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  • 1995-1999  (16)
  • 1
    Electronic Resource
    Electronic Resource
    Zonal drifts of ionospheric irregularities at temperate latitude in the Indian region (1995)
    Springer
    Annales geophysicae 13 (1995), S. 724-729 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The systematic time differences observed in the onset of postsunset VHF scintillations recorded simultaneously at Ujjain (Geogr. lat. 23.2○N, Geogr. long. 75.6○E) and Bhopal (Geogr. lat. 23.2○N, Geogr. long. 77.6○E), situated at the peak of the anomaly crest in the Indian region, have been analysed to determine the zonal drifts of scintillation-producing irregularities. The method is based on the assumption that the horizontal movement of irregularities does not change while crossing the F-region cross-over points of these stations. The calculated velocities of irregularities indicate an eastward drift decreasing from about 180 m s−1 to 55 m s−1 during the course of night. In the premidnight period, the drifts are reduced under the magnetically disturbed conditions. The average east-west extension of irregularites is found to be in the range of 200–500 km.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-995-0724-5
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    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Seasonal and solar cycle association of zonal drifts of ionospheric plasma irregularities in the Indian equatorial region (1996)
    Springer
    Annales geophysicae 14 (1996), S. 297-303 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Long series of simultaneous VHF scintillation observations at two stations situated in near magnetic east-west direction in the vicinity of the dip equator in the Indian region have been employed to investigate the night-time ionospheric plasma zonal drifts. The drifts are found to be predominantly easterly. On comparing the magnitudes of the drifts with those results derived earlier by HF fading technique, monitoring signals from two satellites at a station and spaced receiver experiment, their associations with the season and the degree of solar activity are discussed. On a broader scale, the annual mean sunspot number is shown to have a direct control on the derived drift, the positive relationship even on day to day basis with the solar flux is established. However, the relationship, as understood by the slope of the best fit line, in the Indian region (0.27) is found to be weaker when compared with the similar slope (0.45) in the American sector. There appears to be no geomagnetic activity control on the estimated drifts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-996-0297-y
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    An intense SFE and SSC event in geomagnetic H, Y and Z fields at the Indian chain of observatories (1997)
    Springer
    Annales geophysicae 15 (1997), S. 1301-1308 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Changes in the three components of geomagnetic field are reported at the chain of ten geomagnetic observatories in India during an intense solar crochet that occurred at 1311 h 75° EMT on 15 June 1991 and the subsequent sudden commencement (SSC) of geomagnetic storm at 1518h on 17 June 1991. The solar flare effects (SFE) registered on the magnetograms appear to be an augmentation of the ionospheric current system existing at the start time of the flare. An equatorial enhancement in AH due to SFE is observed to be similar in nature to the latitudinal variation of SQ (H) at low latitude. AF registered the largest effect at 3.6° dip latitude at the fringe region of the electrojet. AZ had positive amplitudes at the equatorial stations and negative at stations north of Hyderabad. The SSC amplitude in the H component is fairly constant with latitude, whereas the Z component again showed larger positive excursions at stations within the electrojet belt. These results are discussed in terms of possible currents of internal and external origin. The changes in the Y field strongly support the idea that meridional current at an equatorial electrojet station flows in the ionospheric dynamo, E.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-997-1301-x
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Decay of the Dst field of geomagnetic disturbance after substorm onset and its implication to storm-substorm relation (1996)
    Springer
    Annales geophysicae 14 (1996), S. 608-618 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract In order to investigate the causal relationship between magnetic storms and substorms, variations of the mid-latitude geomagnetic indices, ASY (asymmetric part) and SYM (symmetric part), at substorm onsets are examined. Substorm onsets are defined by three different phenomena; (1) a rapid increase in the mid-latitude asymmetric-disturbance indices, ASY-D and ASY-H, with a shape of so-called ‘mid-latitude positive bay’; (2) a sharp decrease in the AL index; (3) an onset of Pi2 geomagnetic pulsation. The positive bays are selected using eye inspection and a pattern-matching technique. The 1-min-resolution SYM-H index, which is essentially the same as the hourly Dst index except in terms of the time resolution, does not show any statistically significant development after the onset of substorms; it tends to decay after the onset rather than to develop. It is suggested by a simple model calculation that the decay of the magnetospheric tail current after substorm onset is responsible for the decay of the Dst field. The relation between the IMF southward turning and the development of the Dst field is reexamined. The results support the idea that the geomagnetic storms and substorms are independent processes; that is, the ring-current development is not the result of the frequent occurrence of substorms, but that of enhanced convection caused by the large southward IMF. A substorm is the process of energy dissipation in the magnetosphere, and its contribution to the storm-time ring-current formation seems to be negligible. The decay of the Dst field after a substorm onset is explained by a magnetospheric energy theorem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-996-0608-3
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    Paper (German National Licenses)
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  • 5
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    Unknown
    Ionospheric propagation of magnetohydrodynamic disturbances from the equatorial electrojet (1999)
    American Geophysical Union
    Details
    Publication Date: 1999-03-01
    Print ISSN: 0148-0227
    Electronic ISSN: 2156-2202
    Topics: Geosciences
    Published by American Geophysical Union
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  • 6
    facet.materialart.
    Unknown
    Zonal drifts of ionospheric irregularities at temperate latitude in the Indian region (1995)
    Copernicus
    Details
    Publication Date: 1995-07-31
    Description: The systematic time differences observed in the onset of postsunset VHF scintillations recorded simultaneously at Ujjain (Geogr. lat. 23.2°N, Geogr. long. 75.6°E) and Bhopal (Geogr. lat. 23.2°N, Geogr. long. 77.6°E), situated at the peak of the anomaly crest in the Indian region, have been analysed to determine the zonal drifts of scintillation-producing irregularities. The method is based on the assumption that the horizontal movement of irregularities does not change while crossing the F-region cross-over points of these stations. The calculated velocities of irregularities indicate an eastward drift decreasing from about 180 m s–1 to 55 m s–1 during the course of night. In the premidnight period, the drifts are reduced under the magnetically disturbed conditions. The average east-west extension of irregularites is found to be in the range of 200–500 km.
    Print ISSN: 0992-7689
    Electronic ISSN: 1432-0576
    Topics: Geosciences , Physics
    Published by Copernicus on behalf of European Geosciences Union.
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  • 7
    facet.materialart.
    Unknown
    Decay of the Dst field of geomagnetic disturbance after substorm onset and its implication to storm-substorm relation (1996)
    Copernicus
    Details
    Publication Date: 1996-06-30
    Description: In order to investigate the causal relationship between magnetic storms and substorms, variations of the mid-latitude geomagnetic indices, ASY (asymmetric part) and SYM (symmetric part), at substorm onsets are examined. Substorm onsets are defined by three different phenomena; (1) a rapid increase in the mid-latitude asymmetric-disturbance indices, ASY-D and ASY-H, with a shape of so-called `mid-latitude positive bay\'; (2) a sharp decrease in the AL index; (3) an onset of Pi2 geomagnetic pulsation. The positive bays are selected using eye inspection and a pattern-matching technique. The 1-min-resolution SYM-H index, which is essentially the same as the hourly Dst index except in terms of the time resolution, does not show any statistically significant development after the onset of substorms; it tends to decay after the onset rather than to develop. It is suggested by a simple model calculation that the decay of the magnetospheric tail current after substorm onset is responsible for the decay of the Dst field. The relation between the IMF southward turning and the development of the Dst field is re-examined. The results support the idea that the geomagnetic storms and substorms are independent processes; that is, the ring-current development is not the result of the frequent occurrence of substorms, but that of enhanced convection caused by the large southward IMF. A substorm is the process of energy dissipation in the magnetosphere, and its contribution to the storm-time ring-current formation seems to be negligible. The decay of the Dst field after a substorm onset is explained by a magnetospheric energy theorem.
    Print ISSN: 0992-7689
    Electronic ISSN: 1432-0576
    Topics: Geosciences , Physics
    Published by Copernicus on behalf of European Geosciences Union.
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  • 8
    facet.materialart.
    Unknown
    Seasonal and solar cycle association of zonal drifts of ionospheric plasma irregularities in the Indian equatorial region (1996)
    Copernicus
    Details
    Publication Date: 1996-03-31
    Description: Long series of simultaneous VHF scintillation observations at two stations situated in near magnetic east-west direction in the vicinity of the dip equator in the Indian region have been employed to investigate the night-time ionospheric plasma zonal drifts. The drifts are found to be predominantly easterly. On comparing the magnitudes of the drifts with those results derived earlier by HF fading technique, monitoring signals from two satellites at a station and spaced receiver experiment, their associations with the season and the degree of solar activity are discussed. On a broader scale, the annual mean sunspot number is shown to have a direct control on the derived drift, the positive relationship even on day to day basis with the solar flux is established. However, the relationship, as understood by the slope of the best fit line, in the Indian region (0.27) is found to be weaker when compared with the similar slope (0.45) in the American sector. There appears to be no geomagnetic activity control on the estimated drifts.
    Print ISSN: 0992-7689
    Electronic ISSN: 1432-0576
    Topics: Geosciences , Physics
    Published by Copernicus on behalf of European Geosciences Union.
    Location Call Number Expected Availability
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    PAPER CURRENT
  • 9
    facet.materialart.
    Unknown
    An intense SFE and SSC event in geomagnetic H, Y and Z fields at the Indian chain of observatories (1997)
    Copernicus
    Details
    Publication Date: 1997-10-31
    Description: Changes in the three components of geomagnetic field are reported at the chain of ten geomagnetic observatories in India during an intense solar crochet that occurred at 1311 h 75° EMT on 15 June 1991 and the subsequent sudden commencement (SSC) of geomagnetic storm at 1518 h on 17 June 1991. The solar flare effects (SFE) registered on the magnetograms appear to be an augmentation of the ionospheric current system existing at the start time of the flare. An equatorial enhancement in ΔH due to SFE is observed to be similar in nature to the latitudinal variation of SQ (H) at low latitude. ΔY registered the largest effect at 3.6° dip latitude at the fringe region of the electrojet. ΔZ had positive amplitudes at the equatorial stations and negative at stations north of Hyderabad. The SSC amplitude in the H component is fairly constant with latitude, whereas the Z component again showed larger positive excursions at stations within the electrojet belt. These results are discussed in terms of possible currents of internal and external origin. The changes in the Y field strongly support the idea that meridional current at an equatorial electrojet station flows in the ionospheric dynamo, E.
    Print ISSN: 0992-7689
    Electronic ISSN: 1432-0576
    Topics: Geosciences , Physics
    Published by Copernicus on behalf of European Geosciences Union.
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  • 10
    facet.materialart.
    Unknown
    Frequency dependence of equatorial electrojet effect on geomagnetic micropulsations (1998)
    Springer
    Details
    Publication Date: 1998-10-01
    Print ISSN: 1343-8832
    Electronic ISSN: 1880-5981
    Topics: Geosciences , Physics
    Published by Springer
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