Response of equatorial ionosphere to episodes of asymmetric ring current activity

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.

Download Full-text

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

Annales Geophysicae ◽

10.5194/angeo-36-609-2018 ◽

2018 ◽

Vol 36 (2) ◽

pp. 609-620 ◽

Cited By ~ 5

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)

Download Full-text

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

Annales Geophysicae ◽

10.1007/s00585-000-0252-2 ◽

2000 ◽

Vol 18 (2) ◽

pp. 252-256 ◽

Cited By ~ 4

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)

Download Full-text

Storm-time ring current: model-dependent results

Annales Geophysicae ◽

10.5194/angeo-30-177-2012 ◽

2012 ◽

Vol 30 (1) ◽

pp. 177-202 ◽

Cited By ~ 23

Author(s):

N. Yu. Ganushkina ◽

M. W. Liemohn ◽

T. I. Pulkkinen

Keyword(s):

Magnetic Field ◽

Electric Field ◽

Boundary Conditions ◽

Electric Fields ◽

Ring Current ◽

Current Model ◽

Current Data ◽

Storm Events ◽

Boundary Location ◽

Field Lines

Abstract. The main point of the paper is to investigate how much the modeled ring current depends on the representations of magnetic and electric fields and boundary conditions used in simulations. Two storm events, one moderate (SymH minimum of −120 nT) on 6–7 November 1997 and one intense (SymH minimum of −230 nT) on 21–22 October 1999, are modeled. A rather simple ring current model is employed, namely, the Inner Magnetosphere Particle Transport and Acceleration model (IMPTAM), in order to make the results most evident. Four different magnetic field and two electric field representations and four boundary conditions are used. We find that different combinations of the magnetic and electric field configurations and boundary conditions result in very different modeled ring current, and, therefore, the physical conclusions based on simulation results can differ significantly. A time-dependent boundary outside of 6.6 RE gives a possibility to take into account the particles in the transition region (between dipole and stretched field lines) forming partial ring current and near-Earth tail current in that region. Calculating the model SymH* by Biot-Savart's law instead of the widely used Dessler-Parker-Sckopke (DPS) relation gives larger and more realistic values, since the currents are calculated in the regions with nondipolar magnetic field. Therefore, the boundary location and the method of SymH* calculation are of key importance for ring current data-model comparisons to be correctly interpreted.

Download Full-text

Equatorial night-time F-region zonal electric fields

Annales Geophysicae ◽

10.1007/s00585-995-0871-8 ◽

1995 ◽

Vol 13 (8) ◽

pp. 871-878 ◽

Cited By ~ 3

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.

Download Full-text

Ionization Waves Enhance the Production of X-rays during Streamer Collisions

Atmosphere ◽

10.3390/atmos12091101 ◽

2021 ◽

Vol 12 (9) ◽

pp. 1101

Author(s):

Vernon Cooray ◽

Gerald Cooray ◽

Marcos Rubinstein ◽

Farhad Rachidi

Keyword(s):

Experimental Data ◽

Electric Field ◽

Electric Fields ◽

Time Synchronization ◽

Field Enhancement ◽

Opposite Polarity ◽

X Rays ◽

Weakly Conducting ◽

Ionization Waves ◽

Discharge Gap

Experimental data show that in laboratory sparks, X-rays are produced in time synchronization with the meeting of streamers of opposite polarity just before the final breakdown of the discharge gap. It has been suggested that the electric field enhancement created during the collision of streamers could provide the necessary conditions for electron acceleration, even though some of the theoretical studies show that the duration of the electric field is not long enough to do so. The experimental data on laboratory discharges show that. when streamers of opposite polarity meet each other, a potential or ionization wave that renders the streamer channels conducting is initiated. This paper shows that these ionization waves that convert the discharge channels from weakly conducting to highly conducting are associated with electric fields large enough to accelerate electrons to relativistic energies.

Download Full-text

Using Wavelet Transform To Extract Frequency Content In Electric Field Radiated By Unusual Lightning Activity

Scientific World ◽

10.3126/sw.v14i14.34988 ◽

2021 ◽

Vol 14 (14) ◽

pp. 62-67

Author(s):

Suraj Neupane ◽

Shriram Sharma ◽

Puja Sharma

Keyword(s):

Wavelet Transform ◽

Electric Field ◽

Electric Fields ◽

Time Domain ◽

Opposite Polarity ◽

Frequency Content ◽

Field Change ◽

Polarity Field ◽

Main Activity ◽

Domain Information

In this frequency spectrum electric fields radiated by the unusual lightning activities have been computed using the wavelet transform technique. The unusual lightning activities have very recently been identified activities and are very poorly understood among the lightning community. As the electric fields are very recently identified and are measured in time domain, to the best of our knowledge, their frequency content has not been studied as of today. To understand the physics of the discharge mechanism of such events, the frequency domain information plays a significant role. In order to extract frequency domain information from the time domain electric field signatures the wavelet transform technique has been employed. For the purpose, the electric field pertinent to the unusual activity, has been divided into two parts namely main activity and the preceding opposite polarity field change. From the computation, it is found that the opposite-polarity field change radiates energy in the spectral range of 2 kHz to 173 kHz whereas, the main activity predominantly radiates in the frequency range 2 kHz to 162 kHz. Such a wider spectral range that the unusual activities radiate have not been reported for the other known activities such as positive and negative return strokes. Evidently, the unusual events have some unique origin of discharge unlike the known activities. Further, as the unusual events were noticed in the temperate region (Uppsala, Sweden) and Sub-tropical climatic zone (Kathmandu, Nepal), it should have some common source of origin between two regions.

Download Full-text

Solar and geomagnetic activity effects on mid-latitude F-region electric fields

Annales Geophysicae ◽

10.5194/angeo-26-2911-2008 ◽

2008 ◽

Vol 26 (9) ◽

pp. 2911-2921 ◽

Cited By ~ 5

Author(s):

V. V. Kumar ◽

M. L. Parkinson ◽

P. L. Dyson ◽

R. Polglase

Keyword(s):

Electric Field ◽

Electric Fields ◽

Geomagnetic Activity ◽

High Speed ◽

Theoretical Models ◽

Solar Flux ◽

Quiet Time ◽

F Region ◽

Diurnal Patterns ◽

Ae Index

Abstract. Diurnal patterns of average F-region ionospheric drift (electric field) and their dependence on solar and geomagnetic activity have been defined using digital ionosonde Doppler measurements recorded at a southern mid-latitude station (Bundoora 145.1° E, 37.7° S geographic, 49° S magnetic). A unique database consisting of 300 907 drift velocities was compiled, mostly using one specific mode of operation throughout 1632 days of a 5-year interval (1999–2003). The velocity magnitudes were generally larger during the night than day, except during the winter months (June–August), when daytime velocities were enhanced. Of all years, the largest drifts tended to occur during the high speed solar wind streams of 2003. Diurnal patterns in the average quiet time (AE<75 nT) meridional drifts (zonal electric field) peaked at up to ~6 m s−1 poleward (0.3 mV m−1 eastward) at 03:30 LST, reversing in direction at ~08:30 LST, and gradually reaching ~10 m s−1 equatorward at ~13:30 LST. The quiet time zonal drifts (meridional electric fields) displayed a clear diurnal pattern with peak eastward flows of ~10 m s−1 (0.52 mV m−1 equatorward) at 09:30 LST and peak westward flows around midnight of ~18 m s−1 (0.95 mV m−1 poleward). As the AE index increased, the westward drifts increased in amplitude and they extended over a greater fraction of the day. The perturbation drifts changed in a similar way with decreasing Dst except the daytime equatorward flows strengthened with increasing AE index, whereas they became weak for Dst<−60 nT. The responses in all velocity components to changing solar flux values were small, but net poleward perturbations during the day were associated with large solar flux values (>192×10−22 W m−2 Hz−1). These results help to more fully quantify the response of the mid-latitude ionosphere to changing solar and geomagnetic conditions, as required to refine empirical and theoretical models of mid-latitude electric fields.

Download Full-text

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

Annales Geophysicae ◽

10.5194/angeo-37-807-2019 ◽

2019 ◽

Vol 37 (5) ◽

pp. 807-818 ◽

Cited By ~ 2

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.

Download Full-text

Space weather impact on the equatorial and low latitude F-region ionosphere over India

Annales Geophysicae ◽

10.5194/angeo-24-97-2006 ◽

2006 ◽

Vol 24 (1) ◽

pp. 97-105 ◽

Cited By ~ 20

Author(s):

R. S. Dabas ◽

R. M. Das ◽

V. K. Vohra ◽

C. V. Devasia

Keyword(s):

Magnetic Storm ◽

Electric Fields ◽

Space Weather ◽

Recovery Phase ◽

Equatorial Region ◽

Storm Events ◽

Low Latitude ◽

Equatorial Station ◽

Weather Impact ◽

F Region

Abstract. For a detailed study of the space weather impact on the equatorial and low latitude F-region, the ionospheric response features are analysed during the periods of three recent and most severe magnetic storm events of the present solar cycle which occurred in October and November 2003, and November 2004. The F-layer base height (h'F), peak height (hmF2) and critical frequency (foF2) data, from Trivandrum, an equatorial station and Delhi, a low latitude location, are examined during the three magnetic storm periods. The results of the analysis clearly shows that the height of the F-region (both h'F and hmF2), at the equator and low latitude, simultaneously increases by 200 to 300 km, in association with maximum negative excursion of Dst values around the midnight hours with a large depletion of ionization over the equator, which is followed by an ionization enhancement at low latitude during the recovery phase of the storm. At Delhi, fast variations up to 200 m/s are also observed in the F-layer vertical upward/downward velocity, calculated using Doppler shifts, associated with the maximum negative excursion of Dst. This shows that during magnetic disturbances, the equatorial ionization anomaly (EIA) expands to a much wider latitude than the normal fountain driven by the E/F-layer dynamo electric fields. It is also observed that during the main phase of the storm, at low latitude there is generally an enhancement of F-region ionization with an increase in h'F/hmF2 but in the equatorial region, the ionization collapses with a decrease in h'F/hmF2, especially after sunset hours. In addition, at the equator the normal pre-sunset hours' enhancement in h'F is considerably suppressed during storm periods. This might be due to changes in magnitude and direction of the zonal electric field affecting the upward E×B drift and hence the plasma distribution in the form of a decrease in electron density in the equatorial region and an increase in the low latitude region. In association with disturbance electric fields, the enhanced storm-induced equatorward meridional winds in the thermosphere can also further amplify the F-layer height rise at low latitudes during the post-midnight hours, as observed in two of the storm periods.

Download Full-text

Penetration of the electric fields of the geomagnetic sudden commencement over the globe as observed with the HF Doppler sounders and magnetometers

Earth Planets and Space ◽

10.1186/s40623-020-01350-8 ◽

2021 ◽

Vol 73 (1) ◽

Author(s):

Takashi Kikuchi ◽

Jaroslav Chum ◽

Ichiro Tomizawa ◽

Kumiko K. Hashimoto ◽

Keisuke Hosokawa ◽

...

Keyword(s):

Electric Field ◽

Electric Fields ◽

Sudden Commencement ◽

Ionospheric Currents ◽

Republic Of China ◽

F Region ◽

Electric And Magnetic Fields ◽

Magnetometer Data ◽

Electric Potentials ◽

Geomagnetic Sudden Commencement

AbstractUsing the HF Doppler sounders at middle and low latitudes (Prague, Czech Republic; Tucuman, Argentina; Zhongli, Republic of China, and Sugadaira, Japan), we observed the electric fields of the geomagnetic sudden commencement (SC) propagating near-instantaneously (within 10 s) over the globe. We found that the electric fields of the preliminary impulse (PI) and main impulse (MI) of the SC are in opposite direction to each other and that the PI and MI electric fields are directed from the dusk to dawn and dawn to dusk, respectively, manifesting the nature of the curl-free potential electric field. We further found that the onset and peak of the PI electric field are simultaneous on the day and nightsides (0545, 1250, 1345 MLT) within the resolution of 10 s. With the magnetometer data, we confirmed the near-instantaneous development of the ionospheric currents from high latitudes to the equator and estimated the location of the field-aligned currents that supply the ionospheric currents. The global simultaneity of the electric and magnetic fields does not require the contribution of the magnetohydrodynamic waves in the magnetosphere nor in the F-region ionosphere. The global simultaneity and day–night asymmetry of the electric fields are explained with the ionospheric electric potentials transmitted at the speed of light by the TM0 mode waves in the Earth-ionosphere waveguide.

Download Full-text