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

Chakraborty, Subhadeep; Hajra, Rajkumar

doi:10.5194/angeo-26-47-2008

Cited by 34 publications

(25 citation statements)

References 42 publications

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“…This paper is our attempt at a creation of a practical and useable model for the Indian longitude sector. The present TEC model development was based on statistical analyses on a long-term (1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990) database of TEC from Calcutta situated near the northern crest of the EIA in the Indian zone (Chakraborty & Hajra 2008Hajra 2011). The diurnal TEC dependences on solar ionizing flux (F 10.7 ), equatorial electrodynamics (EEJ), season, and local time were analyzed to develop the model using linear, non-linear, and multiple-regression analyses.…”

Section: Discussionmentioning

confidence: 99%

“…It may be noted that this effect has less impact at 1200 LT compared to other time sectors shown in Figure 1. A detailed discussion about the features and causes of the TEC hysteresis effect may be found in Chakraborty & Hajra (2008) and Hajra (2011). It was shown to exhibit prominent local time effect with temporal flip-over between the ascending and descending phases of the solar cycle.…”

Section: Model Developmentmentioning

confidence: 99%

“…As the solar flux contributions are observed to be the maximum around 0900 LT (Chakraborty & Hajra 2008;Hajra 2011), deviations are estimated from solar flux normalized values around this period. TEC deviations are plotted against the EEJ values.…”

Section: Model Developmentmentioning

confidence: 99%

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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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Section: Discussionmentioning

confidence: 99%

Section: Model Developmentmentioning

confidence: 99%

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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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show abstract

“…Considering solar flux, seasonal and local time dependent features, an empirical formula for monthly mean TEC, applicable in the early morning hours (07:00-09:00 IST), was developed (Chakraborty and Hajra, 2008). In the present analysis slight modification of the formula has been attempted by incorporating an additional term dependent on EEJ so that it may be applicable in the later periods.…”

Section: Empirical Formula For Diurnal Monthly Mean Tec Variationmentioning

confidence: 99%

“…The modified form of the empirical formula may be written as: by the second and third terms respectively. The solar flux contribution is observed to be maximum around 08:00-09:00 IST (Chakraborty and Hajra, 2008). Thereafter, the rate of production may be assumed to remain constant (Garriott and Smith, 1965).…”

Section: Empirical Formula For Diurnal Monthly Mean Tec Variationmentioning

confidence: 99%

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

Chakraborty¹,

Hajra²

2009

Ann. Geophys.

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Abstract. A long-term (1978-1990) database of total electron content (TEC) from a location (Calcutta: 22.58 • N, 88.38 • E geographic, dip: 32 • N) near the northern crest of the equatorial ionization anomaly has extensively been studied to characterize the contribution of fountain effect in the maintenance of ambient ionization. The equatorial electrojet (EEJ) data obtained from ground magnetometer recording are used to assess the contribution of equatorial fountain. Analysis made with instantaneous values, day's maximum values and time-integrated values of EEJ strength exhibit more or less similar features. When instantaneous values of EEJ are considered TEC variations exhibit two maxima in correlation, one around 10:00-12:00 IST and the other around 18:00-20:00 IST. The later maximum in correlation coefficient is conspicuously absent when integrated values of EEJ are considered. An impulse-like feature is reflected in the diurnal TEC variation during the time intervals (09:00-10:00 IST) and (18:00-19:00 IST). The statistical analysis reveals greater correspondence with high level of significance between diurnal TEC and EEJ in the descending epoch of solar cycle than in the ascending one. On the seasonal basis, TEC in the summer solstitial months are observed to be more sensitive to the changes in EEJ strength than in the equinoctial and winter solstitial months. Combining the effects of solar flux, season, local time and EEJ an empirical formula for monthly mean diurnal TEC has been developed and validated using observed TEC data. An estimation of the relative contributions of the several terms appearing in the formula reveals much more solar flux contribution (∼50-70%) in the maintenance of ambient ionization around the present location than the EEJ effects (maximum∼20%).

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Characteristics of low‐latitude TEC during solar cycles 23 and 24 using global ionospheric maps (GIMs) over Indian sector

Dashora

Suresh

2015

JGR Space Physics

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The characteristics of quiet time equatorial and low-latitude total electron content over the Indian sector using global ionospheric map (GIM) data (1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014) are obtained filtering out the solar flare and storm effects. The results are examined and interpreted in the context of large number of previous studies. The newly found features from this study are as follows. Marked difference in nature of equinoctial asymmetry is noted between solar cycles 23 and 24. Long absence of winter anomaly both during low and high solar activity (HSA) in LL (low-latitude) regions is found. Climatology of the diurnal cycle is provided in four categories using new criteria for demarcation of solar activity levels. Highest correlation (~77%) between GIM ionospheric electron content (IEC) and PI (solar EUV proxy index) is noted over equator in contrast to previous studies. The minimum positive contribution of PI in variation of IEC requires minimum of 2 years of data, and if more than 7-8 years of data are used, it saturates. Root-mean-square width of PI can be used to define the HSA. Strong QBO (quasi-biennial oscillations) in IEC is noted in tune with the one in PI over both LL locations but QBO remains surprisingly subdued over equator. The semiannual oscillations in GIM-IEC are found to be stronger at all locations during high solar activity and weaker between 2005 and 2011, whereas the annual oscillations are found to be substantially stronger only during HSA-23 and weakest over southern LL location throughout 17 years.

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

Cited by 34 publications

References 42 publications

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

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

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

Characteristics of low‐latitude TEC during solar cycles 23 and 24 using global ionospheric maps (GIMs) over Indian sector

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