Local time dependence of the equatorial counter electrojet effect in a narrow longitudinal belt

Alex, S.; Mukherjee, Shyamoli

doi:10.1186/bf03352410

Cited by 31 publications

(28 citation statements)

References 26 publications

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“…The noticeable geomagnetically quiet period, usually preceding the high‐speed stream‐generated storms, produces an opportunity to investigate the meteorological influences on the ionosphere since the magnetospheric energy inputs are of minimum in this interval. For the periods of 3–4 January 2008, the weaker daytime EIA and not well‐developed eastward electrojet as observed inFigures 2a and 2d are a commonplace occurrence [e.g., Alex and Mukherjee , 2001; Stening , 1995]. Day‐to‐day variations in eastward equatorial electrojet (EEJ) and counter electrojet (CEJ) are related to various tidal modes and zonal winds of varying magnitude [ Forbes and Lindzen , 1976; Somayajulu et al , 1993; Stening , 1995].…”

Section: Observations and Interpretationmentioning

confidence: 99%

High‐speed stream impacts on the equatorial ionization anomaly region during the deep solar minimum year 2008

Liu

Wei

et al. 2012

J. Geophys. Res.

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[1] To demonstrate high-speed stream effects during the recent deep solar minimum year 2008, we have analyzed manually scaled f o F 2 and h m F 2 at Jicamarca and total electron content (TEC) in the equatorial ionization anomaly (EIA) region over the America longitudinal sector. Our results reveal that a prominent 9 day oscillation appears in the h m F 2 and f o F 2 at the dip equator. The 9 day oscillation amplitudes of f o F 2 are not always positively correlated with TEC in the equatorial ionosphere, and they show nonlinear dependence on the intensity of geomagnetic disturbances. With the outputs of Fejer and Scherliess's (1997) empirical model, we found that this periodicity is also present in equatorial vertical drifts caused by disturbance dynamoelectric field (DDEF) but absent in the drifts due to prompt penetration electric field (PPEF). DDEF effects on the equatorial periodic variations alone are not sufficient to explain the observed phenomena; other mechanisms, such as thermal expansion/contraction and neutral composition changes, are also the plausible causes of the periodic oscillation in the equatorial ionosphere. Further, the complicated patterns appear in the 9 day band-pass-filtered TEC perturbations in the EIA region, and they are quite different from the patterns of global coherent thermospheric oscillations triggered by high-speed streams. We also found that the latitudinal variations of band-passed-filtered TEC present different behaviors involving tilt latitudinal configuration, antiphased correlation between the crests and trough, and south-north asymmetry, which vary as a function of season, local time, or even from event to event.

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Section: Observations and Interpretationmentioning

confidence: 99%

High‐speed stream impacts on the equatorial ionization anomaly region during the deep solar minimum year 2008

Liu

Wei

et al. 2012

J. Geophys. Res.

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“…The seasonal variability (equinox to local summer) in occurrence of CEJ events is observed to be much larger (5–35%) compared to that (32–35%) reported from Addis Ababa (geographic: latitude, 9°N; longitude, 38.8°E; dip: 1°S) [ Mayaud , 1977]. It may be due to limited longitudinal confinement nature of CEJ events – which is attributed to the local wind shear modifying the EEJ fields especially during noontime hours [ Alex and Mukherjee , 2001]. The later occurrence of initiation time during J months is suggested to be related to the northward shifted position of the Sun with respect to the magnetic equator [ Rastogi , 1974].…”

Section: Resultsmentioning

confidence: 99%

“…Although a large number of investigations on theoretical as well as experimental grounds are conducted to find and explain the characteristics of CEJ event, its causes and effects on the equatorial and off‐equatorial ionosphere [ Rajaram and Rastogi , 1974; Deshpande et al , 1977; Raghavarao and Anandarao , 1987; Alex and Mukherjee , 2001; Devasia et al , 2006], the effect of CEJ on diurnal variation of TEC near the anomaly crest region is yet to be fully explored. TEC is an important parameter to describe the state of ionosphere and significant for time delay/range error problems involving global positioning system (GPS) navigation.…”

Section: Introductionmentioning

confidence: 99%

Electrodynamical control of the ambient ionization near the equatorial anomaly crest in the Indian zone during counter electrojet days

Hajra¹,

Chakraborty²,

Paul

2009

Radio Science

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[1] The variability of ambient ionization near the crest of the equatorial anomaly on the days of counter electrojet (CEJ) is studied using a long-term (1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990) database of total electron content (TEC) obtained from Calcutta (geographic: longitude, 88.38°E; latitude, 22.58°N; dip: 32°N), situated virtually below the northern crest of the equatorial anomaly, in conjunction with the equatorial electrojet (EEJ) data of the Indian subcontinent and f o F 2 data from the equatorial stations. On the days of CEJ events the diurnal variations of TEC exhibit deviations (decreases) from monthly mean values, but the feature is not regular throughout the observing period. A larger percentage of CEJ days show decreases in the descending phase (1980)(1981)(1982)(1983)(1984)(1985) of solar cycle compared to the ascending one (1986)(1987)(1988)(1989)(1990). During low to moderate solar activity years the ionosphere near the anomaly crest is found to be more susceptible to CEJ related equatorial electrodynamics than in the high solar activity periods. On the seasonal basis, though the solstitial months of ascending phase exhibit higher percentage occurrence of decreases, the feature is not so prominent in the descending epoch. An attempt is made to relate the decreases in TEC with the prevailing electrodynamics at the magnetic equator for which EEJ, under quiet geomagnetic conditions, may be treated as a proxy index. A statistical analysis reveals positive correlations of TEC decreases with strength and duration of CEJ but anticorrelations with rising slope, strength, and time-integrated value of EEJ as well as initiation time of CEJ. To represent better correspondence of the TEC variability with the equatorial electrodynamics a function combining various EEJ parameters has been generated, which seems to exhibit significant association with TEC decreases on the days of CEJ events.Citation: Hajra, R., S. K. Chakraborty, and A. Paul (2009), Electrodynamical control of the ambient ionization near the equatorial anomaly crest in the Indian zone during counter electrojet days, Radio Sci., 44, RS3009,

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“…Therefore, large depression of Δ H (CEJ signatures) predominantly in the morning hours is also expected to contribute to negative E × B values derived from equation . Possible sources of CEJ have been suggested to be gravity waves associated with vertical local winds (e.g., Raghavarao & Anandarao, ) and solar tidal modes (e.g., Alex & Mukherjee, ; Gurubaran, ). From Figure c it can be observed that there is some correlation between F 10.7 and ionospheric vertical drifts, although the investigated period has a significant amount of missing E × B drift data.…”

Section: Methodsmentioning

confidence: 99%

An Empirical Model of Vertical Plasma Drift Over the African Sector

Dubazane

Habarulema

2018

Space Weather

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Daytime vertical E × B drift can be derived from difference of H‐component magnetic field measurements (ΔH) using a pair of low‐latitude and equatorial latitude magnetometer stations. Knowledge of E × B drift is of utmost importance in space weather‐related predictions since it can significantly affect ionospheric density structures and dynamics. For the first time, we developed a quantitative relationship between equatorial electrojet (ΔH) and vertical E × B drift over the African region using magnetometer data and E × B drift observations from the Communication and Navigation Outage Forecasting System (C/NOFS) satellite during local daytime (0700–1800 LT) from 2008 to 2013 when magnetometer data were available. Additionally, we have constructed vertical E × B drift models over the African sector based on C/NOFS vertical E × B drift data and relevant physical and geophysical inputs. Validating using data not included in model development, our model estimated C/NOFS vertical E × B drift with correlation coefficient values of 0.85 and 0.56 during quiet and disturbed conditions, respectively. The daily pattern of the E × B drift velocity is consistent between the developed model based on C/NOFS data and the climatological Scherliess‐Fejer model. However, the Scherliess‐Fejer model generally overestimated C/NOFS vertical E × B drift (in most cases) with a correlation coefficient of 0.54 during quiet conditions.

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Local time dependence of the equatorial counter electrojet effect in a narrow longitudinal belt

Cited by 31 publications

References 26 publications

High‐speed stream impacts on the equatorial ionization anomaly region during the deep solar minimum year 2008

High‐speed stream impacts on the equatorial ionization anomaly region during the deep solar minimum year 2008

Electrodynamical control of the ambient ionization near the equatorial anomaly crest in the Indian zone during counter electrojet days

An Empirical Model of Vertical Plasma Drift Over the African Sector

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