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1.
We study the interplanetary features and concomitant geomagnetic activity of the two high-speed streams (HSSs) selected by the Whole Heliosphere Interval (WHI) campaign participants: 20 March to 16 April 2008 in Carrington rotation (CR) 2068. This interval was chosen to perform a comprehensive study of HSSs and their geoeffectiveness during this ??deep?? solar minimum. The two HSSs within the interval were characterized by fast solar-wind speeds (peak values >?600 km?s?1) containing large-amplitude Alfvénic fluctuations, as is typical of HSSs during normal solar minima. However, the interplanetary magnetic field (IMF) magnitude [B o] was exceptionally low (??3??C?5 nT) during these HSSs, leading to lower than usual IMF B z values. The first HSS (HSS1) had favorable IMF polarity for geomagnetic activity (negative during northern Spring). The average AE and Dst for the HSS1 proper (HSS1P) were +?258 nT and ??21 nT, respectively. The second HSS (HSS2) had a positive sector IMF polarity, one that is less favorable for geomagnetic activity. The AE and Dst index averages were +?188 nT and ??7 nT, both lower than corresponding numbers for the first event, as expected. The HSS1P geomagnetic activity is comparable to, and the HSS2P geomagnetic activity lower than, corresponding observations for the previous minimum (1996). Both events?? geomagnetic activities are lower than HSS events previously studied in the declining phase (in 2003). In general, V sw was faster for the HSSs in 2008 compared to 1996. The southward IMF B z was lower in the former. The product of these two parameters [V sw and IMF B z ] comprises the solar-wind electric field, which is most directly associated with the energy input into the magnetosphere during the HSS intervals. Thus the combined effects led to the solar wind energy input in 2008 being slightly less than that in 1996. A detailed analysis of magnetic-field variances and Alfvénicity is performed to explore the characteristics of Alfvén waves (a central element in the geoeffectiveness of HSSs) during the WHI. The B z variances in the proto-CIR (PCIR) were ???30 nT2 and <?10 nT2 in the high speed streams proper. 相似文献
2.
The characteristics of latitudinal angles of solar wind flow (θv) observed near earth have been studied during the period 1973-2003. The average magnitude of θv shows distinct enhancements during the declining and maximum phases of the sunspot cycles. A close association of Bz component of IMF in the GSE system and the orientation of meridional flows in the solar wind is found which depends on the IMF sector polarity. This effect has been studied in typical geomagnetic storm periods. The occurrence of non-radial flows is also found to exhibit heliolatitudinal dependence during the years 1975 and 1985 as a characteristic feature of non-radial solar wind expansion from polar coronal holes. 相似文献
3.
The monthly probability of occurrence of southward (B
z
–
) component of IMF estimated independent of the sector polarity observed near earth is found to change with the magnitude of solar wind velocity. The above analysis is done for each month during two years around sunspot minima and maxima in cycle 21. The results will be interpreted in terms of association of southwardB
z
events with solar wind flows of distinct solar origin such as low and high speed solar wind. 相似文献
4.
We report kinematic properties of slow interplanetary coronal mass ejections (ICMEs) identified by SOHO/LASCO, interplanetary scintillation, and in situ observations and propose a modified equation for the ICME motion. We identified seven ICMEs between 2010 and 2011 and compared them with 39 events reported in our previous work. We examined 15 fast (V SOHO?V bg>500 km?s?1), 25 moderate (0 km?s?1≤V SOHO?V bg≤500 km?s?1), and 6 slow (V SOHO?V bg<0 km?s?1) ICMEs, where V SOHO and V bg are the initial speed of ICMEs and the speed of the background solar wind. For slow ICMEs, we found the following results: i) They accelerate toward the speed of the background solar wind during their propagation and reach their final speed by 0.34±0.03 AU. ii) The acceleration ends when they reach 479±126 km?s?1; this is close to the typical speed of the solar wind during the period of this study. iii) When γ 1 and γ 2 are assumed to be constants, a quadratic equation for the acceleration a=?γ 2(V?V bg)|V?V bg| is more appropriate than a linear one a=?γ 1(V?V bg), where V is the propagation speed of ICMEs, while the latter gives a smaller χ 2 value than the former. For the motion of the fast and moderate ICMEs, we found a modified drag equation a=?2.07×10?12(V?V bg)|V?V bg|?4.84×10?6(V?V bg). From the viewpoint of fluid dynamics, we interpret this equation as indicating that ICMEs with 0 km?s?1≤V?V bg≤2300 km?s?1 are controlled mainly by the hydrodynamic Stokes drag force, while the aerodynamic drag force is a predominant factor for the propagation of ICME with V?V bg>2300 km?s?1. 相似文献
5.
We report radial-speed evolution of interplanetary coronal mass ejections (ICMEs) detected by the Large Angle and Spectrometric Coronagraph onboard the Solar and Heliospheric Observatory (SOHO/LASCO), interplanetary scintillation (IPS) at 327 MHz, and in-situ observations. We analyze solar-wind disturbance factor (g-value) data derived from IPS observations during 1997?–?2009 covering nearly the whole period of Solar Cycle 23. By comparing observations from SOHO/LASCO, IPS, and in situ, we identify 39 ICMEs that could be analyzed carefully. Here, we define two speeds [V SOHO and V bg], which are the initial speed of the ICME and the speed of the background solar wind, respectively. Examinations of these speeds yield the following results: i) Fast ICMEs (with V SOHO?V bg>500 km?s?1) rapidly decelerate, moderate ICMEs (with 0 km?s?1≤V SOHO?V bg≤500 km?s?1) show either gradually decelerating or uniform motion, and slow ICMEs (with V SOHO?V bg<0 km?s?1) accelerate. The radial speeds converge on the speed of the background solar wind during their outward propagation. We subsequently find; ii) both the acceleration and the deceleration are nearly complete by 0.79±0.04 AU, and those are ended when the ICMEs reach a 480±21 km?s?1. iii) For ICMEs with (V SOHO?V bg)≥0 km?s?1, i.e. fast and moderate ICMEs, a linear equation a=?γ 1(V?V bg) with γ 1=6.58±0.23×10?6 s?1 is more appropriate than a quadratic equation a=?γ 2(V?V bg)|V?V bg| to describe their kinematics, where γ 1 and γ 2 are coefficients, and a and V are the acceleration and speed of ICMEs, respectively, because the χ 2 for the linear equation satisfies the statistical significance level of 0.05, while the quadratic one does not. These results support the assumption that the radial motion of ICMEs is governed by a drag force due to interaction with the background solar wind. These findings also suggest that ICMEs propagating faster than the background solar wind are controlled mainly by the hydrodynamic Stokes drag. 相似文献
6.
R. P. Kane 《Solar physics》2014,289(7):2669-2675
When a Coronal Mass Ejection (CME) is ejected by the Sun, it reaches the Earth orbit in a modified state and is called an ICME (Interplanetary CME). When an ICME blob engulfs the Earth, short-scale cosmic-ray (CR) storms (Forbush decreases, FDs) occur, sometimes accompanied by geomagnetic Dst storms, if the B z component in the blob is negative. Generally, this is a sudden process that causes abrupt changes. However, sometimes before this abrupt change (FD) due to strong ICME blobs, there are slow, small changes in interplanetary parameters such as steady increases in solar wind speed V, which are small, but can last for several hours. In the present communication, CR changes in such an event are illustrated in the period 1?–?3 October 2013, when V increased steadily from ～?200 km?s?1 to ～?400 km?s?1 during 24 hours on 1 October 2013. The CR intensities decreased by 1?–?2 % during some hours of this 24-hour interval, indicating that CR intensities do respond to these weak but long-lasting increases in interplanetary solar wind speed. 相似文献
7.
The variation of the geomagnetic activity index Ap at the IMF sector boundaries (+ to ? and ? to +) has been studied for three solar cycles, separating data into vernal and autumnal equinoxes. It was found that a reported increase in Ap as an effect of a Hale boundary can be better attributed to the occurrence of a negative IMF Bz component in the geocentric solar magnetospheric coordinate system and to the occurrence of high speed solar wind streams. 相似文献
8.
Ten years data set is used to separate the influence of IMF Bz-component and solar wind speed on the dawn-dusk component of magnetic variations in the summer polar cap. The reference level was chosen from most quiet periods of winter solstices (small polar cap and auroral zone conductivity) to exclude the inner source component. The linear regression analysis was then used to calculate the PC variation response to Bz under different ranges of solar wind speed. As a result, taking into account the value of polar cap conductivity and effects of induced currents, the response of dawn-dusk electric field component to Bz and V was obtained and the potential difference across the polar cap was estimated to be for Bz ? + 1γ. The results give a proof for simultaneous operation in the magnetosphere of two electric field generation mechanisms, related to the boundary layer processes and magnetic field reconnection. The above-mentioned functional form was shown to correlate effectively with AE index (R = 0.73). 相似文献
9.
An analysis, with a representative (canonical) example of solar-flare-generated equatorial disturbances, is presented for the temporal and spatial changes in the solar wind plasma and magnetic field environment between the Sun and one astronomical unit (AU). Our objective is to search for first order global consequences rather than to make a parametric study. The analysis - an extension of earlier planar studies - considers all three plasma velocity and magnetic field components (V r, Vφ, V0, and B r, B0, Bφ) in any convenient heliospheric plane of symmetry such as the ecliptic plane, the solar equatorial plane, or the heliospheric equatorial plane chosen for its ability (in a tilted coordinate system) to order northern and southern hemispheric magnetic topology and latitudinal solar wind flows. Latitudinal velocity and magnetic field gradients in and near the plane of symmetry are considered to provide higher-order corrections of a specialized nature and, accordingly, are neglected, as is dissipation, except at shock waves. The representative disturbance is examined for the canonical case in which one describes the temporal and spatial changes in a homogeneous solar wind caused by a solar-flare-generated shock wave. The ‘canonical’ solar flare is assumed to produce a shock wave that has a velocity of 1000 km s#X2212;1 at 0.08 AU. We have examined all plasma and field parameters at three radial locations: central meridian and 33° W and 90° W of the flare's central meridian. A higher shock velocity (3000 km s#X2212;1) was also used to demonstrate the model's ability to simulate a strongly-kinked interplanetary field. Among the global (first-order) results are the following: (i) incorporation of a small meridional magnetic field in the ambient magnetic spiral field has negligible effect on the results; (ii) the magnetic field demonstrates strong kinking within the interplanetary shocked flow, even reversed polarity that - coupled with low temperature and low density - suggests a viable explanation for observed ‘magnetic clouds’ with accompanying double-streaming of electrons at directions ～ 90° to the heliocentric radius. 相似文献
10.
The behavioural features of the IMF Bz component for different solar wind velocity regimes have been studied. The study revealed a significant difference in variations of the Bz component between high-speed and low-speed regimes. Formation mechanisms for the IMF meridional component as well as the relationship of Bz with dynamical properties of the large-scale magnetic fields on the Sun are discussed. 相似文献
11.
Meena Pokharia Lalan Prasad Chandrasekhar Bhoj Chandni Mathpal 《Journal of Astrophysics and Astronomy》2018,39(5):53
The aim of this paper is to investigate the association of the geomagnetic storms with the magnitude of interplanetary magnetic field IMF (B), solar wind speed (V), product of IMF and wind speed (\(V \cdot B)\), Ap index and solar wind plasma density (\(n_{\mathrm{p}})\) for solar cycles 23 and 24. A Chree analysis by the superposed epoch method has been done for the study. The results of the present analysis showed that \(V \cdot B\) is more geoeffective when compared to V or B alone. Further the high and equal anti-correlation coefficient is found between Dst and Ap index (? 0.7) for both the solar cycles. We have also discussed the relationship between solar wind plasma density (\(n_{\mathrm{p}})\) and Dst and found that both these parameters are weakly correlated with each other. We have found that the occurrence of geomagnetic storms happens on the same day when IMF, V, Ap and \(V \cdot B\) reach their maximum value while 1 day time lag is noticed in case of solar wind plasma density with few exceptions. The study of geomagnetic storms with various solar-interplanetary parameters is useful for the study of space weather phenomenon. 相似文献
12.
S.W.H. Cowley 《Planetary and Space Science》1981,29(8):809-818
The origin of magnetospheric asymmetry effects associated with the equatorial plane component of the interplanetary magnetic field (IMF) is discussed in terms of the forces exerted on open flux tubes mapping into the solar wind. It is argued that the downstream relaxation of the magnetosphere under the action of these stresses towards a state of reduced stress is such as to allow, in effect, partial penetration of this field component (both Bx and By in magnetospheric coordinates) into the magnetosphere. Many of the associated phenomena are therefore qualitatively described by the ‘dipole plus uniform IMF’ model, since this represents the idealization of exactly zero electromagnetic stress and hence gives a lowest order picture of the effects which result from magnetospheric relaxation toward that state. This is true of IMF By-associated effects which are well documented experimentally and which form a rich and consistent set of phenomena which have received considerable attention over the past decade. It is argued here that exactly corresponding phenomena are expected to be associated with the IMF Bx field as well, but because of the differing field direction these will take differing and usually less obvious forms than the similar effects associated with By. The suggested partial penetration of the IMF Bx field should be directly testable in the dipolar field region of the magnetosphere, but in the tail North-South displacements of the current sheet (and possibly magnetopause) are expected to occur instead. Some evidence of the latter displacements are presented. The other major IMF Bx effect should be noon-midnight displacements of the polar cap, such as have been recently reported. Little IMF Bx effect on auroral zone flows is anticipated, by contrast with the dawn-dusk asymmetries in this flow associated with IMF By. 相似文献
13.
The Solar Wind Energy Flux 总被引：1，自引：0，他引：1
The solar-wind energy flux measured near the Ecliptic is known to be independent of the solar-wind speed. Using plasma data from Helios, Ulysses, and Wind covering a large range of latitudes and time, we show that the solar-wind energy flux is independent of the solar-wind speed and latitude within 10?%, and that this quantity varies weakly over the solar cycle. In other words the energy flux appears as a global solar constant. We also show that the very high-speed solar wind (V SW>700?km?s?1) has the same mean energy flux as the slower wind (V SW<700?km?s?1), but with a different histogram. We use this result to deduce a relation between the solar-wind speed and density, which formalizes the anti-correlation between these quantities. 相似文献
14.
The geometry of the open flux area in the polar region is computed by superposing a uniform interplanetary magnetic field (IMF) with various orientation angles to a model of the magnetosphere. It is confirmed that the IMF By component is as important as the Bz component in “opening” the magnetosphere. It is also shown that the computed area of open field lines is remarkably similar to the observed ones which were determined by using the entry of solar electrons. In particular, when the IMF vector is confined in the X-Z-plane and the Bz component has a large positive value, the open area becomes crescent-shaped, coinciding approximately with the cusp region. 相似文献
15.
A well established correlation exists between the IMF By and the cusp field-aligned and horizontal currents (Wilhjelm et al., 1978). The northern and southern cusp currents may be parts of one large scale current system (D'Angelo, 1980) flowing mainly at the magnetopause and driven by the z-component of the solar wind electric field. Primdahl and Spangslev (1981) suggested that the large scale current system seems to shield out the IMF By from the interior of the magnetosphere. This paper proposes that the currents are induced by the change of sign of By at the IMF sector boundary crossings, and argues that the time constant for decay of the currents may well be one week or larger. The percentage errors in inferring the IMF sector polarity from the Godhavn H magnetogram increases with increasing time since the last sector boundary crossing. This is in accordance with a steady decay of the induced currents. Finally experimental tests are proposed to demonstrate the feasability of and possibly distinguish between the mechanisms. 相似文献
16.
A. V. Mordvinov 《Solar physics》2007,246(2):445-456
A comparative analysis of solar and heliospheric magnetic fields in terms of their cumulative sums reveals cyclic and long-term
changes that appear as a magnetic flux imbalance and alternations of dominant magnetic polarities. The global magnetic flux
imbalance of the Sun manifests itself in the solar mean magnetic field (SMMF) signal. The north – south asymmetry of solar
activity and the quadrupole mode of the solar magnetic field contribute the most to the observed magnetic flux imbalance.
The polarity asymmetry exhibits the Hale magnetic cycle in both the radial and azimuthal components of the interplanetary
magnetic field (IMF). Analysis of the cumulative sums of the IMF components clearly reveals cyclic changes in the IMF geometry.
The accumulated deviations in the IMF spiral angle from its nominal value also demonstrate long-term changes resulting from
a slow increase of the solar wind speed over 1965 – 2006. A predominance of the positive IMF B
z
with a significant linear trend in its cumulative signal is interpreted as a manifestation of the relic magnetic field of
the Sun. Long-term changes in the IMF B
z
are revealed. They demonstrate decadal changes owing to the 11/22-year solar cycle. Long-duration time intervals with a dominant
negative B
z
component were found in temporal patterns of the cumulative sum of the IMF B
z
. 相似文献
17.
The relationship between the orientation of the interplanetary magnetic field (IMF), represented by the clock angle which is the angle defined by IMF-By and -Bz components, and the AL and AU indices is examined at various dipole tilt angles for the period of 1978-1988. We use the IMF data obtained from the IMP 8 satellite, AL and AU indices with corrected seasonal variations, and the dipole tilt angle, which is the dipole magnetic latitude of the subsolar point calculated as a function of the day of year and universal time. For both positive (dipole tilted to the Sun) and negative dipole tilt angles, the values of |AL| and AU decrease as the IMF clock angle moves away from 180°, becoming more northward. The indices also tend to become smaller for larger dipole tilt angle, either toward or away from the Sun. This dependence on dipole tilt angle enhances the semiannual variation of geomagnetic activity. 相似文献
18.
M. Tokumaru S. Fujimaki M. Higashiyama A. Yokobe T. Ohmi K. Fujiki M. Kojima 《Solar physics》2012,276(1-2):315-336
Interplanetary scintillation (IPS) measurements of the solar wind speed for the distance range between 13 and 37 R S were carried out during the solar conjunction of the Nozomi spacecraft in 2000?–?2001 using the X-band radio signal. Two large-aperture antennas were employed in this study, and the baseline between the two antennas was several times longer than the Fresnel scale for the X-band. We successfully detected a positive correlation of IPS from the cross-correlation analysis of received signal data during ingress, and estimated the solar wind speed from the time lag corresponding to the maximum correlation by assuming that the solar wind flows radially. The speed estimates range between 200 and 540?km?s?1 with the majority below 400?km?s?1. We examined the radial variation in the solar wind speed along the same streamline by comparing the Nozomi data with data obtained at larger distances. Here, we used solar wind speed data taken from 327 MHz IPS observations of the Solar-Terrestrial Environment Laboratory (STEL), Nagoya University, and in?situ measurements by the Advanced Composition Explorer (ACE) for the comparison, and we considered the effect of the line-of-sight integration inherent to IPS observations for the comparison. As a result, Nozomi speed data were proven to belong to the slow component of the solar wind. Speed estimates within 30 R S were found to be systematically slower by 10?–?15 % than the terminal speeds, suggesting that the slow solar wind is accelerated between 13 and 30 R S. 相似文献
19.
S.-I. Akasofu 《Planetary and Space Science》1979,27(4):425-431
It is shown that the interplanetary quantity ε(t), obtained by Perreault and Akasofu (1978), for intense geomagnetic storms, also correlates well with individual magnetospheric substonns. This quantity is given by , where V and B denote the solar wind speed and the magnitude of the interplanetary magnetic field (IMF), respectively, and θ denotes the polar angle of the IMF; lo is a constant ? 7 Earth radii. The AE index is used in this correlation study. The correlation is good enough to predict both the occurrence and intensity of magnetospheric substonns observed in the auroral zone, by monitoring the quantity ε(t) upstream of the solar wind. 相似文献
20.
Thirteen synoptic maps of expansion rate of the coronal magnetic field (CMF; RBR) calculated by the so-called ‘potential model’ are constructed for 13 Carrington rotations from the maximum phase of solar activity cycle 22 through the maximum phase of cycle 23. Similar 13 synoptic maps of solar wind speed (SWS) estimated by interplanetary scintillation observations are constructed for the same 13 Carrington rotations as the ones for the RBR. The correlation diagrams between the RBR and the SWS are plotted with the data of these 13 synoptic maps. It is found that the correlation is negative and high in this time period. It is further found that the linear correlation is improved if the data are classified into two groups by the magnitude of radial component of photospheric magnetic field, |Bphor|; group 1, 0.0 G ≦ |Brpho| < 17.8 G and group 2, 17.8 G ≦ |Brpho|. There exists a strong negative correlation between the RBR and the SWS for the group 1 in contrast with a weak negative correlation for the group 2. Group 1 has a double peak in the density distribution of data points in the correlation diagram; a sharp peak for high-speed solar wind and a low peak for low-speed solar wind. These two peaks are located just on the axis of maximum variance of data points in the correlation diagram. This result suggests that the solar wind consists of two major components and both the high-speed and the low-speed winds emanating from weak photospheric magnetic regions are accelerated by the same mechanism in the course of solar activity cycle. It is also pointed out that the SWS can be estimated by the RBR of group 1 with an empirical formula obtained in this paper during the entire solar activity cycle. 相似文献