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  • 1
    Electronic Resource
    Electronic Resource
    Propagation of radio waves reflected from the ionosphere during a solar eclipse (1960)
    Springer
    Pure and applied geophysics 45 (1960), S. 123-152 
    Details
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Summary The article first describes in chronological order the observations on the propagation of radio waves during the solar eclipses, and the development of the conflicting results on the similar transmissions of radio signals. The general theory of the absorption of radio waves in the ionosphere is briefly described and therefrom a method is derived to estimate the variation of the absorption of obliquely incident radio waves during a solar eclipse. The variation of field-strength can be studied in terms of the relationship between the vertical incident equivalent frequency of the signals and the critical frequencies of the ionospheric layers at the regions of reflection. The total absorption of radio waves consists of the non-deviative absorption in theD region and the deviative absorption in the higher layers of the ionosphere. During the eclipse, theD region absorption decreases in phase with the progress of the eclipse, but the variation of deviative absorption may differ in each observation. The deviative absorption is large when the equivalent frequency is close to the critical frequency of the layer reflecting the waves or of the layer just penetrated by the waves. The changes in the deviative absorption during an eclipse can be estimated on the basis of the variation of the critical frequencies of the ionospheric layers. The resultant changes in the total absorption during a solar eclipse may thus be estimated. The different types of field strength variation expected during an eclipse are given. The observations of the vertical incident absorption of radio waves and the field strength variations of obliquely incident continuous wave radio signals during the solar eclipse are described and the changes are explained on the basis of the above theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01996580
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  • 2
    Electronic Resource
    Electronic Resource
    Signatures of storm sudden commencements in geomagnetic H, Y and Z fields at Indian observatories during 1958–1992 (1999)
    Springer
    Annales geophysicae 17 (1999), S. 1426-1438 
    Details
    ISSN: 0992-7689
    Keywords: Interplanetary physics (interplanetary shocks) ; Ionosphere (equatorial ionosphere) ; Magnetospheric physics (storms and substorms)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The work describes an intensive study of storm sudden commencement (SSC) impulses in horizontal (H), eastward (Y) and vertical (Z) fields at four Indian geomagnetic observatories between 1958–1992. The midday maximum of δH has been shown to exist even at the low-latitude station Alibag which is outside the equatorial electrojet belt, suggesting that SSC is associated with an eastward electric field at equatorial and low latitudes. The impulses in Y field are shown to be linearly and inversely related to δH at Annamalainagar and Alibag. The average SC disturbance vector is shown to be about 10–20°W of the geomagnetic meridian. The local time variation of the angle is more westerly during dusk hours in summer and around dawn in the winter months. This clearly suggests an effect of the orientation of shock front plane of the solar plasma with respect to the geomagnetic meridian. The δZ at δC have a positive impulse as in δH. The ratio of δZ/δH are abnormally large exceeding 1.0 in most of the cases at Trivandrum. The latitudinal variation of δZ shows a tendency towards a minimum over the equator during the nighttime hours. These effects are explained as (1) resulting from the electromagnetic induction effects due to the equatorial electrojet current in the subsurface conducting layers between India and Sri Lanka, due to channelling of ocean currents through the Palk Strait and (2) due to the concentration of induced currents over extended latitude zones towards the conducting graben between India and Sri Lanka just south of Trivandrum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-999-1426-1
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  • 3
    Electronic Resource
    Electronic Resource
    Geomagnetic storm effects at low latitudes (1999)
    Springer
    Annales geophysicae 17 (1999), S. 438-441 
    Details
    ISSN: 0992-7689
    Keywords: Ionosphere (electric fields and currents) ; Magnetospheric physics (electric fields; storms and substorms)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The geomagnetic horizontal (H) field from the chain of nine observatories in India are used to study the storm-time and disturbance daily variations. The peak decrease in storm-time variation in H showed significant enhancements at the equatorial electrojet stations over and above the normally expected decrease due to the ring current effects corrected for geomagnetic latitudes. The disturbance daily variation of H at equatorial stations showed a large decrease around midday hours over and above the usual dawn-maximum and dusk-minimum seen at any mid-latitude stations around the world. These slow and persistent additional decreases of H of disturbance daily variation at equatorial latitudes could be the effect of a westward electric field due to the Disturbance Ionospheric dynamo coupled with abnormally large electrical conductivities in the E region over the equator.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-999-0438-1
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  • 4
    Electronic Resource
    Electronic Resource
    A study of the noont critical frequencies of theE andF1 layers of the ionosphere (1958)
    Springer
    Pure and applied geophysics 40 (1958), S. 145-156 
    Details
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Summary The mean monthly noon critical frequencies of theE andF1 layers of the ionosphere at a number of stations in different latitudes and their variation with sunspot number have been studied in this paper. It is found that while theE layer approximates to a chapman region, theF1 layer is markedly affected by other agenices, somewhat similar toF2. In high sunspot years,foF1 shows two maxima at middle latitudes with a minimum at the equator.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01980121
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  • 5
    Electronic Resource
    Electronic Resource
    Lunar perturbations in geomagnetic field and in the characteristics ofF-region over huancayo (1970)
    Springer
    Pure and applied geophysics 80 (1970), S. 288-308 
    Details
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Summary The lunar daily (L) and lunar monthly (M) variations in horizontal magnetic field (H), maximum electron density (N max ), height of peak ionisation (h max ), semi-thickness (y m ) of theF 2 layer and total electron content (N t ) at Huancayo for the period January 1960 to December 1961 are described. The lunar tidal variations inh max follow sympathetically the variations inH such that an increase of magnetic field causes the raising of height of peak ionisation. Lunar tides inN max are opposite in phase to that ofh max with a delay of about 1–2 hours, suggesting that an increase of height causes a decrease in maximum electron density. The lunar tides in semi-thickness are very similar in phase to that inh max . The lunar tidal effects in any of the parameters are largest inD-months and least inJ-months. The amplitude of lunar tides in maximum electron density seems to increase with increasing height whereas the phase seems to be constant with height. It is concluded that lunar tides in the ionospheric parameters at magnetic equator are greatly controlled by the corresponding geomagnetic variations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00880215
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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    Midday reversal of equatorial ionospheric electric field (1997)
    Springer
    Annales geophysicae 15 (1997), S. 1309-1315 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A comparative study of the geomagnetic and ionospheric data at equatorial and low-latitude stations in India over the 20 year period 1956–1975 is described. The reversal of the electric field in the ionosphere over the magnetic equator during the midday hours indicated by the disappearance of the equatorial sporadic E region echoes on the ionograms is a rare phenomenon occurring on about 1% of time. Most of these events are associated with geomagnetically active periods. By comparing the simultaneous geomagnetic H field at Kodaikanal and at Alibag during the geomagnetic storms it is shown that ring current decreases are observed at both stations. However, an additional westward electric field is superimposed in the ionosphere during the main phase of the storm which can be strong enough to temporarily reverse the normally eastward electric field in the dayside ionosphere. It is suggested that these electric fields associated with the V × Bz electric fields originate at the magnetopause due to the interaction of the solar wind and the interplanetary magnetic field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-997-1309-2
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  • 8
    Electronic Resource
    Electronic Resource
    Meridional equatorial electrojet current in the American sector (1999)
    Springer
    Annales geophysicae 17 (1999), S. 220-230 
    Details
    ISSN: 0992-7689
    Keywords: Geomagnetism and paleomagnetism (dynamo theories) ; Ionosphere (equatorial ionosphere; ionosphere disturbances)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Huancayo is the only equatorial electrojet station where the daytime increase of horizontal geomagnetic field (H) is associated with a simultaneous increase of eastward geomagnetic field (Y). It is shown that during the counter electrojet period when δH is negative, δY also becomes negative. Thus, the diurnal variation of δY at equatorial latitudes is suggested to be a constituent part of the equatorial electrojet current system. Solar flares are known to increase the H field at an equatorial station during normal electrojet conditions (nej). At Huancayo, situated north of the magnetic equator, the solar flare effect, during nej, consists of positive impulses in H and Y and negative impulse in Z field. During counter electrojet periods (cej), a solar flare produces a negative impulse in H and Y and a positive impulse in Z at Huancayo. It is concluded that both the zonal and meridional components of the equatorial electrojet in American longitudes, as in Indian longitudes, flows in the same, E region of the ionosphere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-999-0220-4
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  • 9
    Electronic Resource
    Electronic Resource
    Morphological aspects of a new type of counter electrojet event (1999)
    Springer
    Annales geophysicae 17 (1999), S. 210-219 
    Details
    ISSN: 0992-7689
    Keywords: Geomagnetism and paleomagnetism (time variations, diurnal to secular) ; Ionosphere (electric fields and currents; equatorial ionosphere)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The study describes the time and space morphologies of a rather new type of counter electrojet event on the basis of data from the excellent chain of magnetic and ionospheric observatories along the Indo-Russian longitude sector. Abnormally large westward currents are observed during almost the whole of the daytime hours on a series of days. These events do not form any vortices in the current system and do not apparently seem to be associated with tidal effects or any solar magnetosphere events or geomagnetic disturbances. The existence of a westward electric field over the equatorial ionosphere has been confirmed by the absence of an equatorial type of sporadic E in the ionograms at Thumba precisely during the periods when δH at Trivandrum minus δH at Alibag is negative. The equatorial F region anomaly was also absent on the counter electrojet day. Such counter electrojet events during the northern winter months of low solar activity years are suggested to be the result of the modified wind system in the ionosphere associated with stratospheric warming events.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-999-0210-6
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  • 10
    Electronic Resource
    Electronic Resource
    Lunar Tide in the F 2 Layer of the Ionosphere near the Geomagnetic Equator (1961)
    [s.l.] : Nature Publishing Group
    Nature 189 (1961), S. 214-215 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] In this communication the analysis of lunar variations of /0F2 a* Leopoldville for the period of three years from November 1953 to October 1956 is presented. From the published hourly values off0F2, daily averages of three-hourly values between 11 hr. to 13 hr. (15 E.M.T.) are computed and are ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/189214a0
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