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1.
Interplanetary transients with particular signatures different from the normal solar wind have been observed behind interplanetary shocks and also without shocks. In this paper we have selected four well-known transient interplanetary signatures, namely: magnetic clouds, helium enhancements and bidirectional electron and ion fluxes, found in the solar wind behind shocks, and undertaken a correlative study between them and the corresponding solar observations. We found that although commonly different signatures appear in a single interplanetary transient event, they are not necessarily simultaneous, that is, they may belong to different plasma regions within the ejecta, which suggests that they may be generated by complex processes involving the ejection of plasma from different solar regions. We also found that more than 90% of these signatures correspond to cases when an H flare and the eruption of a filament occurred near solar central meridian between 1 and 4 days before the observation of the disturbance at 1 AU, the highest association being with flares taking place between 2 and 3 days before. The majority of the H flares were also accompanied by soft X-ray events. We also studied the longitudinal distribution of the associated solar events and found that between 80% and 90% of the interplanetary ejecta were associated with solar events within a longitudinal band of ±30° from the solar central meridian. An east-west asymmetry in the associated solar events seems to exist for some of the signatures. We also look for coronal holes adjacent to the site of the explosive event and find that they were present almost in every case. 相似文献
2.
A sizable total-pressure (magnetic pressure plus kinetic pressure) enhancement was found within the high-speed wind stream observed by Helios 2 in 1976 near 0.3 AU. The proton density and temperature and the magnetic magnitude simultaneously increased for about 6 h. This pressure rise was associated with a comparatively large southward now velocity component (with Vz – 100 km · s–1) and magnetic-field rotation. The pressure enhancement was associated with unusual features in the electron distribution function. It shows a wide angular distribution of electron counting rates in the low-energy (57.8 eV) channel, while previous to the enhancement it exhibits a wide angular distribution of electron count rate in the high-energy (112, 221 and 309 eV) channels, perhaps indicating the mirroring of electrons in the converging field lines of the background magnetic field. These fluid and kinetic phenomena may be explained as resulting from an interplanetary magnetic flux rope which is not fully convected by the flow but moves against the background wind towards the Sun. 相似文献
3.
A. R. Breen W. A. Coles R. R. Grail M. T. Klinglesmith J. Markkanen P. J. Moran B. Tegid P. J. S. Williams 《Annales Geophysicae》1997,14(12):1235-1245
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
4.
《Journal of Atmospheric and Solar》2008,70(17):2078-2100
Coronal mass ejections (CMEs) and high-speed solar wind streams (HSS) are two solar phenomena that produce large-scale structures in the interplanetary (IP) medium. CMEs evolve into interplanetary CMEs (ICMEs) and the HSS result in corotating interaction regions (CIRs) when they interact with preceding slow solar wind. This paper summarizes the properties of these structures and describes their geoeffectiveness. The primary focus is on the intense storms of solar cycle 23 because this is the first solar cycle during which simultaneous, extensive, and uniform data on solar, IP, and geospace phenomena exist. After presenting illustrative examples of coronal holes and CMEs, I discuss the internal structure of ICMEs, in particular the magnetic clouds (MCs). I then discuss how the magnetic field and speed correlate in the sheath and cloud portions of ICMEs. CME speed measured near the Sun also has significant correlations with the speed and magnetic field strengths measured at 1 AU. The dependence of storm intensity on MC, sheath, and CME properties is discussed pointing to the close connection between solar and IP phenomena. I compare the delay time between MC arrival at 1 AU and the peak time of storms for the cloud and sheath portions and show that the internal structure of MCs leads to the variations in the observed delay times. Finally, we examine the variation of solar-source latitudes of IP structures as a function of the solar cycle and find that they have to be very close to the disk center. 相似文献
5.
In this work, solar flare energetic particle fluxes (Ee 42 keV) observed by the HI-SCALE instrument onboard Ulysses, a spacecraft that is probing the heliosphere in 3-D, are utilized as diagnostics of the large-scale structure and topology of the interplanetary magnetic field (IMF) embedded within two well-identified interplanetary coronal mass ejection (ICME) structures. On the basis of the energetic solar flare particle observations firm conclusions are drawn on whether the detected ICMEs have been detached from the solar corona or are still magnetically anchored to it when they arrive at 2.5 AU. From the development of the angular distributions of the particle intensities, we have inferred that portions of the ICMEs studied consisted of both open and closed magnetic field lines. Both ICMEs present a filamentary structure comprising magnetic filaments with distinct electron anisotropy characteristics. Subsequently, we studied the evolution of the anisotropies of the energetic electrons along the magnetic field loop-like structure of one ICME and computed the characteristic decay time of the anisotropy which is a measure of the amount of scattering that the trapped electron population underwent after injection at the Sun. 相似文献
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C. Lacombe C. Salem A. Mangeney J.-L. Steinberg M. Maksimovic J. M. Bosqued 《Annales Geophysicae》2000,18(8):852-865
The solar wind properties depend on , the heliomagnetic latitude with respect to the heliospheric current sheet (HCS), more than on the heliographic latitude. We analyse the wind properties observed by Wind at 1 AU during about 2.5 solar rotations in 1995, a period close to the last minimum of solar activity. To determine , we use a model of the HCS which we fit to the magnetic sector boundary crossings observed by Wind. We find that the solar wind properties mainly depend on the modulus ||. But they also depend on a local parameter, the total pressure (magnetic pressure plus electron and proton thermal pressure). Furthermore, whatever the total pressure, we observe that the plasma properties also depend on the time: the latitudinal gradients of the wind speed and of the proton temperature are not the same before and after the closest HCS crossing. This is a consequence of the dynamical stream interactions. In the low pressure wind, at low ||, we find a clear maximum of the density, a clear minimum of the wind speed and of the proton temperature, a weak minimum of the average magnetic field strength, a weak maximum of the average thermal pressure, and a weak maximum of the average factor. This overdense sheet is embedded in a density halo. The latitudinal thickness is about 5° for the overdense sheet, and 20° for the density halo. The HCS is thus wrapped in an overdense sheet surrounded by a halo, even in the non-compressed solar wind. In the high-pressure wind, the plasma properties are less well ordered as functions of the latitude than in the low-pressure wind; the minimum of the average speed is seen before the HCS crossing. The latitudinal thickness of the high-pressure region is about 20°. Our observations are qualitatively consistent with the numerical model of Pizzo for the deformation of the heliospheric current sheet and plasma sheet. 相似文献
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10.
Qiang Hu 《中国科学:地球科学(英文版)》2017,60(8):1466-1494
We review and summarize the applications of the Grad-Shafranov (GS) reconstruction technique to space plasma structures in the Earth’s magnetosphere and in the interplanetary space. We organize our presentations following the branches of the “academic family tree” rooted on Prof. Bengt U. Ö. Sonnerup, the inventor of the GS method. Special attentions are paid to validations of the GS reconstruction results via (1) the direct validation by co-spatial in-situ measurements among multiple spacecraft, and (2) indirect validation by implications and interpretations of the physical connection between the structures reconstructed and other related processes. For the latter, the inter-comparison and interconnection between the large-scale magnetic flux ropes (i.e., Magnetic Clouds) in the solar wind and their solar source properties are presented. In addition, we also summarize various GS-type (or -like) reconstruction and an extension of the GS technique to toroidal geometry. In particular, we point to a possible advancement with added complexity of “helical symmetry” and mixed helicity, in the hope of stimulating interest in future development. We close by offering some thoughts on appreciating the scientific merit of GS reconstruction in general. 相似文献
11.
We study the evolution (expansion or oscillation) of cylindrically symmetric magnetic flux ropes when the energy dissipation is due to a drag force proportional to the product of the plasma density and the radial speed of expansion. The problem is reduced to a single, second-order, ordinary differential equation for a damped, non-linear oscillator. Motivated by recent work on the interplanetary medium and the solar corona, we consider polytropes whose index, , may be less than unity. Numerical analysis shows that, in contrast to the small-amplitude case, large-amplitude oscillations are quasi-periodic with frequencies substantially higher than those of undamped oscillators. The asymptotic behaviour described by the momentum equation is determined by a balance between the drag force and the gradient of the gas pressure, leading to a velocity of expansion of the flux rope which may be expressed as (1/2)r/t, where r is the radial coordinate and t is the time. In the absence of a drag force, we found in earlier work that the evolution depends both on the polytropic index and on a dimensionless parameter, K. Parameter K was found to have a critical value above which oscillations are impossible, and below which they can exist only for energies less than a certain energy threshold. In the presence of a drag force, the concept of a critical K remains valid, and when K is above critical, the oscillatory mode disappears altogether. Furthermore, critical K remains dependent only on and is, in particular, independent of the normalized drag coefficient, v*. Below critical K, however, the energy required for the flux rope to escape to infinity depends not only on K (as in the conservative force case) but also on v*. This work indicates how under certain conditions a small change in the viscous drag coefficient or the initial energy may alter the evolution drastically. It is thus important to determine v* and K from observations. 相似文献
12.
We present for the first time a statistical study of 50 keV ion events of a magnetospheric origin upstream from Earths bow shock. The statistical analysis of the 50–220 keV ion events observed by the IMP-8 spacecraft shows: (1) a dawn-dusk asymmetry in ion distributions, with most events and lower intensities upstream from the quasi-parallel pre-dawn side (4 LT-6 LT) of the bow shock, (2) highest ion fluxes upstream from the nose/dusk side of the bow shock under an almost radial interplanetary magnetic field (IMF) configuration, and (3) a positive correlation of the ion intensities with the solar wind speed and the index of geomagnetic index Kp, with an average solar wind speed as high as 620 km s–1 and values of the index Kp 2. The statistical results are consistent with (1) preferential leakage of 50 keV magnetospheric ions from the dusk magnetopause, (2) nearly scatter free motion of 50 keV ions within the magnetosheath, and (3) final escape of magnetospheric ions from the quasi-parallel dawn side of the bow shock. An additional statistical analysis of higher energy (290–500 keV) upstream ion events also shows a dawn-dusk asymmetry in the occurrence frequency of these events, with the occurrence frequency ranging between 16%-34% in the upstream region. 相似文献
13.
A model of the magnetosheath structure proposed in a recent paper from the authors is extended to estimate the magnetopause stand-off distance from solar wind data. For this purpose, the relationship of the magnetopause location to the magnetosheath and solar wind parameters is studied. It is shown that magnetopause erosion may be explained in terms of the magnetosheath magnetic field penetration into the magnetosphere. The coefficient of penetration (the ratio of the magnetospheric magnetic field depression to the intensity of the magnetosheath magnetic field Bmz = -Bm sin2/2, is estimated and found approximately to equal 1. It is shown that having combined a magnetosheath model presented in an earlier paper and the magnetosheath field penetration model presented in this paper, it is possible to predict the magnetopause stand-off distance from solar wind parameters. 相似文献
14.
Vasilis P. Tritakis 《Pure and Applied Geophysics》1985,123(3):476-486
A significant tendency is shown for both Etesians and (+, –) sector boundaries of the interplanetary magnetic field (IMF) to occur on the same solar rotation days, during the main period of the Etesians effect (July–August). In addition, the solar activity seems to control the Etesians distribution within the IMF sector structure. In the epoch of maximum there is a significant tendency of Etesians to occur during toward IMF days. In contrast, in the epoch of minimum Etesians occur mainly during away IMF days. Finally, in the epoch of intermediate the Etesians are uniformly distributed in away and toward IMF days. Since these conclusions are statistically significant at high confidence levels, it is fair to assume that IMF and solar activity seem to contribute, to some extent, to the Etesians occurrences, as well as to their distribution within the solar rotation and the IMF sector structure; that is, some solar contribution to the tropospheric circulation is implied. 相似文献
15.
Method of short-term forecast intensity of geomagnetic storms, expected by effect Solar wind magnetic clouds in the Earth’s magnetosphere is developed. The method is based calculation of the magnetic field clouds distribution, suitable to the Earth, the initial satellite measurements therein components of the interplanetary magnetic field in the solar ecliptic coordinate system. Conclusion about the magnetic storm intensity is expected on the basis of analysis of the dynamics of the reduced magnetic field Bz component clouds and established communication intensity of geomagnetic storms on Dst-index values and Bz component of the interplanetary magnetic field vector. 相似文献
16.
B.T. Tsurutani X.-Y. Zhou V.M. Vasyliunas G. Haerendel J.K. Arballo G.S. Lakhina 《Surveys in Geophysics》2001,22(2):101-130
Dayside near-polar auroral brightenings occur when interplanetary shocks impinge upon the Earth's magnetosphere. The aurora first brightens near local noon and then propagates toward dawn and dusk along the auroral oval. The propagation speed of this wave of auroral light is 10 km s-1 in the ionosphere. This speed is comparable to the solar wind speed along the outer magnetosphere. The fundamental shock-magnetospheric interaction occurs at the magnetopause and its boundary layer. Several physical mechanisms transferring energy from the solar wind directly to the magnetosphere and from the magnetosphere to the ionosphere are reviewed. The same physical processes can occur at other solar system magnetospheres. We use the Haerendel (1994) formulation to estimate the acceleration of energetic electrons to 50 keV in the Jovian magnetosphere/ionosphere. Auroral brightenings by shocks could be used as technique to discover planets in other stellar systems. 相似文献
17.
P. A. Chaizy 《Annales Geophysicae》2000,18(3):263-276
Three main physical processes (and associated properties) are currently used to describe the flux and anisotropy time profiles of solar energetic particle events, called SEP profiles. They are (1) the particle scattering (due to magnetic waves), (2) the particle focusing (due to the decrease of the amplitude of the interplanetary magnetic field (IMF) with the radial distance to the Sun) and (3) the finite injection profile at the source. If their features change from one field line to another, i.e. if there is a cross IMF gradient (CFG), then the shape of the SEP profiles will depend, at onset time, on the relative position of the spacecraft to the IMF and might vary significantly on small distance scale (e.g. 106 km). One type of CFG is studied here. It is called intensity CFG and considers variations, at the solar surface, only of the intensity of the event. It is shown here that drops of about two orders of magnitude over distances of 104 km at the Sun (1° of angular distance) can influence dramatically the SEP profiles at 1 AU. This CFG can lead to either an under or overestimation of both the parallel mean free path and of the injection parameters by factor up to, at least, 2/3 and 18, respectively. Multi-spacecraft analysis can be used to identify CFG. Three basic requirements are proposed to identify, from the observation, the type of the CFG being measured. 相似文献
18.
We address the geoeffectiveness of three interplanetary structures in the interplanetary space: magnetic clouds (MCs), interplanetary shocks (IPSs), and corotating interaction regions (CIRs). The geoeffectiveness is evaluated using the geomagnetic indices Kp, AE, and Dst. We find that MCs are more geoeffective than IPSs, or CIRs. The average values of magnetic indices are significantly enhanced during disturbed periods associated with MCs, IPSs and CIRs, compared to the whole interval. The highest effect is noted for MC disturbed periods.Results obtained for the three data sets are used to derive a theoretical (continuous) probability distribution function (PDF) by fitting the histograms representing the percentage of events against the intervals of magnetic index. PDFs allow estimation of the probability of a given level of geomagnetic activity to be reached after the detection, by in situ solar wind observations, of a given interplanetary structure approaching the Earth. 相似文献
19.
《Journal of Atmospheric and Solar》2002,64(2):145-157
The solar wind, magnetosphere, and ionosphere are intrinsically coupled through magnetic field lines. The electrodynamic state of the high-latitude ionosphere is controlled by several geophysical processes, such as the location and rate of magnetic reconnection at the magnetopause and in the magnetotail, and the energisation and precipitation of solar wind and magnetospheric plasmas. Amongst the most observed ionospheric manifestation of solar wind/magnetospheric processes are the convection bursts associated with the so-called flux transfer events (FTEs), magnetic impulse events (MIEs), and travelling convection vortices (TCVs). Furthermore, the large-scale ionospheric convection configuration has also demonstrated a strong correspondence to variations in the interplanetary medium and substorm activity. This report briefly discusses the progress made over the past decade in studies of these transient convection phenomena and outlines some unsettled questions as well as future research directions. 相似文献