Quasi-Bidaily Variation of the Geomagnetic Field in the Indian Equatorial Zone.

Rangarajan, Govindan

doi:10.5636/jgg.46.373

Cited by 7 publications

(6 citation statements)

References 19 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Further, in the case of ∼2‐day oscillation in EEJ strength, it is noted in the present study that often the period of oscillation (least squares method) in EEJ strength is centered near 48 h (not shown here), which is in agreement with earlier observations by Rangarajan [1994]. However, in mesospheric winds, the periodicity varies between 40 and 60 h; predominantly near 52 h in zonal winds but near 46 h in meridional winds (not shown here).…”

Section: Quasi–2‐day Oscillationsupporting

confidence: 93%

“…These varied periodicities in mesospheric winds were also reported by earlier observations [ Craig and Elford , 1981; Salby , 1981c; Cevolani and Kingsley , 1992]. Rangarajan [1994] attributed the difference in periodicity of ∼2‐day oscillations between EEJ strength and mesospheric winds to the local wind effects. Since the winds associated with planetary waves at near off‐EEJ latitudes are more effective than the winds at EEJ latitudes in modulating the ionospheric currents, the winds detected over the equatorial (EEJ latitudes) regions need not always show its influence on the EEJ current system when the winds are different in these two latitude regions.…”

Section: Quasi–2‐day Oscillationsupporting

confidence: 84%

“…In that case also, the mesospheric winds may not show the planetary‐scale oscillations but the geomagnetic field variations would show strong planetary‐scale oscillations. Further, during the alternate counter electrojet days, it is possible that the EEJ strength may show strong ∼2‐day oscillation when the mesospheric winds do not hold any such periodic oscillations [ Rangarajan , 1994]. In the present study, often, it is also observed that only the mesospheric winds showed the strong planetary‐scale oscillations, but not the EEJ strength.…”

Section: Quasi–16‐day (12‐ To 20‐day Band) Oscillationmentioning

confidence: 52%

See 2 more Smart Citations

Mesospheric planetary wave signatures in the equatorial electrojet

Ramkumar

Gurubaran

Rajaram³

2009

J. Geophys. Res.

View full text Add to dashboard Cite

[1] Using five years (1994)(1995)(1996)(1997)(1998) of simultaneous and collocated measurements of horizontal winds associated with mesosphere and lower thermosphere (MLT) region and geomagnetic field measurements in the Indian geomagnetic dip equatorial region, an extensive experimental study has been made on the influences of mesospheric planetary waves on the equatorial electrojet (EEJ). The winds are measured using medium-frequency (MF) radar (1.98 MHz) located at Tirunelveli. The EEJ strength is determined by measuring the geomagnetic field strength at both the geomagnetic dip and off-dip equatorial stations, Trivandrum and Alibag, India. By noting the simultaneous time evolution of spectral signal (Morlet wavelet analysis) in both the EEJ strength and mesospheric winds at 88 km, it is found that mesospheric planetary waves with periodicities of 2-25 days often do propagate up to the ionospheric dynamo region and have their influences on EEJ strength. Sometimes only one of the parameters shows strong spectral signal in this periodicity range. It is also observed that often the diurnal oscillation in EEJ strength and mesospheric winds exhibits coherent variations in amplitude when the signature of mesospheric planetary-scale oscillations is found in the EEJ strength. Also, it is found that variations in high-energy solar radiations (F10.7 is used as a proxy) can influence the EEJ strength at planetary timescales. This leads to an interesting question. What actually causes the vertical coupling between ionosphere and atmosphere through upward propagating planetary waves to be operative only during some (and not all) of the episodes?

show abstract

Section: Quasi–2‐day Oscillationsupporting

confidence: 93%

Section: Quasi–2‐day Oscillationsupporting

confidence: 84%

Section: Quasi–16‐day (12‐ To 20‐day Band) Oscillationmentioning

confidence: 52%

See 1 more Smart Citation

Mesospheric planetary wave signatures in the equatorial electrojet

Ramkumar

Gurubaran

Rajaram³

2009

J. Geophys. Res.

View full text Add to dashboard Cite

show abstract

“… Ito et al [1986] first theoretically suggested that a large‐amplitude global‐scale 2‐day wave can induce an electric current system in the ionosphere through a dynamo mechanism. Takeda and Yamada [1989], Rangarajan [1994], and Yamada [2002] detected quasi‐2‐day variability in geomagnetic field and discussed its possible relationship with the 2‐day wave in the atmosphere; however, no wind measurements supported their results. Gurubaran et al [2001a] identified the signatures of the quasi‐2‐day variability in the equatorial electrojet and showed a reasonable correlation with the 2‐day wave measured by the MF radar situated close to the geomagnetic stations.…”

Section: Introductionmentioning

confidence: 92%

Two‐day wave coupling of the low‐latitude atmosphere‐ionosphere system

Pancheva¹,

Mukhtarov²,

Shepherd³

et al. 2006

J. Geophys. Res.

127

View full text Add to dashboard Cite

[1] Vertical coupling in the low-latitude atmosphere-ionosphere system driven by the 2-day wave in the tropical MLT region has been investigated. The problem is studied from an observational point of view. Three different types of data were analyzed in order to detect and extract the 2-day wave signals. The 2-day wave event during the period from 1 December 2002 to 28 February 2003 was identified in the neutral winds by radar measurements located at four tropical stations. The 2-day variations in the ionospheric electric currents (registered by perturbations in the geomagnetic field) and in the F-region electron densities were detected in the data from 23 magnetometer and seven ionosonde stations situated at low latitudes. Two features for each kind of wave were investigated in detail: the variation with time of the wave amplitude and the zonal wave number. The results show that the westward propagating global 2-day wave with zonal wave number 2 seen in the ionospheric currents and in F-region plasma is forced by the simultaneous 2-day wave activity in the MLT region. The main forcing agent in this atmosphere-ionosphere coupling seems to be the modulated tides, particularly the semidiurnal tide. This tide has a larger vertical wavelength than the diurnal tide and propagates well into the thermosphere. The parameter that appears to be affected, and thus drives the observed 2-day wave response of the ionosphere, is the dynamo electric field.

show abstract

“…In the Indian longitude region, Rangarajan (1994) detected quasi-bi-daily variation (BDV) in geomagnetic field due to equatorial electrojet (EEJ) and planetary solar quiet (Sq) currents. It was shown further that the quasi-stationary signal was stronger in EEJ compared to in Sq.…”

Section: Introductionmentioning

confidence: 99%