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  • 1
    Electronic Resource
    Electronic Resource
    Hale-cycle effects in cosmic-ray intensity during the last four cycles (1996)
    Springer
    Astrophysics and space science 246 (1996), S. 7-14 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Monthly cosmic-ray data from Inuvik (0.16 GV) and Climax (2.96 GV) Neutron Monitor stations has been studied with the aid of solar activity parameters for the time period 1947–1995. Systematic differences in the overall shape of successive 11-year modulation cycles and similarities in the alternate 11-year cycles seem to be related to the polarity reversals of the polar magnetic field of the Sun. This suggests a possible effectiveness of the Hale cycle during even and odd solar activity cycles. Our results can be understood in terms of open and closed models of the heliosphere. Positive north pole of the Sun leads to open heliosphere where particles reach the Earth more easily when their access route is by the heliospheric oolar regions (even cycles) than when they gain access along the current sheet (odd cycles). In this case as the route of access becomes longer due to the waviness of the neutral sheet, the hysteresis effect of cosmic-rays is also longer. This interpretation is explained in terms of different contributions of convection, diffusion and drift mechanisms to the whole modulation process influencing cosmic-ray transport in the heliosphere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00637395
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  • 2
    Electronic Resource
    Electronic Resource
    Energy dissipation during a small substorm (1995)
    Springer
    Annales geophysicae 13 (1995), S. 494-504 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The relative importance of the two most likely modes of input energy dissipation during the substorm of 8 May 1986, with an onset at 12:15 UT (CDAW 9E event), is examined here. The combination of data from the interplanetary medium, the magnetotail and the ground allowed us, first of all, to establish the sequence of phenomena which compose this substorm. In order to calculate the magnetospheric energetics we have improved the Akasofu model, by adding two more terms for the total magnetospheric output energy. The first one represents the energy consumed for the substorm current wedge transformation, supplied by the asymmetric ring current. This was found to be 39% of the solar wind energy entering the magnetosphere from the start of the growth phase up to the end of the expansion phase. The second term represents the energy stored in the tail or returned to the solar wind. Our results suggest that the substorm leaves the magnetosphere in a lower energy state, since, according to our calculations, 23% of the energy that entered the magnetosphere during the whole disturbance was returned back to the solar wind. Finally, it is interesting to note that during the growth phase the driven system grow considerably, consuming 36% of the solar wind energy which entered the magnetosphere during this early phase of the substorm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-995-0494-0
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  • 3
    Electronic Resource
    Electronic Resource
    Observations of flux rope – associated particle bursts with GEOTAIL in the distant tail (1997)
    Springer
    Annales geophysicae 15 (1997), S. 1515-1531 
    Details
    ISSN: 0992-7689
    Keywords: Magnetospheric configuration and dynamics ; Magnetotail
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Geotail energetic particle, magnetic field data and plasma observations (EPIC, MGF and CPI experiments) have been examined for a number of energetic particle bursts in the distant tail (120Re 〈 |XGSM| 〈 130 Re), associated with moving magnetic field structures, following substorm onsets. The features obtained from this data analysis are consistent with the distant magnetotail dynamics determined first by ISEE3 observations and explained in terms of the neutral line model. At the onset of the bursts, before plasma sheet entrance, energetic electrons appear as a field-aligned beam flowing in the tailward direction, followed by anisotro-pic ions. Within the flux rope region, suprathermal ions exhibit a convective anisotropy, which allows determination of the plasma flow velocity, assuming that the anisotropy arises from the Compton-Getting effect. The velocities thus determined in the plasma sheet are estimated to be 200–650 km/s, and compare favourably with the velocities derived from the CPI electron and proton experiment. The estimated length of magnetic field structures varies between 28 and 56 Re and depends on the strength of the westward electrojet intensification. Finally, the three structures reported here show clear magnetic field signatures of flux rope topology. The existence of a strong magnetic field aligned approximately along the Y-axis and centred on the north-to-south excursion of the field, and the bipolar signature in both By and/or Bz components, is consistent with the existence of closed field lines extending from Earth and wrapping around the core of the flux rope structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-997-1515-y
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  • 4
    Electronic Resource
    Electronic Resource
    Study of the longitudinal expansion velocity of the substorm current wedge (1998)
    Springer
    Annales geophysicae 16 (1998), S. 1423-1433 
    Details
    ISSN: 0992-7689
    Keywords: Magnetospheric physics (current systems; magnetosphere-ionosphere interactions)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract In this work we examine simultaneous observations from the two geosynchronous satellites GOES-5 and GOES-6 located at 282°E and 265°E respectively, and from middle and low latitude ground observatories located within 250°E and 294°E geographic longitude, during isolated substorms of moderate activity. The spatial distribution of our observation points allows us to make a detailed study of the azimuthal expansion of the substorm current wedge. The data analysis shows evidence that the substorm initiation and development mechanism include the cross-tail current diversion/disruption, the substorm current wedge formation and the azimuthal expansion of the inner plasma sheet. The triggering mechanism is initially confined in a longitudinally narrow sector, estimated to be less than 15° and located very close to local midnight to the east or to the west. The current disruption region expands both eastward and westward in the magnetotail, so that the location of major field-aligned currents flowing into the ionosphere shifts successively eastward, and the location of the currents flowing out of the ionosphere shifts successively westward. Evidence was found that the perturbation travels toward the west with velocities greater than those expanding the wedge eastward. The drastic decrease of the velocity with the azimuthal distance from the location of the disturbance initiation, i.e., the onset sector, indicates that the energy release is a very localized phenomenon. Finally, the transient D perturbation observed by the geosynchronous satellites suggests that the field-aligned currents forming the wedge have a longitudunally limited extent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-998-1423-9
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  • 5
    Electronic Resource
    Electronic Resource
    Magnetotail response during a strong substorm as observed by GEOTAIL in the distant tail (1998)
    Springer
    Annales geophysicae 16 (1998), S. 528-541 
    Details
    ISSN: 0992-7689
    Keywords: Magnetospheric physics (magnetospheric configuration and dynamics; magnetotail)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Simultaneous energetic particle and magnetic field observations from the GEOTAIL spacecraft in the distant tail (XGSM ≈ -150 Re) have been analysed to study the response of the Earth’s magnetotail during a strong substorm (AE ⩽ 680 nT). At geosynchronous altitude, LANL spacecraft recorded three electron injections between 0030 UT and 0130 UT, which correspond to onsets observed on the ground at Kiruna Ground Observatory. The Earth’s magnetotail responded to this substorm with the ejection of five plasmoids, whose size decreases from one plasmoid to the next. Since the type of magnetic structure detected by a spacecraft residing the lobes, depends on the Z extent of the structure passing underneath the spacecraft, GEOTAIL is first engulfed by a plasmoid structure; six minutes later it detects a boundary layer plasmoid (BLP) and finally at the recovery phase of the substorm GEOTAIL observes three travelling compression regions (TCRs). The time-of-flight (TOF) speed of these magnetic structures was estimated to range between 510 km/s and 620 km/s. The length of these individual plasmoids was calculated to be between 28 Re and 56 Re. The principal axis analysis performed on the magnetic field during the TCR encountered, has confirmed that GEOTAIL observed a 2-D perturbation in the X-Z plane due to the passage of a plasmoid underneath. The first large plasmoid that engulfed GEOTAIL was much more complicated in nature probably due to the external, variable draped field lines associated with high beta plasma sheet and the PSBL flux tubes surrounding the plasmoid. From the analysis of the energetic particle angular distribution, evidence was found that ions were accelerated from the distant X-line at the onset of the burst associated with the first magnetic structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-998-0528-5
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  • 6
    Electronic Resource
    Electronic Resource
    A possible E-W asymmetry of the coronal emission line intensities and K-corona brightness (1994)
    Springer
    Astrophysics and space science 218 (1994), S. 35-57 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The analysis of the daily measurements of the coronal green and red line intensities as well as the K-corona brightness, which have been collected by the Pic-du-Midi Observatory, for the time period 1944–1974, has revealed some very interesting features. North-South (N-S) asymmetries for all these coronal intensities are confirmed again for this time period. The main point of this analysis is a strong evidence of longitudinal distribution of the coronal intensities as derived from the data record. In our effort to confirm this asymmetry, we have examined the yearly and monthly distribution of the asymmetry coefficient in each solar quadrant showing that the northeast (NE) quadrant appears the most active of all. We have also examined the intensity ratios measured at the East and West solar limbs which is continuously greater than the unit. A seasonal variation of this ratio has also been reported with a maximum during the winter period and a minimum during the summer period.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00658065
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  • 7
    Electronic Resource
    Electronic Resource
    Structure of the July 1982 event in relation to the magnetosphere's response (1991)
    Springer
    Astrophysics and space science 180 (1991), S. 173-183 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A large Forbush-type decrease with an amplitude of 16–22% was observed by the world-wide network of cosmic-ray detectors during the period 13–14 July, 1982. Combined neutron-monitor measurements with interplanetary plasma and magnetic field data, auroral data, and Earth's magnetospheric data are used for the study of this event. It is suggested that this interesting event is probably a consequence of the dynamic interactions of the solar wind with the Earth's magnetosphere as it is obvious from the large magnetic storm which was recorded in the auroral electrojet indices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00648176
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  • 8
    Electronic Resource
    Electronic Resource
    Power-spectrum analysis of local geomagnetic disturbances and their relationship to cosmic-ray and aurora intensity (1989)
    Springer
    Earth, moon and planets 45 (1989), S. 1-15 
    Details
    ISSN: 1573-0794
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Power-spectrum analyses have been carried out on two data sets of the geomagnetic K-index from the Athens and Sofia magnetic Observatories. For the period between 1956–1984, periodicities of about 2.8 and 6 months have been obtained. Similar results were found by the auto-correlation technique. Both periods are significant to 0.05 and 0.01 level, respectively. In our attempt to explain transient geomagnetic disturbances caused by other parameters, the K-index was correlated to cosmic-ray and aurora intensity. The best correlation coefficient between K-variations and cosmic-ray data from Athens Neutron-Monitor Station was 0.58 and between K-index and Auroral, activity index was 0.47. An attempt to interpret these periodicities and relationships has been made.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00054657
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  • 9
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    A possible E-W asymmetry of the coronal emission line intensities and K-corona brightness (1994)
    Springer
    Details
    Publication Date: 1994-01-01
    Print ISSN: 0004-640X
    Electronic ISSN: 1572-946X
    Topics: Physics
    Published by Springer
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  • 10
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    Structure of the July 1982 event in relation to the magnetosphere's response (1991)
    Springer
    Details
    Publication Date: 1991-01-01
    Print ISSN: 0004-640X
    Electronic ISSN: 1572-946X
    Topics: Physics
    Published by Springer
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