Partial Counter Electrojet Research Articles

Quantifying the EEJ current with ground-based ionosonde inferred vertical E × B drifts in the morning hours over Ilorin, West Africa

The relationship between the ground-based inferred vertical E × B drifts, Vz, and the magnetic equatorial electrojet current during the year of solar minima was presented. Both the diurnal and seasonal Vz variations are positively directed during the daytime and negative at nighttime. The evening time pre-reversal enhancement occurs around 19:00 LT. The fairly strong linear relationship between the electrojet current strength and Vz exhibited higher correlations during the daytime (06:00–16:00 LT). The maximum morning time proxy parameter described by E = [d (ΔH ILR)/dt]max in the morning hours, indicating the east-west electric field in the EEJ, corresponds reasonably well with the E × B drift and, hence, can be used as a proxy parameter for representing Vz in the morning hours. The daytime EEJ magnitude seasonal changes are connected with a change in conductivity emerging from the action of turbulence and divergence of momentum flux. These waves above the dynamo region are suggested to lead to partial counter electrojet during the equinoctial months.

Unique examples of solar flare effects in geomagnetic H field during partial counter electrojet along CPMN longitude sector

Yamazaki et al. (2009) reported two strong negative crochets during midday (solar flares on 8 June 2000, 3 July 2002), along the Circum-pan pacific magnetometers network (CPMN). The association of these with equatorial counter electrojet was doubted and suggestion was made to investigate the cause of these unique events. Present investigations were motivated by their paper. In this paper, detailed examination of geomagnetic data for the two events is made at all stations within 75°E (Indian) and 160°E (western Pacific) longitude sectors. Latitudinal variations of ΔH on 18 June 2000 showed negative gradient towards the dip equator suggesting a partial counter electrojet both in the Indian and CPMN sectors. A partial counter electrojet also existed from morning to 1300 LT in the western Pacific sector on 3 July 2002. There are two current sheets over the equatorial electrojet region, one at higher level flowing eastward associated with global Sq current system and another intense current layer at 107 km, flowing eastward during normal and westward during partial/full counter electrojet periods. Solar flares are likely to affect the electrojet current more strongly as a result of the absorption, in the lower E-region, of the shorter wavelength solar X-rays flare spectrum.

Evolution of equatorial irregularities under varying electrodynamical conditions: A multitechnique case study from Indian longitude zone

A comprehensive multitechnique study on the postsunset evolutions of equatorial ionization anomaly (EIA) and equatorial plasma density irregularities in the context of the varying electrodynamical conditions under normal equatorial electrojet (EEJ), complete and partial counter electrojet (CEJ) events is presented from the Indian longitude zone. The study involves analysis of scintillation data at VHF (250 MHz) and GPS L1 (1575.42 MHz) frequency, ionosonde data, magnetometer data along with global ionospheric maps (GIMs) of total electron content (TEC) for the vernal equinoctial months (March–April) of 2011. The investigation reveals inefficiency of the noontime peak EEJ to dictate the day‐to‐day variability of postsunset irregularity phenomena. Intensification of EEJ after ∼1530 IST (Indian standard time) on normal EEJ days and significantly enhanced residual fields presumably due to CEJ event after ∼1700 IST on complete and partial CEJ days are found to be associated with the resurgence of EIA and evolution of postsunset irregularities. The results are discussed in terms of superposition effects of electric fields arising from E‐ and F‐ region dynamos.

Highly localized cooling in daytime mesopause temperature over the dip equator during counter electrojet events: First results

The first observations of lowering of mesopause temperature during Counter Electrojet (CEJ) events over a narrow region of ∼ ±150 km centered at around magnetic equator are presented. The daytime mesopause temperature is measured over Trivandrum (8.5°N; 77°E; dip lat. 0.5°N), India using the ground based Multiwavelength Dayglow Photometer. The unique meridional scanning capability of the instrument is extensively used in this study. A lowering of temperature by as much as ∼25 K has been observed during certain CEJ events, which includes a few partial CEJs. The gravity wave tidal interaction through vertically upward wind is proposed to be manifesting as lowering in the mesopause temperature and also as CEJ. These observations are ‘new’ and address to the issues concerning the vertical coupling processes prevailing in the equatorial Mesosphere Lower Thermosphere Ionosphere (MLTI) region.

Response of the equatorial electrojet to solar flare related X-ray flux enhancements

Abstract The response of ionospheric E-region electric fields and currents to solar flare related X-ray flux enhancements are studied at the magnetic equatorial location of Trivandrum (8.5°N, 77°E; dip 0.5°N) using VHF (54.95 MHz) coherent backscatter radar observations in the altitude region of 95–110 km conducted during daytime. The amplitude of the Solar Flare Effects (SFE) observed in the earth’s magnetic field variations at Trivandrum have been examined in relation to that at Alibag and it is found that the ratio of the SFE amplitudes at the two stations lies in the range of 1.8–2.6. The backscattered power of the VHF radar showed a substantial reduction during the peak phase of all the strong X-rank flares studied. It has also been observed that there is a sharp fall in the ratio of the field line integrated Hall conductivity (σ2) to the field line integrated Pedersen conductivity (σ1) in the dynamo region "Equation missing" during strong flare times in relation to normal times. The time variations of mean Doppler frequency (f D ) of the backscattered signals have been observed to indicate a fall close to the peak phase of the strong flare events. Another new result is the radar observed presence of westward electric field for a long duration of 2–3 hours during a partial counter electrojet (CEJ) event that occurred on one of the days (8 July 1992) studied. The implications of the observations are discussed in detail.

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.

Solar flare effects on zonal and meridional currents at the equatorial electrojet station, Annamalainagar

During the normal electrojet period, a solar flare produces a positive change in the horizontal ( H) field, negative changes in the eastward ( Y) field and a negative change in the vertical ( Z) field at a northern electrojet station. On average, the ΔY is about 40% of ΔH. During a counter electrojet period, ΔH, due to a solar flare, is negative and ΔY and ΔZ are positive. During a partial counter electrojet period, ΔH may be smaller at equatorial stations compared with other low latitude stations, and ΔY may be positive, or sometimes of very small magnitude. The observed change of ΔY at an electrojet station is suggested to be the combined effect of the flare on the associated Sq current system and on electrojet related meridional currents. These data confirm the seat of the equatorial meridional current to be in the ionospheric E layer.

Equatorial electrojet reversals and their relation to polar cusp movements during geomagnetic storms

Using ground based magnetic observations, Mukunda Rao et al. have shown that most of the changes in the electrojet during a partial counter-electrojet observed through backscatter recordings at Thumba are also indicated by a simple parameter δ H ST −( H equat−H low lat) Storm Day −( H equat−H low lat)Mean of IQ days In this report ΔH ST is applied to the storm events of 17–19 Sept. 1979 and 16 Feb. 1980. Both the events register a close correlation between ΔH ST variations and the polar cusp movement, similar to those shown by back-scatter radar observations. Thus it appears that the ground based magnetic observations at the equator can also be used as a relatively simple and inexpensive means of studying polar cusp movements.

Manifestations of short-period electric field fluctuations in the equatorial lower thermosphere

Measurements (≏90h) of phase path, P of lower F-region (∼ 200km) reflections at normal incidence over Kodaikanal (dip 3.0°N) revealed the time rate of change of phase path, Ṗ (Doppler frequency shift, Δf) to undergo quasi-periodic fluctuations quite regularly during the day time. The changes in Ṗ which have peak-to-peak amplitudes of 6 to 30 ms−1 (0.1-0.5Hz in Δf) exhibit quasi-periods in the band 60-600s, comprising of two overlapping spectral domains: the shorter-period components (T < 240s) and the longer-period components (T > 300s). The spectral content of the variations in Ṗ is found to depend on the ambient equatorial electrojet strength and associated ionospheric conditions in that, while the longerperiod components persist almost all the time, the shorter-period components tend to cease during the times of disappearance of equatorial sporadic-E (Esq) on ionograms (partial counter-electrojet). Perturbations in the F-region vertical plasma drift, VzF are considered to be primarily responsible for the observed changes in Ṗ, particularly the longer-period (T > 300s) fluctuations. Correlative and visual studies of the simultaneous data (≏ 52h) of phase path at Kodaikanal and of ground level geomagnetic micropulsations at Trivandrum (located similar 200km south of Kodaikanal, dip 0.6°S) showed the absence of a persistent and clear-cut association of the fluctuations in Ṗ with Pc4/Pc5 micropulsations, indicating that hydromagnetic waves are not a primary source of the VzF pulsations. It is suggested that the longer-period (300 < T < 600s) fluctuations in VzF are due to gravity waves related changes in the east-west electric field at E-region altitudes outside the electrojet belt, and mapped along the field lines to F-region levels over Kodaikanal.

Phase variability of Sq (H) on normal quiet days in the equatorial electrojet region

Summary. From a study of ‘abnormal quiet days’ (AQDs) at equatorial latitudes it was found earlier (Sastri) that the occurrence of an abnormal Sq (H) phase confined to the equatorial electrojet belt is closely associated with the incidence of complete or partial counter-electrojet (CEJ) conditions (marked daytime depressions in the H field in the electrojet region) for about 5 hr around the normal time interval of the diurnal maximum of the H field. In this paper, we investigate the causative mechanism of the Sq(H) phase variability on ‘normal quiet days’ (NQDs), defined as days on which the diurnal maximum of the H field occurs in the time interval 0930-1230 LT, in the equatorial electrojet belt using published geomagnetic data of stations in the Indian equatorial region. It is found that much of the phase variability of Sq(H) on NQDs may be caused by the influence of southward (negative) perturbation fields in the H component, similar in nature to those associated with AQDs but of a much smaller amplitude, close to the usual time of the diurnal maximum of the H field. The perturbation fields are noticed to be essentially of the ionospheric dynamo region origin. Possible mechanisms that might give rise to the observed perturbation fields are discussed.

Equatorial enhancement of SSC amplitudes: Solar activity dependence and effect of electric field.

Characteristics of SSC amplitude at low and equatorial latitudes are studied using the data of 332 events observed simultaneously at three stations in the Indian region during the period 1958-1973. It is shown that during daytime both SSC amplitude in H and its equatorial enhancement increase with increased solar activity. During nighttime also the SSC amplitudes are found to vary with solar activity. The daytime equatorial enhancement of SSC's, which is attributed to the currents in the ionospheric E-layer, shows much sharper variation with solar activity than that shown by conductivity in that layer or the jet current intensity. SSC's which occurred during partial counter electrojet events are examined to determine the effect of change in an ambient electric field on their amplitudes. It is found that a westward ambient electric field leads to a reduction in the equatorial enhancement.

Ionospheric VHF scattering near the magnetic equator during partial counter electrojet

During periods of partial counter electrojet, i.e. when ΔH at an equatorial station is positive but lees than ΔH at a non-equatorial low latitude station, the scatter echoes of VHP radio wares from the E-region of the ionosphere are shown to disappear. These events are suggested due to simultaneous flow of eastward current near the peak ionication level of the E-region and the westward current at the base of the E-region.

Solar flare effects in equatorial counter electrojet currents

THE solar flare effect on the horizontal component of the geomagnetic field (H) during the period of counter equatorial electrojet current is characterised by a negative crochet (decrease of the H field) at an equatorial electrojet station and a positive crochet (increase of H field) at a low latitude station outside the electrojet belt. During the period of partial counter electrojet, the crochet in H may be positive at all low latitude stations but the amplitude decreases at stations nearer to the equator. We explain this as the combined effect of the solar flare on the normal eastward currents over the Equator associated with Sq current system (around 107–110 km) as well as on the westward counter electrojet current (∼ 100 km) both flowing simultaneously over the low latitude stations, while at stations outside the equatorial region the solar flare effect is due to only the eastward Sq currents. (The Sq currents are currents in the upper atmosphere arising from convective motion through the geomagnetic field1,2.)