scholarly journals Meridional equatorial electrojet current in the American sector

1999 ◽  
Vol 17 (2) ◽  
pp. 220-230 ◽  
Author(s):  
R. G. Rastogi
Keyword(s):  
Solar Flare ◽  
Geomagnetic Field ◽  
Current System ◽  
Equatorial Electrojet ◽  
Simultaneous Increase ◽  
Equatorial Station ◽  
Counter Electrojet ◽  
Negative Impulse ◽  
Electrojet Current ◽  
E Region

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)

scholarly journals An intense SFE and SSC event in geomagnetic <i>H</i>, <i>Y</i> and <i>Z</i> fields at the Indian chain of observatories

1997 ◽  
Vol 15 (10) ◽  
pp. 1301-1308 ◽  
Author(s):  
R. G. Rastogi ◽  
D. R. K. Rao ◽  
S. Alex ◽  
B. M. Pathan ◽  
T. S. Sastry
Keyword(s):  
Solar Flare ◽  
Geomagnetic Storm ◽  
Geomagnetic Field ◽  
Current System ◽  
Equatorial Electrojet ◽  
Start Time ◽  
Low Latitude ◽  
Ionospheric Current ◽  
Ionospheric Current System ◽  
Solar Flare Effects

Abstract. Changes in the three components of geomagnetic field are reported at the chain of ten geomagnetic observatories in India during an intense solar crochet that occurred at 1311 h 75° EMT on 15 June 1991 and the subsequent sudden commencement (SSC) of geomagnetic storm at 1518 h on 17 June 1991. The solar flare effects (SFE) registered on the magnetograms appear to be an augmentation of the ionospheric current system existing at the start time of the flare. An equatorial enhancement in ΔH due to SFE is observed to be similar in nature to the latitudinal variation of SQ (H) at low latitude. ΔY registered the largest effect at 3.6° dip latitude at the fringe region of the electrojet. ΔZ had positive amplitudes at the equatorial stations and negative at stations north of Hyderabad. The SSC amplitude in the H component is fairly constant with latitude, whereas the Z component again showed larger positive excursions at stations within the electrojet belt. These results are discussed in terms of possible currents of internal and external origin. The changes in the Y field strongly support the idea that meridional current at an equatorial electrojet station flows in the ionospheric dynamo, E.

Detection of radiation from a heated and modulated equatorial electrojet current system

Nature ◽  
1984 ◽  
Vol 311 (5982) ◽  
pp. 134-135 ◽  
Author(s):  
R. J. Lunnen ◽  
H. S. Lee ◽  
A. J. Ferraro ◽  
T. W. Collins ◽  
R. F. Woodman
Keyword(s):  
Current System ◽  
Equatorial Electrojet ◽  
Electrojet Current

scholarly journals The equatorial E-region and its plasma instabilities: a tutorial

2009 ◽  
Vol 27 (4) ◽  
pp. 1509-1520 ◽  
Author(s):  
D. T. Farley
Keyword(s):  
Current System ◽  
Three Dimensional ◽  
Plasma Instabilities ◽  
Basic Physics ◽  
Electrojet Current ◽  
Fluid Theory ◽  
E Region ◽  
Kinetic Effects ◽  
The One ◽  
Observational Techniques

Abstract. In this short tutorial we first briefly review the basic physics of the E-region of the equatorial ionosphere, with emphasis on the strong electrojet current system that drives plasma instabilities and generates strong plasma waves that are easily detected by radars and rocket probes. We then discuss the instabilities themselves, both the theory and some examples of the observational data. These instabilities have now been studied for about half a century (!), beginning with the IGY, particularly at the Jicamarca Radio Observatory in Peru. The linear fluid theory of the important processes is now well understood, but there are still questions about some kinetic effects, not to mention the considerable amount of work to be done before we have a full quantitative understanding of the limiting nonlinear processes that determine the details of what we actually observe. As our observational techniques, especially the radar techniques, improve, we find some answers, but also more and more questions. One difficulty with studying natural phenomena, such as these instabilities, is that we cannot perform active cause-and-effect experiments; we are limited to the inputs and responses that nature provides. The one hope here is the steadily growing capability of numerical plasma simulations. If we can accurately simulate the relevant plasma physics, we can control the inputs and measure the responses in great detail. Unfortunately, the problem is inherently three-dimensional, and we still need somewhat more computer power than is currently available, although we have come a long way.

scholarly journals Induction effects of geomagnetic disturbances in the geo-electric field variations at low latitudes

2017 ◽  
Vol 35 (1) ◽  
pp. 39-51 ◽  
Author(s):  
Vafi Doumbia ◽  
Kouadio Boka ◽  
Nguessan Kouassi ◽  
Oswald Didier Franck Grodji ◽  
Christine Amory-Mazaudier ◽  
...  
Keyword(s):  
Solar Flare ◽  
Electric Field ◽  
West Africa ◽  
Geomagnetic Storm ◽  
Geomagnetic Field ◽  
Equatorial Electrojet ◽  
Geomagnetic Disturbances ◽  
The North ◽  
Low Latitudes ◽  
Dip Equator

Abstract. In this study we examined the influences of geomagnetic activity on the Earth surface electric field variations at low latitudes. During the International Equatorial Electrojet Year (IEEY) various experiments were performed along 5° W in West Africa from 1992 to 1995. Among other instruments, 10 stations equipped with magnetometers and telluric electric field lines operated along a meridian chain across the geomagnetic dip equator from November 1992 to December 1994. In the present work, the induced effects of space-weather-related geomagnetic disturbances in the equatorial electrojet (EEJ) influence area in West Africa were examined. For that purpose, variations in the north–south (Ex) and east–west (Ey) components of telluric electric field were analyzed, along with that of the three components (H,  D and Z) of the geomagnetic field during the geomagnetic storm of 17 February 1993 and the solar flare observed on 4 April 1993. The most important induction effects during these events are associated with brisk impulses like storm sudden commencement (ssc) and solar flare effect (sfe) in the geomagnetic field variations. For the moderate geomagnetic storm that occurred on 17 February 1993, with a minimum Dst index of −110 nT, the geo-electric field responses to the impulse around 11:00 LT at LAM are Ex =  520 mV km−1 and Ey =  400 mV km−1. The geo-electric field responses to the sfe that occurred around 14:30 LT on 4 April 1993 are clearly observed at different stations as well. At LAM the crest-to-crest amplitude of the geo-electric field components associated with the sfe are Ex =  550 mV km−1 and Ey =  340 mV km−1. Note that the sfe impact on the geo-electric field variations decreases with the increasing distance of the stations from the subsolar point, which is located at about 5.13° N on 4 April. This trend does not reflect the sfe increasing amplitude near the dip equator due the high Cowling conductivity in the EEJ belt.

scholarly journals An investigation of solar flare effects on equatorial ionosphere and thermosphere using co-ordinated measurements

2019 ◽  
Vol 71 (1) ◽  
Author(s):  
S. G. Sumod ◽  
Tarun Kumar Pant
Keyword(s):  
Solar Flare ◽  
Equatorial Electrojet ◽  
Field Measurements ◽  
Equatorial Ionosphere ◽  
Electron Content ◽  
Total Electron ◽  
Equatorial Station ◽  
Solar Flare Effects ◽  
Coupling Processes ◽  
Class Flare

AbstractThe response of equatorial ionosphere–thermosphere system to the X3.8 solar flare of January 17, 2005 has been studied using the coordinated measurements of GPS-derived Total Electron Content (TEC), OI 630.0 nm dayglow and magnetic field measurements over a dip equatorial station Trivandrum (8.5° N, 77° E, dip 0.5° N), in India. It has been observed that Equatorial Electrojet (EEJ) as inferred using the ground-based magnetometers and GPS-derived TEC measurements show prompt enhancements during the peak flare, as expected. Interestingly, the temporal evolution of TEC at different latitudes revealed that the X3.8 class flare produced significant weakening of the plasma fountain and hence in the Equatorial Ionization Anomaly (EIA). Furthermore, the response of OI 630.0 nm dayglow during the flare is found to be strongly affected by the prevailing electrodynamics. The plausible physical mechanism for these effects is discussed in context of the current understanding of the neutral and electrodynamical coupling processes.

High-latitude crochet (Solar flare effect) as a trigger of pseud-substorm onset

2021 ◽  
Author(s):  
Masatoshi Yamauchi ◽  
Magnar Johnsen ◽  
Shin-Ichi Othani ◽  
Dmitry Sormakov
Keyword(s):  
Solar Flare ◽  
High Latitude ◽  
Current System ◽  
Geomagnetic Latitude ◽  
Geomagnetic Disturbance ◽  
Substorm Onset ◽  
Ionospheric Conductivity ◽  
New Type ◽  
E Region ◽  
Substorm Activity

&lt;p&gt;Solar flares are known to enhance the ionospheric electron density and thus influence the electric currents in the D- and E-region. &amp;#160;The geomagnetic disturbance caused by this current system is called a &quot;crochet&quot; or &quot;SFE (solar flare effect)&quot;. &amp;#160;Crochets are observed at dayside low-latitudes with a peak near the subsolar region (&quot;subsolar crochet&quot;), in the nightside high-latitude auroral region with a peak where the geomagnetic disturbance pre-exists during solar illumination (&quot;auroral crochet&quot;), and in the cusp (&quot;cusp crochet&quot;). &amp;#160;In addition, we recently found a new type of crochet on the dayside ionospheric current at high latitudes (European sector 70-75 geographic latitude/67-72 geomagnetic latitude) independent from the other crochets. &amp;#160;The new crochet is much more intense and longer in duration than the subsolar crochet and is detected even in AU index for about half the &gt;X2 flares despite the unfavorable latitudinal coverage of the AE stations (~65 geomagnetic latitude) to detect this new crochet (Yamauchi et al., 2020). &amp;#160;&lt;/p&gt;&lt;p&gt;The signature is sometime s seen in AL, causing the crochet signature convoluting with substorms. &amp;#160;From a theoretical viewpoint, X-flares that enhances the ionospheric conductivity may influence the substorm activity, like the auroral crochet. &amp;#160;To understand the substorm-crochet relation in the dayside, we examined SuperMAG data for cases when the onset of the substorm-like AL (SML) behavior coincides with the crochet. &amp;#160;We commonly found a large counter-clockwise &amp;#8710;B vortex centered at 13-15 LT, causing an AU peak during late afternoon and an AL peak near noon at higher latitudes than the high-latitude crochet. &amp;#160;In addition, we could recognize a clockwise &amp;#8710;B vortex in the prenoon sector, causing another poleward &amp;#8710;B, but this signature is not as clear as the afternoon vortex. &amp;#160;With such strong vortex features, it becomes similar to substorms except for its local time. &amp;#160;In some cases, the vortex expends to the nightside sector, where and when nightside onset starts, suggesting triggering of onset. &amp;#160;Thus, the crochet may behave like pseudo-onset at different latitude than midnight substorms, and may even trigger substorm onset.&lt;/p&gt;

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