Spectra of the ac electric fields in the post-sunset F-region at the magnetic equator

Nair, R. Balachandran; Balan, N.; Bailey, G. J.; Rao, P. B.

doi:10.1016/0032-0633(92)90006-a

Cited by 29 publications

(15 citation statements)

References 29 publications

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“…period of about 32 minis always present and it becomes dominant in the premidnight hours. This spectral feature in the temporal variation F region V near the dip equator has also been noticed earlier by Nair et al (1992). A unique aspect of the short-period wave activity in V noticed in our database is the remarkable dayto-day variability of its amplitude at any local time.…”

Section: Data and Analysissupporting

confidence: 54%

“…Points (1) and (3) which have been found as noteworthy trends in the temporal pattern of V by Nair et al (1992) and Subbarao and Krishnamurthy (1994) from analysis of short data samples (7 days and 28 days observations respectively) now stand substantiated. Points (4) and (5) which are reported for the first time here constitute, in our opinion, important additions to our limited knowledge of the short period variation in F region vertical drift in the dip equatorial region.…”

Section: Data and Analysismentioning

confidence: 75%

“…Earle and Kelley (1987) identified atmospheric waves and magnetospheric electric fields as the most likely sources of equatorial zonal electric field variations in the range 1-10 hr during quiet and disturbed periods respectively. Nair et al (1992) and Subbarao and Krishnamurthy (1994) suggested the frequently occurring medium scale gravity waves as the source of shorter period (<1 h) variations of V. in the evening period. These earlier studies are however based on short datasamples and detailed statistical studies of the morphology of the short-period variations in VV are not available.…”

Section: Introductionmentioning

confidence: 99%

“…The vertical drift (V) of F region plasma (hence the causative east-west electric field) at and in the immediate vicinity of the magnetic equator is known to undergo variations on a range of time scales from about a minute to several hours during both quiet and disturbed geomagnetic conditions (e.g., Patel and La Gos, 1985;Earle and Kelley, 1987;Nair et al, 1992;Subbarao and Krishnamurthy, 1994). Earle and Kelley (1987) identified atmospheric waves and magnetospheric electric fields as the most likely sources of equatorial zonal electric field variations in the range 1-10 hr during quiet and disturbed periods respectively.…”

Section: Introductionmentioning

confidence: 99%

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Short-Period(5-33 min) Variations in Vertical Drift of F-Region Plasma near the Magnetic Equator.

Sastri

1995

J. geomagn. geoelec

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Measurements ofFregion vertical drift, V~ made at Kodaikanal (dip 4°N) on 133 days during March 1991-February 1992 under non-equatorial spread-F(ESF) conditions, are analysed forthe characteristics of short-period (5-33 min) variations in Vr in the evening hours (1630-0130 IST). The spectral content of the fluctuations in V. is found to depend on local time. The amplitude of the fluctuations, quantified in terms of the variance (a2), increases during the period of postsunset enhancement of upward vertical drift and decreases thereafter reaching a minimum during 2200-0000 IST. In consonance with this, while fnctuations in Vi in the entire band 5-33 min manifest in the postsunset hours, the longer-period (13-33 min) components dominate thereafter (2200-0000 IST). The amplitude of the fluctuations and its dayto-day variability are higher in local summer than in local winter. On a day-to-day basis, the amplitude of Vi functuations increases with peak height in the interval 1756-2004 IST corresponding to the epoch ofthe evening enhancement in Vr. The results support the view that the short-period variations in Fregion vertical drift near the dip equator during the evening hours could be due to electric fields associated with the commonly occurring atmospheric gravity waves.

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Section: Data and Analysissupporting

confidence: 54%

Section: Data and Analysismentioning

confidence: 75%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Short-Period(5-33 min) Variations in Vertical Drift of F-Region Plasma near the Magnetic Equator.

Sastri

1995

J. geomagn. geoelec

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“…This is done to suppress the short-period (<1-h)¯uctuations in V z which are a common feature of the temporal structure of V z at dip equatorial stations (e.g. Earle and Kelley, 1987;Nair et al, 1992) and to show essentially the ambient vertical plasma drift pattern. The average quiet-day patterns of V z at Kodaikanal and h¢F at Fortaleza shown in Fig.…”

Section: Observationsmentioning

confidence: 99%

Response of equatorial ionosphere to episodes of asymmetric ring current activity

1997

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Abstract. We present the characteristics of the response of equatorial ionospheric zonal electric ®eld and Fregion plasma density to the asymmetric ring current intensi®cations that occurred in succession on 16 December 1991, corresponding to the STEP/EITS-2 campaign period. The study is based on high-timeresolution (1-min) data of asymmetic ring current indices, ASY(H/D) and F-region vertical plasma drift, z measurements at Kodaikanal (10.25°N; 77.5°E; dip 4°), India and quarter-hourly ionosonde data of Fortaleza (4°S; 322°E; dip A9°), Brazil. It is shown that short-lived disturbances in F-layer vertical plasma drift, z and height (h¢F/hpF2) indicative of westward and eastward electric ®elds prevail simultaneously in the dusk (18±21 LT) and predawn (02±05 LT) sectors, respectively, in association with the decay phase of asymmetic ring current events. Electric ®elds of opposite polarity do also seem to manifest at these local times, particularly in the early-morning sector in conjunction with the intensi®cation of the asymmetric ring current. At a given location, electric ®eld disturbances associated with individual asymmetric ring current events are thus bipolar in nature, with ®elds of opposite polarity during the growth and decay phases. The nature and polarity structure of the observed electric ®eld disturbances are in agreement with the theoretical/model predictions of prompt penetration of high-latitude electric ®elds to the equatorial region.

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Quiet time short‐period and day‐to‐day variations in E × B drift studied using 150 km radar echoes from Gadanki

2014

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In this paper we present short-period and day-to-day variations in E × B drift during low solar and magnetically quiet conditions, based on radar observations of daytime 150 km echoes from Gadanki, India. Short-period (<100 min) variations in E × B drift show amplitude as large as 7 m s À1 and display large day-to-day variation. Spectral analysis reveals that drift velocity fluctuations consist of several components of short periods in the range of 4-100 min. Among these periods, the most frequently occurring periods are 6-60 min. Observations also show that amplitudes of these periods increase with increasing period. Interestingly, signal-to-noise ratio (SNR) variations also show periods of 3-19 min, which have also been observed in velocity variations. In addition, amplitudes of the periodic variations in SNR tend to increase with increasing period, which is also similar to those observed in drift velocity fluctuations. No correlation between SNR and velocity variations, however, has been found. Noticeable day-to-day variations in drift velocity are found in all seasons, and the variation is as large as ±25 m s À1 . Day-to-day variations also show wave-like features with period of 2-4 days. Observed E × B drift variations of 7 m s À1 at short time scale and 25 m s À1 on a day-to-day basis indicate zonal electric field variations of 0.25 mV/m and 0.9 mV/m, respectively. We surmise that quiet time E × B drift variations with periods <100 min and 2-4 days are likely to be the manifestations of gravity wave and planetary wave wind-induced electric fields, respectively, consistent with those reported earlier.

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Spectra of the ac electric fields in the post-sunset F-region at the magnetic equator

Cited by 29 publications

References 29 publications

Short-Period(5-33 min) Variations in Vertical Drift of F-Region Plasma near the Magnetic Equator.

Short-Period(5-33 min) Variations in Vertical Drift of F-Region Plasma near the Magnetic Equator.

Response of equatorial ionosphere to episodes of asymmetric ring current activity

Quiet time short‐period and day‐to‐day variations in E × B drift studied using 150 km radar echoes from Gadanki

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