scholarly journals Observational evidence for the plausible linkage of Equatorial Electrojet (EEJ) electric field variations with the post sunset F-region electrodynamics

2009 ◽  
Vol 27 (11) ◽  
pp. 4229-4238 ◽  
Author(s):  
V. Sreeja ◽  
C. V. Devasia ◽  
◽  
Keyword(s):  
Observational Study ◽  
Electric Field ◽  
Solar Maximum ◽  
Equatorial Electrojet ◽  
Observational Evidence ◽  
Related Parameter ◽  
F Region ◽  
Seasonal Characteristics ◽  
Vertical Drift ◽  
Spread F

Abstract. The paper is based on a detailed observational study of the Equatorial Spread F (ESF) events on geomagnetically quiet (Ap≤20) days of the solar maximum (2001), moderate (2004) and minimum (2006) years using the ionograms and magnetograms from the magnetic equatorial location of Trivandrum (8.5° N; 77° E; dip lat ~0.5° N) in India. The study brings out some interesting aspects of the daytime Equatorial Electrojet (EEJ) related electric field variations and the post sunset F-region electrodynamics governing the nature of seasonal characteristics of the ESF phenomena during these years. The observed results seem to indicate a plausible linkage of daytime EEJ related electric field variations with pre-reversal enhancement which in turn is related to the occurrence of ESF. These electric field variations are shown to be better represented through a parameter, termed as "E", in the context of possible coupling between the E- and F-regions of the ionosphere. The observed similarities in the gross features of the variations in the parameter "E" and the F-region vertical drift (Vz) point towards the potential usage of the EEJ related parameter "E" as an useful index for the assessment of Vz prior to the occurrence of ESF.

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 Relationships between pre-sunset electrojet strength, pre-reversal enhancement and equatorial spread-F onset

2010 ◽  
Vol 28 (2) ◽  
pp. 449-454 ◽  
Author(s):  
J. Uemoto ◽  
T. Maruyama ◽  
S. Saito ◽  
M. Ishii ◽  
R. Yoshimura
Keyword(s):  
Electric Field ◽  
Equatorial Electrojet ◽  
Layer Height ◽  
Equatorial Spread F ◽  
Magnetic Latitude ◽  
F Region ◽  
Spread F ◽  
Bottom Side ◽  
E Region ◽  
Height Increase

Abstract. The virtual height of the bottom side F-region (h'F) and equatorial spread-F (ESF) onsets at Chumphon (10.7° N, 99.4° E; 3.3° N magnetic latitude) were compared with the behaviour of equatorial electrojet (EEJ) ground strength at Phuket (8.1° N, 98.3° E; 0.1° N magnetic latitude) during the period from November 2007 to October 2008. Increase in the F-layer height and ESF onsets during the evening hours were well connected with the EEJ ground strength before sunset, namely, both the height increase and ESF onsets were suppressed when the integrated EEJ ground strength for the period from 1 to 2 h prior to sunset was negative. The finding suggests observationally that the pre-sunset E-region dynamo current and/or electric field are related to the F-region dynamics and ESF onsets around sunset.

scholarly journals The role of the F-region vertical drift on the onset time of the equatorial spread F over Ilorin, Nigeria

2019 ◽  
Vol 128 (5) ◽  
Author(s):  
O A Oladipo ◽  
J O Adeniyi ◽  
I A Adimula ◽  
A O Olawepo ◽  
A Olowookere ◽  
...  
Keyword(s):  
Onset Time ◽  
Equatorial Spread F ◽  
F Region ◽  
Vertical Drift ◽  
Spread F

scholarly journals Fast and ultrafast Kelvin wave modulations of the equatorial evening F region vertical drift and spread F development

2015 ◽  
Vol 67 (1) ◽  
Author(s):  
Mangalathayil A Abdu ◽  
Christiano GM Brum ◽  
Paulo P Batista ◽  
Subramanian Gurubaran ◽  
Dora Pancheva ◽  
...  
Keyword(s):  
Kelvin Wave ◽  
F Region ◽  
Vertical Drift ◽  
Spread F

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 On developing a new ionospheric plasma index for Brazilian equatorial F region irregularities

2019 ◽  
Vol 37 (5) ◽  
pp. 807-818 ◽  
Author(s):  
Laysa Cristina Araujo Resende ◽  
Clezio Marcos Denardini ◽  
Giorgio Arlan Silva Picanço ◽  
Juliano Moro ◽  
Diego Barros ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Space Weather ◽  
Ionospheric Plasma ◽  
Monitoring Program ◽  
Plasma Irregularities ◽  
Plasma Drift ◽  
F Region ◽  
Maximum Value ◽  
Spread F

Abstract. F region vertical drifts (Vz) are the result of the interaction between ionospheric plasma with the zonal electric field and the Earth's magnetic field. Abrupt variations in Vz are strongly associated with the occurrence of plasma irregularities (spread F) during the nighttime periods. These irregularities are manifestations of space weather in the ionosphere's environment without necessarily requiring a solar burst. In this context, the Brazilian Space Weather Study and Monitoring Program (Embrace) of the National Institute for Space Research (INPE) has been developing different indexes to analyze these ionospheric irregularities in the Brazilian sector. Therefore, the main purpose of this work is to produce a new ionospheric scale based on the analysis of the ionospheric plasma drift velocity, named AV. It is based on the maximum value of Vz (Vzp), which in turn is calculated through its relationship with the virtual height parameter, h′F, measured by the Digisonde Portable Sounder (DPS-4D) installed in São Luís (2∘ S, 44∘ W; dip: −2.3∘). This index quantifies the time relationship between the Vz peak and the irregularity observed in the ionograms. Thus, in this study, we analyzed 7 years of data, between 2009 and 2015, divided by season in order to construct a standardized scale. The results show there is a delay of at least 15 min between the Vzp observation and the irregularity occurrence. Finally, we believe that this proposed index allows for evaluating the impacts of ionospheric phenomena in the space weather environment.

scholarly journals VHF radar observations of the dip equatorial E-region during sunset in the Brazilian sector

2006 ◽  
Vol 24 (6) ◽  
pp. 1617-1623 ◽  
Author(s):  
C. M. Denardini ◽  
M. A. Abdu ◽  
E. R. de Paula ◽  
C. M. Wrasse ◽  
J. H. A. Sobral
Keyword(s):  
Electric Field ◽  
Equatorial Electrojet ◽  
Magnetic Activity ◽  
Maximum Intensity ◽  
Vhf Radar ◽  
F Region ◽  
Vertical Electric Field ◽  
Tentative Explanation ◽  
E Region ◽  
Activity Condition

Abstract. Using the RESCO 50 MHz backscatter radar (2.33° S, 44.2° W, DIP: –0.5), at São Luís, Brazil, we obtained Range Time Intensity (RTI) maps covering the equatorial electrojet heights during daytime and evening. These maps revealed a scattering region at an altitude of about 108 km during the sunset period. The type of 3-m irregularity region we present here has not been reported before in the literature, to our knowledge. It was mainly observed around the Southern Hemisphere summer-solstice period, under quiet magnetic activity condition. The occurrence of this echo region coincides in local time with the maximum intensity of an evening pre-reversal eastward electric field of the ionospheric F-region. A tentative explanation is proposed here in terms of the theory of the divergence of the equatorial electrojet (EEJ) current in the evening ionosphere presented by Haerendel and Eccles (1992), to explain the partial contribution of the divergence to the development of the pre-reversal electric field. The theory predicts an enhanced zonal electric field and hence a vertical electric field below 300 km as a consequence of the EEJ divergence in the evening. The experimental results of the enhanced echoes from the higher heights of the EEJ region seem to provide evidence that the divergence of the EEJ current can indeed be the driver of the observed scattering region.

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 Observations and modeling of post-midnight uplifts near the magnetic equator

2006 ◽  
Vol 24 (5) ◽  
pp. 1317-1331 ◽  
Author(s):  
M. J. Nicolls ◽  
M. C. Kelley ◽  
M. N. Vlasov ◽  
Y. Sahai ◽  
J. L. Chau ◽  
...  
Keyword(s):  
Electric Field ◽  
Magnetic Equator ◽  
Occurrence Rate ◽  
Plasma Flux ◽  
Numerical Techniques ◽  
Field Reversal ◽  
Radio Observatory ◽  
Density Measurements ◽  
Vertical Drift ◽  
Spread F

Abstract. We report here on post-midnight uplifts near the magnetic equator. We present observational evidence from digital ionosondes in Brazil, a digisonde in Peru, and other measurements at the Jicamarca Radio Observatory that show that these uplifts occur fairly regularly in the post-midnight period, raising the ionosphere by tens of kilometers in the most mild events and by over a hundred kilometers in the most severe events. We show that in general the uplifts are not the result of a zonal electric field reversal, and demonstrate instead that the uplifts occur as the ionospheric response to a decreasing westward electric field in conjunction with sufficient recombination and plasma flux. The decreasing westward electric field may be caused by a change in the wind system related to the midnight pressure bulge, which is associated with the midnight temperature maximum. In order to agree with observations from Jicamarca and Palmas, Brazil, it is shown that there must exist sufficient horizontal plasma flux associated with the pressure bulge. In addition, we show that the uplifts may be correlated with a secondary maximum in the spread-F occurrence rate in the post-midnight period. The uplifts are strongly seasonally dependent, presumably according to the seasonal dependence of the midnight pressure bulge, which leads to the necessary small westward field in the post-midnight period during certain seasons. We also discuss the enhancement of the uplifts associated with increased geomagnetic activity, which may be related to disturbance dynamo winds. Finally, we show that it is possible using simple numerical techniques to estimate the horizontal plasma flux and the vertical drift velocity from electron density measurements in the post-midnight period.

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.

Sign in / Sign up

Export Citation Format

Share Document