of the equatorial anomaly was suppressed. However, the suppression of the equatorial anomaly was not the main cause of the strong depression in foF2 observed by the Southern Hemisphere ionosondes. The latter was associated with an additional bite-out in both TEC and foF2 that occurred on the southern side of the magnetic equator. None of the three storms produced any major negative disturbance outside the range of normal variability of TEC and foF2 at the northern latitude sites for which data was available, despite the absence of the anomaly. The satellite measurements show the strength of the anomaly to be highly variable from day-today and anomaly peaks are frequently not present even on magnetically quiet days. Thus, an absence of anomaly peaks is contained within the normal variability of non-storm days. The north-south asymmetry and seasonal occurrence are consistent with an enhancement of the normal summer-to-winter system carrying compositional changes induced by energyCorrespondence to: K. J. W. Lynn (kenlynn@nbcnet.com.au) inputs at auroral latitudes to equatorial latitudes not usually reached. The ability of associated atmospheric and/or electric field changes to coincidentally switch off the equatorial E region electrojet remains to be explained, as indeed does the large range of variability in equatorial anomaly development from day-to-day evident in the TEC measurements outside periods of geomagnetic disturbance. Some possible positive storm effects occurring on the day preceding the negative storm phase are also noted.

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“…The negative storm effects are more prevalent than the positive storm effects. The morphology of negative and positive storm effects is different because different physical mechanisms are responsible for their formation with varying degrees of importance depending on the intensity of the storm (Mansilla, 2003). There has been significant progress in understanding both types of effects which have very complicated spatial and temporal distributions.…”

Section: Discussionmentioning

confidence: 99%

“…Thermospheric composition changes directly influence the electron concentration in the F2-region. The interplay between storm-induced circulation and the normal (quiet) circulation may also determine the temporal distribution of negative and positive storm effects at low latitudes (Mansilla, 2003). The prompt penetrating electric field and the electric fields generated by the disturbance dynamo also contribute to the occurrence of negative and positive storm effects at the equatorial and low latitudes (Sobral et al, 2001).…”

Section: Discussionmentioning

confidence: 99%