Equatorial electrojet—II. Use of the model to study the equatorial ionosphere

Richmond, A. D.

doi:10.1016/0021-9169(73)90008-1

Cited by 91 publications

(29 citation statements)

References 39 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The quiet-day curve in Figure 2 shows the usual steady decrease of H field in the afternoon due to solar zenith angle-dependent variation of ionospheric conductivity. Note that this feature is more prominent at stations close to the dip equator (TRD, KOD, and ANN) than at stations farther away (ABG and UJJ) because of the well-known contribution of the equatorial electrojet [e.g., Matsushita, 1967;Richmond, 1973]. In contrast, on August 19 a distinct positive baylike increase of H field (marked by arrows in Figure 2) is seen at all the stations from Trivandrum to Ujjain starting around 0730 UT, i.e., during the initial stage of the substorm growth phase.…”

Section: Event Of August 19 1978mentioning

confidence: 99%

Daytime equatorial geomagnetic H field response to the growth phase and expansion phase onset of isolated substorms: Case studies and their implications

Sastri¹,

Rao²,

Rao³

et al. 2001

J. Geophys. Res.

View full text Add to dashboard Cite

Abstract. Observations are presented from the Indian magnetometer network (dipole latitude range 1.2øS to 13.5øN) of short-lived (<1 hr) disturbances in the daytime equatorial geomagnetic H field associated with specific phases of isolated substorms. Three well-documented substorms are examined here, of which the expansion onset of each is closely associated with sudden transitions of interplanetary magnetic field (IMF) Bz/By after a >40-min interval of southward Bz. A positive baylike perturbation is found to prevail during the substorm growth phase, followed by a negative baylike disturbance starting precisely at the onset of expansion phase activity. The amplitude of the positive as well as negative bay-type disturbance showed a clear-cut enhancement at locations inside the equatorial electrojet belt when compared with stations away from the electrojet influence, indicative of a significant contribution of ionospheric currents to the bays. This pattern of response, which is found in two out of the three events studied, constitutes the first-time evidence for the occurrence of equatorial H field perturbations related to the growth phase as well as the expansion phase onset for individual substorms. The H field perturbations are suggested to be signatures of prompt penetration by electric fields associated with rapid changes in magnetospheric convection brought about by the swift transitions in the IMF Bz, before shielding by the ring current becomes effective. In the third event, where the growth phase is weak and prolonged, there is no perceptible simultaneous disturbance in the equatorial H field, while the expansion phase onset is associated with a positive bay of very small amplitude (<4 nT).

show abstract

Section: Event Of August 19 1978mentioning

confidence: 99%

Daytime equatorial geomagnetic H field response to the growth phase and expansion phase onset of isolated substorms: Case studies and their implications

Sastri¹,

Rao²,

Rao³

et al. 2001

J. Geophys. Res.

View full text Add to dashboard Cite

show abstract

“…(5), one can see that when the primary zonal electric field E 0 does not vary with altitude, the current J X must have a height variation similar to that of the Cowling conductivity. But in-situ rocket observations of currents from the equatorial stations in India and Peru show that vertical profiles of J X deviate significantly from that of σ C Subbraya et al, 1972;Richmond, 1973;Muralikrishna, 1975;Pfaff et al, 1997;Prakash and Subbraya, 1999). Subbaraya et al (1972) estimated the elctrojet current intensity from rocket measurements of the total magnetic field using proton precession magnetometers, and the electron density by Langmuir probes from Thumba (magnetic dip 0 • 47 S), India.…”

Section: Introductionmentioning

confidence: 98%

“…It is known that the presence of meridional currents in this region can modify this simple image (Sugiura and Porus, 1969). Several modifications have later been suggested to modify this simple picture (see Richmond, 1991). From Eq.…”

Section: Introductionmentioning

confidence: 99%

On the height variation of the E-region cowling conductivity – effect of charged dust particles

Muralikrishna

Kulkarni

2006

Ann. Geophys.

View full text Add to dashboard Cite

Abstract. Height profiles of the Cowling conductivity in the electrojet region, estimated using the atmospheric parameters given by the existing models like CIRA or MSIS and measured electron density profiles, consistently show the heights of the electrojet current intensity peak to be more than 3 km below those estimated from in-situ measurements using magnetometers on board sounding rockets. Kulkarni and Muralikrishna (2005) attempted to explain this to be due to the effect of neutral dust particles. They reported that neutral dust particles, when they exist in sufficient numbers, can modify the collision parameters, especially in the lower E-region, where dust particles of meteoric origin are known to exist in large numbers, and thereby can modify the Cowling conductivity profile in the electrojet region. This work is extended here to include the effect of charged dust particles. Dust particles can become charged negatively by the attachment of ambient free electrons, and can thus reduce the number density of free electrons especially below the electrojet peak. This can alter the vertical profile of the east-west Hall current driven by the vertical Hall polarization field, thereby causing a net reduction in the electrojet current. Such a decrease in the electrojet current may be observed on the ground magnetograms. This mechanism, as proposed here, can operate only during periods of strong meteor shower activity, when the dust particle density at the assumed deposit height of 103 km can reach extreme values (for example, 5×10 4 cm −3 of 1-µm diameter dust particles). Such a dense dust layer may even cause a reversal in the normally upward vertical Hall polarization field, within the dust layer, causing a reversal of the electrojet currents below the current peak.

show abstract

“…Ideally, we could use values from data gathered by rocket instruments but, in an active electrojet, these small values have proven nearly impossible to measure. Instead, we follow the example of Richmond (1973b) and solve for typical values for E x and U x by introducing known electrojet current profiles into Eqs. (10) and (22).…”

mentioning

confidence: 99%

Evidence and effects of a wave-driven nonlinear current in the equatorial electrojet

Oppenheim

1997

Ann. Geophys.

View full text Add to dashboard Cite

Abstract. Ionospheric two-stream waves and gradientdrift waves nonlinearly drive a large-scale (D.C.) current in the E-region ionosphere. This current flows parallel to, and with a comparable magnitude to, the fundamental Pedersen current. Evidence for the existence and magnitude of wave-driven currents derives from a theoretical understanding of E-region waves, supported by a series of nonlinear 2D simulations of two-stream waves and by data collected by rocket instruments in the equatorial electrojet. Wave-driven currents will modify the large-scale dynamics of the equatorial electrojet during highly active periods. A simple model shows how a wave-driven current appreciably reduces the horizontally flowing electron current of the electrojet. This reduction may account for the observation that type-I radar echoes almost always have a Doppler velocity close to the acoustic speed, and also for the rocket observation that electrojet regions containing gradientdrift waves do not appear also to contain horizontally propagating two-stream waves. Additionally, a simple model of a gradient-drift instability shows that wavedriven currents can cause nonsinusoidal electric fields similar to those measured in situ.

show abstract

Equatorial electrojet—II. Use of the model to study the equatorial ionosphere

Cited by 91 publications

References 39 publications

Daytime equatorial geomagnetic H field response to the growth phase and expansion phase onset of isolated substorms: Case studies and their implications

Daytime equatorial geomagnetic H field response to the growth phase and expansion phase onset of isolated substorms: Case studies and their implications

On the height variation of the E-region cowling conductivity – effect of charged dust particles

Evidence and effects of a wave-driven nonlinear current in the equatorial electrojet

Contact Info

Product

Resources

About