scholarly journals Letter to the editor: Electric field fluctuations (25-35 min) in the midnight dip equatorial ionosphere

2000 ◽  
Vol 18 (2) ◽  
pp. 252-256 ◽  
Author(s):  
J. Hanumath Sastri ◽  
H. Luhr ◽  
H. Tachihara ◽  
T. -I. Kitamura ◽  
J. V. S. V. Rao
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Geomagnetic Latitude ◽  
Equatorial Ionosphere ◽  
Plasma Drift ◽  
F Region ◽  
Vertical Drift ◽  
Field Fluctuations ◽  
Dip Equator ◽  
Electric Fields And Currents

Abstract. Measurements with a HF Doppler sounder at Kodaikanal (10.2°N, 77.5°E, geomagnetic latitude 0.8°N) showed conspicuous quasi-periodic fluctuations (period 25-35 min) in F region vertical plasma drift, Vz in the interval 0047-0210 IST on the night of 23/24 December, 1991 (Ap = 14, Kp < 4-). The fluctuations in F region vertical drift are found to be coherent with variations in Bz (north-south) component of interplanetary magnetic field (IMF), in geomagnetic H/X components at high-mid latitude locations both in the sunlit and dark hemispheres and near the dayside dip equator, suggestive of DP2 origin. But the polarity of the electric field fluctuations at the midnight dip equator (eastward) is the same as the dayside equator inferred from magnetic variations, contrary to what is expected of equatorial DP2. The origin of the coherent occurrence of equatorial electric field fluctuations in the DP2 range of the same sign in the day and night hemispheres is unclear and merits further investigations.Key words: Ionosphere (electric fields and currents; equatorial ionosphere; ionosphere-magnetosphere interactions)

scholarly journals Impact of disturbance electric fields in the evening on prereversal vertical drift and spread F developments in the equatorial ionosphere

2018 ◽  
Vol 36 (2) ◽  
pp. 609-620 ◽  
Author(s):  
Mangalathayil A. Abdu ◽  
Paulo A. B. Nogueira ◽  
Angela M. Santos ◽  
Jonas R. de Souza ◽  
Inez S. Batista ◽  
...  
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Plasma Bubble ◽  
Large Variability ◽  
Plasma Drift ◽  
F Region ◽  
Vertical Drift ◽  
Spread F ◽  
The Impact ◽  
Magnetic Disturbances

Abstract. Equatorial plasma bubble/spread F irregularity occurrence can present large variability depending upon the intensity of the evening prereversal enhancement in the zonal electric field (PRE), that is, the F region vertical plasma drift, which basically drives the post-sunset irregularity development. Forcing from magnetospheric disturbances is an important source of modification and variability in the PRE vertical drift and of the associated bubble development. Although the roles of magnetospheric disturbance time penetration electric fields in the bubble irregularity development have been studied in the literature, many details regarding the nature of the interaction between the penetration electric fields and the PRE vertical drift still lack our understanding. In this paper we have analyzed data on F layer heights and vertical drifts obtained from digisondes operated in Brazil to investigate the connection between magnetic disturbances occurring during and preceding sunset and the consequent variabilities in the PRE vertical drift and associated equatorial spread F (ESF) development. The impact of the prompt penetration under-shielding eastward electric field and that of the over-shielding, and disturbance dynamo, westward electric field on the evolution of the evening PRE vertical drift and thereby on the ESF development are briefly examined. Keywords. Ionosphere (ionospheric irregularities)

scholarly journals Effects of solar eclipse on the electrodynamical processes of the equatorial ionosphere: a case study during 11 August 1999 dusk time total solar eclipse over India

2002 ◽  
Vol 20 (12) ◽  
pp. 1977-1985 ◽  
Author(s):  
R. Sridharan ◽  
C. V. Devasia ◽  
N. Jyoti ◽  
Diwakar Tiwari ◽  
K. S. Viswanathan ◽  
...  
Keyword(s):  
Electric Fields ◽  
Solar Eclipse ◽  
Equatorial Ionosphere ◽  
Hf Radar ◽  
F Region ◽  
Large Enhancement ◽  
Temporal Structures ◽  
E Region ◽  
Field Lines ◽  
Electric Fields And Currents

Abstract. The effects on the electrodynamics of the equatorial E- and F-regions of the ionosphere, due to the occurrence of the solar eclipse during sunset hours on 11 August 1999, were investigated in a unique observational campaign involving ground based ionosondes, VHF and HF radars from the equatorial location of Trivandrum (8.5° N; 77° E; dip lat. 0.5° N), India. The study revealed the nature of changes brought about by the eclipse in the evening time E- and F-regions in terms of (i) the sudden intensification of a weak blanketing ES-layer and the associated large enhancement of the VHF backscattered returns, (ii) significant increase in h' F immediately following the eclipse and (iii) distinctly different spatial and temporal structures in the spread-F irregularity drift velocities as observed by the HF radar. The significantly large enhancement of the backscattered returns from the E-region coincident with the onset of the eclipse is attributed to the generation of steep electron density gradients associated with the blanketing ES , possibly triggered by the eclipse phenomena. The increase in F-region base height immediately after the eclipse is explained as due to the reduction in the conductivity of the conjugate E-region in the path of totality connected to the F-region over the equator along the magnetic field lines, and this, with the peculiar local and regional conditions, seems to have reduced the E-region loading of the F-region dynamo, resulting in a larger post sunset F-region height (h' F) rise. These aspects of E-and F-region behaviour on the eclipse day are discussed in relation to those observed on the control day.Key words. Ionosphere (electric fields and currents; equatorial ionosphere; ionospheric irregularities)

scholarly journals Equatorial night-time F-region zonal electric fields

1995 ◽  
Vol 13 (8) ◽  
pp. 871-878 ◽  
Author(s):  
S. S. Hari ◽  
B. V. Krishna Murthy
Keyword(s):  
Seasonal Variation ◽  
Electric Field ◽  
Electric Fields ◽  
Night Time ◽  
Equatorial Station ◽  
F Region ◽  
Vertical Drift ◽  
Longitudinal Gradients ◽  
Cycle Maximum ◽  
E Region

Abstract. Night-time F-region vertical electrodynamic drifts at the magnetic equatorial station, Trivandrum are obtained for a period of 2 years, 1989 and 1990 (corresponding to solar cycle maximum epoch), using ionosonde h'F data. The seasonal variation of the vertical drift is found to be associated with the longitudinal gradients of the thermospheric zonal wind. Further, the seasonal variation of the prereversal enhancement of the vertical drift is associated with the time difference between the sunset times of the conjugate E-regions (magnetic field line linked to F-region) which is indicative of the longitudinal gradients of the conductivity (of the E-region). The vertical drifts and the causative zonal electric fields at Trivandrum are compared with those at Jicamarca and F-region zonal electric field models. It is seen that the night-time downward drift (as also the causative westward electric field) at Jicamarca is greater than that at Trivandrum. The prereversal enhancement of the drift is greater at Jicamarca than at Trivandrum during the summer and the equinoxes, whereas during the winter the opposite is the case.

scholarly journals Morphological aspects of a new type of counter electrojet event

1999 ◽  
Vol 17 (2) ◽  
pp. 210-219 ◽  
Author(s):  
R. G. Rastogi
Keyword(s):  
Electric Fields ◽  
Current System ◽  
Equatorial Ionosphere ◽  
Geomagnetic Disturbances ◽  
Counter Electrojet ◽  
F Region ◽  
New Type ◽  
Northern Winter ◽  
Sporadic E ◽  
Electric Fields And Currents

Abstract. The study describes the time and space morphologies of a rather new type of counter electrojet event on the basis of data from the excellent chain of magnetic and ionospheric observatories along the Indo-Russian longitude sector. Abnormally large westward currents are observed during almost the whole of the daytime hours on a series of days. These events do not form any vortices in the current system and do not apparently seem to be associated with tidal effects or any solar magnetosphere events or geomagnetic disturbances. The existence of a westward electric field over the equatorial ionosphere has been confirmed by the absence of an equatorial type of sporadic E in the ionograms at Thumba precisely during the periods when ∆H at Trivandrum minus ∆H at Alibag is negative. The equatorial F region anomaly was also absent on the counter electrojet day. Such counter electrojet events during the northern winter months of low solar activity years are suggested to be the result of the modified wind system in the ionosphere associated with stratospheric warming events.Key words. Geomagnetism and paleomagnetism (time variations · diurnal to secular) · Ionosphere (electric fields and currents; equatorial ionosphere)

scholarly journals Electrodynamics of the equatorial F-region ionosphere during pre-sunrise period

2009 ◽  
Vol 27 (1) ◽  
pp. 107-111 ◽  
Author(s):  
S. R. Prabhakaran Nayar ◽  
T. J. Mathew ◽  
C. V. Sreehari ◽  
S. G. Sumod ◽  
C. V. Devasia ◽  
...  
Keyword(s):  
Electric Field ◽  
Doppler Radar ◽  
Striking Feature ◽  
Plasma Drift ◽  
F Region ◽  
Vertical Drift

Abstract. The electrodynamics of the pre-sunrise equatorial F-region is investigated using HF Doppler radar and digital ionosonde. The observations are limited to those days for which the radar probing frequency is below the foF2 value. The ionosphere observation using HF Doppler radar exhibit interesting features during pre-sunrise period similar to the post sunset pre-reversal enhancement. The most striking feature observed during pre-sunrise period is the sudden downward excursion in the vertical drift around local sunrise followed by an upward turning. Pre-sunrise observations of vertical plasma drift and the sunrise downward excursion followed by an upward turning after the ground sunrise related to the zonal electric field at the equatorial F-region are the most significant results not reported earlier.

scholarly journals Response of equatorial ionosphere to episodes of asymmetric ring current activity

1997 ◽  
Vol 15 (10) ◽  
pp. 1316-1323 ◽  
Author(s):  
J. H. Sastri ◽  
M. A. Abdu ◽  
J. H. A. Sobral
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Ring Current ◽  
Opposite Polarity ◽  
Equatorial Region ◽  
Local Times ◽  
High Time Resolution ◽  
Plasma Drift ◽  
F Region ◽  
Current Events

Abstract. We present the characteristics of the response of equatorial ionospheric zonal electric field and F-region plasma density to the asymmetric ring current intensifications that occurred in succession on 16 December 1991, corresponding to the STEP/EITS-2 campaign period. The study is based on high-time- resolution (1-min) data of asymmetic ring current indices, ASY(H/D) and F-region vertical plasma drift, Vz measurements at Kodaikanal (10.25°N; 77.5°E; dip 4°), India and quarter-hourly ionosonde data of Fortaleza (4°S; 322°E; dip –9°), Brazil. It is shown that short-lived disturbances in F-layer vertical plasma drift, Vz and height (h'F/hpF2) indicative of westward and eastward electric fields prevail simultaneously in the dusk (18–21 LT) and predawn (02–05 LT) sectors, respectively, in association with the decay phase of asymmetic ring current events. Electric fields of opposite polarity do also seem to manifest at these local times, particularly in the early-morning sector in conjunction with the intensification of the asymmetric ring current. At a given location, electric field disturbances associated with individual asymmetric ring current events are thus bipolar in nature, with fields of opposite polarity during the growth and decay phases. The nature and polarity structure of the observed electric field disturbances are in agreement with the theoretical/model predictions of prompt penetration of high-latitude electric fields to the equatorial region.

scholarly journals Method of characteristics in spherical geometry applied to a Harang-discontinuity situation

1998 ◽  
Vol 16 (4) ◽  
pp. 413-424 ◽  
Author(s):  
O. Amm
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Method Of Characteristics ◽  
Geomagnetic Latitude ◽  
Spherical Geometry ◽  
Magnetic Disturbance ◽  
Time Step ◽  
Ratio Distribution ◽  
Hall Conductance ◽  
Primary Output

Abstract. The method of characteristics for obtaining spatial distributions of ionospheric electrodynamic parameters from ground-based spatial observations of the ground magnetic disturbance and the ionospheric electric field is presented in spherical geometry. The method includes tools for separation of the external magnetic disturbance, its continuation to the ionosphere, and calculation of ionospheric equivalent currents. Based on these and the measured electric field distribution, the ionospheric Hall conductance is calculated as the primary output of the method. By estimating the Hall- to-Pedersen conductance ratio distribution, the remaining ionospheric electrodynamic parameters are inferred. The method does not assume ∇×E=0 to allow to study time-dependent situations. The application of this method to a Harang discontinuity (HD) situation on 27 October 1977, 17:39 UT, reveals the following: (1) The conductances at and north of the HD are clearly reduced as compared to the eastern electrojet region. (2) Plasma flow across the HD is observed, but almost all horizontal current is diverted into upward-flowing field-aligned currents (FACs) there. (3) The FACs connected to the Hall currents form a latitudinally aligned sheet with a magnitude peak between the electrically and magnetically defined HD, where break-up arcs are often observed. Their magnitude is larger than that of the more uniformly distributed FACs connected to the Pedersen currents. They also cause the southward shift of the magnetically defined HD with respect to the electrically defined one. (4) A tilt of the HD with respect to geomagnetic latitude as proposed by an earlier study on the same event, which used composite vector plot technique, and by statistical studies, is not observed in our single time-step analysis.Key words. Ionosphere · Electric fields and currents · Instruments and techniques · Magnetospheric physics · Current systems

F-region nocturnal zonal plasma drift velocities of the brazilian equatorial ionosphere during maximum solar

2005 ◽  
Author(s):  
Daniela Cristina Santana Arruda ◽  
José Humberto Andrade Sobral ◽  
Mangalathayil Ali Abdu ◽  
Vivian Moreira de Castilho and Ricardo Arlen Buriti
Keyword(s):  
Equatorial Ionosphere ◽  
Plasma Drift ◽  
F Region

scholarly journals Simultaneous optical, CUTLASS HF radar, and FAST spacecraft observations: signatures of boundary layer processes in the cusp

2004 ◽  
Vol 22 (2) ◽  
pp. 511-525 ◽  
Author(s):  
K. Oksavik ◽  
F. Søraas ◽  
J. Moen ◽  
R. Pfaff ◽  
J. A. Davies ◽  
...  
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Broad Band ◽  
Spectral Width ◽  
Hf Radar ◽  
Optical Data ◽  
Low Energy Electrons ◽  
Field Lines ◽  
Auroral Phenomena ◽  
Electric Fields And Currents

Abstract. In this paper we discuss counterstreaming electrons, electric field turbulence, HF radar spectral width enhancements, and field-aligned currents in the southward IMF cusp region. Electric field and particle observations from the FAST spacecraft are compared with CUTLASS Finland spectral width enhancements and ground-based optical data from Svalbard during a meridional crossing of the cusp. The observed 630nm rayed arc (Type-1 cusp aurora) is associated with stepped cusp ion signatures. Simultaneous counterstreaming low-energy electrons on open magnetic field lines lead us to propose that such electrons may be an important source for rayed red arcs through pitch angle scattering in collisions with the upper atmosphere. The observed particle precipitation and electric field turbulence are found to be nearly collocated with the equatorward edge of the optical cusp, in a region where CUTLASS Finland also observed enhanced spectral width. The electric field turbulence is observed to extend far poleward of the optical cusp. The broad-band electric field turbulence corresponds to spatial scale lengths down to 5m. Therefore, we suggest that electric field irregularities are directly responsible for the formation of HF radar backscatter targets and may also explain the observed wide spectra. FAST also encountered two narrow highly structured field-aligned current pairs flowing near the edges of cusp ion steps. Key words. Ionosphere (electric fields and currents). Magnetosphere physics (magnetopause, cusp, and boundary layers; auroral phenomena)

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