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  • 1
    Electronic Resource
    Electronic Resource
    The sunspot cycle and solar and lunar daily variations inH (1972)
    Springer
    Pure and applied geophysics 98 (1972), S. 146-152 
    Details
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Summary Results of sunspot cycle influence on solar and lunar ranges at a low latitude station, Alibag, outside the equatorial electrojet belt, show that the sunspot cycle association in solar ranges is three times that of the lunar ranges in thed- andj-seasons. This is in general agreement with the earlier results for non-polar latitude stations. The association with sunspot number of individual lunar amplitudes is greatest for lunar semidiurnal harmonic in thej-season. During this season, the sunspot cycle influence on lunar variations is more than that on solar variations, thereby indicating that the lunar current is situated at a level more favourable for sunspot cycle influence than the level of the current associated with solar variations. With the increase in solar activity a shift appears in the times of maxima of semidiurnal lunar variation towards a later lunar hour ine- andj-seasons and in the year.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00875589
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  • 2
    Electronic Resource
    Electronic Resource
    Geomagnetic solar and lunar daily variations at Alibag, India (1984)
    Springer
    Pure and applied geophysics 122 (1984), S. 89-109 
    Details
    ISSN: 1420-9136
    Keywords: Solar daily variation ; Lunar daily variation ; Solar-cycle modulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Geomagnetic solar and lunar daily variationsS andL, at Alibag, India are derived, by the well-known Chapman-Miller method, from the series of homogeneous mean hourly magnetic data of the years 1932 to 1972. The data for all the three elements — declinationD and horizontal and vertical intensitiesH andZ — are analysed, by dividing the data suitably for a study of the seasonal variations, the effect of the changes in the solar and magnetic activities onS andL, the oceanic dynamo contribution toL, and their interactions with each other. The main results are as follows. (i) ForS the daily pattern and its seasonal progression conform to the type expected from a northern-hemisphere station. On the other hand, the amplitudes of all the four harmonics ofL systematically have higher values in winter, and inD andZ the harmonics show large phase differences between summer and winter. The pattern ofL in winter suggests that the lunar current system consists of a single set of vortices in the summer hemisphere rather than the conventional vortices, one set in each of the hemispheres. (ii) Solar-cycle modulation on the solar ranges as well as on the amplitudes of the first three harmonics ofS is greater than that expected solely from the increase in E-region conductivity, whereas the corresponding modulation onL is comparable to that on the E-region conductivity. (iii) With increasing magnetic activity the first harmonic ofS shows an increase, and the first three harmonics ofL indicate a general decrease, in amplitude. (iv) Of the variability inS 96%, but inL only 32%, is found to be accounted for by the combined effect of the variations in the solar and magnetic activities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00879651
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  • 3
    Electronic Resource
    Electronic Resource
    Lunar and luni-solar variations of the geomagnetic field in the Indian region (1972)
    Springer
    Pure and applied geophysics 95 (1972), S. 131-140 
    Details
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Summary Lunar and luni-solar geomagnetic components have been computed upto four harmonics for low latitude station Alibag, outside equatorial electrojet belt, and the equatorial electrojet stations Annamalainagar, Kodaikanal and Trivandrum in the south Indian region. The computations are confined to data of very high solar activity period 1958–61. Amplitudes of lunar semidiurnal component (L 2), in the horizontal intensity (H), undergo an equatorial enhancement. Phase difference of 2 hrs is noticed inL 2 (H) between nonelectrojet and electrojet stations. In the vertical intensity (Z), L 2 is maximum ine andj-seasons at Trivandrum, close to the magnetic equator. Ind-season, however, maximumL 2 (Z) occurs at Annamalainagar (dip 5°.4N). The phase difference between the electrojet and nonelectrojet stations observed inL 2 (H) is not noticed inL 2 (Z). The differential vertical upward drift motion of charged particles may explain the observed phase difference inL 2 (H). Seasonal variations in amplitudes and times of maxima are noticed at all the stations inL 2 (H) andL 2 (Z). Similar variation is also noticed at Alibag inL 2 of declination (D).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00878861
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  • 4
    Electronic Resource
    Electronic Resource
    On Ps6 and longer period geomagnetic pulsations in the Indian equatorial region (1994)
    Springer
    Annales geophysicae 12 (1994), S. 655-663 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Adopting an appropriate procedure suitable for processing the amplitude-time records based on the two-component spectral analysis technique, the statistical information on Ps6 and other longer periods are worked out on the geomagnetic field registrations in the Indian longitudinal regions at and away from the equatorial electrojet influence. The storm interval during 21 and 22 September 1982 has been chosen for the analysis, as violent and regular cyclic variations of the geomagnetic field were recorded in all the three components of the field at the Indian observatories. The procedure, when applied to two intervals of afternoon and night conditions of equatorial ionosphere, showed practically the same polarisation characteristics in the H-D plane at all the frequencies under the equatorial electrojet. At far away places from this influence, the ellipticities are found to be relatively to the west during the afternoon. These, along with the other results, are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-994-0655-6
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  • 5
    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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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    Observations of Pc5 micropulsation-related electric field oscillations in the equatorial ionosphere (1994)
    Springer
    Annales geophysicae 12 (1994), S. 565-573 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A 54.95-MHz coherent backscatter radar, an ionosonde and the magnetometer located at Trivandrum in India (8.5○N, 77○E, 0.5○N dip angle) recorded large-amplitude ionospheric fluctuations and magnetic field fluctuations associated with a Pc5 micropulsation event, which occurred during an intense magnetic storm on 24 March 1991 (Ap=161). Simultaneous 100-nT-level fluctuations are also observed in the H-component at Brorfelde, Denmark (55.6○N gm) and at Narsarsuaq, Greenland (70.6○N gm). Our study of the above observations shows that the E-W electric field fluctuations in the E- and F-regions and the magnetic field fluctuations at Thumba are dominated by a near-sinusoidal oscillation of 10 min during 1730–1900 IST (1200-1330 UT), the amplitude of the electric field oscillation in the equatorial electrojet (EEJ) is 0.1-0.25 mV m−1 and it increases with height, while it is about 1.0 mV m−1 in the F-region, the ground-level H-component oscillation can be accounted for by the ionospheric current oscillation generated by the observed electric field oscillation in the EEJ and the H-component oscillations at Trivandrum and Brorfelde are in phase with each other. The observations are interpreted in terms of a compressional cavity mode resonance in the inner magnetosphere and the associated ionospheric electric field penetrating from high latitudes to the magnetic equator.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-994-0565-7
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  • 8
    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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  • 9
    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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  • 10
    Electronic Resource
    Electronic Resource
    Ovsiannikov's method and the construction of partially invariant solutions (1987)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 28 (1987), S. 1473-1476 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: A plausibility argument presented by the first two authors in an earlier paper [J. Math. Phys. 26, 3042 (1985)] concerning the existence of partially invariant solutions for some equations of the Fokker–Planck type is made precise by the explicit construction of one such solution. In the process a substantial simplification of Ovsiannikov's method for finding partially invariant solutions is achieved. In addition, the class of partially invariant solutions obtained by Ovsiannikov for the equations of transonic flow of a gas is enlarged.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.527501
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