On the equatorial anomaly of the ionospheric total electron content near the northern anomaly crest region

Huang, Yinn‐Nien; Cheng, Kang; Chen, Sen-Wen

doi:10.1029/ja094ia10p13515

Cited by 97 publications

(71 citation statements)

References 8 publications

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“…Evidence for the electrodynamic coupling between the E-region and F-region ionosphere has also been found in plasma density data in the equatorial anomaly region. Studies have shown that the intensity and latitude of the equatorial anomaly crests vary with the intensity of the equatorial electrojet (Dunford 1967;MacDougall 1969;Rastogi and Rajaram 1971;Rush and Richmond 1973;Raghavarao et al 1978;Balan and Iyer 1983;Huang et al 1989;Rastogi and Klobuchar 1990;Rama Rao et al 2006;Stolle et al 2008). The most comprehensive study was made by Stolle et al (2008), involving 5 years of CHAMP electron density observations along with radar and geomagnetic field measurements.…”

Section: Eej Intensity and Equatorial F-region Parametersmentioning

confidence: 99%

Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents

2016

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A record of the geomagnetic field on the ground sometimes shows smooth daily variations on the order of a few tens of nano teslas. These daily variations, commonly known as Sq, are caused by electric currents of several μA/m 2 flowing on the sunlit side of the Eregion ionosphere at about 90-150 km heights. We review advances in our understanding of the geomagnetic daily variation and its source ionospheric currents during the past 75 years. Observations and existing theories are first outlined as background knowledge for the nonspecialist. Data analysis methods, such as spherical harmonic analysis, are then described in detail. Various aspects of the geomagnetic daily variation are discussed and interpreted using these results. Finally, remaining issues are highlighted to provide possible directions for future work.

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Section: Eej Intensity and Equatorial F-region Parametersmentioning

confidence: 99%

Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents

2016

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“…The electron production by photo-ionization of neutral atoms and molecules is proportional to the intensity of solar radiation, governed by the Beer Lambert law. It is also determined by the density and properties of the neutrals (Golton & Walker 1971;Rastogi & Sharma 1971;Huang et al 1989;Klobuchar et al 1991;Wu et al 2004). The plasma transport contribution varies with the altitude and is most important above the ionospheric E-layer.…”

Section: Model Developmentmentioning

confidence: 99%

An empirical model of ionospheric total electron content (TEC) near the crest of the equatorial ionization anomaly (EIA)

Hajra

Chakraborty²,

Tsurutani

et al. 2016

J. Space Weather Space Clim.

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We present a geomagnetic quiet time (Dst > À50 nT) empirical model of ionospheric total electron content (TEC) for the northern equatorial ionization anomaly (EIA) crest over Calcutta, India. The model is based on the 1980-1990 TEC measurements from the geostationary Engineering Test Satellite-2 (ETS-2) at the Haringhata (University of Calcutta, India: 22.58°N, 88.38°E geographic; 12.09°N, 160.46°E geomagnetic) ionospheric field station using the technique of Faraday rotation of plane polarized VHF (136.11 MHz) signals. The ground station is situated virtually underneath the northern EIA crest. The monthly mean TEC increases linearly with F 10.7 solar ionizing flux, with a significantly high correlation coefficient (r = 0.89-0.99) between the two. For the same solar flux level, the TEC values are found to be significantly different between the descending and ascending phases of the solar cycle. This ionospheric hysteresis effect depends on the local time as well as on the solar flux level. On an annual scale, TEC exhibits semiannual variations with maximum TEC values occurring during the two equinoxes and minimum at summer solstice. The semiannual variation is strongest during local noon with a summer-to-equinox variability of 50-100 TEC units. The diurnal pattern of TEC is characterized by a pre-sunrise (0400-0500 LT) minimum and near-noon (1300-1400 LT) maximum. Equatorial electrodynamics is dominated by the equatorial electrojet which in turn controls the daytime TEC variation and its maximum. We combine these long-term analyses to develop an empirical model of monthly mean TEC. The model is validated using both ETS-2 measurements and recent GNSS measurements. It is found that the present model efficiently estimates the TEC values within a 1-r range from the observed mean values.

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“…The neutral wind further introduces asymmetries in the anomalous distribution of the ionization with larger plasma flow (towards the hemisphere of the stronger poleward wind) and a stronger anomaly crest occurring in the opposite hemispheres (Balan and Bailey, 1995). The latitudes of the anomaly crests and the strength of the anomaly are found to vary with day, month, season, solar activity, as well as longitudes (Rush and Richmond, 1973;Huang et al, 1989). The world's largest value of total electron content (TEC) is observed around the equatorial anomaly crest.…”

Section: Introductionmentioning

confidence: 99%

“…The peculiarity of the database is that it contains both the descending (1979)(1980)(1981)(1982)(1983)(1984)(1985) and ascending (1986-1990) phases of the solar cycles. The solar activity dependent features have been discussed in various papers (Golton and Walker, 1971;Rastogi and Sharma, 1971;Huang et al, 1989;Klobuchar et al, 1991;Prasad and Rama Rao, 1993;Feichter and Leitinger, 1997;Gupta and Singh, 2001;Jayachandran et al, 2004;Wu et al, 2004). These are mostly based on data for one solar cycle or less, or observations were made from mid/higher latitude regions.…”

Section: Introductionmentioning

confidence: 99%

Solar control of ambient ionization of the ionosphere near the crest of the equatorial anomaly in the Indian zone

Chakraborty¹,

Hajra²

2008

Ann. Geophys.

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Abstract. Long-term (1978Long-term ( -1990 total electron content (TEC) data have been analyzed to show the dependence of ambient ionization on EUV radiation from the Sun. TEC observations were made at Calcutta (22.58 • N, 88.38 • E geographic, dip: 32 • N), situated virtually below the northern crest of the equatorial ionization anomaly. Day-to-day changes in TEC at different local times do not show any significant correlation with F10.7 solar flux. A good correlation is, however, observed between the F10.7 solar flux and the monthly mean TEC when both are considered on a long-term basis, i.e. either in the ascending (1986)(1987)(1988)(1989)(1990) or in the descending (1979-1985) phase. In the early morning hours the correlation coefficient maximizes around the 08:00-10:00 h IST interval. The flux independent nature of diurnal TEC is evident around the noon time hours of only a few months in the descending phase for F10.7 values greater than 150 unit. Variation of TEC for the whole time period (1979)(1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990)) also exhibits a prominent hysteresis effect. The remarkable feature of the hysteresis effect is its local time dependence, leading to a temporal flip-over. Solar flux-normalized TEC values show a clear seasonal dependence with asymmetrical variations in the two equinoxes. The amplitudes of the equinoctial peaks reveal a prominent local time dependence. A further normalization leads to a typical local time variation of TEC. Based on solar flux, seasonal and local time dependent features of TEC, an empirical formula has been developed to represent the TEC variation in the early morning hours. It yields a quantitative estimate of the solar flux dependent nature of the TEC variation. The formula has been validated using the available TEC data and data from the neural network.

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On the equatorial anomaly of the ionospheric total electron content near the northern anomaly crest region

Cited by 97 publications

References 8 publications

Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents

Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents

An empirical model of ionospheric total electron content (TEC) near the crest of the equatorial ionization anomaly (EIA)

Solar control of ambient ionization of the ionosphere near the crest of the equatorial anomaly in the Indian zone

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