Ionospheric evidence for a nonlinear relationship between the solar e.u.v. and 10.7 cm fluxes during an intense solar cycle

Balan, N.; Bailey, G. J.; Jayachandran, B.

doi:10.1016/0032-0633(93)90043-2

Cited by 87 publications

(82 citation statements)

References 20 publications

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“…IEC max and magnetic activity (A p ) are found to be positively correlated in summer in high solar activity. This is in conformity with the results of Balan et al (1993) at di erent latitudes. Winter IEC max shows positive correlation with A p in low solar activity and negative correlation in high solar activity in both the solar cycles.…”

Section: Resultssupporting

confidence: 93%

Long term ionospheric electron content variations over Delhi

Gupta

Singh

2000

Ann. Geophys.

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Abstract. Ionospheric electron content (IEC) observed at Delhi (geographic co-ordinates: 28.63°N, 77.22°E; geomagnetic co-ordinates: 19.08°N, 148.91°E; dip Latitude 24.8°N), India, for the period 1975±80 and 1986± 89 belonging to an ascending phase of solar activity during ®rst halves of solar cycles 21 and 22 respectively have been used to study the diurnal, seasonal, solar and magnetic activity variations. The diurnal variation of seasonal mean of IEC on quiet days shows a secondary peak comparable to the daytime peak in equinox and winter in high solar activity. IEC max (daytime maximum value of IEC, one per day) shows winter anomaly only during high solar activity at Delhi. Further, IEC max shows positive correlation with F 10.7 up to about 200 ux units at equinox and 240 units both in winter and summer; for greater F 10.7 values, IEC max is substantially constant in all the seasons. IEC max and magnetic activity (A p ) are found to be positively correlated in summer in high solar activity. Winter IEC max shows positive correlation with A p in low solar activity and negative correlation in high solar activity in both the solar cycles. In equinox IEC max is independent of A p in both solar cycles in low solar activity. A study of day-to-day variations in IEC max shows single day and alternate day abnormalities, semi-annual and annual variations controlled by the equatorial electrojet strength, and 27-day periodicity attributable to the solar rotation.

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Section: Resultssupporting

confidence: 93%

Long term ionospheric electron content variations over Delhi

Gupta

Singh

2000

Ann. Geophys.

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“…Present observations support the saturation-like effect only for a few months of the descending phase -this may be due to the peculiar position of the observing station relative to the equatorial anomaly crest. The same effect at larger values of F10.7 for all latitudes from 17 • N to 47 • N and in all seasons was reported by Balan et al (1993) using TEC data for the period (1980)(1981)(1982)(1983)(1984)(1985). The saturation effect may be due to an inherent deficiency of F10.7 to represent the variation of EUV, for a 2800-MHz radio flux exceeding 200 units.…”

Section: Resultssupporting

confidence: 79%

“…Further, the flux independent nature is absent in the other time periods of the diurnal TEC variation. Most of the workers (Balan et al, 1993;Gupta and Sing, 2001) obtained a linear relationship between the TECmax and the F10.7 for solar flux values up to about 200 flux units. Gupta and Singh (2001), considering TEC data from Delhi for the rising phases of the 21st and 22nd solar cycles, found the saturation effect at different seasons with a nonlinear fit.…”

Section: Resultsmentioning

confidence: 98%

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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“…This tendency is suggested in the international reference ionosphere (IRI) empirical model [Bilitza et al, 1993], which is based on a large database of ionosonde measurements of electron density. It has also been inferred from ionospheric electron content (IEC) measurements which increase up to F10.7=180 but then level off [Balan et al, 1993[Balan et al, , 1994a. In contrast to the IEC measurements, Richards et al [1994a] found that measured NmF2 at Millstone Hill and Hobart showed little or no dependence on daily F10.7 index at solar maximum in 1990 even though the daily F10.7 index varied from 120 to 250 over this period.…”

Section: Introductionmentioning

confidence: 98%

Seasonal and solar cycle variations of the ionospheric peak electron density: Comparison of measurement and models

Richards¹

2001

J. Geophys. Res.

150

167

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Abstract. This paper examines the ability of empirical and physical models to reproduce the peak electron density of the midlatitude ionospheric F2 region (NrnF2) from 1976 to 1980. The data from all midlatitude stations show a tendency toward a semiannual variation in noon NrnF2 with peaks at the equinoxes for all levels of solar activity. The Southern Hemisphere semiannual variation is more pronounced than in the Northern Hemisphere primarily because the winter density is relatively low in the Southern Hemisphere. At most locations the equinox density peaks are approximately equal. However, the September peak is much weaker than the March peak at most

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Ionospheric evidence for a nonlinear relationship between the solar e.u.v. and 10.7 cm fluxes during an intense solar cycle

Cited by 87 publications

References 20 publications

Long term ionospheric electron content variations over Delhi

Long term ionospheric electron content variations over Delhi

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

Seasonal and solar cycle variations of the ionospheric peak electron density: Comparison of measurement and models

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