Latitudinal and vertical parameters of the equatorial electrojet from an autonomous data set

Onwumechili, C. Agodi; Ezema, P.O.

doi:10.1016/0021-9169(92)90161-d

Cited by 18 publications

(6 citation statements)

References 21 publications

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“…To account for the induction effect, we introduced in our model an identical series of mirror currents in the ground. This follows the approach of Onwumechili and Ezema [1992], who reported good results of their EEJ study when assuming a conductosphere below a depth of 200 km.…”

Section: Data Selection and Processing Approachmentioning

confidence: 98%

Noon‐time equatorial electrojet: Its spatial features as determined by the CHAMP satellite

2004

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[1] New observations obtained by the satellite CHAMP reveal a detailed picture of the noon-time equatorial electrojet (EEJ). The low orbit of CHAMP and its high-precision magnetometers reveal the spatial structure of the EEJ with unprecedented accuracy. Data from more than two and a half years have been used to investigate average features and also the global characteristics of the EEJ. Rather than interpreting the magnetic signatures, we determined the horizontal current distribution by using a very general current model (series of line currents). This makes the results independent of satellite altitude and ambient field geometry. The procedure for determining the structure of the electrojet is fully automated, giving an objective response. Some of the spatial features of the noon-time EEJ are as follows: The electrojet current peaks right at the dip equator. There is no deviation from it either on a seasonal basis or with longitude. The width of the EEJ (%4°in latitude) at half the peak value of the current density profile is for a given longitude fairly constant, independent of the amplitude. Return currents north and south of the eastward current are a common feature of the EEJ. They peak at latitudes some 5°a way from the dip equator. The intensity of the EEJ varies strongly from day to day. The average peak current density exhibits a clear dependence on longitude. Peaks show up over South America and Indonesia. The average current density follows closely the monthly mean of the solar flux index, F10.7. The total EEJ eastward current is about three times as strong as the return current. The total current and the peak current density are related to each other by a power law. This suggests that the longitude dependence of the EEJ intensity can be explained by the varying cross-sectional area of the Cowling channel.

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Section: Data Selection and Processing Approachmentioning

confidence: 98%

Noon‐time equatorial electrojet: Its spatial features as determined by the CHAMP satellite

2004

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“…The empirical study of Doumouya et al [2003] is based on ground observatory data and cannot offer a complete characterization of the EEJ in longitude. The empirical model of Onwumechili and Ezema [1992] was based on POGO satellite data and provided measurements of several important quantities (mean peak current density, mean total eastward current, mean latitudinal extent, etc. ), but did not offer longitudinal or seasonal profiles of the EEJ.…”

Section: Introductionmentioning

confidence: 99%

Spatio‐temporal characterization of the equatorial electrojet from CHAMP, Ørsted, and SAC‐C satellite magnetic measurements

2007

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[1] The equatorial electrojet (EEJ) is an eastward electric current on the day-side, flowing in a narrow band along the dip equator in the ionospheric E region. Recent magnetic observations from the CHAMP, Ørsted, and SAC-C satellites, comprising more than 95,000 dip equator crossings from 1999 to 2006, have provided an unprecedented longitudinal coverage of the EEJ magnetic signature. We have used these data to construct an empirical model of the EEJ current climatological mean and day to day variability as a function of longitude, local time, season, and solar flux. Our model has been successfully verified against vertical drift data from the JULIA radar at Jicamarca. We have also used the EEJ observations to estimate the self-correlation of the EEJ, confirming short longitudinal correlation lengths of 15°and finding a temporal correlation length of 2.4 h. Our model's predictions of the eastward electric field and its standard deviation may provide useful input to various kinds of ionospheric simulations. Coefficients and software are available online at http://models.geomag.us/EEJ.html and http://www.earthref.org.Citation: Alken, P., and S. Maus (2007), Spatio-temporal characterization of the equatorial electrojet from CHAMP, Ørsted, and SAC-C satellite magnetic measurements,

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“…We also calculated the magnetic field on the ground from this current intensity profile by using discrete line currents at 108 km height and mirror currents at a depth of 200 km. This approach is based on Lühr et al (2004) and Onwumechili and Ezema (1992) and yields the sum of the EEJ external and induced magnetic field components, which is shown by the purple line in Figure 4. The zero references for both x and y axes are shown by green lines.…”

Section: Resultsmentioning

confidence: 99%

Evolution of the Geomagnetic Daily Variation at Tatuoca, Brazil, From 1957 to 2019: A Transition From Sq to EEJ

et al. 2020

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The magnetic equator in the Brazilian region has moved over 1,100 km northward since 1957, passing the geomagnetic observatory Tatuoca (TTB), in northern Brazil, around 2013. We recovered and processed TTB hourly mean values of the geomagnetic field horizontal (H) component from 1957 until 2019, allowing the investigation of long-term changes in the daily variation due to the influence of secular variation, solar activity, season, and lunar phase. The H day-today variability and the occurrence of the counter electrojet at TTB were also investigated. Until the 1990s, ionospheric solar quiet currents dominated the quiet-time daily variation at TTB. After 2000, the magnitude of the daily variation became appreciably greater due to the equatorial electrojet (EEJ) contribution. The H seasonal and day-today variability increased as the magnetic equator approached, but their amplitudes normalized to the average daily variation remained at similar levels. Meanwhile, the amplitude of the lunar variation, normalized in the same way, increased from 5% to 12%. Within the EEJ region, the occurrence rate of the morning counter electrojet (MCEJ) increased with proximity to the magnetic equator, while the afternoon counter electrojet (ACEJ) did not. EEJ currents derived from CHAMP and Swarm satellite data revealed that the MCEJ rate varies with magnetic latitude within the EEJ region while the ACEJ rate is largely constant. Simulations with the Thermosphere-Ionosphere-Electrodynamics General Circulation Model based on different geomagnetic main field configurations suggest that long-term changes in the geomagnetic daily variation at TTB can be attributed to the main field secular variation.

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Latitudinal and vertical parameters of the equatorial electrojet from an autonomous data set

Cited by 18 publications

References 21 publications

Noon‐time equatorial electrojet: Its spatial features as determined by the CHAMP satellite

Noon‐time equatorial electrojet: Its spatial features as determined by the CHAMP satellite

Spatio‐temporal characterization of the equatorial electrojet from CHAMP, Ørsted, and SAC‐C satellite magnetic measurements

Evolution of the Geomagnetic Daily Variation at Tatuoca, Brazil, From 1957 to 2019: A Transition From Sq to EEJ

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