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  • 1
    Electronic Resource
    Electronic Resource
    Electron cyclotron waves in the presence of parallel electric fields in the Earth’s auroral plasma (1997)
    Springer
    Annales geophysicae 15 (1997), S. 24-28 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The electron cyclotron waves that originate at low altitudes (〈0.5 RE) and observed by ground facilities have been studied in the presence of a weak parallel electric field in auroral magnetoplasma consisting of trapped energetic auroral electrons and cold background electrons of ionospheric origin. The model distribution for auroral trapped electrons is taken as Maxwellian ring distribution. An expression for the growth rate has been obtained in the presence of parallel electric field assuming that the real frequency in the whistler mode is not affected by the presence of the electric field. The results show that waves grow (or damp) in amplitude for a parallel (or antiparallel) electric field. The influence of the electric field is more pronounced at a shorter wavelength spectrum. An increase in population of energetic electrons increases the growth rate and thus, plays a significant role in the wave excitation process in the auroral regions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-997-0024-3
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  • 2
    Electronic Resource
    Electronic Resource
    Nighttime enhancements in ionospheric electron content: seasonal and solar cycle variation (1995)
    Springer
    Annales geophysicae 13 (1995), S. 256-261 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Various characteristics of anomalous nighttime enhancement in ionospheric electron content (IEC) at Lunping (14.08°N geomagnetic), a station near the crest of the equatorial anomaly, have been presented by considering the IEC data for the 21st solar cycle. Out of a total of 1053 enhancements, 354 occur in pre-midnight and 699 occur in post-midnight hours, which indicates an overall dominance of post-midnight events at Lunping. The occurrence is more frequent during summer, less during the equinox and least during winter months. All the characteristics of the enhancements have seasonal dependencies and they reach their maximum values during summer months. The occurrence of the pre-midnight events show positive and post-midnight events show negative correlation with solar activity. The results have been discussed and compared with those at low-latitude stations in India and Hawaii and at the mid-latitude station, Tokyo.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-995-0256-z
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    Paper (German National Licenses)
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  • 3
    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)
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