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1.
The velocities of the stationary extra-ecliptic solar wind are analyzed depending on the heliolatitudes, heliocentric distances, and solar activity. An analysis has been performed using the direct measurements of the solar plasma flux velocities onboard Ulysses and the simultaneous ground-based IPS observations. The arguments for the hypothesis that primary high-speed (V ∼ 900 km/s) flows exist at the corona bottom and are directly related to the photosphere and solar magnetic fields are presented. The possible mechanism by which high-speed streams are generated is generally considered.  相似文献   

2.
Based on the magnetopause observations near the Earth by the Prognoz/Interball satellites in 1972–2000, the empirical model of this boundary has been proposed, and the magnetopause behavior at different parameters of the oncoming solar wind has been studied. For the first time, it has been detected that the Earth’s magnetopause is compressed by ∼5% in the direction perpendicular to the plane including the vectors of the solar wind velocity and IMF. At the same time, any dependence of the subsolar magnetopause position on the IMF B z component has not been revealed in the Progrnoz/Interball data. The proposed magnetopause model can be used to model the position and shape of the near-Earth bow shock.  相似文献   

3.
A complex of geophysical phenomena (geomagnetic pulsations in different frequency ranges, VLF emissions, riometer absorption, and auroras) during the initial phase of a small recurrent magnetic storm that occurred on February 27–March 2, 2008, at a solar activity minimum has been analyzed. The difference between this storm and other typical magnetic storms consisted in that its initial phase developed under a prolonged period of negative IMF B z values, and the most intense wave-like disturbances during the storm initial phase were observed in the dusk and nighttime magnetospheric sectors rather than in the daytime sector as is observed in the majority of cases. The passage of a dense transient (with N p reaching 30 cm−3) in the solar wind under the southward IMF in the sheath region of the high-speed solar wind stream responsible for the discussed storm caused a great (the AE index is ∼1250 nT) magnetospheric substorm. The appearance of VLF chorus, accompanied by riometer absorption bursts and Pc5 pulsations, in a very long longitudinal interval of auroral latitudes (L ∼ 5) from premidnight to dawn MLT hours has been detected. It has been concluded that a sharp increase in the solar wind dynamic pressure under prolonged negative values of IMF B z resulted in the global (in longitude) development of electron cyclotron instability in the Earth’s magnetosphere.  相似文献   

4.
The spatio-temporal evolution of geomagnetic pulsation bursts at frequencies of 1–3 Hz, observed at the Mondy (MLT ≈ 1200; Mlat = 46.8°; L = 2.16) and Borok (MLT ≈ 0820; Mlat = 54.0°; L = 2.94) midlatitude observatories and Lovozero auroral observatory (MLT ≈ 0820; Mlat = 64.2°; L = 5.36), has been studied. The considered bursts were registered in daytime sector of the magnetosphere after sudden impulses (SIs) caused by dramatic increases in the solar wind dynamic pressure and registered on board the WIND satellite. The SI onset time corresponds to the Sc* time shown in the Geomagnetic Indices Bulletin. The possible relationship between the excitation of these bursts and the variations in the particle partial density in the range of energies 0.03–45 keV per unit charge has been studied. The bursts were registered on board the LANL geosynchronous satellites. A comparison of the particle partial density variations measured on the satellites and the variation temperature anisotropy (A = T⊥/T‖ − 1) with the variations in the pulsation burst amplitude on the ground indicated that the partial density maximum and the minimum (A ≤ 0) of the electron temperature anisotropy index in the vicinity of local noon coincide in time with the pulsation generation instant. A comparison of the electron partial density variations on the LANL-1994 and LANL-97A geosynchronous satellites spaced in longitude and the spatio-temporal variations in the development of bursts make it possible to assume that 1–3 Hz geomagnetic pulsations are excited in the vicinity of local noon and subsequently propagate along the ionospheric waveguide.  相似文献   

5.
The two-position radio sounding of the solar wind by the Galileo and Cassini spacecraft has been first performed. These spacecraft followed the Sun from east to west from May 12 to 24, 2000 and sounded the regions spaced in radial directions by several millions of kilometers. Stable correlation has been revealed between fluctuation effects detected in spatially spaced radio-sounding paths of disturbed plasma structures of the coronal mass ejection (CME) type. The radio effects have been found to correlate also with the data on the solar wind density near the Earth orbit. It has been shown that the two-position radio-sounding method together with the data on solar radiation in the X-ray and optic ranges and with the results of local plasma measurements provides information on the structure and velocity of the propagation of CMEs from the photosphere to the Earth orbit. In the most powerful event recorded on May 13, 2000, the CME velocity at the heliocentric distances of about 15R ⊙ (R ⊙ is the solar radius) reached 1200 km/s. At (15–25) R ⊙, the velocity was about 1300 km/s. At distances larger than 25R ⊙, disturbance was decelerated from 1300 to 450 km/s near the Earth orbit.  相似文献   

6.
The characteristics of dayside auroras during the large (16–24 nT) positive values of the IMF B z component, observed on January 14, 1988, during the interaction between the Earth’s magnetosphere and the body of the interplanetary magnetic cloud, have been studied based on the optical observations on Heiss Island. A wide band of diffuse red luminosity with an intensity of 1–2 kilorayleigh (kR) was observed during 6 h in the interval 1030–1630 MLT at latitudes higher than 75° CGL. Rayed auroral arcs, the brightness of which in the 557.7 nm emission sharply increased to 3–7 kR in the postnoon sector immediately after the polarity reversal of the IMF B y component from positive to negative, were continuously registered within the band. Bright auroral arcs were observed at the equatorward edge of red luminosity. It has been found out that the red auroral intensity increases and the band equatorward boundary shifts to lower latitudes with increasing solar wind dynamic pressure. However, a direct proportional dependence of the variations in the auroral features on the dynamic pressure variations has not been found. It has been concluded that the source of bright discrete auroras is located in the region of the low-latitude boundary layer (LLBL) on closed geomagnetic field lines. The estimated LLBL thickness is ∼3 R e . It has been concluded that the intensity of the dayside red band depends on the solar wind plasma density, whereas the position of the position equatorward boundary depends on the dynamic pressure value and its variations.  相似文献   

7.
The results of studying the distribution character of the amplitudes and time intervals between wave packets of Pi2 geomagnetic pulsations, observed during the nighttime development of magnetospheric substorms and in the absence of these phenomena, have been presented. The analog records from the midlatitude Borok Geophysical Observatory (geographic coordinates φ = 58.03°; λ = 38.97°) for 1995 and 1997 have been used to analyze Pi2 pulsations. Three groups of pulsations have been analyzed: Pi2 observed during sub-storms related to the external impact on the magnetosphere, Pi2 spontaneously originating during substorms, and Pi2 observed in the absence of substorms on the nightside of the magnetosphere. Interplanetary magnetic field B y and B z components and the solar wind dynamic pressure (ρV 2) have been considered as possible triggers of magnetospheric substorms. It has been indicated that the distributions of the amplitude and the duration of time intervals between Pi2 bursts are approximated by the power and exponential functions, respectively, which is typical of intermittent processes. The hypothesis that the processes of magnetospheric plasma turbulization can be among the Pi2 pulsation burst sources has been put forward. It is assumed that the obtained characteristic values can be used to qualitatively estimate the degree of plasma turbulence on the nightside of the magnetosphere when a sequence of Pi2 wave packets is excited.  相似文献   

8.
The results of studying the simultaneous observations of burst regimes of long-period irregular pulsations at frequencies of 2.0–6.0 mHz (the series of ipcl bursts) in the region of the dayside polar cusp and magnetic field disturbances in the nightside auroral oval are presented. The data on the magnetic field at Mirny (MIR, Φ = 76.93°; Λ = 122.92°) and Yellowknife (YKC, Φ = 69.94°; Λ = 294.38°) antipodal observatories as well as the AE index values (http://www.cetp.ipsl.fr/~isgi/homepag1.htm) have been used in an analysis. It has been found out that 87% (group I) and 13% (group II) of events were registered against a back-ground of substorm activity and a quiet nightside magnetosphere, respectively. It has been revealed that several morphological characteristics of the group-I and -II ipcl bursts differ depending on the conditions in the nightside magnetosphere. It has been indicated that the intervals between peaks and the amplitudes of ipcl bursts of both types are distributed according to the exponential and power laws. The results indicate that magnetospheric plasma turbulence develops in the region where burst regimes are formed. It is assumed that the substorm processes in the magnetotail manifest themselves in plasma turbulence in the dayside cusp.  相似文献   

9.
Giant pulsations are nearly monochromatic ULF-pulsations of the Earth’s magnetic field with periods of about 100 s and amplitudes of up to 40 nT. For one such event ground-magnetic observations as well as simultaneous GEOS-2 magnetic and electric field data and proton flux measurements made in the geostationary orbit have been analysed. The observations of the electromagnetic field indicate the excitation of an odd-mode type fundamental field line oscillation. A clear correlation between variations of the proton flux in the energy range 30–90 keV with the giant pulsation event observed at the ground is found. Furthermore, the proton phase space density exhibits a bump-on-the-tail signature at about 60 keV. Assuming a drift-bounce resonance instability as a possible generation mechanism, the azimuthal wave number of the pulsation wave field may be determined using a generalized resonance condition. The value determined in this way, m = −21±4, is in accord with the value m = −27±6 determined from ground-magnetic measurements. A more detailed examination of the observed ring current plasma distribution function f shows that odd-mode type eigenoscillations are expected for the case ∂f/∂W ≥ 0, much as observed. This result is different from previous theoretical studies as we not only consider local gradients of the distribution function in real space, but also in velocity space. It is therefore concluded that the observed giant pulsation is the result of a drift-bounce resonance instability of the ring current plasma coupling to an odd-mode fundamental standing wave. The generation of the bump-on-the-tail distribution causing ≥f/≥W ≥ 0 can be explained due to velocity dispersion of protons injected into the ring current. Both this velocity dispersion and the necessary substorm activity causing the injection of protons into the nightside magnetosphere are observed.  相似文献   

10.
The features of the amplitude distributions of magnetic impulse events have been investigated using the observations from a number of high-latitude observatories in the Northern and Southern hemispheres. It has been shown that the tails of the statistical distribution functions of the impulse amplitudes are approximated by a power law of the form f(A) = A −α, where A is the impulse amplitude and α is the exponent. Therefore, the magnetic-impulse generation regime corresponds to the features of the on-off intermittency model. The distribution of the magnetic impulse amplitudes has been analyzed for various geomagnetic latitudes, local times, seasons, solar activity cycle phases, and interplanetary conditions. It has been found that most statistical distributions of magnetic impulse amplitudes have the exponent α larger than 2, which is typical of the chaotic regimes called “strong turbulence.” In some cases, the exponent α is close to 1, which is typical of the regimes generated in a weakly turbulent medium. Qualitative estimates of the plasma wave turbulence level in the high-latitude magnetosphere have been obtained.  相似文献   

11.
In this paper, we examine the nature of the main source of the sporadic solar wind on the Sun: coronal mass ejections (CMEs). Analysis of data from Mark 3 and Mark 4, the Digital Prominence Monitor (MLSO), and STEREO (EUVI) spacecraft has revealed the existence of two types of CMEs: gradual and impulse. They differ in the place, velocity, and angular size at the instant of their emergence. The source of gradual CMEs is located in the corona, at a distance of 1.1 R 0 < R ≤ 1.7 R 0 from the center of the Sun. They start moving from a state of rest, having an angular size ≈15–65° (in the heliographic coordinate system). Impulse CMEs are probably formed under the Sun’s photosphere. This may be due to the supersonic emergence of magnetic tubes (ropes) from the convective zone. The possibility of this phenomenon has been demonstrated earlier in theory. The radial velocity of such tubes at the photospheric level may be 100 km/s or higher; the minimum angular size is ∼1°.  相似文献   

12.
The solar wind velocity distribution in the heliosphere is best represented using a v-map, where velocity contours are plotted in heliographic latitude-longitude coordinates. It has already been established that low-speed regions of the solar wind on the source surface correspond to the maximum bright regions of the K-corona and the neutral line of the coronal magnetic field. In this analysis, v-maps on the source surface for Carrington rotations (CRs) 1787-1795, during 1987, have been prepared using the interplanetary scintillation measurements at Research Institute of Atmospherics (RIA), Nagoya Univ., Japan. These v-maps were then used to study the time evolution of the low-speed (\leq450 km s−1) belt of the solar wind and to deduce the distribution of solar wind velocity on the heliospheric current sheet. The low-speed belt of the solar wind on the source surface was found to change from one CR to the next, implying a time evolution. Instead of a slow and systematic evolution, the pattern of distribution of solar wind changed dramatically at one particular solar rotation (CR 1792) and the distributions for the succeeding rotations were similar to this pattern. The low-speed region, in most cases, was found to be close to the solar equator and almost parallel to it. However, during some solar rotations, they were found to be organised in certain longitudes, leaving regions with longitudinal width greater than 30○ free of low-speed solar wind, i.e. these regions were occupied by solar wind with velocities greater than 450 km s−1. It is also noted from this study that the low-speed belt, in general, followed the neutral line of the coronal magnetic field, except in certain cases. The solar wind velocity on the heliospheric current sheet (HCS) varied in the range 300–585 km s−1 during the period of study, and the pattern of velocity distribution varied from rotation to rotation.  相似文献   

13.
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.  相似文献   

14.
The effect of the mutual orientation of the Poynting vector P of the electromagnetic energy density in the solar wind and the vector M of the Earth’s magnetic moment (taking into account its orbital and diurnal motions) on the geomagnetic activity has been examined for the first time using the measurements of the solar wind parameters on the Earth orbit in 1963–2005. The component P m of the vector P along the vector M is shown to have a pronounced annual variation with the extrema in November and May and a diurnal variation with the extrema at ∼6 and 18 UT. The phases of the variations are shown to be determined only by the geometric parameters and are independent of the sign of the sector structure of the interplanetary magnetic field. The experimental data on the planetary and high-latitude geomagnetic activity, which is a response to changes in the orientation of P relative to M, are presented. The power of the sources of the electromagnetic energy of the solar wind during strong geomagnetic disturbances is also estimated.  相似文献   

15.
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.  相似文献   

16.
Geomagnetic disturbances in the Canadian region are compared with their solar and heliospheric sources during the decline phase of solar activity, when recurrent solar wind streams from low-latitude coronal holes were clearly defined. A linear correlation analysis has been performed using the following data: the daily and hourly indices of geomagnetic activity, solar wind velocity, and coronal hole area. The obtained correlation coefficients were rather low between the coronal hole areas and geomagnetic activity (0.17–0.48), intermediate between the coronal hole areas and the solar wind velocity (0.40–0.65), and rather high between the solar wind velocity and geomagnetic activity (0.50–0.70). It has been indicated that the correlation coefficient values can be considerably increased (by tens of percent in the first case and about twice in the second case) if variations in the studied parameters related to changes in the ionosphere (different illumination during a year) and variations in the heliolatitudinal shift of the coordinate system between the Earth, the Sun, and a spacecraft are more accurately taken into account.  相似文献   

17.
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.  相似文献   

18.
The relationship between the IMF azimuthal angle and plasma velocity has been studied independently for three types of solar wind streams (recurrent and transient high-speed streams and low-speed background wind) based on the interplanetary medium parameters measured in the near-Earth orbits in 1964–1996. The relationships between the IMF azimuthal angle cotangent and plasma velocity are close to linear but strongly differ from one another and from the theoretical relationship for all types of streams. These differences area caused by the magnetic field disturbance on the time scales smaller than a day, and the effect of this disturbance has been studied quantitatively. The effective periods of rotation of the IMF sources on the Sun, depending on the solar cycle phase, have been obtained from the relations between the IMF azimuthal angle cotangent and plasma velocity. During the most part of the solar cycle, the periods of rotation of the IMF sources are close to the period of rotation of the solar equator but abruptly increase to the values typical of the solar circumpolar zones in the years of solar minimums.  相似文献   

19.
A new index of wave activity (ULF index) is applied to analyze daytime magnetic pulsations in the Pc5 range (f = 2–7 mHz) during ten successive recurrent magnetic storms (CIR (corotating interaction region) storms) of 2006. The most intense daytime geomagnetic Pc5 pulsations on the Earth’s surface in all phases of CIR storms are predominantly observed in the pre-noon sector at latitudes higher than 70°, while those in CME storms (storms initiated by coronal mass ejection (CME)) are observed at latitudes lower than 70°. A comparison of wave activity during CIR and CME storms has shown that the amplitude of Pc5 pulsations in CIR storms is much smaller than that in CME storms and the spectrum maximum is observed at lower frequencies and higher latitudes. At the same time, the mechanism of ULF wave generation during both types of magnetic storms seems to be similar, namely, resonance of magnetic field lines due to the development of the Kelvin-Helmholtz instability caused by an approach of a high-velocity solar wind stream to the Earth’s magnetosphere. Since resonance oscillations are excited only in the closed magnetosphere, the higher-latitude position of the Pc5 pulsation intensity maximum in CIR storms points to larger dimensions of the daytime magnetosphere during CIR storms as compared to CME storms.  相似文献   

20.
EISCAT observations of interplanetary scintillation have been used to measure the velocity of the solar wind at distances between 15 and 130R (solar radii) from the Sun. The results show that the solar wind consists of two distinct components, a fast stream with a velocity of 800 km s–1 and a slow stream at 400 kms–1. The fast stream appears to reach its final velocity much closer to the Sun than expected. The results presented here suggest that this is also true for the slow solar wind. Away from interaction regions the flow vector of the solar wind is purely radial to the Sun. Observations have been made of fast wind/slow wind interactions which show enhanced levels of scintillation in compression regions.  相似文献   

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