Counter Electrojet Research Articles

The Response of the D and E Regions of the Equatorial Ionosphere to Solar Flare Events

AbstractUsing measurements from a ground‐based magnetometer and an in‐house developed quasi‐two‐dimensional theoretical ionospheric model (QTD), the differential response of D and E regions of the equatorial ionosphere to the solar flare events which occurred on 20 February 2002 (M1.5 class), and 24 September 2011 (X1.9 class) has been investigated. The ground‐based magnetometer at Tirunelveli (8.71°N, 77.75°E, 2.9°S dip latitude) was used to monitor variations in the magnetic field (ΔH) during the two events. An abrupt increase in ΔH [positive Solar Flare Effect (SFE)] was noted during both the flare events, a signature of the prompt response to the flare. The ΔH, however, was seen to get weakened (reversed SFE) on 20 February 2002 at a time delay of about 10 min post flare peak. The weakening in ΔH happened during local noon (∼11:30 LT), a period when there was no sign of the counter electrojet (CEJ). The QTD model was used to simulate the ratio of field line integrated Hall to Pedersen conductivity and variations in the east–west currents during the flare events. Model simulations show differential response in the conductivity ratio at the D and E‐regions of the ionosphere during the period when the ionospheric current system was undergoing alternations manifesting as ΔH variations in the ground‐based magnetometer observations. We show that in addition to the changes in conductivity during a solar flare, the electric field variations also modulate ionospheric currents to produce differential footprints in ΔH as positive/negative SFE, SFE*, or reversed SFE.

FoF2 Seasonal Prediction With IRI-2016 Over Quiet Activity at Dakar Station

This study deals with comparison between Dakar station ionospheric F2 layer critical frequency (foF2) data and both subroutines (CCIR and URSI) of IRI-2016 model predictions. Dakar station is located near the crest of the African Equatorial Ionization Anomaly (EIA) region. Comparisons are made for very quiet activity during the four seasons (spring, summer, autumn and winter) over both solar cycles 21 and 22. The quietest days per season are determined by taking the five days with the lowest aa. The relative standard deviation of modeled foF2 values is used to assess the quality of IRI model prediction. Model predictions are suitable with observed data by day than by night. The accuracy is better during spring season and poor during winter season. During all seasons, both model subroutines don’t express the signature of the observed vertical drift E×B. But they express an intense counter electrojet at the place of mean intensity or high electrojet.

Ionospheric Electrodynamic Response to Solar Flares in September 2017

AbstractsIn this work, the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model is used to investigate the responses of ionospheric electrodynamic processes to the solar flares at the flare peaks and the underlying physical mechanisms on September 6 and 10, 2017. Simulations show that solar flares increased global daytime currents and reduced the eastward electric fields during the daytime from the equator to middle latitudes. Furthermore, westward equatorial electric fields and equatorial counter electrojets occurred in the early morning. At the flare peak, these electrodynamic responses are predominantly related to the enhanced E‐region conductivity by flares, as the responses of neutral winds and F‐region conductivity to flares are negligible. Specifically, the Cowling conductance enhancement is not the major process causing the reduction of zonal electric fields. This electric field reduction is primarily associated with the decrease of the ratio between the field line‐integrated wind‐driven currents and the conductance. The flare‐induced conductivity enhancement is larger but the background wind speed is smaller in the E‐region than in the F‐region, as a result, the increase of total integrated wind‐driven currents is less than the conductance enhancement.

Effects of Subauroral Polarization Streams on the Equatorial Electrojet During the Geomagnetic Storm on June 1, 2013

AbstractIn this study, the effect of disturbance dynamo electric field (DDEF) induced by subauroral polarization streams (SAPS) on the variations of the equatorial electrojet (EEJ) and its counter electrojet (CEJ) during the geomagnetic storm on June 1, 2013 is analyzed in detail for the first time. Observations from ground‐based magnetometers showed that the SAPS‐induced EEJ flows westward and eastward in the daytime and dawn/dusk sectors, respectively. The effects of SAPS on EEJ are mainly associated with the changes of zonal ionospheric electric field, while the changes in the ionospheric conductivity play a secondary role. By using Thermosphere Ionosphere Electrodynamic General Circulation Model simulations, the zonal electric field induced by SAPS associated with the DDEF is examined. The results of the simulations show that the DDEF has a significant impact on the EEJ variability. The daytime westward EEJ at the dip equator is mainly driven by disturbance zonal wind, with secondary contributions from disturbance meridional wind. A similar mechanism can be observed in the dawn/dusk sector when the eastward EEJ is produced; however, it has a much weaker intensity than that during the daytime.

Defining different type of CEJ currents based on ground-based geomagnetic data record at Langkawi station, Malaysia

A negative decrement in geomagnetic data in equatorial region is not necessarily cause by the well-known counter electrojet, CEJ but it is also can be affected by solar activity such as a solar flare. Relying on this matter, we did a comparison between CEJ and unusual solar flare effect called as SFE* on geomagnetic data before introducing several types of CEJ that can be extracted from EUEL index. This study used ground data from MAGDAS network located in Langkawi (LKW) with 1-minutes resolution during solar cycle 24 and applied EUEL index. From the results, it is crucial to ensure the minimum duration of EUEL depletion is within an hour because less than an hour depletion could be possibly cause by solar activity. Four interval of time that has been introduced in our study composed of several types of CEJ which are morning CEJ, afternoon CEJ and evening CEJ, with additional the controversial CEJ occurrence which is night CEJ. We also successfully demonstrated a rare CEJ occurrence that associated with solar flare effect using EUEL index.

Imprints of Sunspot Cycles on Normal and Abnormal Geomagnetic Fields: Case Study From Equatorial and Low‐Latitude Sites of India

AbstractThe quiet time characteristics of equatorial electrojet (EEJ), counter electrojet (CEJ), and solar quiet (Sq) day geomagnetic field over two decades (1980–2002) are established using Principal component analysis (PCA) from equatorial (Ettaiyapuram) and off‐equatorial (Hyderabad) Magnetic Observatories, India, over sunspot cycles 21–23. The patterns of normal field shows that the diurnal amplitudes were strong during equinox compared to other seasons. Varying contributions of abnormal field in different Lloyd's seasons were evident in different phases of sunspot cycle. The diurnal amplitudes have reduced from the 21st to the 23rd sunspot maxima following the trend of weakening of sunspot cycle. Analysis of seasonal means shows evening CEJs were more pronounced when compared to morning and afternoon in different phases of sunspot cycle. The abnormal field variations have a strong correlation with the occurrence of afternoon CEJs during solar minima; a correlation of seasonal occurrences of CEJs with phases of sunspot cycles is revealed.

Evolution of the Geomagnetic Daily Variation at Tatuoca, Brazil, From 1957 to 2019: A Transition From Sq to EEJ

AbstractThe magnetic equator in the Brazilian region has moved over 1,100 km northward since 1957, passing the geomagnetic observatory Tatuoca (TTB), in northern Brazil, around 2013. We recovered and processed TTB hourly mean values of the geomagnetic field horizontal (H) component from 1957 until 2019, allowing the investigation of long‐term changes in the daily variation due to the influence of secular variation, solar activity, season, and lunar phase. The H day‐to‐day variability and the occurrence of the counter electrojet at TTB were also investigated. Until the 1990s, ionospheric solar quiet currents dominated the quiet‐time daily variation at TTB. After 2000, the magnitude of the daily variation became appreciably greater due to the equatorial electrojet (EEJ) contribution. The H seasonal and day‐to‐day variability increased as the magnetic equator approached, but their amplitudes normalized to the average daily variation remained at similar levels. Meanwhile, the amplitude of the lunar variation, normalized in the same way, increased from 5% to 12%. Within the EEJ region, the occurrence rate of the morning counter electrojet (MCEJ) increased with proximity to the magnetic equator, while the afternoon counter electrojet (ACEJ) did not. EEJ currents derived from CHAMP and Swarm satellite data revealed that the MCEJ rate varies with magnetic latitude within the EEJ region while the ACEJ rate is largely constant. Simulations with the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model based on different geomagnetic main field configurations suggest that long‐term changes in the geomagnetic daily variation at TTB can be attributed to the main field secular variation.

Evaluating Solar Quiet Variation of the Horizontal Geomagnetic Field using Nonlinear Time Series Analysis Techniques

In this present paper, the nonlinear time series techniques were used to analyse solar quiet variation in the horizontal component of the geomagnetic field (SqH) data collected from the INTERMAGNET during the year 2012. The complexity of the nonlinear dynamics based on estimated time delay (τ) and embedding dimension (m) are expressed by Lyapunov exponents (LE). The positive values of the Lyapunov exponent for the Addis Abba (AAE), Eskdalemuir (ESK), Hartebeesthoek (HBK), Hermanus (HER), Mbour (MBO), Sodankyla (SOD) and Tamanrasset (TAM) time series are 0.0027, 0.0118, 0.0082, 0.0042, 0.0027, 0.016 and 0.0036 respectively for the year 2012. We observed positive values of Lyapunov exponent which are more significant at high latitudes (ESK and SOD) and mid latitudes (TAM, HBK and HER) which are located outside the electrojet region. The low latitudes (AAE and MBO) have low values of Lyapunov exponent which are located within electrojet region. The internal dynamics and inherent irregularities of ionosphere may be responsible for the occurrence of chaos during the Sq (H) variation, which show evidence of nonlinear properties. The external factors such as counter electrojet (CEJ) and equatorial electrojet (EEJ) might be responsible for inherent dynamics.This may possibly be the reason for the higher and lower values of Lyapunov exponents during SqH.

Influence of Nonmigrating Tides and Geomagnetic Field Geometry on the Diurnal and Longitudinal Variations of the Equatorial Electrojet

AbstractIn this study, equatorial electrojets (EEJs) simulated by the Thermosphere‐Ionosphere Electrodynamics General Circulation Model (TIE‐GCM) were compared with those observed by ground‐based magnetometers and the Challenging Minisatellite Payload (CHAMP) satellite. Simulations were performed with or without nonmigrating tidal forcing at the lower boundary and in the frame of the International Geomagnetic Reference Field (IGRF) or dipole field. The model forced by the nonmigrating tides could qualitatively reproduce the local time and longitudinal variation of an EEJ in the frame of the IGRF with accuracy. The tides were important in causing the later local time occurrence of the EEJ peak in the Peruvian sector, and they favored the occurrence of the morning counterelectrojet (CEJ) in the frame of the IGRF. The difference in the EEJ peak intensity between the Peruvian and Indian stations was enhanced due to the tidal effect. The net effect of the tides on the two‐station difference was almost doubled in the dipole field compared with that in the IGRF. The TIE‐GCM with a tidal input could reproduce a Wavenumber‐4 longitudinal structure of the noontime EEJ, but it underestimated the peak EEJ in the East Asia sector. The magnetically eastward electric field and the neutral zonal wind at noontime in the E region in the TIE‐GCM were both weak in the East Asia sector. This model‐data discrepancy was at least partly due to insufficient lower boundary forcing in this longitudinal sector.

Penetration electric fields observed at middle and low latitudes during the 22 June 2015 geomagnetic storm

Prompt penetration electric fields were detected during the intense geomagnetic storm on 22 June, 2015 by the HF Doppler sounders at middle and low latitudes; Prague (Czech Republic), Iitate, Oarai, Onna (Japan), and Zhongli (Republic of China). The storm was initiated by the storm sudden commencement (SC) at 1833 UT, immediately followed by the main phase with the minimum SYM-H of − 139 nT at 2017 UT. The convection electric field was found to be up to 5.1 mV/m at low latitudes, which is enough to cause ionospheric disturbances such as the enhancement of the total electron content, equatorial ionization anomaly and so on. The electric fields of the SC and main phase are westward in the night (0330 MLT), while eastward in the evening (1930 MLT). The main phase electric field intensified the eastward equatorial electrojets (EEJ) at Huancayo in South America on the dayside (1330 MLT) and the westward EEJ on the nightside at Guam in the western Pacific (0330 MLT) and Tirunelveli in India (00 MLT). The eastward direction of the evening-time electric field agrees with a feature of the evening anomaly of the penetration electric field, while the intensity is suppressed because of the sunlit condition in the evening in the summer solstice. The sudden northward turning of the interplanetary magnetic field (IMF) caused a transition from the main phase to the recovery phase, when the EEJ turned into the counterelectrojet (CEJ). It was found that the HF Doppler sounders detected an impulsive eastward overshielding electric field at 2005 UT on the nightside during the northward IMF-driven CEJ with the duration of 17 min and intensity of 8.0 mV/m at Iitate (0500 MLT) and 11.8 mV/m at Prague (2130 MLT). The impulsive overshielding electric field was accompanied by the anti-sunward plasma flows at middle latitude (50°–60° GML) equatorward of the dusk sunward convection as observed with SuperDARN, which signifies intensification of the Region-2 field-aligned currents at the flow reversal. Substorm signatures are identified with intensified westward auroral electrojet and magnetic dipolarization as detected by the geosynchronous orbit satellite, ETS-VIII. Consequently, the stormtime substorm may provide strong overshielding electric fields to the middle latitude ionosphere on the nightside.

Investigation on the Variability of the Geomagnetic Daily Current During Sudden Stratospheric Warmings

AbstractThe magnetic field records of the magnetometer networks in the American, East Asian‐Australian, and European‐African sectors were employed in this present work. We used them to investigate equatorial electrojet (EEJ), counter electrojet (CEJ), tidal variability in EEJ strength and ionospheric current during the 2005/2006 and 2008/2009 sudden stratospheric warming (SSW) events. In addition to the well‐investigated tidal variability in EEJ strength over the American and East Asian sectors, we investigated that of the African sector for the first time. Interestingly, the tidal components in EEJ strength during both SSW events clearly exhibit marked longitudinal differences with high, moderate, and low amplitudes in the American, East Asian, and African sectors, respectively. An exception found around day 71 in the African sector after the 2008/2009 SSW event had higher solar diurnal tidal component as compared to that of the Asian sector. Over the American sector, solar and lunar semidiurnal tides were strongly associated with CEJ current during both SSW events, whereas at the African and East Asian sectors such variabilities are not evident. A solar diurnal tidal component was strongly related to a reduction in the EEJ strength over the East Asian sector. In addition, a prolonged period of CEJ occurrence that begins during the SSW precondition and ends when the SSW was evolving characterized the African sector during both SSW events. There is a steady shift in phase at later hours when both SSW events are evolving.

The Role of the Phase of QBO in Modulating the Influence of the SSW Effect on the Equatorial Ionosphere

AbstractThis study investigates the role of stratospheric quasi‐biennial oscillation (QBO) in modulating the response of equatorial/low‐latitude ionosphere over the Indian sector to the major sudden stratospheric warmings (SSWs) occurred during the period 2003 to 2013. The analysis based on the equatorial electrojet‐induced surface magnetic field, total electron content, and mesospheric wind data reveals that the equatorial ionosphere responds in distinctly different ways to the SSWs occurred during different QBO phases. The peaking time of the equatorial electrojet and occurrence time of counter electrojet displays a shift toward morning/evening sector during the westward/eastward phase of the QBO as inferred from the zonal mean zonal wind at 10‐hPa level (~30 km). The analysis reveals that the enhancement and depletions seen in total electron content over both the equatorial and low‐latitude ionosphere display a shift toward morning/evening during the westward/eastward phase of the QBO. The upper mesospheric tides (diurnal and semidiurnal) estimated using the meteor radar measured winds over the dip equator also exhibit similar shift in their phases. The occurrence of periodic counter electrojets during the SSW period is found to be coinciding with enhancement in polar stratospheric temperature and in close association with the increased amplitude of the semidiurnal tide. These observations clearly vindicate that the phase of the QBO plays a crucial role in structuring the equatorial electrodynamics and electron density distribution over the low‐latitudes during the SSW events.

Occurrences of counter electrojets and possible ionospheric TEC variations round new Moon and full Moon days across the low latitude Indian region

Abstract The present paper investigates the alterations in ionospheric Total Electron Content (TEC) over a low latitude location Bangalore (Geographic latitude 12.9 ∘ N {12.9^{\circ }}\hspace{2.38387pt}\text{N} and longitude 77.6 ∘ E {77.6^{\circ }}\hspace{2.38387pt}\text{E} ; Geomagnetic latitude 4 . 5 ∘ N 4.{5^{\circ }}\hspace{2.38387pt}\text{N} ) in India, corresponding to the new Moon and full Moon days which are associated with abnormality in the eastward Equatorial Electrojet (EEJ) currents. It has been well established that even during certain geomagnetic quiet days, the EEJ current direction is reversed, resulting in a westward electrojet current called Counter Electrojet (CEJ) which is more prominent around the new Moon and full Moon days, favored by Sun–Moon–Earth alignments and lunar orbital characteristics. The Global Positioning System (GPS) derived TEC at Bangalore is investigated for full Moon and new Moon and their adjacent days during the period 2008–2015. The presence of CEJ during these days suggests the foremost role of driving EEJ current over the equator in the alterations of spatiotemporal distributions of TEC over the low latitude region. The deviations in quiet time TEC during new Moon and full Moon days are quantified in this study that may give a thrust towards modeling of lunar tidal effects in the flipped ionospheric parameter over the Indian region. The study would also support analysis of future solar eclipse effects on ionosphere those involve additional photoionization production/recombination processes corresponding to the passage of lunar shadow and cooling effects. Moreover, the results underpin modeling and mitigation of ionospheric error in the satellite-based positioning, navigation, and communication applications.

Signatures of substorm related overshielding electric field at equatorial latitudes under steady southward IMF Bz during main phase of magnetic storm

During the geomagnetic storm periods, the convection electric field penetrates promptly to equatorial latitudes, causing an eastward electric field in the dayside ionosphere. Occasionally, the polarity of the dayside ionospheric electric field is inverted when the Interplanetary Magnetic Field (IMF) turns northward. In this paper, interesting observations of the strong westward electric field in the day side equatorial latitudes are presented, as evidenced by strong Counter Electrojet (CEJ) at Indian and Japanese sectors under the steady southward IMF Bz. The westward electric field perturbations are quite large with CEJ amplitude of ∼−120 nT over the Indian sector (14–15 December 2006) and ∼−220 nT for Japanese sector (7–8 November 2004). The plausible mechanisms for the observed overshielding electric fields under steady southward IMF Bz have been investigated in light of the possible role of substorm activity. The clear signatures of substorm were observed at geosynchronous particle flux measurements from LANL (Los Alamos National Laboratory) satellite and associated with sudden decrease in AL index. The observed variations of asymmetric ring current shows the enhancement of Partial Ring Current (PRC) at the dusk sector further supporting the substorm onset during that period which will probably enhance the overshielding due to increased Region 2 Field-Aligned Currents (R2 FACs). The observations of such significantly large amplitudes of CEJ associated with the substorm related overshielding events are sparse and the results bring out the important role of substorm onset and the development of PRC in accordance with the R2 FACs during intense magnetic storms which alter the day time equatorial electric field perturbations.

Longitudinal variability of the equatorial counter electrojet during the solar cycle 24

Ground and space-based geomagnetic data were used in the investigation of the longitudinal, seasonal and lunar phase dependence of the equatorial counter electrojet (CEJ) occurrence in the Peruvian, Brazilian, African, Indian and Philippine sectors during geomagnetically quiet days from the solar cycle 24 (2008 to 2018). We found that CEJ events occur more frequently during the morning (MCEJ) than in the afternoon (ACEJ). The highest MCEJ and ACEJ occurrence rates were observed for the Brazilian sector. Distinct seasonal dependence was found for each longitudinal sector under investigation. The lunar phase dependence was determined for the first time for the Philippine sector (longitude 125°E), and it was shown to be less pronounced than in the Peruvian, Brazilian and African sectors. We demonstrate that differences in CEJ rates derived from ground-based and satellite data can arise from the longitudinal separation between low-latitude and equatorial stations that are used to determine the signal and its consequent time delay in their sunrise/sunset times at ionospheric heights.

Relationship between plasma bubble and ionospheric current, equatorial electrojet, and equatorial counter electrojet

In recent years, it has been clarified from previous studies that plasma bubbles and equatorial electrojets (EEJs) are related. In general, EEJs are calculated by subtracting the magnetic field H component of the magnetic equator from that at low latitude. However, in this study, EE-index data at Langkawi (magnetic equator), which includes all local current systems, were used for the analysis during the period from January 1, 2011, to November 8, 2014. By using the EE-index, it was found that plasma bubbles tend to occur for larger EEJ strengths. This result differs from the previous studies. In addition, if an equatorial counter electrojet (CEJ) occurs, it is understood that plasma bubbles will rarely occur due to the westward current; however, we found that when the lunar tidal effect is strong, plasma bubbles can occur even in conjunction with CEJs. Finally, we want to find the relationship between plasma bubbles and ionospheric current to predict them.

The Occurrence of Sporadic-E Layer over Equatorial Anomaly Crest Region Bhopal

Ionospheric anomaly crest regions are most challenging for scientific community to understand its mechanism and investigation, for this purpose we are investigating some inospheric result for this region. The study is based on the ionogram data recorded by IPS-71 Digital Ionosonde installed over anomaly crust region Bhopal (Geo. Lat. 23.2° N, Geo. Long 77.4° E, Dip latitude 18.4°) over a one year period from January 2010 to December 2010. The studies were examined in four different variations such as: Hourly variation, diurnal variation, seasonal variation and hourly-seasonal variation. The occurrence probability of this layer is highest in summer solstice, moderate during equinox and low during winter solstice. Remarkable occurrence peaks appear from June to July in summer and from December to January in winter. The layer occurrence showed a double peak variation with distinct layer groups, in the morning between 0000–0400 UT and the other during evening between 1100–1600 UT. The morning layer descent was associated with layer density increase indicating the strengthening of the layer while it decreased during the evening layer descent. The result indicates the presence of semi-diurnal tide over the location while the higher descent velocities could be due to the modulation of the ionization by gravity waves along with the tides. The irregularities associated with the gradient-drift instability disappear during the counter electrojet and the current flow is reversed in westward.

Equatorial Counter Electrojet Longitudinal and Seasonal Variability in the American Sector

AbstractThe equatorial electrojet occasionally reverses during morning and afternoon hours, leading to periods of westward current in the ionospheric E region that are known as counter electrojet (CEJ) events. We present the first analysis of CEJ climatology and CEJ dependence on solar flux and lunar phase for the Brazilian sector, based on an extensive ground‐based data set for the years 2008 to 2017 from the geomagnetic observatory Tatuoca (1.2°S, 48.5°W), and we compare it to the results found for Huancayo (12.0°S, 75.3°W) observatory in the Peruvian sector. We found a predominance of morning CEJ events for both sectors. The afternoon CEJ occurrence rate in the Brazilian sector is twice as high as in the Peruvian sector. The afternoon CEJ occurrence rate strongly depends on season, with maximum rates occurring during the northern‐hemisphere summer for the Brazilian sector and during the northern‐hemisphere winter for the Peruvian sector. Significant discrepancies between the two sectors are also found for morning CEJ rates during the northern‐hemisphere summer. These longitudinal differences are in agreement with a CEJ climatology derived from contemporary Swarm satellite data and can be attributed in part to the well‐known longitudinal wave‐4 structure in the background equatorial electrojet strength that results from nonmigrating solar tides and stationary planetary waves. Simulations with the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model show that the remaining longitudinal variability in CEJ during northern summer can be explained by the effect of migrating tides in the presence of the varying geomagnetic field in the South Atlantic Anomaly.

Constraints on Scale Lengths of Equatorial Electrojet and Counter Electrojet Phenomena From the Indian Sector

AbstractThe present study investigates the longitudinal variability of equatorial electrojet (EEJ) and counter electrojet (CEJ) phenomena using concurrent data from three equatorial and low‐latitude paired stations/sites at 5°, 15°, and 20° longitudinal separation in the Indian sector: (i) Minicoy (72°E, dip latitude 01.32°) and Alibag (72°E, dip latitude 14.06°), (ii) Vencode (77°E, dip latitude 01.02°) and Hyderabad (77°E, dip latitude12.34°), and (iii) Campbell Bay (93°E, dip latitude −0.79°) and Nabagram (93°E, dip latitude 06.79°). The observations, over a period of 12 months, at 72°E and 77°E, and 10 months at 93°E, for the year 2015, reflect the variability in both amplitude and occurrence phenomena at close spatial scales. Significant day‐to‐day variability of EEJ and CEJ is observed, with increasing spatial separation. The closely spaced sites, MNC and VEN, show expected similarity but present striking differences in certain monthly averaged patterns. Concurrent observations from three longitudes reveal increasing EEJ amplitudes from west to east and a new observation of increasing CEJ amplitudes from east to west. From these longitudinal trends, we confirm that EEJ strengths are controlled by the large‐scale DE3 nonmigrating tide. A marked difference in CEJ amplitude between MNC and VEN suggests that scale lengths of CEJ and EEJ are different, and we infer that CEJ are primarily generated by short‐scale length variations in the middle atmosphere caused by localized interactions of planetary and gravity waves and are also influenced by the DE3 nonmigrating tide.

Vertical coupling between the mesopause region and sporadic-E layer during equatorial counter electrojet events – A case study

This paper presents a case study exploring the variability of daytime ionospheric sporadic E (Es) during Counter Equatorial Electrojet (CEJ) events over Trivandrum (8.5°N, 77°E, 0.5°N dip lat.), a dip equatorial station in India. It makes use of collocated measurements of (a) daytime mesopause temperature estimated using a Multiwavelength Dayglow Photometer, (b) base height of sporadic E-layer i.e. Esq obtained from a Digital Ionosonde, (c) Equatorial Electrojet (EEJ) induced magnetic field at the surface measured using a Proton Precession Magnetometer and (d) neutral meridional and zonal winds measured using meteor wind radar. The study addresses why, only on certain CEJ days, the Es layer turns into a blanketing Es layer, also referred to as Esb layer, appearing for a brief period and almost simultaneously as the CEJ induced magnetic field on the surface is either zero or very small, and not on all the CEJ days despite the reversal of the zonal winds in the dynamo region (∼98 km). Further, a simulation using the simultaneously measured zonal wind and temperature shows that during CEJ, especially when the zonal wind reverses and the mesopause temperature lowers, the conditions are in fact less favourable for the ionization to converge resulting in Esb. On the other hand, on such occasions, the meridional wind exhibits a tendency to turn equatorward with time with the changeover gradually happening as the altitude decreases. These observations have been discussed to allude to the possible role of the overall wind system and its spatio-temporal changes in the ionospheric altitudes which could influence the gradual transition of Esq to Esb over the dip equator.