[en] Short note

[en] Complete text of publication follows. The equation of pitch angle diffusion is offered, which also allows to model change of pitch angle distribution from time. Two examples are presented. The first example is evolution of pitch angle distribution of protons during a typical moderate magnetic storm. The second example is evolution of pitch angle distribution of protons during the 2 - 7 May 1998 storm. The received results are compared among themselves and to results of other works.

[en] The ATS-6 data for a period of 1975-76 is used for the study of slab thickness during two moderate storms (Ksub(p)<=4^-) around the crest of the anomaly, Ahmedabad and a very great (Ksub(p)<=7), a great (Ksub(p)<=4) and a moderate storm (Ksub(p)<=6⁺) outside the equatorial anomaly region, Delhi. While at Ahmedabad, on the average, the slab thickness is found to be above the frequency. Comparison of slab thickness with foF2 and the equatorial magnetic record (for Ahmedabad only) shows that the foF2 changes alone cannot be held responsible for the slab thickness variation and thus entry of the plasma flux from the plasmasphere cannot be ruled out. The pressure variation effect of storm-time heating on the slab thickness at Ahmedabad is that even for Ksub(p)=8, the thermal expansion and the contraction effects are unable to explain complete quantitative and qualitative features of the observations

[en] A theoretical study has been made of the process to refill geomagnetic force tubes with a thermal ionospheric plasma after a magnetic disturbance. As shown by analytical and numerical calculations, the characteristic time of filling and the maximum possible total electron content are proportional to the tube volume and equal to tau approximately 0.17L⁴ of a day and N infinity approximately 10¹²L⁴ cm^-2, respectively. It is typical during a long period of magnetically quiet conditions that at L < 3 the electron content is closed to a limited value of N infinity approximately L⁴, whereas at L > 3 the electron content is proportional to the duration of the quiet period and does not depend on the value of L. Incomplete filling of the force tubes with a thermal plasma causes the ionospheric light ion through to be produced within the range of L-shells for which tau(L) >> t

[en] The relationship between disappearing solar fragments and geomagnetic disturbances was investigated. It is shown that long-delay storms are associated with filaments well removed from the disc centre, and particularly in the case of large filaments and prominences, the proportion of events that produce long-delay storms increases with angular distance from the centre

[en] Complete text of publication follows. The complex system of the Earth's magnetosphere corresponds to an open spatially extended nonequilibrium (input - output) dynamical system. The non-extensive Tsallis entropy has been recently introduced (Balasis et al., 2008) as an appropriate information measure to investigate dynamical complexity in the magnetosphere. The method has been employed for analyzing Dst time series and gave promising results, detecting the complexity dissimilarity among different physiological and pathological magnetospheric states (i.e., pre-storm activity and intense magnetic storms, respectively). This paper explores the applicability and effectiveness of a variety of computable entropy measures (e.g. Block entropy, Kolmogorov entropy, T complexity and Approximate entropy) to the investigation of dynamical complexity in the magnetosphere. We show that as the magnetic storm approaches there is clear evidence of significant lower complexity in the magnetosphere. The observed higher degree of organization of the system agrees with that inferred previously (Balasis et al., 2006), from an independent linear fractal spectral analysis based on wavelet transforms. This convergence between nonlinear and linear analyses provides a more reliable detection of the transition from the quiet-time to the storm-time magnetosphere, thus showing evidence that the occurrence of an intense magnetic storm is imminent. More precisely, we claim that our results suggest an important principle: significant complexity decrease and accession of persistency in Dst time series can be confirmed as the magnetic storm approaches, which can be used as diagnostic tools for the magnetospheric injury (global instability). Overall, Approximate entropy and Tsallis entropy yield superior results for detecting dynamical complexity changes in the magnetosphere in comparison to the other entropy measures presented herein. Ultimately, the analysis tools developed in the course of this study for the treatment of Dst index can provide convenience for space weather applications.

[en] Complete text of publication follows. One of the modern and popular uses of ground magnetometer data is to identify field line resonance frequencies through cross-phase or cross-amplitude analysis and infer the equatorial mass density in the magnetosphere. Most studies on this topic to date focus on the observations along a specific meridian, and, as the Earth rotates, the observations constantly advance in local time. This study presents the field line resonance analysis using data gathered by a number of magnetometer networks in North America, such as McMAC, Falcon, IGPP-LANL, THEMIS, CARISMA, AUTUMN, and Alaskan stations. The observations provide two-dimensional snapshots of the equatorial mass density over a range of L-values and local hours. Using the October 2007 magnetic storm as an example, we will show the spatiotemporal features of density structure observed by the combined two-dimensional magnetometer network and how they are compared with the results obtained by observations along a single meridian.

[en] The latitudinal variation of the effect of the great storm of 17 Dec. 71 is investigated by choosing stations of varying latitudes but of approximately the same longitude. In addition, three stations, one each in the American, African and Indian zone, are chosen to find the longitudinal changes produced during this storm. It is seen that the storm is mainly a negative one in the southern hemisphere of this longitude sector. The noon biteout is enhanced on the major storm day, viz., 17 Dec. 71, at the American equator, with large evening peaks on both 17th and 18th. The northern hemisphere does not exhibit any large change in the critical frequency of the F layer. The reported changes in TEC measurements are not reflected in the parameter f₀F₂ at Lindau

[en] First, we present and compare experimental data on magnetospheric cold plasma density and plasmapause position obtained, for two magnetically disturbed days (14 and 6 July 1977), by the three following techniques: - analysis of multi-component whistlers recorded at Kerguelen (L = 3.7) and General Belgrano (L approximately equal to 4.5), Antarctica; - in situ measurements from the relaxation sounded and the mutual impedance experiment on board GEOS-1; - broadband VLF spectra telemetered from the ISIS satellites to Kerguelen. In the vicinity of the plasmapause, the equarorial electron density profiles derived from whistlers and GEOS-1 data are similar. Outside the plasmasphere, the agreement between results is better when the hybrid model -rather than R^-4 ones- is assumed in whistler analysis. Inside the plasmasphere, the radial decrease of the electron density above L = 4 follows roughly a L^-4 law. Then, all the data are used to study the structure and the dynamical behavior of the dayside plasmasphere. On July 14, the response of the plasmapause to substorms is complex and occurs with some delay, increasing with the magnetic local time. We observe successively: a plasmapause deformation near 12 MLT, detached plasma elements in the early afternoom sector and a reduced size plasmaphere, with a pronounced duskside bulge, in the 12-19 MLT sector. On July 6, the plasmasphere structure and the cold plasma drifts in the equatorial plane are those of quiet magnetic periods as long as there is no energy injection into the ring current. As soon as the injection associated with the magnetic storm begins, the equatorial structure of the dayside plasmasphere becomes irregular. It appears, between approximately 3.5 and 4 Rsub(E), a trough-like depression which remains in the view of the ground-based station during more than six hours; the electron densities in the trough-like region are of the order of 300 cm^-3, whereas they were between 500 and 550 cm^-3 before the magnetic storm

[en] Given the infrequency of extreme geomagnetic storms, it is significant to note the concentration of three extreme geomagnetic storms in 1941, whose intensities ranked fourth, twelfth, and fifth within the aa index between 1868–2010. Among them, the geomagnetic storm on 1941 March 1 was so intense that three of the four Dst station magnetograms went off scale. Herein, we reconstruct its time series and measure the storm intensity with an alternative Dst estimate (Dst*). The source solar eruption at 09:29–09:38 GMT on February 28 was located at RGO AR 13814 and its significant intensity is confirmed by large magnetic crochets of ∣35∣ nT measured at Abinger. This solar eruption most likely released a fast interplanetary coronal mass ejection with estimated speed 2260 km s⁻¹. After its impact at 03:57–03:59 GMT on March 1, an extreme magnetic storm was recorded worldwide. Comparative analyses on the contemporary magnetograms show the storm peak intensity of minimum Dst* ≤ −464 nT at 16 GMT, comparable to the most and the second most extreme magnetic storms within the standard Dst index since 1957. This storm triggered significant low-latitude aurorae in the East Asian sector and their equatorward boundary has been reconstructed as 38.°5 in invariant latitude. This result agrees with British magnetograms, which indicate an auroral oval moving above Abinger at 53.°0 in magnetic latitude. The storm amplitude was even more enhanced in equatorial stations and consequently casts caveats on their usage for measurements of the storm intensity in Dst estimates.