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  • 11
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    Effects of prolonged southward IMF Bz on low latitude ionospheric electron density (2014)
    Wiley
    Details
    Publication Date: 2014-06-17
    Description: The present work describes the low latitude ionospheric variability during an unusually prolonged (~33 hours) geomagnetically disturbed condition that prevailed during 15-16 July 2012. The low latitude electron density in summer hemisphere, investigated using ground and satellite based observations, responded to this by generating strong negative ionospheric storm on 16 July. The maximum electron density on 16 July over Indian low latitudes was reduced by more than 50% compared to that on a geomagnetically quiet day (14 July 2012). In contrast to the extreme reduction in total electron content (TEC) in the northern hemisphere, TEC from a winter hemispheric station revealed substantial (~23 TECU) enhancements on the same day. This contrasting hemispherical response in TEC is suggested to be due to the combined effects of strong interhemispheric, and solar driven day-night winds. Further, very weak equatorial electrojet (EEJ) strength on 16 July indicated that the westward electric field perturbations in the low latitude ionosphere were possibly due to the disturbance dynamo effect associated with meridional circulation from polar to equatorial latitudes. Interestingly, despite reduction in the integrated EEJ strength on 15 July, the low latitude electron density showed substantial enhancement highlighting the significant effect of the positive ionospheric storm on the low latitude ionosphere. The roles of electro-dynamical/neutral-dynamical and compositional disturbances are discussed in view of these observations to understand low latitude ionospheric response when geomagnetic disturbance persists for longer duration.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 12
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    Gravity wave signatures in the dip equatorial ionosphere –thermosphere system during the annular solar eclipse of 15 January 2010 (2014)
    Wiley
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    Publication Date: 2014-05-08
    Description: The present work pertains to the eclipse induced gravity wave modulations in the ionosphere-thermosphere region over Trivandrum (8.5°N, 77°E, dip 2°N) during the annular solar eclipse of 15 January 2010. ENWi rocket payload measured horizontal winds and electron densities at E region altitudes and ionosonde derived foF1 and foF2 parameters are used to analyze the characteristics of the eclipse induced gravity waves. The analysis reveals an intensification of gravity waves with periods around 30-100 min during the peak phase of the eclipse. The vertical wavelength of the prevalent wave is found to be around 2 km. The role of gravity wave induced winds in generating blanketing Es over the equator is also examined.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 13
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    Pre-assessment of the “strength” and “latitudinal extent” of L-band scintillation: A case study (2013)
    Wiley
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    Publication Date: 2013-01-28
    Description: [1]  Forecasting the strength of nighttime L-band scintillation well in advance of their actual occurrence by making use of the background conditions has been attempted over the Indian zone with an eye on operational forecasting capability. It has been shown that the base height of the equatorial F -region as early as 1930 h LT shows a linear relation to the maximum altitudinal extent of medium-scale irregularities that are responsible for the L-band scintillation during the course of the night and these in turn get mapped to latitudes away from the equator defining the latitude range that gets affected by their presence. On the other hand, the average value of the vertical total electron content between 1830 h LT and 1930 h LT on a given day is shown to control the maximum strength of the scintillation represented by S 4 index on the day. The above analysis, although it has been carried out for the equatorial station Trivandrum, is applicable to other latitudes as well. Having demonstrated the control of the background ionospheric-thermospheric conditions, it has been shown that the averaged vertical total electron content around the prereversal enhancement (1830 h LT to 1930 h LT) along with the actual base height information at 1930 h LT over the magnetic equator would enable one to forecast the maximum possible S 4 in a given latitudinal region as early as 1930 h and issue necessary forewarning alerts wherever needed.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 14
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    Ionospheric impact on the geopotential height profile of the temperature by balloon-borne GPS radiosondes? (2013)
    Wiley
    Details
    Publication Date: 2013-01-31
    Description: [1]  We have studied the potential inaccuracies in the geopotential height, its manifestation in the altitude profile of temperature measured by balloon-borne GPS radiosonde (GPS sonde), and its association with the variations in ionospheric plasma density, particularly in the Indian low latitude region. Using results from a GPS sonde inter-comparison campaign, conducted at Gadanki (13.5°N, 79.2°E, 6.4°N geomagnetic latitude) at different local times of a day, we show that differences in temperature at different geopotential heights vary with respect to the local time of the day in October 2010. However, differences in temperature become negligible and within the limits of experimental uncertainty if the comparison is made with respect to the time of measurements during the ascent rather than with respect to the GPS-derived geopotential height. We show that the origin of the mismatch rests with the inaccurate estimation of geopotential height by the two GPS sondes and not due to any inaccuracy in their measurements itself. Differences in the geopotential height estimates are larger during late afternoon, resulting in larger temperature differences between the sondes, and least during late evening/early morning hours. The uncertainty in the geopotential height estimation remains well synchronized with the magnitude and variations in the total electron content (TEC) of the ionosphere. This study exhorts us to account for the local ionospheric variations while extracting the geopotential height profiles of temperature from GPS sonde measurements, especially in the low and equatorial regions where there are large spatial and temporal variations in the ionospheric densities.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 15
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    Impact of the perturbation zonal velocity variation on the spatio/temporal occurrence pattern of L-band scintillation – a case study (2015)
    Wiley
    Details
    Publication Date: 2015-07-01
    Description: The earlier evolved method for the forecast of the spatio-temporal variation of L-band scintillation based on the expected variation of the perturbations, under favorable ionospheric/thermospheric conditions, has been refined by duly accounting for the local time variation of the zonal velocity of the perturbations. The unique combination of the two geostationary satellites (GSAT-8 and GSAT-10) over the Indian zone has been used to estimate the typical LT dependence of the perturbation velocities by closely following identifiable features in the scintillation pattern. The measured velocities, that registered a steady decrease with the progression of night, had been shown to significantly alter the forecast pattern of the scintillations with respect to longitude and local time. The significant improvement in the forecast pattern has been demonstrated through a case study putting the forecast method on a firmer footing.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 16
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    The impact of the 17 March 2015- St. Patrick's Day storm on the evolutionary pattern of Equatorial Ionization Anomaly over the Indian longitudes using high resolution spatio-temporal TEC maps – New insights (2016)
    Wiley
    Details
    Publication Date: 2016-09-23
    Description: The impact of the St. Patrick's Day storm (17 March 2015) on the major equatorial electro-dynamical process viz., the Equatorial Ionization Anomaly (EIA) has been assessed using 2D (5 ° lat. x 5 ° long.) total electron content (TEC) maps generated from the ground based SBAS (Satellite Based Augmentation System) enabled receiver data. The various aspects of EIA specifically the i) evolution/devolution, ii) longitudinal structure, and iii) its variability during different phases of a geomagnetic storm, have been brought out. These 2D TEC maps, which have a large latitudinal (5̊ S-45° N) and longitudinal (55-110° E) coverage, show the complete reversal in the longitudinal structure/pattern of EIA during the recovery phase of the storm as compared to the quiet day. These results have been explained in the light of the combined effects of the storm associated processes such as i) the penetration electric fields of magnetosphere origin, ii) storm-induced thermospheric winds, and, iii) activation of the consequent disturbance dynamo effectively distorting the longitudinal wave number 4 (WN4) structure of the EIA. It has been shown unambiguously that even a separation of ~10°-15° longitude could experience significantly different forcings. The relevance and the far reaching consequences of the study in the light of the current trends and requirements for reliable satellite based navigation are highlighted.
    Print ISSN: 1539-4964
    Electronic ISSN: 1542-7390
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 17
    Electronic Resource
    Electronic Resource
    A case-study of the low-latitude thermosphere during geomagnetic storms and its new representation by improved MSIS model (1998)
    Springer
    Annales geophysicae 16 (1998), S. 1513-1518 
    Details
    ISSN: 0992-7689
    Keywords: Low-latitude thermosphere ; MSIS model ; Stormtime model predictions, FP spectroscopic temperatures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The thermospheric temperatures from low and equatorial latitudes during geomagnetically disturbed periods are known to exhibit significant deviations from atmospheric model predictions. Also, the oscillatory features seen in the observations are not accounted for by the models. A simple relation has been established between the difference in the observed and model-predicted temperatures and the rate of change of Dst, the magnetic index representing the ring current variabilities. Using this relation, a correction term has been added to the latest MSIS-90 model algorithm and almost all the observed variations in neutral temperatures spectroscopically determined from Mt. Abu, a low-latitude station in India, are successfully reproduced for two moderate geomagnetic storms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-998-1513-8
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  • 18
    Electronic Resource
    Electronic Resource
    A question on the discriminants of involutions of central division algebras (1993)
    Springer
    Mathematische Annalen 297 (1993), S. 575-580 
    Details
    ISSN: 1432-1807
    Keywords: 16K20 ; 12G05
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01459519
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  • 19
    Electronic Resource
    Electronic Resource
    Resolutions for some filtered algebras (1962)
    Springer
    Mathematische Annalen 148 (1962), S. 341-348 
    Details
    ISSN: 1432-1807
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01451141
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  • 20
    Electronic Resource
    Electronic Resource
    On the global dimension of some algebras (1963)
    Springer
    Mathematische Zeitschrift 81 (1963), S. 108-111 
    Details
    ISSN: 1432-1823
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01111656
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