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Journal articles on the topic 'Counter equatorial electrojet'

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Author: Grafiati

Published: 6 September 2023

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1

Sastry, T. S., and S. V. S. Sarma. "Equatorial Counter-Electrojet and Magnetic Pulsations." Journal of geomagnetism and geoelectricity 49, no. 10 (1997): 1247–51. http://dx.doi.org/10.5636/jgg.49.1247.

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2

Rastogi, R. G. "Meridional equatorial electrojet current in the American sector." Annales Geophysicae 17, no. 2 (February 28, 1999): 220–30. http://dx.doi.org/10.1007/s00585-999-0220-4.

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Abstract. Huancayo is the only equatorial electrojet station where the daytime increase of horizontal geomagnetic field (H) is associated with a simultaneous increase of eastward geomagnetic field (Y). It is shown that during the counter electrojet period when ∆H is negative, ∆Y also becomes negative. Thus, the diurnal variation of ∆Y at equatorial latitudes is suggested to be a constituent part of the equatorial electrojet current system. Solar flares are known to increase the H field at an equatorial station during normal electrojet conditions (nej). At Huancayo, situated north of the magnetic equator, the solar flare effect, during nej, consists of positive impulses in H and Y and negative impulse in Z field. During counter electrojet periods (cej), a solar flare produces a negative impulse in H and Y and a positive impulse in Z at Huancayo. It is concluded that both the zonal and meridional components of the equatorial electrojet in American longitudes, as in Indian longitudes, flows in the same, E region of the ionosphere.Key words. Geomagnetism and paleomagnetism (dynamo theories) · Ionosphere (equatorial ionosphere; ionosphere disturbances)

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3

Akiyama, T., A. Yoshikawa, A. Fujimoto, and T. Uozumi. "Relationship between plasma bubble and ionospheric current, equatorial electrojet, and equatorial counter electrojet." Journal of Physics: Conference Series 1152 (January 2019): 012022. http://dx.doi.org/10.1088/1742-6596/1152/1/012022.

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4

Rastogi, R. G. "Morphological aspects of a new type of counter electrojet event." Annales Geophysicae 17, no. 2 (February 28, 1999): 210–19. http://dx.doi.org/10.1007/s00585-999-0210-6.

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

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5

Rabiu, A. Babatunde, Olanike Olufunmilayo Folarin, Teiji Uozumi, Nurul Shazana Abdul Hamid, and Akimasa Yoshikawa. "Longitudinal variation of equatorial electrojet and the occurrence of its counter electrojet." Annales Geophysicae 35, no. 3 (April 7, 2017): 535–45. http://dx.doi.org/10.5194/angeo-35-535-2017.

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Abstract. We examined the longitudinal variability of the equatorial electrojet (EEJ) and the occurrence of its counter electrojet (CEJ) using the available records of the horizontal component H of the geomagnetic field simultaneously recorded in the year 2009 (mean annual sunspot number Rz = 3.1) along the magnetic equator in the South American, African, and Philippine sectors. Our results indicate that the EEJ undergoes variability from one longitudinal representative station to another, with the strongest EEJ of about 192.5 nT at the South American axis at Huancayo and a minimum peak of 40.7 nT at Ilorin in western Africa. Obtained longitudinal inequality in the EEJ was explicable in terms of the effects of local winds, dynamics of migratory tides, propagating diurnal tide, and meridional winds. The African stations of Ilorin and Addis Ababa registered the greatest % of CEJ occurrence. Huancayo in South America, with the strongest electrojet strength, was found to have the least occurrence of the CEJ. It is suggested that activities that support strong EEJ inhibits the occurrence of the CEJ. Percentage of occurrence of the CEJ varied with seasons across the longitudes. The order of seasonal variation of morning occurrence does not tally with the evening occurrence order at any station. A semiannual equinoctial maximum in percentage of morning occurrence of the CEJ was obtained at Huancayo and Addis Ababa. Only Addis Ababa recorded equal equinoctial maxima in percentage of evening occurrence of the CEJ. The seasonal distribution of the occurrences of the CEJ at different time regimes implies a seasonal variability of causative mechanisms responsible for the occurrence of the CEJ.

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6

Mengistu, Endalkachew, and Tsegaye Kassa. "Temporal characteristics of the Equatorial Electrojet and Counter Electrojet over Ethiopian sector." Advances in Space Research 55, no. 2 (January 2015): 566–75. http://dx.doi.org/10.1016/j.asr.2014.10.031.

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7

Somayajulu, V. V., K. S. Viswanathan, K. S. V. Subbarao, and L. Cherian. "Distortions in the height structure of the equatorial electrojet during counter electrojet events." Journal of Atmospheric and Terrestrial Physics 56, no. 1 (January 1994): 51–58. http://dx.doi.org/10.1016/0021-9169(94)90175-9.

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8

Denardini, C. M., M. A. Abdu, H. C. Aveiro, L. C. A. Resende, P. D. S. C. Almeida, Ê. P. A. Olívio, J. H. A. Sobral, and C. M. Wrasse. "Counter electrojet features in the Brazilian sector: simultaneous observation by radar, digital sounder and magnetometers." Annales Geophysicae 27, no. 4 (April 3, 2009): 1593–603. http://dx.doi.org/10.5194/angeo-27-1593-2009.

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Abstract. In the present work we show new results regarding equatorial counter electrojet (CEJ) events in the Brazilian sector, based on the RESCO radar, two set of fluxgate magnetometer systems and a digital sounder. RESCO radar is a 50 MHz backscatter coherent radar installed in 1998 at São Luís (SLZ, 2.33° S, 44.60° W), an equatorial site. The Digital sounder routinely monitors the electron density profile at the radar site. The magnetometer systems are fluxgate-type installed at SLZ and Eusébio (EUS, 03.89° S, 38.44° W). From the difference between the horizontal component of magnetic field at SLZ station and the same component at EUS (EEJ ground strength) several cases of westward morning electrojet and its normal inversion to the eastward equatorial electrojet (EEJ) have been observed. Also, the EEJ ground strength has shown some cases of CEJ events, which been detected with the RESCO radar too. Detection of these events were investigated with respect to their time and height of occurrence, correlation with sporadic E (Es) layers at the same time, and their spectral characteristics as well as the radar echo power intensity.

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9

Bolaji, Olawale, Oluwafisayo Owolabi, Elijah Falayi, Emmanuel Jimoh, Afolabi Kotoye, Olumide Odeyemi, Babatunde Rabiu, et al. "Observations of equatorial ionization anomaly over Africa and Middle East during a year of deep minimum." Annales Geophysicae 35, no. 1 (January 20, 2017): 123–32. http://dx.doi.org/10.5194/angeo-35-123-2017.

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Abstract. In this work, we investigated the veracity of an ion continuity equation in controlling equatorial ionization anomaly (EIA) morphology using total electron content (TEC) of 22 GPS receivers and three ground-based magnetometers (Magnetic Data Acquisition System, MAGDAS) over Africa and the Middle East (Africa–Middle East) during the quietest periods. Apart from further confirmation of the roles of equatorial electrojet (EEJ) and integrated equatorial electrojet (IEEJ) in determining hemispheric extent of EIA crest over higher latitudes, we found some additional roles played by thermospheric meridional neutral wind. Interestingly, the simultaneous observations of EIA crests in both hemispheres of Africa–Middle East showed different morphology compared to that reported over Asia. We also observed interesting latitudinal twin EIA crests domiciled at the low latitudes of the Northern Hemisphere. Our results further showed that weak EEJ strength associated with counter electrojet (CEJ) during sunrise hours could also trigger twin EIA crests over higher latitudes.

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10

Gurubaran, S. "The equatorial counter electrojet: Part of a worldwide current system?" Geophysical Research Letters 29, no. 9 (May 2002): 51–1. http://dx.doi.org/10.1029/2001gl014519.

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11

Rastogi, R. G., and A. Patil. "Equatorial counter-electrojet and the F2-layer of the ionosphere." Journal of Atmospheric and Terrestrial Physics 51, no. 2 (February 1989): 139–43. http://dx.doi.org/10.1016/0021-9169(89)90113-x.

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12

Chandrasekhar, N. Phani, R. K. Archana, Nandini Nagarajan, and Kusumita Arora. "Variability of equatorial counter electrojet signatures in the Indian region." Journal of Geophysical Research: Space Physics 122, no. 2 (February 2017): 2185–201. http://dx.doi.org/10.1002/2016ja022904.

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13

Archana, R. K., N. Phani Chandrasekhar, Kusumita Arora, and Nandini Nagarajan. "Constraints on Scale Lengths of Equatorial Electrojet and Counter Electrojet Phenomena From the Indian Sector." Journal of Geophysical Research: Space Physics 123, no. 8 (August 2018): 6821–35. http://dx.doi.org/10.1029/2018ja025213.

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14

Stening, R. J. "The enigma of the counter equatorial electrojet and lunar tidal influences in the equatorial region." Advances in Space Research 12, no. 6 (1992): 23–32. http://dx.doi.org/10.1016/0273-1177(92)90036-w.

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15

Soares, Gabriel, Yosuke Yamazaki, Jürgen Matzka, Katia Pinheiro, Achim Morschhauser, Claudia Stolle, and Patrick Alken. "Equatorial Counter Electrojet Longitudinal and Seasonal Variability in the American Sector." Journal of Geophysical Research: Space Physics 123, no. 11 (November 2018): 9906–20. http://dx.doi.org/10.1029/2018ja025968.

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16

Manju, G., T. K. Pant, C. V. Devasia, S. Ravindran, and R. Sridharan. "Electrodynamical response of the Indian low-mid latitude ionosphere to the very large solar flare of 28 October 2003 – a case study." Annales Geophysicae 27, no. 10 (October 9, 2009): 3853–60. http://dx.doi.org/10.5194/angeo-27-3853-2009.

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Abstract. The electrodynamic effects on the low-mid latitude ionospheric region have been investigated using GPS (global positioning system) data, ionosonde data and ΔH values, during the very large solar flare (X17.2/4B) of 28 October 2003. The results bring out the flare induced unusual behaviour of the equatorial ionosphere on this day just prior to sunset. The important observations are i) Large and prolonged Ne enhancements observed from ionosonde data just after the flare-related peak enhancement in EUV flux. The observed enhancement in Ne is due to the increase in ionization production due to the enhanced EUV flux and the persistence of the enhancement is probably due to the prompt penetration related upliftment of the F layer (just prior to the flare peak phase) to higher altitudes, where recombination rates are lower. ii) A significant enhancement in total electron content (TEC) (~10 TEC units) at regions around the Equatorial Ionization Anomaly (EIA) crest region (Ahmedabad) during the flare in association with the flare related EUV flux enhancement. iii) Similar enhancements seen at stations of Jodhpur and Delhi in the mid latitude sector. iv)The flare related flux enhancements in different longitude sectors in the equatorial electrojet region have been shown to produce positive and negative variations in electrojet strength indicating the presence of current systems having positive and negative polarities in different longitude sectors. Thus the flare effect reveals the longitudinal variation of the counter electrojet events in the Equatorial Electrojet (EEJ) region.

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17

Chakrabarty, D., R. Sekar, H. Chandra, R. Narayanan, B. M. Pathan, and K. S. V. Subbarao. "Characterizations of the diurnal shapes of OI 630.0 nm dayglow intensity variations: inferences." Annales Geophysicae 20, no. 11 (November 30, 2002): 1851–55. http://dx.doi.org/10.5194/angeo-20-1851-2002.

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Abstract. Measurements of OI 630.0 nm thermospheric dayglow emission by means of the Dayglow Photometer (DGP) at Mt. Abu (24.6° N, 73.7° E, dip lat 19.09° N), a station under the crest of Equatorial Ionization Anomaly (EIA), reveal day-to-day changes in the shapes of the diurnal profiles of dayglow intensity variations. These shapes have been characterized using the magnetometer data from equatorial and low-latitude stations. Substantial changes have been noticed in the shapes of the dayglow intensity variations between 10:00–15:00 IST (Indian Standard Time) during the days when normal and counter electrojet events are present over the equator. It is found that the width (the time span corresponding to 0.8 times the maximum dayglow intensity) of the diurnal profile has a linear relationship with the integrated electrojet strength. Occasional deviation from this linear relationship is attributed to the presence of substantial mean meridional wind.Key words. Ionosphere (equatorial ionosphere; ionosphere – atmosphere interactions; ionospheric disturbances)

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18

Olatunbosun, LG, A. O. Olabode, and EA Ariyibi. "Variability of Equatorial Electrojet (EEJ) at EIA regions." Physics & Astronomy International Journal 6, no. 1 (January 25, 2022): 1–4. http://dx.doi.org/10.15406/paij.2022.06.00241.

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The EEJ is a worldwide solar-driven wind that results in the solar quiet (Sq) current system in the E region of the earth’s ionosphere. The variability of some features such as EEJ, are very important in understanding the complex nature of the ionosphere, especially the low-latitude ionosphere. The magnetometer data from stations located near the equator and outside the edge of the electrojet strip for Africa and India stations were used to estimate and investigate the variability of EEJ in African and Indian Low-Latitudes. The stations are Addis Ababa, Ethiopia (geographic lat/long: 9.03oN/38.76oE) and at Mbour, Senegal for African region (geographic lat/long 14.392oN/343.042oE) and Hyderabad, India (geographic lat/long: 17.413oN/78.555oE) and Beijing Ming Tombs, China for Indian region (geographic lat/long: 40.3oN/116.2oE). The data in XYZ orientation was used to estimate the EEJ strength. The result shows that EEJ exhibits diurnal and seasonal variations and that its variability is stronger in African station than in Indian station, so also is the occurrence of counter electrojet (CEJ).

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19

Soares, Gabriel, Yosuke Yamazaki, Jürgen Matzka, Katia Pinheiro, Claudia Stolle, Patrick Alken, Akimasa Yoshikawa, Teiji Uozumi, Akiko Fujimoto, and Atul Kulkarni. "Longitudinal variability of the equatorial counter electrojet during the solar cycle 24." Studia Geophysica et Geodaetica 63, no. 2 (April 2019): 304–19. http://dx.doi.org/10.1007/s11200-018-0286-0.

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20

Ebihara, Y., T. Tanaka, and T. Kikuchi. "Counter equatorial electrojet and overshielding after substorm onset: Global MHD simulation study." Journal of Geophysical Research: Space Physics 119, no. 9 (September 2014): 7281–96. http://dx.doi.org/10.1002/2014ja020065.

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21

Sridharan, S., S. Sathishkumar, and S. Gurubaran. "Variabilities of mesospheric tides and equatorial electrojet strength during major stratospheric warming events." Annales Geophysicae 27, no. 11 (November 4, 2009): 4125–30. http://dx.doi.org/10.5194/angeo-27-4125-2009.

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Abstract. The present study demonstrates the relationship between the high latitude northern hemispheric major sudden stratospheric warming (SSW) events and the reversal in the afternoon equatorial electrojet (EEJ), often called the counter-electrojet (CEJ), during the winter months of 1998–1999, 2001–2002, 2003–2004 and 2005–2006. As the EEJ current system is driven by tidal winds, an investigation of tidal variabilities in the MF radar observed zonal winds during the winters of 1998–1999 and 2005–2006 at 88 km over Tirunelveli, a site close to the magnetic equator, shows that there is an enhancement of semi-diurnal tidal amplitude during the days of a major SSW event and a suppression of the same immediately after the event. The significance of the present results lies in demonstrating the latitudinal coupling between the high latitude SSW phenomenon and the equatorial ionospheric current system with clear evidence for major SSW events influencing the day-to-day variability of the CEJ.

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22

Doumouya, V., J. Vassal, Y. Cohen, O. Fambitakoye, and M. Menvielle. "Equatorial electrojet at African longitudes: first results from magnetic measurements." Annales Geophysicae 16, no. 6 (June 30, 1998): 658–66. http://dx.doi.org/10.1007/s00585-998-0658-9.

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Abstract. In the framework of the French participation in the International Equatorial Electrojet Year (IEEY), ten magnetotelluric stations were installed between November 1992 and November 1994 along a 1200-km-long meridian profile, between Lamto (latitude 6.2°N, Côte d'Ivoire) to the south and Tombouctou (latitude 16.7°N, Mali) to the north. These stations measured digitally the three components of the magnetic field and the two components of the telluric electric field, and operated over a period of 20 months. The magnetic data is used to study the features of the equatorial electrojet (EEJ) in West African longitude. The measurement of the telluric electric field variations will be presented elsewhere. Hourly mean values are used to study the morphological structure of the regular diurnal variation SR of the three components (H, D, and Z) of the earth magnetic field and to characterize the EEJ during magnetically quiet days. The occurrences of the counter-electrojet (CEJ) are set forth, emphasizing its seasonal variability. Assumed to be a current ribbon, the EEJ main parameters (the position of its center, its width, and the amplitude of its current density at the center) are determined. A preliminary analysis of the time variations of these parameters is presented over period of 20 months (from January 1993 to August 1994). Results are compared with those obtained during previous experiments of the same kind.

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23

Vineeth, C., T. K. Pant, K. K. Kumar, Lijo Jose, S. G. Sumod, and S. Alex. "Counter equatorial electrojet: Analysis of the variability in daytime mesopause temperature and winds." Journal of Atmospheric and Solar-Terrestrial Physics 75-76 (February 2012): 115–21. http://dx.doi.org/10.1016/j.jastp.2011.07.005.

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24

Kelley, M. C., R. R. Ilma, and G. Crowley. "On the origin of pre-reversal enhancement of the zonal equatorial electric field." Annales Geophysicae 27, no. 5 (May 5, 2009): 2053–56. http://dx.doi.org/10.5194/angeo-27-2053-2009.

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Abstract. In November 2004, a large and variable interplanetary electric field (IEF) was felt in the reference frame of the Earth. This electric field penetrated to the magnetic equator and, when the Jicamarca Radio Observatory (JRO) was in the dusk sector, resulted in a reversal of the normal zonal component of the field. In turn, this caused a counter-electrojet (CEJ), a westward current rather than the usual eastward current. At the time of the normal pre-reversal enhancement (PRE) of the eastward field, the Jicamarca incoherent scatter radar (ISR) observed that the westward component became even more westward. Two of the three current explanations for the PRE depend on the neutral wind patterns. However, this unique event was such that the neutral wind-driven dynamos could not have changed. The implication is that the Haerendel-Eccles mechanism, which involves partial closure of the equatorial electrojet (EEJ) after sunset, must be the dominant mechanism for the PRE.

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25

Zhou, Yun-Liang, Hermann Lühr, Hong-wen Xu, and Patrick Alken. "Comprehensive Analysis of the Counter Equatorial Electrojet: Average Properties as Deduced From CHAMP Observations." Journal of Geophysical Research: Space Physics 123, no. 6 (June 2018): 5159–81. http://dx.doi.org/10.1029/2018ja025526.

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26

Alex, S., and S. Mukherjee. "Local time dependence of the equatorial counter electrojet effect in a narrow longitudinal belt." Earth, Planets and Space 53, no. 12 (December 2001): 1151–61. http://dx.doi.org/10.1186/bf03352410.

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27

Woodman, Ronald F., and Jorge L. Chau. "First Jicamarca radar observations of two-streamEregion irregularities under daytime counter equatorial electrojet conditions." Journal of Geophysical Research: Space Physics 107, A12 (December 2002): SIA 18–1—SIA 18–8. http://dx.doi.org/10.1029/2002ja009362.

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28

Ezema, P. O., C. A. Onwumechili, and S. O. Oko. "Geomagnetically quiet day ionospheric currents over the Indian sector—III. Counter equatorial electrojet currents." Journal of Atmospheric and Terrestrial Physics 58, no. 5 (April 1996): 565–77. http://dx.doi.org/10.1016/0021-9169(95)00057-7.

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Sandwidi, Sibri Alphonse, Christian Zoundi, Doua Allain Gnabahou, and Frederic Ouattara. "foF2 Seasonal Prediction With IRI-2016 Over Quiet Activity at Dakar Station." Applied Physics Research 13, no. 3 (November 11, 2021): 1. http://dx.doi.org/10.5539/apr.v13n3p1.

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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.

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30

Tsunoda, Roland T., and Warner L. Ecklund. "On the nature of radar echoes below 95 km during counter streaming in the equatorial electrojet." Geophysical Research Letters 26, no. 17 (September 1, 1999): 2717–20. http://dx.doi.org/10.1029/1999gl900563.

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31

Vineeth, C., N. Mridula, P. Muralikrishna, K. K. Kumar, and T. K. Pant. "First observational evidence for the connection between the meteoric activity and occurrence of equatorial counter electrojet." Journal of Atmospheric and Solar-Terrestrial Physics 147 (September 2016): 71–75. http://dx.doi.org/10.1016/j.jastp.2016.07.007.

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32

Talari, Prashanthi, and Sampad Kumar Panda. "Occurrences of counter electrojets and possible ionospheric TEC variations round new Moon and full Moon days across the low latitude Indian region." Journal of Applied Geodesy 13, no. 3 (July 26, 2019): 245–55. http://dx.doi.org/10.1515/jag-2019-0014.

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Abstract The present paper investigates the alterations in ionospheric Total Electron Content (TEC) over a low latitude location Bangalore (Geographic latitude {12.9^{\circ }}\hspace{2.38387pt}\text{N} and longitude {77.6^{\circ }}\hspace{2.38387pt}\text{E}; Geomagnetic latitude 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.

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33

Ajesh, A., T. K. Pant, C. Vineeth, N. Mridula, and K. K. Kumar. "Vertical coupling between the mesopause region and sporadic-E layer during equatorial counter electrojet events – A case study." Advances in Space Research 62, no. 7 (October 2018): 1787–99. http://dx.doi.org/10.1016/j.asr.2018.07.001.

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34

Hajra, R., S. K. Chakraborty, and A. Paul. "Electrodynamical control of the ambient ionization near the equatorial anomaly crest in the Indian zone during counter electrojet days." Radio Science 44, no. 3 (June 2009): n/a. http://dx.doi.org/10.1029/2008rs003904.

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35

Cherkos, Alemayehu Mengesha. "Solar Flux Effects on the Variations of Equatorial Electrojet (EEJ) and Counter-Electrojet (CEJ) Current across the Different Longitudinal Sectors during Low and High Solar Activity." Journal of Astronomy and Space Sciences 40, no. 2 (June 2023): 45–57. http://dx.doi.org/10.5140/jass.2023.40.2.45.

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This study examined the effect of solar flux (F10.7) and sunspots number (R) on the daily variation of equatorial electrojet (EEJ) and morning/afternoon counter electrojet (MCEJ/ACEJ) in the ionospheric E region across the eight longitudinal sectors during quiet days from January 2008 to December 2013. In particular, we focus on both minimum and maximum solar cycle of 24. For this purpose, we have collected a 6-year ground-based magnetic data from multiple stations to investigate EEJ/CEJ climatology in the Peruvian, Brazilian, West & East African, Indian, Southeast Asian, Philippine, and Pacific sectors with the corresponding F10.7 and R data from satellites simultaneously. Our results reveal that the variations of monthly mean EEJ intensities were consistent with the variations of solar flux and sunspot number patterns of a cycle, further indicating that there is a significant seasonal and longitudinal dependence. During the high solar cycle period, F10.7 and R have shown a strong peak around equinoctial months, consequently, the strong daytime EEJs occurred in the Peruvian and Southeast Asian sectors followed by the Philippine regions throughout the years investigated. In those sectors, the correlation between the day Maxima EEJ and F10.7 strengths have a positive value during periods of high solar activity, and they have relatively higher values than the other sectors. A predominance of MCEJ occurrences is observed in the Brazilian (TTB), East African (AAE), and Peruvian (HUA) sectors. We have also observed the CEJ dependence on solar flux with an anti-correlation between ACEJ events and F10.7 are observed especially during a high solar cycle period.

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Nayak, C. K., D. Tiwari, K. Emperumal, and A. Bhattacharyya. "The equatorial ionospheric response over Tirunelveli to the 15 January 2010 annular solar eclipse: observations." Annales Geophysicae 30, no. 9 (September 25, 2012): 1371–77. http://dx.doi.org/10.5194/angeo-30-1371-2012.

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Abstract. In this paper we present a case study of the annular solar eclipse effects on the ionization of E and F regions of equatorial ionosphere over Tirunelveli [77.8° E, 8.7° N, dip 0.4° N] by means of digital ionosonde on 15 January 2010. The maximum obscuration of the eclipse at this station was 84% and it occurred in the afternoon. The E and F1 layers of the ionosphere showed very clear decrease in their electron concentrations, whereas the F2 layer did not show appreciable changes. A reduction of 30% was observed in the foF1 during the maximum phase of the eclipse. During the beginning phase of the eclipse, an enhancement of 0.97 MHz was observed in the foF2 as compared to that of the control days. But the foF2 decreased gradually as the eclipse progressed and a decrease of 0.59 MHz was observed towards the end phase of the eclipse. Observed variations in the h'F2 and hmF2 showed lower values than the control days, although hmF2 was found to increase a bit during the eclipse. Observed variability in the E, F1 and F2 layer ionospheric parameters on the eclipse day and their departure from the control days are discussed as the combined effect of annular eclipse and presence of counter equatorial electrojet (CEEJ).

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Yadav, V., B. Kakad, C. K. Nayak, G. Surve, and K. Emperumel. "Occurrence of blanketing E<sub>s</sub> layer (E<sub>sb</sub>) over the equatorial region during the peculiar minimum of solar cycle 24." Annales Geophysicae 32, no. 5 (May 26, 2014): 553–62. http://dx.doi.org/10.5194/angeo-32-553-2014.

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Abstract. A thin and highly dense sporadic E layer, which can occasionally block the upper ionospheric layers, is called blanketing sporadic E (Esb). We present the statistical seasonal local time occurrence pattern of Esb at equatorial station Tirunelveli (8.7° N, 77.8° E, dip latitude 0.7° N) during the extended minimum of solar cycle 24 (2007–2009). In spite of nearly the same average solar activity during both 2007 and 2009, considerable differences are noticed in the seasonal occurrence of Esb during this period. The percentage of Esb occurrence is found to be the highest during the summer solstice (&geq; 50%) for both 2007 and 2009, which is in general accordance with the earlier studies. The occurrences of Esb during the vernal equinox (~ 33%) and January–February (~ 28%) are substantial in 2009 as compared to those during the same seasons in 2007. We find that, during winter (January–February), ~ 75% of Esb occurred during or just after the period of sudden stratospheric warming (SSW). We suggest that enhanced Esb occurrence during winter (January–February) and the vernal equinox of 2009 could be associated with SSW-driven changes in the E region ambient conditions. Furthermore, the close association of Esb with counter equatorial electrojet (CEEJ) suggested by earlier studies is re-examined carefully using the scenario of Esb occurrence on non-CEEJ days. Such an exercise is crucial as we are unaware whether the physical mechanisms driving Esb and CEEJ are linked or not. We find that, of all the seasons, the association of Esb and CEEJ is strongest during winter (November–December).

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Devasia, C. V., N. Jyoti, K. S. V. Subbarao, Diwakar Tiwari, C. Raghava Reddi, and R. Sridharan. "On the role of vertical electron density gradients in the generation of type II irregularities associated with blanketing ES(ESb) during counter equatorial electrojet events: A case study." Radio Science 39, no. 3 (May 22, 2004): n/a. http://dx.doi.org/10.1029/2002rs002725.

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Devasia, C. V., V. Sreeja, and S. Ravindran. "Solar cycle dependent characteristics of the equatorial blanketing E<sub><i>s</i></sub> layers and associated irregularities." Annales Geophysicae 24, no. 11 (November 21, 2006): 2931–47. http://dx.doi.org/10.5194/angeo-24-2931-2006.

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Abstract. The occurrence of blanketing type Es (Esb) layers and associated E-region irregularities over the magnetic equatorial location of Trivandrum (8.5° N; 77° E; dip ~0.5°) during the summer solstitial months of May, June, July and August has been investigated in detail for the period 1986–2000 to bring out the variabilities in their characteristics with the solar cycle changes. The study has been made using the ionosonde and magnetometer data of Trivandrum from 1986–2000 along with the available data from the 54.95 MHz VHF backscatter radar at Trivandrum for the period 1995–2000. The appearance of blanketing Es layers during these months is observed to be mostly in association with the occurrence of afternoon Counter Electrojet (CEJ) events. The physical process leading to the occurrence of a CEJ event is mainly controlled by the nature of the prevailing electro dynamical/neutral dynamical conditions before the event. Hence it is natural that the Esb layer characteristics like the frequency of occurrence, onset time, intensity, nature of gradients in its top and bottom sides etc are also affected by the nature of the background electro dynamical /neutral dynamical processes which in turn are strongly controlled by the solar activity changes. The occurrence of Esb layers during the solstitial months is found to show very strong solar activity dependence with the occurrence frequency being very large during the solar minimum years and very low during solar maximum years. The intensity of the VHF radar backscattered signals from the Esb irregularities is observed to be controlled by the relative roles of the direction and magnitude of the prevailing vertical polarization electric field and the vertical electron density gradient of the prevailing Esb layer depending on the phase of the solar cycle. The gradient of the Esb layer shows a more dominant role in the generation of gradient instabilities during solar minimum periods while it is the electric field that has a more dominant role during solar maximum periods.

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Vineeth, C., T. Kumar Pant, and R. Sridharan. "Equatorial counter electrojets and polar stratospheric sudden warmings – a classical example of high latitude-low latitude coupling?" Annales Geophysicae 27, no. 8 (August 12, 2009): 3147–53. http://dx.doi.org/10.5194/angeo-27-3147-2009.

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Abstract. Favored occurrences of Equatorial Counter Electrojets (CEJs) with a quasi 16-day periodicity over Trivandrum (8.5° N, 76.5° E, 0.5° N diplat.) in association with the polar Stratospheric Sudden Warming (SSW) events are presented. It is observed that, the stratospheric temperature at ~30 km over Trivandrum shows a sudden cooling prior to the SSWs and the CEJs of maximum intensity which occurs around this time. In general stronger CEJs are associated with more intense SSW events. The stratospheric zonal mean zonal wind over Trivandrum also exhibits a distinctly different pattern during the SSW period. These circulation changes are proposed to be conducive for the upward propagation of the lower atmospheric waves over the equatorial latitudes. The interaction of such waves with the tidal components at the upper mesosphere and its subsequent modification are suggested to be responsible for the occurrence of CEJs having planetary wave periods.

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Archana, R. K., Kusumita Arora, and Nandini Nagarajan. "Prompt penetration effects on Equatorial Electrojet from the Indian sector." Earth, Planets and Space 75, no. 1 (August 14, 2023). http://dx.doi.org/10.1186/s40623-023-01874-9.

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AbstractThe morphology of prompt penetration effects (PP) in the Equatorial Electrojet (EEJ) at Vencode (VEN, Geomagnetic latitude 0.29ºN) was studied using 5-min samples of EEJ and interplanetary Ey component data from 2011 to 2015. In contrast to previous studies that mainly focused on storm-time PP events, our study investigated the characteristics of PP effects on EEJ during both quiet and disturbed periods. Our findings reaffirm earlier reports of high PP efficiency during local noon for both quiet and disturbed days. Moreover, PP amplitudes were greater when IMF-Bz was oriented northward compared to southward, indicating the presence of overshielding effects even during quiet conditions. Additionally, we examined seasonal variations in PP amplitudes and observed weaker PP during the solstice compared to the equinox. Furthermore, our study analysed the equatorial counter electrojet (CEJ) caused by PP events associated with northward-turning IMF-Bz. We report 15% of CEJs at VEN associated with PP effects; a few PP events were observed while the equatorial electric field at VEN was already westward (i.e. PP within CEJ), indicating the combined effects of magnetospheric and ionospheric perturbations. Identifying CEJs caused by PP during quiet days helps to differentiate between magnetospheric and ionospheric mechanisms/processes. Additionally, we investigated the spatial variability in PP amplitudes at closely spaced sites, utilizing one year of concurrent data from Minicoy (MNC, Geomagnetic latitude 0.19ºN), VEN, and Campbell Bay (CBY, Geomagnetic latitude 0.29ºN) situated at geographic longitudes 72º, 77º and 93º, respectively. Our results showed significant differences in PP amplitudes between VEN-CBY and MNC-CBY, separated by 15º and 20º longitude, respectively. Observations from the three equatorial sites demonstrated a longitudinal trend, with PP amplitudes increasing westward towards MNC, inverse to the amplitudes of EEJ. Graphical Abstract

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Le, Guan, Guiping Liu, Endawoke Yizengaw, and Christoph R. Englert. "Intense Equatorial Electrojet and Counter Electrojet caused by the 15 January 2022 Tonga Volcanic Eruption: Space and Ground‐based Observations." Geophysical Research Letters, May 27, 2022. http://dx.doi.org/10.1029/2022gl099002.

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Santos, A. M., C. G. M. Brum, I. S. Batista, J. H. A. Sobral, M. A. Abdu, J. R. Souza, S. S. Chen, et al. "Anomalous responses of the F ₂ layer over the Brazilian equatorial sector during a counter electrojet event: A CASE STUDY." Journal of Geophysical Research: Space Physics, August 9, 2022. http://dx.doi.org/10.1029/2022ja030584.

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