Electrojet Stations Research Articles

INVESTIGATING THE VARIATIONS OF HORIZONTAL (H) AND VERTICAL (Z) COMPONENTS OF THE GEOMAGNETIC FIELD AT SOME EQUATORIAL ELECTROJET STATIONS

This research is monitoring equatorial geomagnetic current which causes atmospheric instabilities and affects high frequency and satellite communication. It presents the variations of Horizontal (H) and vertical (Z) component of the geomagnetic field at some Equatorial Electrojet (EEJ) Stations during quiet days. Data from five (5) observatories along the magnetic equator were used for the study. Daily baseline values for each of the geomagnetic element 𝐻 and Z were obtained. The monthly average of the diurnal variation and the seasonal variations were found. Results showed that the variations of the geomagnetic element of both H and Z differ in magnitudes from one stations to another along the geomagnetic Equator due to the differences of their geomagnetic latitude. The Amplitude curves for Z) are seen to be conspicuously opposite to that of H), and there is absence of CEJ in Z- Component but present in H- Components. The values during the pre-sunrise hours are low compare to daytime hours. Minimum variations of dH was observed during June solstice and maximum variations was observed during Equinox season. This study shows that daily variations of (H) and (Z) occur in all the stations. The enhancement in H is as a result of EEJ current

INVESTIGATING THE VARIATIONS OF HORIZONTAL (H) AND VERTICAL (Z) COMPONENTS OF THE GEOMAGNETIC FIELD AT SOME EQUATORIAL ELECTROJET STATIONS

This research is monitoring equatorial geomagnetic current which causes atmospheric instabilities and affects high frequency and satellite communication. It presents the variations of Horizontal (H) and vertical (Z) component of the geomagnetic field at some Equatorial Electrojet (EEJ) Stations during quiet days. Data from five (5) observatories along the magnetic equator were used for the study. Daily baseline values for each of the geomagnetic element 𝐻 and Z were obtained. The monthly average of the diurnal variation and the seasonal variations were found. Results showed that the variations of the geomagnetic element of both H and Z differ in magnitudes from one stations to another along the geomagnetic Equator due to the differences of their geomagnetic latitude. The Amplitude curves for Z) are seen to be conspicuously opposite to that of H), and there is absence of CEJ in Z- Component but present in H- Components. The values during the pre-sunrise hours are low compare to daytime hours. Minimum variations of dH was observed during June solstice and maximum variations was observed during Equinox season. This study shows that daily variations of (H) and (Z) occur in all the stations. The enhancement in H is as a result of EEJ current.

On the Variation of Geomagnetic H-Component during Solar Quiet Days

The hourly variation of the H-component of the geometric field from two equatorial electrojet stations, Huancayo and Addis Ababa, and one non-equatorial electrojet station, Alibag, were studied to find out the trend of solar quiet variation of H for the year 2008. The dH amplitudes of the electrojet stations showed enhancement in H, while there was no enhancement in the non-electrojet station which was located far away from the dip equator. The day-to-day monthly diurnal variation was, however, observed in all the three stations. Also, at nighttime, the dH amplitudes of all the stations were non-zero which we attributed to non-ionospheric current sources like the magnetosphere since at night there was no solar radiations. For seasonal variations, an Equinoctial maximum, J-Solstitial maximum, and S-Solstitial maximum were observed in the equatorial stations while the non-equatorial station recorded an equinoctial minimum, J-solstitial minimum and D-Solstitial minimum.

Solar quiet variation of the horizontal and vertical components of geomagnetic field using wavelet analysis

The solar quiet (Sq) variations of horizontal and vertical (SqH and SqZ) components of the geomagnetic field obtained from both the Northern Hemisphere and Southern Hemisphere of the International Real-Time Magnetic Observatory Network (INTERMAGNET) during solar maximum year 2001 were investigated. The results show enlargement of the SqH component of the geomagnetic field during the daytime, attributed to equatorial electrojet (EEJ) current closer to the geomagnetic equator at the electrojet stations (BNG and MBO), which are produced from large eastward flow of the current. It was observed that SqZ is positive at the southward and negative at the northward hemispheres. SqZ is amplified at HER and HBK around the daytime. Wavelet power spectrum based approach was employed to analyse the SqH, SqZ, and rate of induction (SqZ/SqH) time series in a sequence of time scaling from January to December. The higher energy of SqH and SqZ of the wavelet coefficients is noticeable at high frequency. The monthly variation rate of induction (SqZ/SqH) analyses during the Sq variations are associated with the influence of equatorwards penetration of electric fields from the field-aligned current, Earth conductivity, effect of the ocean, and ionospheric conductivity.

Characterization of seasonal and longitudinal variability of EEJ in the Indian region

AbstractThis paper presents the seasonal and longitudinal variability of the equatorial electrojet (EEJ) based on geomagnetic variation data from two electrojet stations in the northern Indian Ocean at a longitudinal separation of ~15°: i.e., at 77°E and at 93°E. One complete year of data is used (i.e., from November 2011 to October 2012) at the two longitudes and compared with the climatological model of the equatorial electrojet (EEJM‐2.0). The results of our analysis show that (i) the monthly averaged hourly values of EEJ strength at 77°E and 93°E are overall in agreement with global characteristics of EEJ with significant departures over the year of study, (ii) the monthly average hourly daytime values at Campbell Bay and Vencode show poor correlation (r < 0.7) for 5 out of 10 months, (iii) comparison of observed EEJ strength at respective longitudes and the current densities derived from EEJM‐2.0 show overall agreement with significant differences for monthly mean hourly daytime values at respective longitudes, and (iv) day‐to‐day variability in noontime EEJ amplitudes between the two longitudes is >10 nT, >20 nT for 30% of quiet days, sorted by planetary index (Kp) <1 and <2. This variability is reflected in monthly average values (V) mechanisms for persistent differences in EEJ on day‐to‐day basis are sought from perturbation of westward ion drifts by neutral winds caused by the upward propagation of gravity waves from troposphere/stratosphere into the mesosphere. These mechanisms have been identified theoretically and experimentally. The four‐wave structure of ionospheric current densities obtained by EEJM‐2.0 and other contemporary models closely resembles atmospheric tidal signatures and has a common origin. The magnitude and persistence of these differences, at short spatial scales (15°), are significant observation. These effects are reflected in the monthly and seasonal signatures of EEJ and contribute to the contemporary models.

Ionospheric responses to the October 2003 superstorm: Longitude/local time effects over equatorial low and middle latitudes

Ionospheric responses to the major magnetic storm disturbances of October 2003 are investigated using database selected in the Brazilian and Japanese‐Asian longitude sectors. Data obtained from latitudinally spaced digisondes in the equatorial and low‐latitude sites in Brazil and from the Asian and Japanese ionosonde network, the total electron content data from the extensive Japanese GPS receiver chain, and magnetometer data from the Pacific equatorial electrojet stations are analyzed during the period 28–31 October. Prompt penetrating (PP) dawn‐dusk polar cap electric fields produce large F region plasma uplift on the dayside and eveningside, while the associated westward electric field on the nightside produces large downdraft of the F region plasma, and causes development of westward electrojet current, observed for the first time. Episodes of PP electric field effects appear to be of larger intensity over Brazil than over Asian longitudes. Equatorial anomaly, development due to undershielding as well as overshielding electric fields, was observed in the Brazilian and in the Asian sectors. Disturbance dynamo electric field causes large nighttime F layer uplifts that are modulated by strong meridional winds in both sectors. The disturbance electric field local time variation patterns are compared with the results of recent global model (MTIEGCM) simulation by Richmond et al. (2003) and validated in some cases. Transients of transequatorial winds, flipping direction from southward to northward, in the widely separated longitude sectors, were diagnosed to be present toward the final recovery phase of the storm. These results are presented and discussed in this paper.

Day-to-day correlation of equatorial electrojet at two stations separated by 2000 km

Abstract. Day-to-day fluctuations of the daily range of the geomagnetic field H at the equatorial electrojet stations Ancon (ANC, 77.0° W) and Sao Luis (SLZ, 44.2° W) are described for the period January–June 1993. The H field started increasing between midnight and sunrise, reaching a peak shortly before noon. The daily range of H was maximum during March and April and minimum during June. Regardless of the month, the range in H was significantly larger at ANC than at SLZ. The 27-day running mean of the range of H varied from 80 nT to 125 nT at SLZ and from 105 nT to 180 nT at ANC. The day-to-day values of the range of H showed very faithful variations at the two stations. The deviations of the daily range of H from its 27-day running mean values showed good correlation between the two stations. Some large storm-time effects were seen at both stations. The correlation was still significant, when data were corrected for Dst index values. It is suggested that the range in H at the two electrojet stations, separated by more than 2000 km, are affected by some common sources other than the ring current, which need to be identified. Spectral analysis of the range of H shows remarkable similarity at the two stations, with a dominant period of 15 days at both stations.

Day-to-day variability of the equatorial electrojet current in the South American sector

Abstract A comparison of the geomagnetic H field data at Ancon, Peru and Buriticupa, Brazil for the period December 1990 and January 1991 revealed the presence of a significant correlation in day-to-day variability in the solar daily variation of H at the two stations, which are separated by about 2000 km. It is suggested that the day-to-day variability in the time as well as in the magnitude of the daily peak of the H field at an equatorial electrojet station is due to the superimposition of a semi-diurnal wave of the electric field over the normal mean daily variation.

Magnetic storm effects at equatorial electrojet stations

Abstract It is shown that there are distinctly two different mechanisms for the interaction of solar wind with the earth’s magnetosphere to produce electric field in the ionospheric heights at low and middle latitudes. A persistent or slowly varying southward Interplanetary magnetic field i.e. negative IMF-Bz generates dawn to dusk electric field at polar latitudes and a westward (dusk to dawn) electric field at dayside electrojet region which is anti-Sq in direction. A rapid increase of IMF-Bz (northward turning) imposes a westward (dusk to dawn) electric field at all latitudes of the dayside hemisphere. The process involved is the imposition of -V × Bz electric field at the magnetosphere transmitted instantaneously to the magnetic equator through the polar latitudes. The changes in the H field at ground are largest at stations close to the magnetic equator and the midday longitudes. During magnetic storms, associated with the southward IMF-Bz, there are definite enhancements in the decrease of H field at the dayside equatorial electrojet stations. These changes may be coincident with the development of auroral or magnetospheric ring currents. These enhancements may be observed during the main phase as well as during the recovery phase of the magnetic storm, but the essential condition is that the IMF-Bz has to be steadily significant southward. Sometimes during the storm period abnormally large changes in H field at day side equatorial electrojet regions are observed associated with large sudden changes in IMF-Bz following the second mechanism of solar wind magnetospheric interaction. Thus the equatorial magnetic storm effects are due to combined effects of disturbance ring current, slow and steady IMF-Bz as well as due to sudden large changes in IMF-Bz.

Variability of horizontal component of geomagnetic element (H) with mean quiet-day variation

[1] The variability of Sq(H) with mean quiet-day variation at equatorial electrojet latitudes and other latitudes has been studied using the correlation between the hourly amplitudes of the H variations dH, at these stations. It was found that these hourly amplitudes of H under equatorial electrojet regions are well correlated with themselves. High significant correlation was established among them. On the other hand, low correlation was found among pairs of equatorial electrojet stations and other latitude stations not under the equatorial electrojet. It was discovered that most times, the variation in the current intensities of the worldwide part of Sq (WSq) and the equatorial electrojet (EEJ) have contrasting phases. It was concluded that the very low correlation coecients calculated and the contrasting phases of EEJ and WSq current intensities were due to the fact that changes in EEJ current intensity are controlled mainly by Ez, while changes in WSq current are driven mainly by Ey. INDEX TERMS: 2409 Ionosphere: Current systems; 2736 Magnetospheric Physics: Magnetosphere/ionosphere interactions; 2712 Magnetospheric Physics: Electric fields; KEYWORDS: Equatorial electrojet; Geomagnetic field; Current system.

Geomagnetic field variations at the equatorial electrojet station in Sri Lanka, Peredinia

Abstract. The paper discusses the variations of the horizontal (H), vertical (Z) and eastward (Y) components of the geomagnetic field at Peredinia (PRD), an electrojet station in Sri Lanka, with the time of the day, season, sudden commencement (SSC) and during geomagnetic storms. The daily variation of H showed a large peak around midday. The daily variation of Z appeared to be almost a time gradient curve of the daily variation of H, showing a maximum around 09:00 LT (75° EMT) when the H field was increasing fastest and not at noon when Δ H was the maximum. Storm time variation of H resembled the variation of the Dst index but that of Z showed a large minimum about 2-3h before the time of minimum Dst or at the time of maximum time gradient of Dst variation. These features are compared with corresponding variations at the equatorial stations Trivandrum (TRD) in India, and remarkable similarity in all observations is noticed at PRD and TRD. It is suggested that the observed abnormal features of Z variations at electrojet stations in India-Sri Lanka are due to (i) direct effect of the ionospheric electrojet current (ii) the induction effect of the image current by the average spatially extended conductivity region and (iii) the induction current in the local subsurface conductor. It is suggested that the conductor responsible for the observed features in Z in India and Sri Lanka has to have extended spatial domain to latitudes well south of India, rather than confined to narrow Palk Strait.

Electromagnetic induction by the equatorial electrojet

SUMMARY This paper discusses the effects of currents induced inside the Earth at equatorial latitudes due to the currents in the ionosphere and the magnetosphere. The horizontal (H), vertical (Z) and eastward (Y) components of the geomagnetic field at equatorial and low-latitude stations around the world are examined for effects due to solar daily (Sq) variations during normal as well as counter electrojet days, during solar flares, during storm sudden commencements (SSCs) and during the main phase of the magnetic storms. The Sq(Z) variations show an abnormally large positive peak at Indian electrojet stations and to a lesser extent at Koror in the forenoon hours when the temporal gradient of Sq(H) is largest. At Indian longitudes this abnormality is largest during equinoxes and December solstices. The nighttime bay disturbance, solar flares and SSC produce large impulses in the Z field at Indian stations and at Koror. The latitudinal extent of this abnormality is larger for events with shorter periods. The disturbance equatorial ring current produces a large decrease of Z field around the period in the middle of main phase of the storm when the Dst index is rapidly decreasing and not when Dst is most negative. A strong decrease in the Z field is observed at Yauca in the American sector during the main phase of the storm. The induction effects on the equatorial electrojet seem to be absent in central and eastern parts of South America, and in the African region. The significant induction effects observed in the recording of the Z field at Peredinia in Sri Lanka suggest a wide latitude of abnormal conductivity anomaly distribution in the Indo-Sri Lanka longitude sector. Our present understanding of the conductor being in Palk Strait between India and Sri Lanka needs to be revised on the basis of results described in this paper.

Electromagnetic induction due to solar flares at equatorial stations

The solar flare effects (sfe) in the horizontal ( H), vertical ( Z) and eastward ( Y) geomagnetic fields at the equatorial electrojet stations around the world operating during International Geophysical Year and International Geophysical Cooperation Year (IGY–IGC, 1957–59) period have been examined. The amplitude of sfe( H) at any station was maximum around midday hours. The amplitude of sfe( Z) showed an abnormally large positive value at Trivandrum in spite of it being only 0.3° south of the magnetic equator. The ratio of Δ Z/Δ H exceeded 1.0 in most of the cases, the mean value being 1.34. During counter electrojet period both Δ H and Δ Z were negative maintaining similar high Δ Z/Δ H values. These abnormal values of Δ Z at Trivandrum are due to induction of electrojet current in the conducting graben in Palk Strait, between India and Sri Lanka. The latitudinal extent of induction effects in sfe( Z) in India depends on the sharpness of the temporal growth of the flare.

Solar flare effects on the geomagnetic elements during normal and counter electrojet periods

The paper describes the study of solar flare effects (sfe) on horizontal (H), eastward (Y) and vertical (Z) components of the geomagnetic field at the Indo-USSR chain of magnetic observatories extending from the magnetic latitudes 0° to 45°N, a network not available any where else in the world. Events are selected when strong, normal and reversed (counter) equatorial electrojet are in existence as well as when only a partial counter electrojet is present. During a strong and normal electrojet event time, sfe consists of a positive impulse in H at all stations, the amplitude of H following the latitudinal variation similar to that of the quiet day monthly mean, Sq (H). The sfe in Y is negative at all the stations. Sfe in Z shows positive impulse at the four-electrojet stations and negative at other stations. During a counter electrojet period the effect of solar flare on H field is negative impulse at electrojet stations, positive at low latitude and again negative at stations north of Sq focus. Sfe in Y is small at all the equatorial nd negative at higher latitude stations. However, sfe (Z) is negative at the equatorial latitudes. During a partial counter electrojet period the observed effect is the combination of an increase of the planetary current component and the decrease of the electrojet component, giving rise to a negative impulse in H at equatorial stations and apositive impulse in H, increasing with increasing distance from the equator. These results are presented and discussed.

<i>Letter to the Editor:</i> Geomagnetic storm effects at low latitudes

Abstract. The geomagnetic horizontal (H) field from the chain of nine observatories in India are used to study the storm-time and disturbance daily variations. The peak decrease in storm-time variation in H showed significant enhancements at the equatorial electrojet stations over and above the normally expected decrease due to the ring current effects corrected for geomagnetic latitudes. The disturbance daily variation of H at equatorial stations showed a large decrease around midday hours over and above the usual dawn-maximum and dusk-minimum seen at any mid-latitude stations around the world. These slow and persistent additional decreases of H of disturbance daily variation at equatorial latitudes could be the effect of a westward electric field due to the Disturbance Ionospheric dynamo coupled with abnormally large electrical conductivities in the E region over the equator.Key words. Ionosphere (electric fields and currents) · Magnetospheric physics (electric fields; storms and substorms)

Meridional equatorial electrojet current in the American sector

Abstract. Huancayo is the only equatorial electrojet station where the daytime increase of horizontal geomagnetic field (H) is associated with a simultaneous increase of eastward geomagnetic field (Y). It is shown that during the counter electrojet period when ∆H is negative, ∆Y also becomes negative. Thus, the diurnal variation of ∆Y at equatorial latitudes is suggested to be a constituent part of the equatorial electrojet current system. Solar flares are known to increase the H field at an equatorial station during normal electrojet conditions (nej). At Huancayo, situated north of the magnetic equator, the solar flare effect, during nej, consists of positive impulses in H and Y and negative impulse in Z field. During counter electrojet periods (cej), a solar flare produces a negative impulse in H and Y and a positive impulse in Z at Huancayo. It is concluded that both the zonal and meridional components of the equatorial electrojet in American longitudes, as in Indian longitudes, flows in the same, E region of the ionosphere.Key words. Geomagnetism and paleomagnetism (dynamo theories) · Ionosphere (equatorial ionosphere; ionosphere disturbances)

Geomagnetic storm effects at low latitudes

The geomagnetic horizontal (H) field from the chain of nine observatories in India are used to study the storm-time and disturbance daily variations. The peak decrease in storm-time variation in H showed significant enhancements at the equatorial electrojet stations over and above the normally expected decrease due to the ring current effects corrected for geomagnetic latitudes. The disturbance daily variation of H at equatorial stations showed a large decrease around midday hours over and above the usual dawn-maximum and dusk-minimum seen at any mid-latitude stations around the world. These slow and persistent additional decreases of H of disturbance daily variation at equatorial latitudes could be the effect of a westward electric field due to the Disturbance Ionospheric dynamo coupled with abnormally large electrical conductivities in the E region over the equator.Key words. Ionosphere (electric fields and currents) · Magnetospheric physics (electric fields; storms and substorms)

Meridional equatorial electrojet current in the American sector

Huancayo is the only equatorial electrojet station where the daytime increase of horizontal geomagnetic field (H) is associated with a simultaneous increase of eastward geomagnetic field (Y). It is shown that during the counter electrojet period when ∆H is negative, ∆Y also becomes negative. Thus, the diurnal variation of ∆Y at equatorial latitudes is suggested to be a constituent part of the equatorial electrojet current system. Solar flares are known to increase the H field at an equatorial station during normal electrojet conditions (nej). At Huancayo, situated north of the magnetic equator, the solar flare effect, during nej, consists of positive impulses in H and Y and negative impulse in Z field. During counter electrojet periods (cej), a solar flare produces a negative impulse in H and Y and a positive impulse in Z at Huancayo. It is concluded that both the zonal and meridional components of the equatorial electrojet in American longitudes, as in Indian longitudes, flows in the same, E region of the ionosphere.Key words. Geomagnetism and paleomagnetism (dynamo theories) · Ionosphere (equatorial ionosphere; ionosphere disturbances)

Disturbance diurnal electric field in Indian and American equatorial electrojet regions

Abstract The yearly mean Disturbance Daily (SD) variation, i.e., solar daily variation on International Disturbed days (Sd) minus that on International Quiet days (Sq) of the geomagnetic H field at Huancayo, an equatorial electrojet station in American zone, for any of the years 1954–61 shows a dawn-maximum and a dusk-minimum as observed at any low and middle latitude station. Contrary to this, the SD(H) variation at Kodaikanal, an equatorial station in the Indian zone, shows a prominent minimum around noon hours besides the usual dawn-maximum and dusk-minimum for any of these years. The amplitude of SD(H) at Huancayo or at Kodaikanal decreases with the decreasing solar activity. Seasonally, SD(H) is larger during equinoctial than during solsticial months. For any particular season, the SD(H) averaged for all hours of the day is lower at Huancayo than at Kodaikanal, while the Sq(H) at Huancayo is always greater than the corresponding amplitude of Sq(H) at Kodaikanal. Thus the sources of electrojet electric fields on quiet and on disturbed days seem to be different and need to be identified.

Storm sudden commencements in geomagnetic H, y and Z fields at the Equatorial Electrojet Station, Annamalainagar

The signature of storm sudden commencements at the Equatorial Electrojet Station, Annamalainagar, are shown to consist of a positive impulse in horizontal field, H, and a negative impulse in eastward field, Y, in the same manner as the solar flare effect (sfe) at the same station. The signature of SSC in the vertical component consists of a positive impulse, opposite to the sfe impulse in Z. The amplitudes of SSC impulse in H and Y indicate a maximum around midday suggesting an equatorial electrojet effect on these. The SSC effects on the eastward field (Y) at equatorial electrojet stations consist of a global part due to the compression of the magnetosphere and another a localised effect due to the electric field communicated from the interaction of the solar wind with the interplanetary magnetic field Bz component to the equatorial latitudes.