Seasonal parameters of the equatorial electrojet at different longitudinal zones

Yacob, A.

doi:10.1016/0021-9169(66)90072-9

Cited by 20 publications

(8 citation statements)

References 10 publications

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“…The semiannual variation is a well‐known feature of the strength of the EEJ as reflected in the peak Δ H at an equatorial station [ Chapman and Raja Rao , ; Yacob , ; Rastogi and Iyer , ; Rastogi et al ., ; Alken and Maus , ], which is captured by the amplitudes of PC1 for Δ H TIR at different levels of solar activity, as can be seen from Figure b. From the nature of the first three principal components for Δ H TIR displayed in Figure a, it is clear that PC1 contributes the most to day‐to‐day variations of quiet time Δ H TIR in the morning hours close to 11 LT. Its contribution to the day‐to‐day variations of Δ H TIR in the afternoon hours is much smaller and may be obliterated by the contributions of PC2 and PC3.…”

Section: Resultsmentioning

confidence: 99%

Principal components of quiet time temporal variability of equatorial and low‐latitude geomagnetic fields

Bhattacharyya¹,

Okpala

2015

JGR Space Physics

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Diurnal variations of the horizontal component of the geomagnetic field ΔH on International Quiet days of 1999–2012, measured hourly at two stations in the same longitude zone in the Northern Hemisphere, near and away from the dip equator, have been subjected to principal component analysis. This technique is also applied to the difference ΔHEEJ of ΔH at these two stations, which is attributed to the equatorial electrojet (EEJ). The first three principal components, PC1–PC3, account for 91–96% of the variances in the data. Maximum contribution to the quiet day variations in ΔH around its peak in the morning hours at both the stations, and in the EEJ, comes from the day‐to‐day variation of the amplitude of PC1. Patterns of day‐to‐day variations of PC1 amplitudes for the equatorial station and the EEJ are essentially semiannual modulated by solar EUV flux, superimposed on a longer timescale solar EUV flux‐dependent trend. Contributions from PC2 and to a lesser extent from PC3 are seen to be responsible for the absence of semiannual variations in ΔH in the afternoon hours at the equatorial station. Distribution of amplitudes of PC2 and PC3 for ΔHEEJ for weak electrojet days shows seasonal features in accordance with greater occurrence of afternoon (morning) counter electrojet during June (December) solstice. During the extended solar minimum, PC3 amplitudes for ΔH at the equatorial station and for the EEJ display annual variation. Possible sources for these seasonal features in the variations of equatorial ΔH are discussed.

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Section: Resultsmentioning

confidence: 99%

Principal components of quiet time temporal variability of equatorial and low‐latitude geomagnetic fields

Bhattacharyya¹,

Okpala

2015

JGR Space Physics

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“…The semiannual variation in the equatorial electrojet has been known for a long time [ Chapman and Raja Rao , ; Yacob , ; Alken and Maus , ], but the mechanism is not known. Chapman and Raja Rao [] pointed out that the magnitude of the semiannual variation exceeds what is expected from the seasonal variation in the solar zenith angle χ .…”

Section: Resultsmentioning

confidence: 99%

Ground magnetic effects of the equatorial electrojet simulated by the TIE‐GCM driven by TIMED satellite data

et al. 2014

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Quiet time daily variations of the geomagnetic field near the magnetic equator due to the equatorial electrojet are simulated using the National Center for Atmospheric Research Thermosphere-Ionosphere Electrodynamics General Circulation Model (TIE-GCM) and compared to those observed by ground-based magnetometers. Simulations are run both with and without tidal forcing at the height of the model lower boundary (∼97 km). When the lower boundary forcing is off, the wind that generates an electromotive force in the model is primarily the vertically nonpropagating diurnal tide, which is excited in the thermosphere due to daytime solar ultraviolet heating. The lower boundary tidal forcing adds the effect of upward propagating tides, which are excited in the lower atmosphere and propagate vertically to the thermosphere. The main objective of this study is to evaluate the relative importance of these thermospherically generated tides and upward propagating tides in the generation of the equatorial electrojet. Fairly good agreement is obtained between model and observations when the model is forced by realistic lower boundary tides based on temperature and wind measurements from the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite, as determined by Wu et al. (2012). The simulation results show that the effect of upward propagating tides increases the range of the geomagnetic daily variation in the magnetic-northward component at the magnetic equator approximately by 100%. It is also shown that the well-known semiannual change in the daily variation is mostly due to upward propagating tides, especially the migrating semidiurnal tide. These results indicate that upward propagating tides play a substantial role in producing the equatorial electrojet and its seasonal variability.

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“…It is known for a long time that the equatorial electrojet shows a prominent semiannual variation (e.g., Chapman and Raja Rao 1965;Yacob 1966;Bhargava et al 1973). The amplitude of the semiannual variation of EEJ is much greater than that expected from the seasonal change in the ionospheric conductivity.…”

Section: Eejmentioning

confidence: 97%

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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Seasonal parameters of the equatorial electrojet at different longitudinal zones

Cited by 20 publications

References 10 publications

Principal components of quiet time temporal variability of equatorial and low‐latitude geomagnetic fields

Principal components of quiet time temporal variability of equatorial and low‐latitude geomagnetic fields

Ground magnetic effects of the equatorial electrojet simulated by the TIE‐GCM driven by TIMED satellite data

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

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