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Journal articles on the topic 'Equatorial E-region'

Author: Grafiati
Published: 6 September 2023

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1

Raghavarao, R., A. K. Patra, and S. Sripathi. "Equatorial E region irregularities: a review of recent observations." Journal of Atmospheric and Solar-Terrestrial Physics 64, no. 12-14 (August 2002): 1435–43. http://dx.doi.org/10.1016/s1364-6826(02)00107-4.

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2

Kherani, Esfhan A., and Eurico R. de Paula. "Observations of Quasi-Periodic Electric Field Disturbances in the E Region before and during the Equatorial Plasma Bubble." Atmosphere 12, no. 9 (August 27, 2021): 1106. http://dx.doi.org/10.3390/atmos12091106.

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Wave-like electric field disturbances in the ionosphere before the Equatorial Plasma Bubble (EPB) are the subject of numerous recent studies that address the issue of possible short-term forecasting of EPB. We report the observations of the Equatorial Quasi-Periodic-Electric field Disturbances (QP-EDs) of the Field-aligned Irregularities (FAI) in the E region before the EPB occurrence in the F region. They are observed from 30 MHz coherent scatter radar during the SpreadFEx campaign 2005 carried out in Brasil. The presently reported QP-EDs at the equatorial E region below an altitude of 110 km are undescribed so far. Though QP-EDs characteristics vary on a day-to-day basis, consistent features are their intensification before the EPB, and their simultaneous occurrence with EPBs. This study highlights the monitoring of QP-EDs in the short-term forecasting of EPBs and further reveals the robust energetics of vertical coupling between E and F regions.
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3

Onohara, A. N., I. S. Batista, and H. Takahashi. "The ultra-fast Kelvin waves in the equatorial ionosphere: observations and modeling." Annales Geophysicae 31, no. 2 (February 7, 2013): 209–15. http://dx.doi.org/10.5194/angeo-31-209-2013.

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Abstract. The main purpose of this study is to investigate the vertical coupling between the mesosphere and lower thermosphere (MLT) region and the ionosphere through ultra-fast Kelvin (UFK) waves in the equatorial atmosphere. The effect of UFK waves on the ionospheric parameters was estimated using an ionospheric model which calculates electrostatic potential in the E-region and solves coupled electrodynamics of the equatorial ionosphere in the E- and F-regions. The UFK wave was observed in the South American equatorial region during February–March 2005. The MLT wind data obtained by meteor radar at São João do Cariri (7.5° S, 37.5° W) and ionospheric F-layer bottom height (h'F) observed by ionosonde at Fortaleza (3.9° S; 38.4° W) were used in order to calculate the wave characteristics and amplitude of oscillation. The simulation results showed that the combined electrodynamical effect of tides and UFK waves in the MLT region could explain the oscillations observed in the ionospheric parameters.
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4

Hari, S. S., and B. V. Krishna Murthy. "Equatorial night-time F-region zonal electric fields." Annales Geophysicae 13, no. 8 (August 31, 1995): 871–78. http://dx.doi.org/10.1007/s00585-995-0871-8.

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Abstract. Night-time F-region vertical electrodynamic drifts at the magnetic equatorial station, Trivandrum are obtained for a period of 2 years, 1989 and 1990 (corresponding to solar cycle maximum epoch), using ionosonde h'F data. The seasonal variation of the vertical drift is found to be associated with the longitudinal gradients of the thermospheric zonal wind. Further, the seasonal variation of the prereversal enhancement of the vertical drift is associated with the time difference between the sunset times of the conjugate E-regions (magnetic field line linked to F-region) which is indicative of the longitudinal gradients of the conductivity (of the E-region). The vertical drifts and the causative zonal electric fields at Trivandrum are compared with those at Jicamarca and F-region zonal electric field models. It is seen that the night-time downward drift (as also the causative westward electric field) at Jicamarca is greater than that at Trivandrum. The prereversal enhancement of the drift is greater at Jicamarca than at Trivandrum during the summer and the equinoxes, whereas during the winter the opposite is the case.
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5

Sridharan, R., C. V. Devasia, N. Jyoti, Diwakar Tiwari, K. S. Viswanathan, and K. S. V. Subbarao. "Effects of solar eclipse on the electrodynamical processes of the equatorial ionosphere: a case study during 11 August 1999 dusk time total solar eclipse over India." Annales Geophysicae 20, no. 12 (December 31, 2002): 1977–85. http://dx.doi.org/10.5194/angeo-20-1977-2002.

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Abstract. The effects on the electrodynamics of the equatorial E- and F-regions of the ionosphere, due to the occurrence of the solar eclipse during sunset hours on 11 August 1999, were investigated in a unique observational campaign involving ground based ionosondes, VHF and HF radars from the equatorial location of Trivandrum (8.5° N; 77° E; dip lat. 0.5° N), India. The study revealed the nature of changes brought about by the eclipse in the evening time E- and F-regions in terms of (i) the sudden intensification of a weak blanketing ES-layer and the associated large enhancement of the VHF backscattered returns, (ii) significant increase in h' F immediately following the eclipse and (iii) distinctly different spatial and temporal structures in the spread-F irregularity drift velocities as observed by the HF radar. The significantly large enhancement of the backscattered returns from the E-region coincident with the onset of the eclipse is attributed to the generation of steep electron density gradients associated with the blanketing ES , possibly triggered by the eclipse phenomena. The increase in F-region base height immediately after the eclipse is explained as due to the reduction in the conductivity of the conjugate E-region in the path of totality connected to the F-region over the equator along the magnetic field lines, and this, with the peculiar local and regional conditions, seems to have reduced the E-region loading of the F-region dynamo, resulting in a larger post sunset F-region height (h' F) rise. These aspects of E-and F-region behaviour on the eclipse day are discussed in relation to those observed on the control day.Key words. Ionosphere (electric fields and currents; equatorial ionosphere; ionospheric irregularities)
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6

Farley, D. T. "The equatorial E-region and its plasma instabilities: a tutorial." Annales Geophysicae 27, no. 4 (April 2, 2009): 1509–20. http://dx.doi.org/10.5194/angeo-27-1509-2009.

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Abstract. In this short tutorial we first briefly review the basic physics of the E-region of the equatorial ionosphere, with emphasis on the strong electrojet current system that drives plasma instabilities and generates strong plasma waves that are easily detected by radars and rocket probes. We then discuss the instabilities themselves, both the theory and some examples of the observational data. These instabilities have now been studied for about half a century (!), beginning with the IGY, particularly at the Jicamarca Radio Observatory in Peru. The linear fluid theory of the important processes is now well understood, but there are still questions about some kinetic effects, not to mention the considerable amount of work to be done before we have a full quantitative understanding of the limiting nonlinear processes that determine the details of what we actually observe. As our observational techniques, especially the radar techniques, improve, we find some answers, but also more and more questions. One difficulty with studying natural phenomena, such as these instabilities, is that we cannot perform active cause-and-effect experiments; we are limited to the inputs and responses that nature provides. The one hope here is the steadily growing capability of numerical plasma simulations. If we can accurately simulate the relevant plasma physics, we can control the inputs and measure the responses in great detail. Unfortunately, the problem is inherently three-dimensional, and we still need somewhat more computer power than is currently available, although we have come a long way.
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7

Cousins, A. W. J., and J. A. R. Caldwell. "DDO photometry of E-region stars and equatorial standards -- II." Monthly Notices of the Royal Astronomical Society 281, no. 2 (July 11, 1996): 522–30. http://dx.doi.org/10.1093/mnras/281.2.522.

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8

Sinha, H. S. S., R. Pandey, Shweta Sharma, and R. N. Misra. "Nighttime E region plasma irregularities over an equatorial station Trivandrum." Journal of Atmospheric and Solar-Terrestrial Physics 73, no. 17-18 (November 2011): 2444–52. http://dx.doi.org/10.1016/j.jastp.2011.10.005.

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9

Chau, J. L., R. F. Woodman, and L. A. Flores. "Statistical characteristics of low-latitude ionospheric field-aligned irregularities obtained with the Piura VHF radar." Annales Geophysicae 20, no. 8 (August 31, 2002): 1203–12. http://dx.doi.org/10.5194/angeo-20-1203-2002.

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Abstract. We present a summary of the statistical characteristics of echoes from ionospheric (E- and F-region) field-aligned irregularities obtained with the Piura VHF radar. This radar is located at ~ 7.0° dip latitude, just outside the equatorial electrojet (EEJ) region. Our results are based on (1) intermittent observations made between 1991 and 1999 just few days a year, and (2) continuous observations made between January 2000 and June 2001. During most of the intermittent observations, simultaneous measurements of EEJ and equatorial spread F (ESF) irregularities were performed with the Jicamarca VHF radar. From the continuous measurements, we have obtained the diurnal and seasonal characteristics of a variety of parameters (percentage of occurrence, signal-to-noise ratio and/or Doppler velocities) from the lower and upper E-region irregularities and also from F-region irregularities over Piura. For example, we have found that (1) the E-region echoes are stronger and occur more frequently during local summer (i.e. between December and March); (2) between May and June, the E-region echoes are weaker and occur less frequently; moreover, during these months, a semidiurnal wave with large amplitudes is observed in the meridional wind (> 100 ms- 1); (3) there is vertical wavelength of about 20 km in the Doppler velocity, particularly after midnight; (4) the lower (upper) E-region Doppler velocities are influenced mainly by meridional winds (equatorial F-region vertical drifts). In addition, we have observed that the seasonal and daily occurrences of Piura F-region irregularities are similar to the occurrence of topside ESF irregularities over Jicamarca. The likelihood of occurrence of F-region irregularities over Piura and, therefore, topside ESF over Jicamarca is greater when there are no E-region irregularities over Piura. On the other hand, there is more probability of observing bottomtype/bottomside ESF irregularities over Jicamarca when E-region irregularities are observed over Piura.Key words. Ionosphere (ionospheric irregularities; equatorial ionosphere; instruments and techniques)
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10

Oppenheim, Meers M., Axel F. vom Endt, and Lars P. Dyrud. "Electrodynamics of meteor trail evolution in the equatorial E-region ionosphere." Geophysical Research Letters 27, no. 19 (October 1, 2000): 3173–76. http://dx.doi.org/10.1029/1999gl000013.

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11

Singh, A., and K. D. Cole. "Electrodynamic effects of metal ions in the noon equatorial E-region." Journal of Atmospheric and Terrestrial Physics 50, no. 12 (December 1988): 1093–98. http://dx.doi.org/10.1016/0021-9169(88)90098-0.

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12

Sreeja, V., and C. V. Devasia. "Observational evidence for the plausible linkage of Equatorial Electrojet (EEJ) electric field variations with the post sunset F-region electrodynamics." Annales Geophysicae 27, no. 11 (November 10, 2009): 4229–38. http://dx.doi.org/10.5194/angeo-27-4229-2009.

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Abstract. The paper is based on a detailed observational study of the Equatorial Spread F (ESF) events on geomagnetically quiet (Ap≤20) days of the solar maximum (2001), moderate (2004) and minimum (2006) years using the ionograms and magnetograms from the magnetic equatorial location of Trivandrum (8.5° N; 77° E; dip lat ~0.5° N) in India. The study brings out some interesting aspects of the daytime Equatorial Electrojet (EEJ) related electric field variations and the post sunset F-region electrodynamics governing the nature of seasonal characteristics of the ESF phenomena during these years. The observed results seem to indicate a plausible linkage of daytime EEJ related electric field variations with pre-reversal enhancement which in turn is related to the occurrence of ESF. These electric field variations are shown to be better represented through a parameter, termed as "E", in the context of possible coupling between the E- and F-regions of the ionosphere. The observed similarities in the gross features of the variations in the parameter "E" and the F-region vertical drift (Vz) point towards the potential usage of the EEJ related parameter "E" as an useful index for the assessment of Vz prior to the occurrence of ESF.
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13

Horvath, I., and E. A. Essex. "Vertical <i>E</i> × <i>B</i> drift velocity variations and associated low-latitude ionospheric irregularities investigated with the TOPEX and GPS satellite data." Annales Geophysicae 21, no. 4 (April 30, 2003): 1017–30. http://dx.doi.org/10.5194/angeo-21-1017-2003.

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Abstract. With a well-selected data set, the various events of the vertical E × B drift velocity variations at magnetic-equator-latitudes, the resultant ionospheric features at low-and mid-latitudes, and the practical consequences of these E × B events on the equatorial radio signal propagation are demonstrated. On a global scale, the development of a equatorial anomaly is illustrated with a series of 1995 global TOPEX TEC (total electron content) maps. Locally, in the Australian longitude region, some field-aligned TOPEX TEC cross sections are combined with the matching Guam (144.86° E; 13.59° N, geographic) GPS (Global Positioning System) TEC data, covering the northern crest of the equatorial anomaly. Together, the 1998 TOPEX and GPS TEC data are utilized to show the three main events of vertical E × B drift velocity variations: (1) the pre-reversal enhancement, (2) the reversal and (3) the downward maximum. Their effects on the dual-frequency GPS recordings are documented with the raw Guam GPS TEC data and with the filtered Guam GPS dTEC/min or 1-min GPS TEC data after Aarons et al. (1997). During these E × B drift velocity events, the Port Moresby (147.10° E; - 9.40° N, geographic) virtual height or h'F ionosonde data (km), which cover the southern crest of the equatorial anomaly in the Australian longitude region, show the effects of plasma drift on the equatorial ionosphere. With the net (D) horizontal (H) magnetic field intensity parameter, introduced and called DH or Hequator-Hnon-equator (nT) by Chandra and Rastogi (1974), the daily E × B drift velocity variations are illustrated at 121° E (geographic) in the Australian longitude region. The results obtained with the various data show very clearly that the development of mid-latitude night-time TEC increases is triggered by the westward electric field as the appearance of such night-time TEC increases coincides with the E × B drift velocity reversal. An explanation is offered with the F-region dynamo theory and electrodynamics, and with the ionospheric-plasmaspheric coupling. A comparison is made with the published model results of SUPIM (Sheffield University Plasmasphere-Ionosphere Model; Balan and Bailey, 1995) and experimental results of Park (1971), and the good agreement found is highlighted.Key words. Ionosphere (electric fields; equatorial ionosphere; mid-latitude ionosphere)
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14

Hysell, D. L., E. Kudeki, and J. L. Chau. "Possible ionospheric preconditioning by shear flow leading to equatorial spread <i>F</i>." Annales Geophysicae 23, no. 7 (October 14, 2005): 2647–55. http://dx.doi.org/10.5194/angeo-23-2647-2005.

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Abstract. Vertical shear in the zonal plasma drift speed is apparent in incoherent and coherent scatter radar observations of the bottomside F region ionosphere made at Jicamarca from about 1600–2200 LT. The relative importance of the factors controlling the shear, which include competition between the E and F region dynamos as well as vertical currents driven in the E and F regions at the dip equator, is presently unknown. Bottom-type scattering layers arise in strata where the neutral and plasma drifts differ widely, and periodic structuring of irregularities within the layers is telltale of intermediate-scale waves in the bottomside. These precursor waves appear to be able to seed ionospheric interchange instabilities and initiate full-blown equatorial spread F. The seed or precursor waves may be generated by a collisional shear instability. However, assessing the viability of shear instability requires measurements of the same parameters needed to understand shear flow quantitatively - thermospheric neutral wind and off-equatorial conductivity profiles. Keywords. Ionosphere (Equatorial ionosphere; ionospheric irregularities) – Space plasma physics (Waves and instabilities)
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15

Savio Odriozola, Siomel, Francisco Carlos de Meneses Jr., Polinaya Muralikrishna, Alexandre Alvares Pimenta, and Esfhan Alam Kherani. "Rocket in situ observation of equatorial plasma irregularities in the region between E and F layers over Brazil." Annales Geophysicae 35, no. 3 (March 16, 2017): 413–22. http://dx.doi.org/10.5194/angeo-35-413-2017.

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Abstract. A two-stage VS-30 Orion rocket was launched from the equatorial rocket launching station in Alcântara, Brazil, on 8 December 2012 soon after sunset (19:00 LT), carrying a Langmuir probe operating alternately in swept and constant bias modes. At the time of launch, ground equipment operated at equatorial stations showed rapid rise in the base of the F layer, indicating the pre-reversal enhancement of the F region vertical drift and creating ionospheric conditions favorable for the generation of plasma bubbles. Vertical profiles of electron density estimated from Langmuir probe data showed wave patterns and small- and medium-scale plasma irregularities in the valley region (100–300 km) during the rocket upleg and downleg. These irregularities resemble those detected by the very high frequency (VHF) radar installed at Jicamarca and so-called equatorial quasi-periodic echoes. We present evidence suggesting that these observations could be the first detection of this type of irregularity made by instruments onboard a rocket.
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16

Hafsa Siddiqui, Varsha Kachneria, and A. M. Aslam. "The Occurrence of Sporadic-E Layer over Equatorial Anomaly Crest Region Bhopal." Geomagnetism and Aeronomy 58, no. 8 (December 2018): 1061–66. http://dx.doi.org/10.1134/s001679321808008x.

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17

Gupta, S. P. "Thin layers of ionization observed by rocketborne probes in equatorial E region." Advances in Space Research 19, no. 1 (January 1997): 169–73. http://dx.doi.org/10.1016/s0273-1177(96)00048-8.

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18

Pfaff, R. F., M. C. Kelley, B. G. Fejer, N. C. Maynard, L. H. Brace, B. G. Ledley, L. G. Smith, and R. F. Woodman. "Comparative in situ studies of the unstable day-time equatorial E-region." Journal of Atmospheric and Terrestrial Physics 47, no. 8-10 (August 1985): 791–811. http://dx.doi.org/10.1016/0021-9169(85)90055-8.

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19

de la Vega, Matías, Alicia Favetto, and Ana Osella. "Solar quiet geomagnetic variations and E-region neutral winds at equatorial latitudes." Journal of Atmospheric and Terrestrial Physics 57, no. 10 (August 1995): 1129–33. http://dx.doi.org/10.1016/0021-9169(94)00128-b.

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20

MUKHOPADHYAY, R. K., and T. K. SARKAR. "Middle atmospheric oscillation over India and its possible association with Indian summer monsoon." MAUSAM 41, no. 1 (February 22, 2022): 75–80. http://dx.doi.org/10.54302/mausam.v41i1.2296.

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In this paper the middle atmospheric oscillations of the zonal wind in upper stratosphere and lower mesosphere have been analysed and studied using the rocket sonde wind data of Thumba and Balasore It was observed that in the mean, picture, t e semi-annual oscillation at on was predominant in the equatorial Indian region (i, e.,over Thumba ) while the annual wave was predominant over tropical Indian region (i.e over Balasore), During good monsoon year, a strong semi-annual wave over tropical Indian region was observed . The amplitude of this semi-annual wave was also found to be significantly higher over the equatorial Indian region during good monsoon year, The study seem3 to reveal a close association of the middle atmospheric oscillations over India with the summer monsoon.
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21

Brahmanandam, P. S., Y. H. Chu, K. H. Wu, H. P. Hsia, C. L. Su, and G. Uma. "Vertical and longitudinal electron density structures of equatorial E- and F-regions." Annales Geophysicae 29, no. 1 (January 10, 2011): 81–89. http://dx.doi.org/10.5194/angeo-29-81-2011.

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Abstract. From global soundings of ionospheric electron density made with FORMOSAT 3/COSMIC satellites for September 2006–August 2009, day-night variations in vertical and longitudinal structures of the electron densities in equatorial E- and F-regions for different seasons are investigated for the first time. The results reveal that the wavenumber-3 and wavenumber-4 patterns dominated the nighttime (22:00–04:00 LT) F-region longitudinal structures in solstice and in equinox seasons, respectively. In daytime (08:00–18:00 LT) F-region, the wavenumber-4 patterns governed the longitudinal structures in the September equinox and December solstice, and wavenumber-3 in March equinox and June solstice respectively. A comparison of the daytime and nighttime longitudinal electron density structures indicates that they are approximately 180° out of phase with each other. It is believed that this out of phase relation is very likely the result of the opposite phase relation between daytime and nighttime nonmigrating diurnal tidal winds that modulate background E-region dynamo electric field at different places, leading to the day-night change in the locations of the equatorial plasma fountains that are responsible for the formation of the F-region longitudinal structures. Further, a good consistency between the locations of the density structures in the same seasons of the different years for both daytime and nighttime epochs has been noticed indicating that the source mechanism for these structures could be the same.
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22

Patra, A. K., S. Sripathi, and D. Tiwari. "Coupling effect of the equatorial F region irregularities on the low latitude E region instability processes." Geophysical Research Letters 31, no. 17 (September 2004): n/a. http://dx.doi.org/10.1029/2004gl020486.

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23

Uemoto, J., T. Maruyama, S. Saito, M. Ishii, and R. Yoshimura. "Relationships between pre-sunset electrojet strength, pre-reversal enhancement and equatorial spread-F onset." Annales Geophysicae 28, no. 2 (February 8, 2010): 449–54. http://dx.doi.org/10.5194/angeo-28-449-2010.

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Abstract. The virtual height of the bottom side F-region (h'F) and equatorial spread-F (ESF) onsets at Chumphon (10.7° N, 99.4° E; 3.3° N magnetic latitude) were compared with the behaviour of equatorial electrojet (EEJ) ground strength at Phuket (8.1° N, 98.3° E; 0.1° N magnetic latitude) during the period from November 2007 to October 2008. Increase in the F-layer height and ESF onsets during the evening hours were well connected with the EEJ ground strength before sunset, namely, both the height increase and ESF onsets were suppressed when the integrated EEJ ground strength for the period from 1 to 2 h prior to sunset was negative. The finding suggests observationally that the pre-sunset E-region dynamo current and/or electric field are related to the F-region dynamics and ESF onsets around sunset.
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24

Fukao, S., T. Yokoyama, T. Tayama, M. Yamamoto, T. Maruyama, and S. Saito. "Eastward traverse of equatorial plasma plumes observed with the Equatorial Atmosphere Radar in Indonesia." Annales Geophysicae 24, no. 5 (July 3, 2006): 1411–18. http://dx.doi.org/10.5194/angeo-24-1411-2006.

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Abstract. The zonal structure of radar backscatter plumes associated with Equatorial Spread F (ESF), probably modulated by atmospheric gravity waves, has been investigated with the Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia (0.20° S, 100.32° E; dip latitude 10.1° S) and the FM-CW ionospheric sounders on the same magnetic meridian as the EAR. The occurrence locations and zonal distances of the ESF plumes were determined with multi-beam observations with the EAR. The ESF plumes drifted eastward while keeping distances of several hundred to a thousand kilometers. Comparing the occurrence of the plumes and the F-layer uplift measured by the FM-CW sounders, plumes were initiated within the scanned area around sunset only, when the F-layer altitude rapidly increased. Therefore, the PreReversal Enhancement (PRE) is considered as having a zonal variation with the scales mentioned above, and this variation causes day-to-day variability, which has been studied for a long time. Modulation of the underlying E-region conductivity by gravity waves, which causes inhomogeneous sporadic-E layers, for example, is a likely mechanism to determine the scale of the PRE.
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25

Neelakshi, J., Reinaldo R. Rosa, Siomel Savio, Stephan Stephany, Francisco C. de Meneses, Esfhan Alam Kherani, and P. Muralikrishna. "Multifractal characteristics of the low latitude equatorial ionospheric E–F valley region irregularities." Chaos, Solitons & Fractals 156 (March 2022): 111808. http://dx.doi.org/10.1016/j.chaos.2022.111808.

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26

Pandey, Kuldeep, R. Sekar, B. G. Anandarao, S. P. Gupta, and D. Chakrabarty. "Estimation of nighttime dip-equatorial E-region current density using measurements and models." Journal of Atmospheric and Solar-Terrestrial Physics 146 (August 2016): 160–70. http://dx.doi.org/10.1016/j.jastp.2016.06.002.

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27

Reinisch, B. W., M. Abdu, I. Batista, G. S. Sales, G. Khmyrov, T. A. Bullett, J. Chau, and V. Rios. "Multistation digisonde observations of equatorial spread F in South America." Annales Geophysicae 22, no. 9 (September 23, 2004): 3145–53. http://dx.doi.org/10.5194/angeo-22-3145-2004.

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Abstract. Directional ionogram and F-region drift observations were conducted at seven digisonde stations in South America during the COPEX campaign from October to December 2002. Five stations in Brazil, one in Argentina, and one in Peru, monitored the ionosphere across the continent to study the onset and development of F-region density depletions that cause equatorial spread F (ESF). New ionosonde techniques quantitatively describe the prereversal uplifting of the F layer at the magnetic equator and the eastward motion of the depletions over the stations. Three of the Brazilian stations were located along a field line with a 350-km apex over the equator to investigate the relation of the occurrence of ESF and the presence of sporadic E-layers at the two E-region intersections of the field line. No simple correlation was found.
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28

Yokoyama, T., D. L. Hysell, A. K. Patra, Y. Otsuka, and M. Yamamoto. "Zonal asymmetry of daytime 150-km echoes observed by Equatorial Atmosphere Radar in Indonesia." Annales Geophysicae 27, no. 3 (March 2, 2009): 967–74. http://dx.doi.org/10.5194/angeo-27-967-2009.

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Abstract. Multi-beam observations of the daytime ionospheric E-region irregularities and the so-called 150-km echoes with the 47-MHz Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia (0.20° S, 100.32° E, 10.36° S dip latitude) are presented. 150-km echoes have been frequently observed by the EAR, and their characteristics are basically the same as the equatorial ones, except for an intriguing zonal asymmetry; stronger echoes in lower altitudes in the east directions, and weaker echoes in higher altitudes in the west. The highest occurrence is seen at 5.7° east with respect to the magnetic meridian, and the altitude gradually increases as viewing from the east to west. Arc structures which return backscatter echoes are proposed to explain the asymmetry. While the strength of radar echoes below 105 km is uniform within the wide coverage of azimuthal directions, the upper E-region (105–120 km) echoes also show a different type of zonal asymmetry, which should be generated by an essentially different mechanism from the lower E-region and 150-km echoes.
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Denardini, C. M., M. A. Abdu, E. R. de Paula, C. M. Wrasse, and J. H. A. Sobral. "VHF radar observations of the dip equatorial E-region during sunset in the Brazilian sector." Annales Geophysicae 24, no. 6 (July 3, 2006): 1617–23. http://dx.doi.org/10.5194/angeo-24-1617-2006.

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Abstract. Using the RESCO 50 MHz backscatter radar (2.33° S, 44.2° W, DIP: –0.5), at São Luís, Brazil, we obtained Range Time Intensity (RTI) maps covering the equatorial electrojet heights during daytime and evening. These maps revealed a scattering region at an altitude of about 108 km during the sunset period. The type of 3-m irregularity region we present here has not been reported before in the literature, to our knowledge. It was mainly observed around the Southern Hemisphere summer-solstice period, under quiet magnetic activity condition. The occurrence of this echo region coincides in local time with the maximum intensity of an evening pre-reversal eastward electric field of the ionospheric F-region. A tentative explanation is proposed here in terms of the theory of the divergence of the equatorial electrojet (EEJ) current in the evening ionosphere presented by Haerendel and Eccles (1992), to explain the partial contribution of the divergence to the development of the pre-reversal electric field. The theory predicts an enhanced zonal electric field and hence a vertical electric field below 300 km as a consequence of the EEJ divergence in the evening. The experimental results of the enhanced echoes from the higher heights of the EEJ region seem to provide evidence that the divergence of the EEJ current can indeed be the driver of the observed scattering region.
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Mo, Xiaohua, and Donghe Zhang. "Quasi-10 d wave modulation of an equatorial ionization anomaly during the Southern Hemisphere stratospheric warming of 2002." Annales Geophysicae 38, no. 1 (January 3, 2020): 9–16. http://dx.doi.org/10.5194/angeo-38-9-2020.

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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.
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31

Dabas, R. S., R. M. Das, V. K. Vohra, and C. V. Devasia. "Space weather impact on the equatorial and low latitude F-region ionosphere over India." Annales Geophysicae 24, no. 1 (March 7, 2006): 97–105. http://dx.doi.org/10.5194/angeo-24-97-2006.

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Abstract. For a detailed study of the space weather impact on the equatorial and low latitude F-region, the ionospheric response features are analysed during the periods of three recent and most severe magnetic storm events of the present solar cycle which occurred in October and November 2003, and November 2004. The F-layer base height (h'F), peak height (hmF2) and critical frequency (foF2) data, from Trivandrum, an equatorial station and Delhi, a low latitude location, are examined during the three magnetic storm periods. The results of the analysis clearly shows that the height of the F-region (both h'F and hmF2), at the equator and low latitude, simultaneously increases by 200 to 300 km, in association with maximum negative excursion of Dst values around the midnight hours with a large depletion of ionization over the equator, which is followed by an ionization enhancement at low latitude during the recovery phase of the storm. At Delhi, fast variations up to 200 m/s are also observed in the F-layer vertical upward/downward velocity, calculated using Doppler shifts, associated with the maximum negative excursion of Dst. This shows that during magnetic disturbances, the equatorial ionization anomaly (EIA) expands to a much wider latitude than the normal fountain driven by the E/F-layer dynamo electric fields. It is also observed that during the main phase of the storm, at low latitude there is generally an enhancement of F-region ionization with an increase in h'F/hmF2 but in the equatorial region, the ionization collapses with a decrease in h'F/hmF2, especially after sunset hours. In addition, at the equator the normal pre-sunset hours' enhancement in h'F is considerably suppressed during storm periods. This might be due to changes in magnitude and direction of the zonal electric field affecting the upward E×B drift and hence the plasma distribution in the form of a decrease in electron density in the equatorial region and an increase in the low latitude region. In association with disturbance electric fields, the enhanced storm-induced equatorward meridional winds in the thermosphere can also further amplify the F-layer height rise at low latitudes during the post-midnight hours, as observed in two of the storm periods.
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32

Zickgraf, Franz-Josef. "Disk Winds of B[e] Supergiants." International Astronomical Union Colloquium 169 (1999): 40–48. http://dx.doi.org/10.1017/s025292110007175x.

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AbstractThe class of B[e] supegiants is characterized by a two-component stellar wind consisting of a normal hot star wind in the polar zone and a slow and dense disk-like wind in the equatorial region. The properties of the disk wind are discussed using satellite UV spectra of stars seen edge-on, i.e. through the equatorial disk. These observations show that the disk winds are extremely slow, v∞ ≃ 50 ‒ 90 km s−1, i.e. a factor of ~ 10 slower than expected from the spectral types. Optical emission lines provide a further means to study the disk wind. This is discussed for line profiles of forbidden lines formed in the disk.
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33

Dhanya, R., S. Gurubaran, and K. Emperumal. "Lower E-region echoes over the magnetic equator as observed by the MF radar at Tirunelveli (8.7° N, 77.8° E) and their relationship to <I>E<sub>sq</sub></I> and <I>E<sub>sb</sub></I>." Annales Geophysicae 26, no. 8 (August 15, 2008): 2459–70. http://dx.doi.org/10.5194/angeo-26-2459-2008.

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Abstract. The spaced antenna medium frequency (MF) radar at Tirunelveli (8.7° N, 77.8° E, geographic; 1.7° N, magnetic dip), the only one of its kind currently operating close to the magnetic equator, has provided an opportunity to investigate the electrodynamical processes related to the equatorial electrojet (EEJ) and their influence on the radar scatterers at medium frequencies in the lower E-region heights (90–98 km). Making use of the full correlation analysis that enables determination of useful geometrical parameters from the ground diffraction pattern, the present work delineates for the first time the characteristics of the radar scatterers during the occurrences of equatorial sporadic E (Esq) and blanketing sporadic E (Esb) noticed in simultaneous ionospheric sounding records at Tirunelveli. The ground magnetometer data provide indirect information on the strength of the EEJ and afternoon reverse EEJ or counterelectrojet (CEJ). The results presented in this work also reveal the height dependence of the radar echo intensity and some of the geometrical parameters at certain times, thus clearly bringing out the complex interplay of various physical processes in the probing region.
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34

Janhunen, P. "On recent developments in E-region irregularity simulationsand a summary of related theory." Annales Geophysicae 13, no. 7 (July 31, 1995): 791–806. http://dx.doi.org/10.1007/s00585-995-0791-7.

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Abstract. Theoretical and simulation approaches to E-region irregularities (gradient drift and Farley-Buneman instabilities) are reviewed, and an account is given of some relevant observations. A new hybrid linear dispersion relation is also derived and presented. The most important problem that cannot be explained by more straightforward theories is the saturation of the phase velocity to the ion acoustic speed (Cs saturation). This phenomenon is well-known from equatorial electrojet radar observations. Recent particle simulations have yielded an interesting new explanation for the (Cs saturation, which has been named flow angle stabilization: the phase velocity is not actually (Cs saturated, but the flow angle distribution of the spatial power spectrum is highly asymmetric. The asymmetry is such that the most intense waves propagate at the k·E < 0 edge of the linearly unstable sector, and thus the phase velocity of the most intense waves is close to (Cs. Depending on the level of larger scale turbulence, the radar observes varying degrees of (Cs saturation. If the larger scale turbulence level is high (equatorial electrojet case), the local flow angle fluctuates, and there are always sub-regions within the scattering volume with local flow angles favourable for the detection of the most intense waves. Under these conditions, the spectra show (Cs saturation. If the larger scale turbulence level is lower, there will not always be enough mixing of the flow angle for even the most intense waves to be observed. In these cases, the mean Doppler shift will be proportional to the electric field, i.e. it will obey the linear theory.
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35

Patra, A. K. "On the interpretation of the VHF radar echoes from the equatorial lower E region." Geophysical Research Letters 29, no. 14 (July 2002): 40–1. http://dx.doi.org/10.1029/2001gl013358.

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36

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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37

Oppenheim, M. "Evidence and effects of a wave-driven nonlinear current in the equatorial electrojet." Annales Geophysicae 15, no. 7 (July 31, 1997): 899–907. http://dx.doi.org/10.1007/s00585-997-0899-z.

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Abstract. Ionospheric two-stream waves and gradient-drift waves nonlinearly drive a large-scale (D.C.) current in the E-region ionosphere. This current flows parallel to, and with a comparable magnitude to, the fundamental Pedersen current. Evidence for the existence and magnitude of wave-driven currents derives from a theoretical understanding of E-region waves, supported by a series of nonlinear 2D simulations of two-stream waves and by data collected by rocket instruments in the equatorial electrojet. Wave-driven currents will modify the large-scale dynamics of the equatorial electrojet during highly active periods. A simple model shows how a wave-driven current appreciably reduces the horizontally flowing electron current of the electrojet. This reduction may account for the observation that type-I radar echoes almost always have a Doppler velocity close to the acoustic speed, and also for the rocket observation that electrojet regions containing gradient-drift waves do not appear also to contain horizontally propagating two-stream waves. Additionally, a simple model of a gradient-drift instability shows that wave-driven currents can cause nonsinusoidal electric fields similar to those measured in situ.
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38

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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39

Mačukanović-Jocić, Marina, Danijela Stešević, Dragana Rančić, and Zora Dajić Stevanović. "Pollen morphology and the flower visitors of Chaerophyllum coloratum L. (Apiaceae)." Acta Botanica Croatica 76, no. 1 (March 1, 2017): 1–8. http://dx.doi.org/10.1515/botcro-2016-0039.

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Abstract The pollen features of Chaerophyllum coloratum L., endemic to the Dinaric Alps, have been examined by both light microscopy and scanning electron microscopy in order to contribute to a better understanding of the taxonomic status of the species. Flower visitors have also been observed and analyzed with the aim of clarifying certain pollination aspects of the species including flower attractiveness especially to honeybees, and also in order to ascertain its contribution to the bee pasture. The pollen grains of C. coloratum are isopolar, radially symmetrical and medium sized. Polar axis (P) is 26.83±1.77 μm length, and equatorial diameter (E) is 9.17±0.57 μm length. P/E ratio amounts 2.90±0.10 indicating a perprolate shape. In an equatorial view, the grains are constricted in the equatorial region (bone-shaped), with obtuse polar caps. In polar view, they are triangular with obtuse angles and furrows in the sides of the triangle (interangular). The grains are tricolporate with three straight ectocolpi arranged regularly meridionally, of mean length 14.43±2.17 μm, each of which has one endopore. The characteristic internal thickenings around the protruding, clearly visible endopores (costae) in the constricted equatorial region are obvious in light microscopy. The ornamentation is psilate, irregularly rugulate (“cerebroid”), the exine surface is rather undulating. With regard to the observed flower visitors, the following pollination types occurred: melittophily, myophily, sapromyophily, cantharophily, and phalaenophily, and the most frequent pollinator was the honeybee.
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40

Guerrero, Pablo, Gracia Liébanas, and Reyes Peña-Santiago. "Nematodes of the order Dorylaimida from Andalucía Oriental, Spain. The genus Enchodelus Thorne, 1939. 3. Description of two new and one known species with rounded tail and medium-sized odontostyle." Nematology 10, no. 5 (2008): 711–33. http://dx.doi.org/10.1163/156854108785787208.

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Abstract Two new and one known species belonging to the genus Enchodelus from the southeast of the Iberian Peninsula are described and illustrated. Enchodelus ameliae sp. n. is a medium-sized nematode (1.37-1.55 mm) with lip region offset by constriction, odontostyle 30-32 μm long, female reproductive system amphidelphic with tripartite uterus, vulva almost equatorial (V = 47-50), spicules 49-60 μm long, 11-14 spaced ventromedian supplements and short rounded conoid tail. Enchodelus longispiculus sp. n. is characterised by its medium-sized body (1.32-1.87 mm), lip region offset by shallow depression, odontostyle 27-31 μm long, female reproductive system amphidelphic with tripartite uterus, vulva pre-equatorial (V = 41-48), spicules 63-72 μm long, 8-14 spaced ventromedian supplements and short rounded conoid tail. Enchodelus hopedoroides is redescribed on the basis of Andalusian material and observations on the Swiss holotype. These three species share some features, such as medium-sized odontostyle (ca 30 μm long), tripartite uterus and short, rounded, tail. They are compared in detail with other similar species, namely E. altherri, E. analatus, E. arcticus, E. georgiensis, E. hopedorus and E. ponorensis. A key to their identification is provided.
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41

Liu, J. Y., P. K. Rajesh, I. T. Lee, and T. C. Chow. "Airglow observations over the equatorial ionization anomaly zone in Taiwan." Annales Geophysicae 29, no. 5 (May 5, 2011): 749–57. http://dx.doi.org/10.5194/angeo-29-749-2011.

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Abstract. Airglow imaging at mid-latitude stations often show intensity modulations associated with medium scale travelling ionospheric disturbances (MSTID), while those carried out near the equatorial regions reveal depletions caused by equatorial plasma bubbles (EPB). Two all sky cameras are used to observe plasma depletions in the 630.0 nm emission over the equatorial ionization anomaly (EIA) region, Taiwan (23° N, 121° E; 13.5° N Magnetic) during 1998–2002 and 2006–2007. The results show EPB and MSTID depletions in different solar activity conditions. Several new features of the EPB depletions such as bifurcation, secondary structure on the walls, westward tilt, etc., are discussed in this paper. Evidence of tilted depletions with secondary structures developing on the eastern wall that later evolve to appear as bifurcations, are presented for the first time. Moreover, detail investigations are carried out using International Reference Ionosphere (IRI) model as well as the electron density from Ionosonde and Global Positioning System (GPS) Occultation Experiment (GOX) onboard FORMOSAT-3/COSMIC satellite, to understand the conditions that favor the propagation of MSTID to the latitude of Taiwan.
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42

RAO, KUSUMAG. "On the mean meridional circulation during the contrasting periods of normal and below normal monsoon activity." MAUSAM 36, no. 1 (April 5, 2022): 13–20. http://dx.doi.org/10.54302/mausam.v36i1.1577.

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For the contrasting periods of normal and below normal monsoon activity, the mean meridional circulation (M.M.C.) over 80 deg. E was computed. It was found that during monsoon months this region is characterized by rising motion over 35 deg. Nand sinking motion over 15 deg. N. During a monsoon break period sinking motion over 15 deg. N is intensified mainly due to local cooling. Strong rising motion occurs over equatorial regions to compensate for this sinking motion.
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43

Haldoupis, C., D. T. Farley, and K. Schlegel. "Type-1 echoes from the mid-latitude E-Region ionosphere." Annales Geophysicae 15, no. 7 (July 31, 1997): 908–17. http://dx.doi.org/10.1007/s00585-997-0908-2.

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Abstract. This paper presents more data on the properties of type-1 irregularities in the nighttime mid-latitude E-region ionosphere. The measurements were made with a 50-MHz Doppler radar system operating in Crete, Greece. The type-1 echoes last from several seconds to a few minutes and are characterized by narrow Doppler spectra with peaks corresponding to wave phase velocities of 250–350 m/s. The average velocity of 285 m/s is about 20% lower than nominal E-region ion-acoustic speeds, probably because of the presence of heavy metallic ions in the sporadic-E-layers that appear to be associated with the mid-latitude plasma instabilities. Sometimes the type-1 echoes are combined with a broad spectrum of type-2 echoes; at other times they dominate the spectrum or may appear in the absence of any type-2 spectral component. We believe these echoes are due to the modified two-stream plasma instability driven by a polarization electric field that must be larger than 10 mV/m. This field is similar in nature to the equatorial electrojet polarization field and can arise when patchy nighttime sporadic-E-layers have the right geometry.
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44

Chandra, H., S. Sharma, C. V. Devasia, K. S. V. Subbarao, R. Sridharan, J. H. Sastri, and J. V. S. V. Rao. "Sporadic-E associated with the Leonid meteor shower event of November 1998 over low and equatorial latitudes." Annales Geophysicae 19, no. 1 (January 31, 2001): 59–69. http://dx.doi.org/10.5194/angeo-19-59-2001.

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Abstract. Rapid radio soundings were made over Ahmedabad, a low latitude station during the period 16–20 November 1998 to study the sporadic-E layer associated with the Leonid shower activity using the KEL Aerospace digital ionosonde. Hourly ionograms for the period 11 November to 24 November were also examined during the years from 1994 to 1998. A distinct increase in sporadic-E layer occurrence is noticed on 17, 18 and 19 November from 1996 to 1998. The diurnal variations of f0Es and fbEs also show significantly enhanced values for the morning hours of 18 and 19 November 1998. The ionograms clearly show strong sporadic-E reflections at times of peak shower activity with multiple traces in the altitude range of 100–140 km in few ionograms. Sporadic-E layers with multiple structures in altitude are also seen in some of the ionograms (quarter hourly) at Thumba, situated near the magnetic equator. Few of ionograms recorded at Kodaikanal, another equatorial station, also show sporadic- E reflections in spite of the transmitter power being significantly lower. These new results highlighting the effect of intense meteor showers in the equatorial and low latitude E-region are presented.Key words. Ionosphere (equatorial ionosphere) – Radio science (ionospheric physics)
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45

Cueva, R. Y. C., E. R. de Paula, and A. E. Kherani. "Statistical analysis of radar observed F region irregularities from three longitudinal sectors." Annales Geophysicae 31, no. 12 (December 3, 2013): 2137–46. http://dx.doi.org/10.5194/angeo-31-2137-2013.

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Abstract. Equatorial Spread F (ESF) is a manifestation of ionospheric interchange instabilities in the nighttime equatorial F region. These instabilities generate plasma density irregularities with scale sizes ranging from centimetres to thousands of kilometres. The irregularities can be detected from a variety of instruments such as digisonde, coherent and incoherent scatter radars, in situ space probes, and airglow photometers. In the present study, occurrence statistics of the ESF, based on various parameters are presented using data obtained from the VHF radars located at three longitudinally separated equatorial stations: Christmas Island (2° N, 202.6° E, 2.9° N dip latitude), São Luís (2.59° S, 315.8° E, 0.5° S dip latitude) and Jicamarca (12° S, 283.1° E, 0.6° N dip latitude). The ESF parameters presented here are the onset altitude, onset time (onset refers to first appearance of signal in the radar field of view) of the bottom-type and plume, and the peak altitude of the plume. Recent studies have used these parameters to classify the spread F occurrence characteristics. The present study reveals novel features namely, the dependence of ESF parameters on the seasonal, solar flux, declination angle and longitudinal dependence from the three radar sites. In addition, we also present an empirical model to determine the nature of these ESF parameters as a function of the solar flux which may enable us to forecast (with 30 min to 1 h tolerance) the plume occurrence at any longitude located in between São Luís and Christmas Island.
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46

Hanumath Sastri, J., H. Luhr, H. Tachihara, T. I. Kitamura, and J. V. S. V. Rao. "Letter to the editor: Electric field fluctuations (25-35 min) in the midnight dip equatorial ionosphere." Annales Geophysicae 18, no. 2 (February 29, 2000): 252–56. http://dx.doi.org/10.1007/s00585-000-0252-2.

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Abstract. Measurements with a HF Doppler sounder at Kodaikanal (10.2°N, 77.5°E, geomagnetic latitude 0.8°N) showed conspicuous quasi-periodic fluctuations (period 25-35 min) in F region vertical plasma drift, Vz in the interval 0047-0210 IST on the night of 23/24 December, 1991 (Ap = 14, Kp < 4-). The fluctuations in F region vertical drift are found to be coherent with variations in Bz (north-south) component of interplanetary magnetic field (IMF), in geomagnetic H/X components at high-mid latitude locations both in the sunlit and dark hemispheres and near the dayside dip equator, suggestive of DP2 origin. But the polarity of the electric field fluctuations at the midnight dip equator (eastward) is the same as the dayside equator inferred from magnetic variations, contrary to what is expected of equatorial DP2. The origin of the coherent occurrence of equatorial electric field fluctuations in the DP2 range of the same sign in the day and night hemispheres is unclear and merits further investigations.Key words: Ionosphere (electric fields and currents; equatorial ionosphere; ionosphere-magnetosphere interactions)
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47

Bhuyan, P. K., and K. Bhuyan. "The equatorial ionization anomaly at the topside F region of the ionosphere along 75°E." Advances in Space Research 43, no. 11 (June 2009): 1676–82. http://dx.doi.org/10.1016/j.asr.2008.09.027.

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48

Zhang, Xiaolin, and Allan J. Clarke. "Observations of Interannual Equatorial Freshwater Jets in the Western Pacific." Journal of Physical Oceanography 45, no. 11 (November 2015): 2848–65. http://dx.doi.org/10.1175/jpo-d-14-0245.1.

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AbstractObservations of TRITON moored array salinity and temperature in the very wet western equatorial Pacific at 137°E, 147°E, and 156°E since the late 1990s reveal the importance of rainfall to the interannual flow and El Niño–Southern Oscillation (ENSO) dynamics. Past work has shown that in this region a fresher surface isohaline layer is embedded in a thicker isothermal layer. Array estimates of dynamic height relative to the 50–70-m isothermal layer depth (ILD) indicate a near-surface salinity-driven contribution to the monthly sea level anomaly that is uncorrelated with, and smaller than, monthly anomalous sea surface height (SSH) estimated from altimeter data. Despite the smaller size of , its meridional gradient dominates the total sea level meridional gradient. Thus, the corresponding shallow equatorially trapped interannual freshwater jet dominates the near-surface zonal interannual flow. This jetlike flow has a meridional scale of only about 2°–3° of latitude, an amplitude of 23 cm s−1, and is associated with the zonal back and forth displacement of the western equatorial warm/fresh pool that is fundamental to El Niño. The jet is not directly forced by the interannual freshwater surface flux but rather by wind stress anomalies that are mostly east of the warm/fresh pool edge during La Niña and mostly west of it during El Niño. A conceptual coupled ocean–atmosphere instability model is proposed to understand these observations. Calculations show that Aquarius satellite sea surface salinity (SSS) data match the TRITON in situ data well and that the satellite SSS can be used to estimate , and hence , geostrophically.
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Sharma, P., and R. Raghavarao. "Simultaneous occurrence of ionization ledge and counterelectrojet in the equatorial ionosphere: observational evidence and its implications." Canadian Journal of Physics 67, no. 2-3 (February 1, 1989): 166–72. http://dx.doi.org/10.1139/p89-028.

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In this paper we present observational evidence for the simultaneous occurrence of an ionization ledge in the topside and a counterelectrojet in the E-region altitudes of the equatorial ionosphere. The following morphological features of the ionization ledge are found to be the same as those of the counterelectrojet phenomenon: namely, occurrence on a sequence of days in succession, preferential occurrence during a solar minimum period as compared with a solar maximum period, occurrence in a limited longitudinal belt, and lunar control of the occurrence as revealed by our data.There is also a high degree of correlation on both magnetically quiet and magnetically disturbed days between the ionization ledge and the counterelectrojet. Our study brings out a close coupling in the occurrence and morphological features of the two low-latitude phenomena, even though they are widely separated in altitude. The implications of such a correlation, with special reference to the understanding of the dynamical coupling of the E and F regions in the equatorial ionosphere, are briefly discussed.We also report a hitherto unreported feature of the ionization anomaly, viz., its occurrence on certain days in a narrow (~30°) longitude belt. The observational evidence presented in this paper may lead to new insights into the understanding of the interrelationships between the three phenomena, the ionization ledge, the ionization anomaly, and the counterelectrojet, in the equatorial ionosphere.
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Pan, C. J., C. H. Liu, J. Röttger, and S. Y. Su. "A three dimensional study of E region irregularity patches in the equatorial anomaly region using the Chung-Li VHF radar." Geophysical Research Letters 21, no. 17 (August 15, 1994): 1763–66. http://dx.doi.org/10.1029/94gl01195.

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