E-region Electric Field Research Articles

The Temporal Evolution of F-Region Equatorial Ionization Anomaly Owing to the 2022 Tonga Volcanic Eruption

The dynamic evolutions of the noon ionospheric Equatorial Ionization Anomaly (EIA) owing to the 2022 Tonga volcanic eruption were investigated using the ionospheric plasma measurements from the Swarm satellite, the science experiment of the Constellation Observing Systems for Meteorology, Ionosphere, and Climate (COSMIC) mission, and the thermospheric wind observations from the Ionospheric Connection Explorer (ICON). At 14.1 universal time (UT), the noon EIA was enhanced for the upward plasma drifts, when the F2-layer was significantly uplifted from 360 km to 410 km. At 15.6 UT, because of the downward drifts, the intensity of the EIA reduced, and hmF2 decreased to 270 km. At 17–18 UT, the EIA recovered and reformed, and hmF2 increased to 350 km. A two-peak structure in the plasma was observed at Swarm altitudes. The temporal evolution might be related to the vertical plasma drifts (both downward and upward) from the E-region electric field.

The time delay between the equatorial ionization anomaly and the equatorial electrojet in the eastern Asian and American sectors

The daily evolution of the Equatorial Ionization Anomaly (EIA) and the Equatorial Electrojet (EEJ) exhibits phase difference, which reflects the response time of the F-region equatorial plasma fountain to the E-region electric field variation. Studies on this response time contribute to clarifying the relative importance of different influence factors on the low-latitude E- and F-region coupling process. However, the solar-cycle, seasonal and longitudinal dependence of this response time has not yet been comprehensively revealed. In this paper, the occurrence time of the daytime most developed northern EIA crest (TEIA), the occurrence time of the daytime strongest EEJ (TEEJ), and their time delay (δT = TEIA-TEEJ) during 2008 to 2018 are derived from total electron content and magnetometer data, and the seasonal and solar-cycle variations of these parameters are analyzed and compared between the eastern Asian and American sectors. Main results are as follows. (1) TEIA and δT share similar seasonal and solar-cycle variation patterns, which are different from TEEJ. (2) The prevailing seasonal variation pattern of TEIA is generally consistent in the two sectors, which is earlier (later) in the boreal winter (summer). This feature is not determined by the variations of TEEJ or EEJ strength. (3) The solar-cycle variation pattern of TEIA is different between the eastern Asian and American sectors, but the 11-yr averaged TEIA is nearly the same in the two sectors. The solar-cycle and longitudinal dependencies are probably due to the combined effect of electric field, meridional wind, and local geomagnetic field configuration.

Quasi-10 d wave modulation of an equatorial ionization anomaly during the Southern Hemisphere stratospheric warming of 2002

Abstract. The present paper studies the perturbations in an equatorial ionization anomaly (EIA) region during the Southern Hemisphere (SH) sudden stratospheric warming (SSW) of 2002, using the location of EIA crests derived from global positioning system (GPS) station observations, the total electron content (TEC) obtained by the International GNSS (global navigation satellite system) Service (IGS) global ionospheric TEC map (GIMs) and the equatorial electrojet (EEJ) estimated by the geomagnetic field in the Asian sector. The results indicate the existence of an obvious quasi-10 d periodic oscillation in the location and TEC of the northern and southern EIA crest. An eastward phase progression of the quasi-10 d wave producing the SH SSW of 2002 is also identified in polar stratospheric temperature. Previous studies have shown that a strong quasi-10 d planetary wave with zonal wave numbers s=1 extended from the lower stratosphere to the mesosphere and lower thermosphere during the SH SSW of 2002 (Palo et al., 2005). Moreover, the EEJ driven by the equatorial zonal electric field exhibits quasi-10 d oscillation, suggesting the enhanced quasi-10 d planetary wave associated with SSW penetrates into the ionosphere E region and produces oscillation in the EIA region through modulating the E-region electric fields. Our results reveal some newer features of ionospheric variation that have not been reported during Northern Hemisphere (NH) SSWs.

Equatorial E Region Electric Fields and Sporadic E Layer Responses to the Recovery Phase of the November 2004 Geomagnetic Storm

AbstractEquatorial E region electric fields (EEFs) inferred from coherent radar data, sporadic‐E (Es) layers observed from a digital ionosonde data, and modeling results are used to study the responses of the equatorial E region over São Luís (SLZ, 2.3°S, 44.2°W, ~−7° dip angle), Brazil, during the super storm of November 2004. The EEF is presented in terms of the zonal (Ey) and vertical (Ez) components in order to analyze the corresponding characteristics of different types of Es seen in ionograms and simulated with the E region ionospheric model. We bring out the variabilities of Ey and Ez components with storm time changes in the equatorial E region. In addition, some aspects of the electric fields and Es behavior in three cases of weak, very weak, and strong Type II occurrences during the recovery phase of the geomagnetic storm are discussed. The connection between the enhanced occurrence and suppressions of the Type II irregularities and the q‐type Es (Esq) controlled by electric fields, with the development or disruption of the blanketing sporadic E (Esb) layers produced by wind shear mechanism, is also presented. The mutual presence of Esq along with the Esb occurrences is a clear indicator of the secular drift of the magnetic equator and hence that of the equatorial electrojet (EEJ) over SLZ. The results show evidence about the EEJ and Es layer electrodynamics and coupling during geomagnetic disturbance time electric fields.

Equatorial E region electric fields at the dip equator: 2. Seasonal variabilities and effects over Brazil due to the secular variation of the magnetic equator

AbstractIn this work, the seasonal dependency of the E region electric field (EEF) at the dip equator is examined. The eastward zonal (Ey) and the daytime vertical (Ez) electric fields are responsible for the overall phenomenology of the equatorial and low‐latitude ionosphere, including the equatorial electrojet (EEJ) and its plasma instability. The electric field components are studied based on long‐term backscatter radars soundings (348 days for both systems) collected during geomagnetic quiet days (Kp ≤ 3+), from 2001 to 2010, at the São Luís Space Observatory (SLZ), Brazil (2.33°S, 44.20°W), and at the Jicamarca Radio Observatory (JRO), Peru (11.95°S, 76.87°W). Among the results, we observe, for the first time, a seasonal difference between the EEF in these two sectors in South America based on coherent radar measurements. The EEF is more intense in summer at SLZ, in equinox at JRO, and has been highly variable with season in the Brazilian sector compared to the Peruvian sector. In addition, the secular variation on the geomagnetic field and its effect on the EEJ over Brazil resulted that as much farther away is the magnetic equator from SLZ, later more the EEJ is observed (10 h LT) and sooner it ends (16 h LT). Moreover, the time interval of type II occurrence decreased significantly after the year 2004, which is a clear indication that SLZ is no longer an equatorial station due to the secular variation of the geomagnetic field.

Influence of uncertainties of the empirical models for inferring the E-region electric fields at the dip equator

Daytime E-region electric fields play a crucial role in the ionospheric dynamics at the geomagnetic dip latitudes. Due to their importance, there is an interest in accurately measuring and modeling the electric fields for both climatological and near real-time studies. In this work, we present the daytime vertical (Ez) and eastward (Ey) electric fields for a reference quiet day (February 7, 2001) at the Sao Luis Space Observatory, Brazil (SLZ, 2.31°S, 44.16°W). The component Ez is inferred from Doppler shifts of type II echoes (gradient drift instability) and the anisotropic factor, which is computed from ion and electron gyro frequencies as well as ion and electron collision frequencies with neutral molecules. The component Ey depends on the ratio of Hall and Pedersen conductivities and Ez. A magnetic field-line-integrated conductivity model is used to obtain the anisotropic factor for calculating Ez and the ionospheric conductivities for calculating Ey. This model uses the NRLMSISE-00, IRI-2007, and IGRF-11 empirical models as input parameters for neutral atmosphere, ionosphere, and geomagnetic field, respectively. Consequently, it is worth determining the uncertainties (or errors) in Ey and Ez associated with these empirical model outputs in order to precisely define the confidence limit for the estimated electric field components. For this purpose, errors of ±10 % were artificially introduced in the magnitude of each empirical model output before estimating Ey and Ez. The corresponding uncertainties in the ionospheric conductivity and electric field are evaluated considering the individual and cumulative contribution of the artificial errors. The results show that the neutral densities and temperature may be responsible for the largest changes in Ey and Ez, followed by changes in the geomagnetic field intensity and electron and ions compositions.

Analysis of post-sunset F-region vertical plasma drifts during Counter Electrojet days using multi frequency HF Doppler Radar

In this paper, through a case study, an attempt has been made to bring out the relationship between post noon E-region electric field and post sunset F-region vertical plasma drift on quiet time Counter Electrojet (CEJ) days. Study carried out using the data from a multi frequency HF Doppler Radar and Digital Ionosonde located over Trivandrum (8.5° N; 77° E; 0.5° N dip lat.) a geomagnetic dip equatorial station in India during quite time CEJ days of the years 2004 and 2006, revealed some interesting aspects of the E region electrodynamics and post sunset F region electrodynamics. It has been observed that, in contrast to the normal electrojet (EEJ) days, the Pre-Reversal Enhancement (PRE) is either weakened or inhibited on CEJ days and the field reversal takes place much earlier than that on a normal day. It is suggested that even after the effects of the field reversal ceases to show up in the ground magnetic data, the reversed field may persist and shows up as a decrease in the PRE experienced by the F-region. In other words, the study indicates that the EEJ associated electrodynamics have a significant role in controlling the PRE.

Signatures of moderate (M-class) and low (C and B class) intensity solar flares on the equatorial electrojet current: Case studies

The present investigation brings out, in contrast to the earlier works, the changes in the equatorial electrojet (EEJ) current in response to a few moderate (M-class) and low (C and B class) intensity solar flares during 2005–2010. Special care is taken to pick these flare events in the absence of prompt electric field perturbations associated with geomagnetic storms and substorms that also affect the electrojet current. Interestingly, only the normalized (with respect to the pre-flare level) deviations of daytime EEJ (and not the deviations alone) change linearly with the increases in the EUV and X-ray fluxes. These linear relationships break down during local morning hours when the E-region electric field approaches zero before reversal of polarity. This elicits that the response of EEJ strength corresponding to less-intense flares can be appropriately gauged only when the local time variation of the quiet time E-region zonal electric field is taken into account. The flare events enhanced the EEJ strength irrespective of normal or counter electrojet (CEJ) conditions that shows that solar flares change the E-region ionization density and not the electric field. In addition, the enhancements in the X-ray and EUV fluxes, for these flares occurring during this solar minimum period, are found to be significantly correlated as opposed to the solar maximum period, indicating the differences in the solar processes in different solar epochs.

First measurements of radar coherent scatter by the Radio Aurora Explorer CubeSat

The Radio Aurora Explorer CubeSat detected the first radar echoes during the solar storm of March 8, 2012. The 300 s ground‐to‐space bi‐static radar experiment was conducted in conjunction with the Poker Flat Incoherent Scatter Radar in the local morning (∼8 am) over Poker Flat, Alaska. The geomagnetic conditions for theEregion field‐aligned irregularity generation were optimal due to strong (about 1500 m/s)F region ion drifts and sufficient E region ionization (electron densities were ∼2 × 1011 m−3). The corresponding Eregion electric field of ∼80 mV/m was larger than the excitation threshold for the Farley‐Buneman instability. An auto‐correlation analysis resolved, for the first time, the distribution of auroralEregion backscatter with 3 km resolution in altitude and sub‐degree resolution in aspect angle. Moreover, the measured Doppler velocities of the UHF scatter shows the phase speed saturation of the meter‐scale plasma waves. The measured Doppler velocity is in excellent agreement with theCs cos θ formula for auroral E region irregularities.

Signatures of 2-day wave in the E-region electric fields and their relationship to winds and ionospheric currents

Abstract. We analyze the effects of the 2-day wave activity in the EEJ using one coherent scatter radar and eight magnetometer stations located close to the dip equator. The wavelet analysis of the magnetometer data reveals a 2-day signature in the semidiurnal geomagnetic tide. The E-region zonal background ionospheric electric field, derived from coherent radar measurements, shows 2-day oscillations in agreement with such oscillations in the magnetometers data. An anticorrelation between the amplitude of the tidal periodicites (diurnal and semidiurnal) and that of the 2-day signature is also shown in the electric fields. The results are compared with simultaneous observations of 2-day planetary wave in meridional winds and ionosonde data. Further, our results are discussed based on the analysis of the magnetic activity.

Response of the equatorial electrojet to solar flare related X-ray flux enhancements

Abstract The response of ionospheric E-region electric fields and currents to solar flare related X-ray flux enhancements are studied at the magnetic equatorial location of Trivandrum (8.5°N, 77°E; dip 0.5°N) using VHF (54.95 MHz) coherent backscatter radar observations in the altitude region of 95–110 km conducted during daytime. The amplitude of the Solar Flare Effects (SFE) observed in the earth’s magnetic field variations at Trivandrum have been examined in relation to that at Alibag and it is found that the ratio of the SFE amplitudes at the two stations lies in the range of 1.8–2.6. The backscattered power of the VHF radar showed a substantial reduction during the peak phase of all the strong X-rank flares studied. It has also been observed that there is a sharp fall in the ratio of the field line integrated Hall conductivity (σ2) to the field line integrated Pedersen conductivity (σ1) in the dynamo region "Equation missing" during strong flare times in relation to normal times. The time variations of mean Doppler frequency (f D ) of the backscattered signals have been observed to indicate a fall close to the peak phase of the strong flare events. Another new result is the radar observed presence of westward electric field for a long duration of 2–3 hours during a partial counter electrojet (CEJ) event that occurred on one of the days (8 July 1992) studied. The implications of the observations are discussed in detail.

Large-scale E-region electric field structure due to gravity wave winds

Oscillatory neutral wind motions, such as those of atmospheric gravity waves which propagate through the E-region of the ionosphere, appear to produce local electric fields in the source region. Although the net effect of these oscillatory fields vanishes outside the source region, the local fields themselves are not shorted out along the magnetic field lines, as is usually assumed. We present in situ measurements of neutral winds and the correlated electric fields, and show that local electric fields of the order of a few mV/m can be sustained by the neutral wind motions.

Long wave part of the plasma turbulence spectrum in the lower e-region

In the lower polar E-region electric field and plasma density fluctuations were measured with rocket-borne instrumentation (a floating double probe system and a retarding potential analyzer) during the ROSE project. The observational data are presented and compared with the recently developed theory (Gurevich et al. 1996) for long wave ionospheric plasma oscillations induced by the neutral turbulence. The measured shape and anisotropy of the plasma turbulence spectra at ionospheric heights below about 95 km are well described by this theory. Significant amplification of the low frequency plasma fluctuations in strongly disturbed ionospheric conditions is established.

Pi(c) magnetic pulsations: their relation to ionospheric currents

The association of the phase of the H and D components of the Pi(c) pulsations with the phase of the broadscale H component magnetic bays confirms that Pi(c) pulsations result from auroral electron precipitation induced conductivity enhancements of existing current systems. Statistically determined relationships between the time delays and phases of the H and D components of magnetic Pi(c) pulsations with respect to the optical pulsations are used to infer a delay between the E-region Hall and Pedersen current fluctuations associated with the pulsating electron fluxes. Theoretical modelling of an auroral pulsation patch, as per Oguti and Hayashi, is used to show that the polarization of the Pi(c) pulsations is controlled principally by the delay between the Hall and Pedersen currents and the direction of the background E-region electric field.

Sporadic- E velocity measurement—interpretation and application to ionospheric E-region electric field determination

At Ibadan, the closely spaced antenna method (D1 method) had been used in the past to obtain the drift velocities of equatorial type sporadic- E ( Esq) irregularities. In view of known positive correlation between Esq and electrojet parameters, the possibility that the observed velocities might represent electron drift velocities in the electrojet is examined. It is shown that 1. (a) in magnitude, direction and temporal variations, the observed velocities are consistent with this interpretation, and 2. (b) the observed velocities could be used to make reasonable estimates of the associated E-region electric fields.

Quiet day variation of geomagnetic H-field at low latitudes.

The paper discusses the daily variation of the geomagnetic H-field averaged over the Five International Quiet days, Sq(H), at low latitude stations. The Sq(H) at a station near the dip equator during a low sunspot year represents an increase from about 0600 LT to 1600 LT and an almost constant value from 1600 LT throughout the night time. During a high sunspot year the H-field continues to decrease from noon to evening and through the night time up to sunrise, there being no period in the night when the field remains constant.The harmonic analysis of Sq(H) curves shows that the local time of maximum of the diurnal as well as the semidiurnal wave advances towards local noon with the increase of the average sunspot number. During minimum sunspot years the daily maximum in H occurs almost at 1100 LT while during maximum sunspot years the maximum occurs at about 1200 LT.The amplitudes (C1) of the diurnal and (C2) of the semidiurnal waves are shown to increase linearly with sunspot number. For any of the stations, the rate of increase of the diurnal component with sunspot number is about 2.5 times which is remarkably larger than the corresponding rate of about 1.8 times for the semidiurnal component, such that the ratio C1/C2 at the low latitude stations is about 1.7 in 1964 and about 2.0 in 1959.The monthly mean daily range, rSq(H), shows a predominant semiannual variation with equinoxial peaks at the equatorial stations and a predominant annual variation with summer maximum at the non-equatorial station Alibag. A linear increase of the annual mean daily range with Zurich mean sunspot number Rz is established, the rate of increase being larger towards the equator.The dependence of the diurnal range on the sunspot number is due to enhanced E-region ionization with increasing sunspot number. The delay in the time of diurnal maximum with increasing Rz, the semiannual variation of rSq(H) at equatorial stations and the annual variation of rSq(H) at nonequatorial stations are suggested to be due to the effects of E-region electric fields.

Infrasonic wave generation by aurora

A comparison of the characteristics of auroral infrasonic waves (AIW) in the passband from 10 to 100 sec. period is given for trans-auroral zone stations. The morphology of 2 Hz auroral infrasound observed at Kiruna, Sweden is described. An important asymmetry in the generation of AIW bow waves, with respect to poleward or equatorward motion of auroral electrojet arcs, is shown to be related to the morphology of the ionospheric E-region electric field during an auroral substorm. Auroral radar studies of AIW source arcs are presented. Incoherent scatter radar observations of electron density profiles of auroral arcs are used to describe the differences in arcs that do or do not produce AIW in an attempt to explain the asymmetry in AIW generation by supersonic auroral arcs. An infinite line-current induction model of an auroral electrojet moving transverse to its axis above a conducting earth is used to determine the relationship of an AIW to the surface magnetic perturbation produced by the electrojet. The role of the auroral electrojet in AIW production is discussed in a study of polar magnetic substorms wherein westward traveling auroral surges and the eastern ends of westward auroral electrojets were found to be strong sources of AIW. Theoretical work on the generation of AIW's is reviewed and evaluated with respect to the observed characteristics of AIW substorms. Lorentz force and Joule heat are discussed as probable source terms for the production of the acoustic energy within an auroral electrojet. The important unsolved problems in understanding auroral infrasound are outlined.

Effects of E-region electric fields on F-region parameters at the magnetic equator

The effects of E-region electric fields on F-region parameters like height of constant electron density contours ( h N ) and semi-thickness, at an equatorial station, Trivandrum, are investigated. The E-region east-west electric field ( E y ) has been deduced using the horizontal magnetic field values from the ground magnetograms. It is found that the semi-thickness parameter and h N follow closely the E-region electric field ( E y ) variations in the forenoon and noon periods. In the afternoon, it is shown that there is close association between h N and E y , when the electric field variations are large. On a day-to-day basis also, h N and the E-region electric field show very good correlation in the forenoon and noon hours. It is also shown that higher levels are affected more than the lower levels in the F-region by E y .

On the control of the F-region drift velocity by the E-region electric field: experimental evidence

Experimental evidence is presented which shows a good correlation between velocity variations of (1) the vertical motions of the F-region electrons in the equatorial ionosphere, and (2) the horizontal motions of electrons in the underlying E-region.