Fine structure of Pi2-type geomagnetic pulsations

An analysis of the BEAR experiment and Polar satellite data showed that several ionospheric sources could act almost simultaneously in the area of Pi2-type geomagnetic pulsations. The aim of this study is to locate these sources and determine their coherence in the narrow-frequency band of (6–10) × 10⁻³ Hz. By using gradient analysis methods, we revealed the local sources of oscillations coherent (phased), that allows one to treat their contributions as manifestations of the fine structure of the field of Pi2 pulsations.     

Studies on the latitudinal distribution of ground-based geomagnetic pulsations and fluctuations in the interplanetary medium using discrete mathematical analysis methods

Ground-based geomagnetic Pc5 (2–7 mHz) pulsations, caused by the passage of dense transients (density disturbances) in the solar wind, were analyzed. It was shown that intensive bursts can appear in the density of the solar wind and its fluctuations, up to Np ～ 30–50 cm³, even during the most magnetically calm year in the past decades (2009). The analysis, performed using one of the latest methods of discrete mathematical analysis (DMA), is presented. The energy functional of a time-series fragment (called “anomaly rectification” in DMA terms) of two such events was calculated. It was established that fluctuations in the dynamic pressure (density) of the solar wind (SW) cause the global excitation of Pc5 geomagnetic pulsations in the daytime sector of the Earth’s magnetosphere, i.e., from polar to equatorial latitudes. Such pulsations started and ended suddenly and simultaneously at all latitudes. Fluctuations in the interplanetary magnetic field (IMF) have turned up to be less geoeffective in exciting geomagnetic pulsations than fluctuations in the SW density. The pulsation generation mechanisms in various structural regions of the magnetosphere were probably different. It was therefore concluded that the most probable source of ground-based pulsations are fluctuations of the corresponding periods in the SW density.     

Precipitation of energetic electrons and Pi3 geomagnetic pulsations at polar latitudes

Precipitation of electrons with energies of 0.3–1.5 MeV has been analyzed based on the CORONAL-F satellite data at polar latitudes of the Northern Hemisphere on December 13, 2003. The instants of electron precipitation have been compared with the ground-based observations of geomagnetic disturbances and auroras near the satellite orbit projection. It has been indicated that precipitation of energetic electrons in the high-latitude nightside sector is accompanied by the simultaneous development of bay-like magnetic field disturbances on the Earth’s surface and the appearance of riometer absorption bursts and Pi3 geomagnetic pulsations, and auroras.     

Substorm onset identification using neural networks and Pi2 pulsations

The pattern recognition capabilities of artificial neural networks (ANNs) have for the first time been used to identify Pi2 pulsations in magnetometer data, which in turn serve as indicators of substorm onsets and intensifications. The pulsation spectrum was used as input to the ANN and the network was trained to give an output of +1 for Pi2 signatures and –1 for non-Pi2 signatures. In order to evaluate the degree of success of the neural-network procedure for identifying Pi2 pulsations, the ANN was used to scan a number of data sets and the results compared with visual identification of Pi2 signatures. The ANN performed extremely well with a success rate of approximately 90% for Pi2 identification and a timing accuracy generally within 1 min compared to visual identification. A number of potential applications of the neural-network Pi2 scanning procedure are discussed.     

Specific features of the characteristics of midlatitude substorm and nonsubstorm Pi2 geomagnetic pulsations and their generation conditions

The specific features of the diurnal and seasonal variations in different characteristics of two Pi2 geomagnetic pulsation groups (observed during magnetospheric substorms and when these substorms are absent) and the pulsation generation geophysical conditions have been experimentally studied based on observations at the Borok midlatitude observatory. It has been indicated that the dynamics of the occurrence frequency of Pi2 substorm and nonsubstorm bursts and their amplitude, duration, and intervals between peaks depending on the local time and season is identical in many respects. It has been found that substorm Pi2 bursts are mostly observed when the IMF is sunward and the solar wind electric field (Ey) is positive, whereas nonsubstorm bursts are observed when the IMF is antisunward and Ey is negative. The fundamental differences in the diurnal and seasonal variations in index α, which characterizes the slope of the distribution function of the two-group Pi2 burst amplitudes, have been revealed. It has been found that the index α value substantially depends on Ey and the IMF longitude (ψ). It has been assumed that the plasma sheet turbulence of the metastable magnetotail is responsible for reconnection and the generation of substorm and nonsub-storm Pi2 pulsation bursts.     

Planetary distribution of geomagnetic pulsations during a geomagnetic storm at solar minimum

We investigate the features of the planetary distribution of wave phenomena (geomagnetic pulsations) in the Earth’s magnetic shell (the magnetosphere) during a strong geomagnetic storm on December 14–15, 2006, which is untypical of the minimum phase of solar activity. The storm was caused by the approach of the interplanetary magnetic cloud towards the Earth’s magnetosphere. The study is based on the analysis of 1-min data of global digital geomagnetic observations at a few latitudinal profiles of the global network of ground-based magnetic stations. The analysis is focused on the Pc5 geomagnetic pulsations, whose frequencies fall in the band of 1.5–7 mHz (T ～ 2–10 min), on the fluctuations in the interplanetary magnetic field (IMF) and in the solar wind density in this frequency band. It is shown that during the initial phase of the storm with positive IMF Bz, most intense geomagnetic pulsations were recorded in the dayside polar regions. It was supposed that these pulsations could probably be caused by the injection of the fluctuating streams of solar wind into the Earth’s ionosphere in the dayside polar cusp region. The fluctuations arising in the ionospheric electric currents due to this process are recorded as the geomagnetic pulsations by the ground-based magnetometers. Under negative IMF Bz, substorms develop in the nightside magnetosphere, and the enhancement of geomagnetic pulsations was observed in this latitudinal region on the Earth’s surface. The generation of these pulsations is probably caused by the fluctuations in the field-aligned magnetospheric electric currents flowing along the geomagnetic field lines from the substorm source region. These geomagnetic pulsations are not related to the fluctuations in the interplanetary medium. During the main phase of the magnetic storm, when fluctuations in the interplanetary medium are almost absent, the most intense geomagnetic pulsations were observed in the dawn sector in the region corresponding to the closed magnetosphere. The generation of these pulsations is likely to be associated with the resonance of the geomagnetic field lines. Thus, it is shown that the Pc5 pulsations observed on the ground during the magnetic storm have a different origin and a different planetary distribution.     

Investigation of the damping of geomagneticPi2 pulsations using generalized spectral analysis

Summary The method of spectral analysis has been modified to render the spectrum not only a function of frequency, but also of damping. The generalized spectra of damped geomagnetic pulsations, recorded at the observatories of Budkov and Dymer, are computed. The degree of damping of these pulsations in the X and Y-components at both stations is determined. The results are compared with results obtained using other methods.     

SABRE observations of Pi2 pulsations: case studies

The characteristics of substorm-associated Pi2 pulsations observed by the SABRE coherent radar system during three separate case studies are presented. The SABRE field of view is well positioned to observe the differences between the auroral zone pulsation signature and that observed at mid-latitudes. During the first case study the SABRE field of view is initially in the eastward electrojet, equatorward and to the west of the substorm-enhanced electrojet current. As the interval progresses, the western, upward field-aligned current of the substorm current wedge moves westward across the longitudes of the radar field of view. The westward motion of the wedge is apparent in the spatial and temporal signatures of the associated Pi2 pulsation spectra and polarisation sense. During the second case study, the complex field-aligned and ionospheric currents associated with the pulsation generation region move equatorward into the SABRE field of view and then poleward out of it again after the third pulsation in the series. The spectral content of the four pulsations during the interval indicate different auroral zone and mid-latitude signatures. The final case study is from a period of low magnetic activity when SABRE observes a Pi2 pulsation signature from regions equatorward of the enhanced substorm currents. There is an apparent mode change between the signature observed by SABRE in the ionosphere and that on the ground by magnetometers at latitudes slightly equatorward of the radar field of view. The observations are discussed in terms of published theories of the generation mechanisms for this type of pulsation. Different signatures are observed by SABRE depending on the level of magnetic activity and the position of the SABRE field of view relative to the pulsation generation region. A twin source model for Pi2 pulsation generation provides the clearest explanation of the signatures observed.     

Frequency-direction analysis of geomagnetic pulsations

Summary A new method is presented of computer processing of amplitude-time records. The method is based on a two-component spectral analysis, suitable for investigating a planar stationary oscillatory event. The method is applied to the study of the fine structure of short-period geomagnetic pulsations. Apart from a semi-quantitative representation of the directional distribution of the pulsation event in the plane of oscillation, the proposed method enables one to obtain quantitative information on the frequency components, representing the pulsation — the distribution of the overall energy in the spectrum of the pulsation, the ellipticity of the polarization ellipses, the orientation of the major axes of the ellipses, and the sense of rotation of the disturbance vector.     

Frequency-direction analysis of geomagnetic pulsations

Summary Using the method of two-component spectral analysis of planar oscillation events by means of computer processing of A-t records, a series of about 100 samples of geomagnetic beating-type pulsations pc3 was treated. The quantitative data obtained on the internal structure of the pulsations (frequency spectra and polarization characteristics) were treated statistically. The pattern of the daily variations of the frequencies and amplitudes of the fundamental amplitude-dominating frequency components of the pulsations and the daily variations of the polarization characteristics of these components, the ellipticity of the polarization ellipses, the directions of the main axes of these ellipses and the sense of rotation of the disturbance vector along the ellipses were obtained.A part of the results was reported at the XVth General Assembly of the IUGG, Moscow, August 1971.     

Analysis on observational results of Pi2 geomagnetic pulsation in Henan region

IntroductionThere are many kinds of fluctuations in magnetosphere plasma, frequencies concerned are ofa broad range (10--3~106 Hi). Except for electro-magnetic waves (whistled, hydromagnetic wave Alven wave), there is static electric wave mode (plasma wave -- election acoustic wave, ionacoustic wave). Among them, a main fluctuation of hydromagnetic wave phenomena is geomagnetic pulsation. Dungey (1954) believed at first in 1954 that this kind of pulsations can be attributed to hydromagnetic w…     

河南地区Pi2地磁脉动观测结果分析di

1996年9月我们在河南信阳——汤阴布设了由６个测点组成的测线,对Pi2地磁脉动进行了同时观测,并对该南北测线上Pi2地磁脉动出现的同时性进行了探讨．分析结果指出,Pi2地磁脉动首先出现在测线最南端的信阳测点,越往北同一变化出现的时间越晚．该区域地表的南北向似传播速度约为140ｋｍ/s．基于Pi2地磁脉动随时间变化的不稳定性,以及基子波的可延伸性与局部化特性,我们选择合适的基子波形式,利用子波变换分析了Pi2脉动所含主要的周期变化成分的周期和振幅随时间的变化,指出其周期和振幅都随时间有复杂的变化形式．      

Three-component spectral analysis of geomagnetic pulsations

nua m¶rt; nma aaua a, umua m nma, m n¶rt;um umau nuau un nmam. m¶rt; annua aaum nauu Pi2 u Pc3 u amu u u ¶rt;. ¶rt;a ma m ¶rt; nmam nuau aamumu u u auum m aum amumu.     

The recording of Pc1 geomagnetic pulsations using a microcomputer preprocessing system

In the past slow-speed frequency-modulated analogue tape recording techniques have provided the most convenient method for recording ground-based Pc1 pulsation data on a continuous basis. With events occurring often only a few hours in a week, and a Nyquist frequency of 4–5 Hz, direct digital recording is not practical because of the bulk of data accumulated. However, with the recent availability of reasonably priced microcomputers and advanced signal processing techniques it is now possible to preprocess digital data in the field and store only events of interest. A two-component induction coil magnetometer incorporating a Z80 based 64K RAM microcomputer-floppy disk preprocessing system is described. It is capable of recording Pc1 signals in the 0.2–4 Hz band at middle-to-low latitudes with a minimum detectable signal level of 3 pT. The reliability and limitations of the preprocessing techniques utilizing FFT autospectral analysis to recognize Pc1 signals are discussed.     

Statistical observations of spatial characteristics of Pi1B pulsations

We have examined the spatial and temporal correlation of high-latitude Pi1B and Pi2 pulsations, mid-latitude Pi2 pulsations, and auroral substorm onsets identified in the IMAGE far ultraviolet imager (FUV) data. Numerous search coil and fluxgate magnetometers at high latitudes (65–80° in Antarctica and Greenland) and mid-latitude fluxgate magnetometers are used. We find that Pi1B onset times agree well with onset times of intense isolated auroral substorms identified by the IMAGE FUV instrument: Pi1B onsets occurred within the 2 min cadence of the imager. For any given event, we find that Pi1B are localized to approximately 4 h of local time and 7° of magnetic latitude relative to the initial auroral brightening location as observed by IMAGE FUV. Not surprisingly, we also find that Pi1B pulsations occur typically between 2100 and 0200 MLT. Comparison to Pi2 records from these and other lower-latitude stations shows that in almost all cases Pi1B activity coincides within ±2 min with Pi2 activity. Power law fits showed that Pi1B amplitude fell off with distance^−2.9 for two strong events (i.e., similar to the r⁻³ falloff of the signal from a dipolar source), and only slightly more rapidly than the falloff of Pi2 activity (d^−2.8). Given the global nature of Pi2 pulsations versus the localized nature of Pi1B events in this study, we conclude that the mechanism that drives Pi1B pulsations is likely different from that responsible for Pi2 pulsations.     

Features of the latitudinal distribution of the annual variation of the geomagnetic field level and circumpolar current system in 1964

The results of investigations of the latitudinal distribution of annual variation of the geomagnetic field level in the seasons of 1964 (International Quiet Sun Year) using the data from 95 world magnetic observatories located at various longitudes in the latitude range 83° N–90° S are reported. The latitudinal features of the X, Y, and Z components of the geomagnetic field have been analyzed. It has been shown that the amplitudes (summer-winter differences) of the annual variation are maximal in the polar regions, decrease continuously to zero towards the equator, and are identical for both the Northern and Southern hemispheres with a half-year delay (local summer). The amplitudes of the equinox-winter difference in the equinox periods are smaller than those in summer, but are manifested simultaneously in the Northern and Southern hemispheres. An equivalent circumpolar current system has been constructed, which is responsible for the annual variation of the geomagnetic field level. Its parameters have been determined.     

Statistical characteristics of the spatial distribution of Pc3-4 geomagnetic pulsations at high latitudes in the antarctic regions

The diumal variations in the parameters of Pc3 (20–60 mHz) and Pc4 (10–19 mHz) pulsations at latitudes of the dayside cusp and polar cap have been studied using data of the magnetic stations of the trans-Antarctic meridional profile for the time interval from January to March 1997 (local summer) under weakly disturbed geomagnetic conditions (AE ≤ 250 nT). The technique for estimating pulsation parameters is based on the separation of the wave packets and noise. The diumal variations in the hourly average parameters of the wave packets in the Pc3 and Pc4 bands and noise in the Pc3-4 band (10–60 mHz)—the average number of wave packets, energy of wave packets and noise, and energy of a single wave packet—turned out to be different for the stations located deep in the polar cap (Φ ～ 87°) and at the latitudes of the dayside polar cusp (Φ ～ 70°) and auroral oval (Φ ～ 66°). Several sources of pulsations caused by different channels of wave energy penetration into the magnetosphere through the dayside cusp, dayside magnetopause, and dawn flank of the magnetotail apparently exist at high latitudes.     

Global Pi3 geomagnetic pulsations as a response of large variations in the solar wind and IMF during the magnetic storm of August 5, 2011

Spatial-temporal and spectral features of ground geomagnetic pulsations in the frequency range of 1–5 mHz at the initial phase of a strong magnetic storm of the 24th cycle of solar activity (August 5–6, 2011, with a Dst-variation in the storm maximum of ?110 nT) are analyzed. Large opposite in sign amplitudes of variations in IMF parameters (from ?20 to +20 nT) at a high velocity of the solar wind (～650 km/s) accompanied by intense bursts in solar-wind density (up to ～50 cm^?3) were distinctive feature of interplanetary medium conditions causing the storm. Geomagnetic Pi3 pulsations global in longitude and latitude and in-phase in the middle and equatorial latitudes were found. The onset of pulsation generation was caused by a pulse of dynamic pressure of the solar wind (～20 nPa), i.e., by a considerable compression of the magnetosphere. The maximum (2–3 mHz) in the amplitude spectrum of near-equatorial pulsations coincided with the maximum of pulsations in the daytime polar cap. After the next jump of the dynamic pressure of the solar wind (～35 nPa), an additional maximum appeared in the pulsation spectrum in the frequency band of ～3.5–4.5 mHz. Global pulsations suddenly stopped after a sharp decrease in the solar-wind dynamic pressure and corresponding extension of the magnetosphere. The obtained results are compared with the time dynamics of the position and shape of the plasmapause.