Variability of equatorial counter electrojet signatures in the Indian region

Chandrasekhar, N.; Archana, R. K.; Nagarajan, N.; Arora, Kusumita

doi:10.1002/2016ja022904

Cited by 12 publications

(21 citation statements)

References 57 publications

(87 reference statements)

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“…It has been established earlier that the eastward electric field ( E region) at equator shows a four‐wave longitudinal structure with a crest at 100°E and a trough at 60°E longitude, attributed to DE3 nonmigrating tide (Lühr et al, ). Similar trend was noted in comparison of CBY and VEN and EEJ and CEJ strengths (Chandrasekhar et al, , , )(from 93–77°). Additionally, using a year's concurrent data with MNC (72°), the westward decrease in EEJ strength as well as increase strength of westward currents demonstrated in a separate analysis (Archana R. K., personal communication, June 25, 2018).…”

Section: Discussionsupporting

confidence: 85%

Effect of Disturbance Electric Fields on Equatorial Electrojet Over Indian Longitudes

et al. 2018

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Prompt penetration (PP) and ionospheric disturbance dynamo (Ddyn) are two expressions of the disturbed electric field developed during a geomagnetic storm in the Earth's ionosphere. Earlier investigations treated these two processes independently over longitudinal separation beyond 20°. In the present study, we investigate the conjunction of these phenomena on equatorial electrojet at 20° longitude separations using daytime magnetic field data from three equatorial sites viz., Minicoy, Vencode, and Campbell Bay and three low‐latitude sites viz., Alibag, Hyderabad, and Nabagram, located within 20° longitude over Indian region, during three intense storms (Dst <− 150 nT). We propose a statistical method to identify PP signatures from large data set. In addition, we distinguish the signatures of PP and Ddyn during early recovery phase of intense storms and compute pure Ddyn signature in the late recovery phase. It is seen that the effect of PP is similar at the three equatorial sites for each storm. We find that signatures of Ddyn are amplified at Minicoy and Vencode compared to Campbell Bay, and their magnitude decreases toward low‐latitude stations, also reflected in the current vector patterns. Our investigations of intense geomagnetic storms show that PP effect dominates the main phase, followed by a combined effect of PP and Ddyn in the early recovery phase. Eventually the Ddyn signature dominates in the late recovery phase with decreasing amplitudes of Ddyn with increasing time. Such investigations can provide new information about variations in ionospheric parameters.

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Section: Discussionsupporting

confidence: 85%

Effect of Disturbance Electric Fields on Equatorial Electrojet Over Indian Longitudes

et al. 2018

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“…From the plots it is also evident that larger amplitudes of CEJ are seen at MNC and VEN and that the scatter in EEJ peak values is also greater compared to CBY. The difference in the CEJ occurrence pattern with relatively large number of events at VEN than at CBY has been reported and also the effect of CEJ occurrence reducing peak values of EEJ (Chandrasekhar et al, ). The present study also shows this trend in the amplitude as well as in the occurrence pattern of CEJ during disturbed periods ( Kp > =3) at this short spatial separation.…”

Section: Observations and Resultsmentioning

confidence: 97%

“…Subsequently, studies have reported that CEJ phenomena have a limited longitudinal extent, compared between continents and, in some instances, sites as close as 30° apart, as well as from satellite data (Alex & Mukherjee, ; Kane, ; Kane & Trivedi, ; McCreadie, ; Rangarajan & Rastogi, ; Rao & Rajarao, ; Rastogi, ; Vichare & Rajaram, ). Recent studies by Chandrasekhar et al () reported significant longitudinal variability in CEJ phenomena at 15° separation, suggesting that the ionospheric electrodynamics and associated atmospheric‐ionospheric effects could vary considerably at such spatial separation.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2018

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

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“…The overall decrease in the H-component from the dip equator to the focus during a CEJ event may represent magnetic disturbance associated with a ring current or sub-storm activity (Arora et al 1993). Recently, Chandrasekhar et al (2017), studying the variability of CEJ signatures between two different longitudes (stations located at Campbell Bay and Vencode), attributed the occurrence of the CEJ to longer wavelength processes such as diurnal and semidiurnal tides. …”

Section: Resultsmentioning

confidence: 99%

“…The occurrence of a CEJ during quiet days has been attributed to the tidal winds or additional current systems in the ionospheric dynamo region (Bhargava and Sastri 1977;Bhargava et al 1980;Rastogi et al 1992;Arora et al 1993;Somayajulu et al 1993a;Stening et al 1996;Alex and Mukherjee 2001;Gurubaran 2002;Sridharan et al 2002;Chandrasekhar et al 2017). The signature of the CEJ over the Indian sector has been illustrated by Vichare and Rajaram (2011) using Oersted satellite data.…”

Section: Introductionmentioning

confidence: 99%

The afternoon counter-electrojet current system along the 75°E meridian during the IEEY

Bhardwaj

Rao

2017

Earth Planets Space

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In the present study, the technique of principal component analysis (PCA) is applied to analyze the hourly mean values of geomagnetic field components D, H, and Z along an Indo-Russian chain of stations during the International Equatorial Electrojet Year (IEEY) from January 1992 to June 1993. This technique (PCA) is found to be suitable for separating the normal electrojet (NEJ) and counter-electrojet (CEJ) variations, and the first two principal components (PCs) are able to describe the characteristics of NEJ-and CEJ-related field variations. It is found that the first principal component (PC-1) for H, D, and Z varies as a function of time with latitude and depicts the well-known Sq variations, whereas PC-2(H) does not show any variations at all latitudes during NEJ days. On CEJ days, PC-2(H) shows a large negative excursion at equatorial stations (KAN to BAN). The NEJ-and CEJ-related current systems are determined by combining the hourly inequalities in D and H. PC-1 brings out a well-defined anticlockwise loop for NEJ days, with its focus near the dip latitude (~35°N), and a clockwise loop for CEJ days with a well-defined focus near the dip latitude (~20°N) around noon local time. The CEJ-related current system is marked by intense westward current flow in the equatorial belt and is shown to close its path by forming a clockwise loop extending from the dip equator to midlatitudes. Comparison with a numerically simulated current system, caused by various tidal modes, emphasizes the significance of antisymmetric semidiurnal tidal modes in the generation of CEJ events.

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Variability of equatorial counter electrojet signatures in the Indian region

Cited by 12 publications

References 57 publications

Effect of Disturbance Electric Fields on Equatorial Electrojet Over Indian Longitudes

Effect of Disturbance Electric Fields on Equatorial Electrojet Over Indian Longitudes

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

The afternoon counter-electrojet current system along the 75°E meridian during the IEEY

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