共查询到20条相似文献，搜索用时 31 毫秒
1.
We present the solar wind plasma parameters obtained from the Ulysses spacecraft during its second pole-to-pole fast latitude scan near the 2001 solar maximum. We study the solar wind properties
from the electron density and core temperature measurements made by the radio receiver on Ulysses using the method of quasi-thermal noise spectroscopy. We analyze these parameters as functions of heliographic latitude and
distance. We present their histograms normalized to 1 AU and find a bimodal distribution for the electron core temperature.
The cooler population can be associated with the fast wind flow emanating from coronal holes present at various latitudes.
We discuss a slight north/south asymmetry found for the electron density. Finally, we compare the present results to those
obtained during the 1996 solar minimum and 1991 solar maximum. 相似文献
2.
We present the analysis of a large solar near-relativistic electron event observed by the Ulysses and the ACE spacecraft on 8 November 2000, when Ulysses was located at a heliocentric distance of 2.4 AU and at a heliographic latitude of ??80° S. We use a particle propagation model to infer the local interplanetary transport conditions and the injection histories of the near-relativistic electrons observed by both spacecraft. We find different local transport conditions for each set of observations. The inferred injection profiles for both spacecraft extend for several hours; but the injection at Ulysses was smaller and started later. The association with type II radio emission suggests that the heliospheric electrons were provided by coronal shock acceleration. An analysis of the in situ magnetic field and plasma measurements indicates that the global configuration of the heliosphere (disturbed by transient structures) could play a role in shaping the characteristics of solar energetic particle events observed from different locations. 相似文献
3.
G. D. Parker 《Solar physics》1987,108(1):77-87
Long-lived brightness structures in the solar electron corona persist over many solar rotation periods and permit an observational determination of coronal magnetic tracer rotation as a function of latitude and height in the solar atmosphere. For observations over 1964–1976 spanning solar cycle 20, we compare the latitude dependence of rotation at two heights in the corona. Comparison of rotation rates from East and West limbs and from independent computational procedures is used to estimate uncertainty. Time-averaged rotation rates based on three methods of analysis demonstrate that, on average, coronal differential rotation decreases with height from 1.125 to 1.5 R
S. The observed radial variation of differential rotation implies a scale height of approximately 0.7 R
S for coronal differential rotation.Model calculations for a simple MHD loop show that magnetic connections between high and low latitudes may produce the observed radial variations of magnetic tracer rotation. If the observed tracer rotation represents the rotation of open magnetic field lines as well as that of closed loops, the small scale height for differential rotation suggests that the rotation of solar magnetic fields at the base of the solar wind may be only weakly latitude dependent. If, instead, closed loops account completely for the radial gradients of rotation, outward extrapolation of electron coronal rotation may not describe magnetic field rotation at the solar wind source. Inward extrapolations of observed rotation rates suggest that magnetic field and plasma are coupled a few hundredths of a solar radius beneath the photosphere. 相似文献
4.
L. K. Jian C. T. Russell J. G. Luhmann P. J. MacNeice D. Odstrcil P. Riley J. A. Linker R. M. Skoug J. T. Steinberg 《Solar physics》2011,273(1):179-203
During the latitudinal alignment in 2004, ACE and Ulysses encountered two stream interaction regions (SIRs) each Carrington rotation from 2016 to 2018, at 1 and 5.4 AU, respectively.
More SIR-driven shocks were observed at 5.4 AU than at 1 AU. Three small SIRs at 1 AU merged to form a strong SIR at 5.4 AU.
We compare the Enlil model results with spacecraft observations from four aspects: i) the accuracy of the latest versions of models (WSA v2.2 and Enlil v2.7) vs. old versions (WSA v1.6 and Enlil v2.6), ii) the sensitivity to different solar magnetograms (MWO vs. NSO), iii) the sensitivity to different coronal models (WSA vs. MAS), iv) the predictive capability at 1 AU vs. 5.4 AU. We find the models can capture field sector boundaries with some time offset. Although the new versions have improved
the SIR timing prediction, the time offset can be up to two days at 1 AU and four days at 5.4 AU. The models cannot capture
some small-scale structures, including shocks and small SIRs at 1 AU. For SIRs, the temperature and total pressure are often
underestimated, while the density compression is overestimated. For slow wind, the density is usually overestimated, while
the temperature, magnetic field, and total pressure are often underestimated. The new versions have improved the prediction
of the speed and density, but they need more robust scaling factors for magnetic field. The Enlil model results are very sensitive
to different solar magnetograms and coronal models. It is hard to determine which magnetogram-coronal model combination is
superior to others. Higher-resolution solar and coronal observations, a mission closer to the Sun, together with simulations
of greater resolution and added physics, are ways to make progress for the solar wind modeling. 相似文献
5.
E. K. J. Kilpua J. G. Luhmann J. Gosling Y. Li H. Elliott C. T. Russell L. Jian A. B. Galvin D. Larson P. Schroeder K. Simunac G. Petrie 《Solar physics》2009,256(1-2):327-344
It has been realized for some time that the slow solar wind with its embedded heliospheric current sheet often exhibits complex features suggesting at least partially transient origin. In this paper we investigate the structure of the slow solar wind using the observations by the Wind and STEREO spacecraft during two Carrington rotations (2054 and 2055). These occur at the time of minimum solar activity when the interplanetary medium is dominated by recurrent high-speed streams and large-scale interplanetary coronal mass ejections (ICMEs) are rare. However, the signatures of transients with small scale-sizes and/or low magnetic field strength (comparable with the typical solar wind value, ～?5 nT) are frequently found in the slow solar wind at these times. These events do not exhibit significant speed gradients across the structure, but instead appear to move with the surrounding flow. Source mapping using models based on GONG magnetograms suggests that these transients come from the vicinity of coronal source surface sector boundaries. In situ they are correspondingly observed in the vicinity of high density structures where the dominant electron heat flux reverses its flow polarity. These weak transients might be indications of dynamical changes at the coronal hole boundaries or at the edges of the helmet streamer belt previously reported in coronagraph observations. Our analysis supports the idea that even at solar minimum, a considerable fraction of the slow solar wind is transient in nature. 相似文献
6.
High-latitude interplanetary mass ejections (ICMEs) observed beyond 1 AU are not studied very often. They are useful for improving
our understanding of the 3D heliosphere. As there are only few such events registered by the Ulysses spacecraft, the task of detecting their solar counterparts is a challenge, especially during high solar activity periods,
because there are dozens coronal mass ejections (CMEs) registered by SOHO that might be chosen as candidates. We analyzed
a high-latitude ICME registered by the Ulysses spacecraft on 18 January 2002. Our investigation focused on the correlation between various plasma parameters that allow
the identification to be made of the ICME and its components such as the forward shock, the magnetic cloud and the reverse
shock. 相似文献
7.
I. G. Richardson 《Solar physics》2014,289(10):3843-3894
Previous studies have discussed the identification of interplanetary coronal mass ejections (ICMEs) near the Earth based on various solar wind signatures. In particular, methods have been developed of identifying regions of anomalously low solar wind proton temperatures (T p) and plasma compositional anomalies relative to the composition of the ambient solar wind that are frequently indicative of ICMEs. In this study, similar methods are applied to observations from the Ulysses spacecraft that was launched in 1990 and placed in a heliocentric orbit over the poles of the Sun. Some 279 probable ICMEs are identified during the spacecraft mission, which ended in 2009. The identifications complement those found independently in other studies of the Ulysses data, but a number of additional events are identified. The properties of the ICMEs detected at Ulysses and those observed near the Earth and in the inner heliosphere are compared. 相似文献
8.
P. N. Pathak 《Solar physics》1971,20(2):462-473
Using solar wind velocity data obtained by Mariner-2 and IMP-1 spacecrafts, an attempt has been made to study its correlation with 5303 coronal intensity. It is shown that the long-lasting regions of enhanced 5303 intensity in the solar corona are well correlated with recurrent streams of solar wind having high velocity. The time-lag between the central meridian passage (CMP) of the coronal features and the detection of the solar wind streams at the spacecraft is found to be smaller than that implied by a radial solar wind. Significant positive correlations for Mariner-2 data are obtained for coronal intensity at heliolatitudes 5°S–10°N with a time-lag of + 2 days while for IMP-1 data, high positive correlations are obtained for the southern heliolatitudes (10°–25°S) without any time-lag. It should be noted that the average heliographic latitudes for Mariner-2 and IMP-1 were 4°N and 4°S respectively during the periods covered by the present analysis. The implications of the results are discussed.Presented at IUCSTP Symposium on Solar-Terrestrial Physics, Leningrad, May 1970. 相似文献
9.
In 2001 the Ulysses spacecraft crossed the ecliptic plane near perihelion. The heliographic longitude with respect to the Earth was within ±20° of the west solar limb while it was ±15° of the ecliptic plane, which meant that coronal mass ejections seen off the solar west limb were likely to pass over Ulysses. On 10 May the largest >38 keV electron intensity of the mission, since the Jovian encounter in 1992, was observed, which was accompanied by a fast perpendicular shock. This event was preceded by a fast coronal mass ejection some two and a half days earlier which is the probable source of the shock. However, both the ACE spacecraft and Ulysses observed, simultaneously, an intense, prompt electron event on 7 May from a solar flare associated with earlier coronal mass ejections also observed off the west limb; Ulysses was magnetically connected to a longitude well behind the west limb. ACE did not observe any (at the 0.1% level) energetic electrons which were associated with the 10 May event seen at Ulysses. We discuss in detail the energetic particles seen at the two spacecraft during 7–11 May, with the objective of understanding the origin of the intense electron event seen on 10 May and the manner in which particles escaping from the shock populate the inner heliosphere. The energy spectrum of the ions at both ACE and Ulysses exhibits a maximum at around 400 keV; this form of the spectrum was seen at the shock itself. It appears that the strong shock driven by the fast coronal mass ejection is able to populate a large fraction of the inner heliosphere with accelerated ions. The shock-accelerated electrons do not pervade the inner heliosphere in the same manner as the ions. We suggest that the electron acceleration was enhanced by the presence of multiple coronal mass ejections. 相似文献
10.
Interplanetary magnetic field and solar wind plasma density observed at 1 AU during Solar Cycle 23?–?24 (SC-23/24) minimum were significantly smaller than those during its previous solar cycle (SC-22/23) minimum. Because the Earth’s orbit is embedded in the slow wind during solar minimum, changes in the geometry and/or content of the slow wind region (SWR) can have a direct influence on the solar wind parameters near the Earth. In this study, we analyze solar wind plasma and magnetic field data of hourly values acquired by Ulysses. It is found that the solar wind, when averaging over the first (1995.6?–?1995.8) and third (2006.9?–?2008.2) Ulysses’ perihelion (\({\sim}\,1.4~\mbox{AU}\)) crossings, was about the same speed, but significantly less dense (\({\sim}\,34~\%\)) and cooler (\({\sim}\,20~\%\)), and the total magnetic field was \({\sim}\,30~\%\) weaker during the third compared to the first crossing. It is also found that the SWR was \({\sim}\,50~\%\) wider in the third (\({\sim}\,68.5^{\circ}\) in heliographic latitude) than in the first (\({\sim}\,44.8^{\circ}\)) solar orbit. The observed latitudinal increase in the SWR is sufficient to explain the excessive decline in the near-Earth solar wind density during the recent solar minimum without speculating that the total solar output may have been decreasing. The observed SWR inflation is also consistent with a cooler solar wind in the SC-23/24 than in the SC-22/23 minimum. Furthermore, the ratio of the high-to-low latitude photospheric magnetic field (or equatorward magnetic pressure force), as observed by the Mountain Wilson Observatory, is smaller during the third than the first Ulysses’ perihelion orbit. These findings suggest that the smaller equatorward magnetic pressure at the Sun may have led to the latitudinally-wider SRW observed by Ulysses in SC-23/24 minimum. 相似文献
11.
Previous studies of the source regions of solar wind sampled by ACE and Ulysses showed that some solar wind originates from open magnetic flux rooted in active regions. These solar wind sources were labeled active-region sources when the open flux was from a strong field region with no corresponding coronal hole in the NSO He 10830 Å synoptic coronal-hole maps. Here, we present a detailed investigation of several of these active-region sources using ACE and Ulysses solar wind data, potential field models of the corona, and solar imaging data. We find that the solar wind from these active-region sources has distinct signatures, e.g., it generally has a higher oxygen charge state than wind associated with helium-10830 Å coronal-hole sources, indicating a hotter source region, consistent with the active region source interpretation. We compare the magnetic topology of the open field lines of these active-region sources with images of the hot corona to search for corresponding features in EUV and soft X-ray images. In most, but not all, cases, a dark area is seen in the EUV and soft X-ray image as for familiar coronal-hole sources. However, in one case no dark area was evident in the soft X-ray images: the magnetic model showed a double dipole coronal structure consistent with the images, both indicating that the footpoints of the open field lines, rooted deep within the active region, lay near the separatrix between loops connecting to two different opposite polarity regions. 相似文献
12.
Analysis of the Interball-1 spacecraft data (1995 – 2000) has shown that the solar wind ion flux sometimes increases or decreases abruptly by more than
20% over a time period of several seconds or minutes. Typically, the amplitude of such sharp changes in the solar wind ion
flux (SCIFs) is larger than 0.5×108 cm−2 s−1. These sudden changes of the ion flux were also observed by the Solar Wind Experiment (SWE), on board the Wind spacecraft, as the solar wind density increases and decreases with negligible changes in the solar wind velocity. SCIFs occur
irregularly at 1 AU, when plasma flows with specific properties come to the Earth’s orbit. SCIFs are usually observed in slow,
turbulent solar wind with increased density and interplanetary magnetic field strength. The number of times SCIFs occur during
a day is simulated using the solar wind density, magnetic field, and their standard deviations as input parameters for a period
of five years. A correlation coefficient of ∼0.7 is obtained between the modelled and the experimental data. It is found that
SCIFs are not associated with coronal mass ejections (CMEs), corotating interaction regions (CIRs), or interplanetary shocks;
however, 85% of the sector boundaries are surrounded by SCIFs. The properties of the solar wind plasma for days with five
or more SCIF observations are the same as those of the solar wind plasma at the sector boundaries. One possible explanation
for the occurrence of SCIFs (near sector boundaries) is magnetic reconnection at the heliospheric current sheet or local current
sheets. Other probable causes of SCIFs (inside sectors) are turbulent processes in the slow solar wind and at the crossings
of flux tubes. 相似文献
13.
Previous studies of the source regions of solar wind sampled by ACE and Ulysses showed that some solar wind originates from open magnetic flux rooted in active regions. These solar wind sources were labeled active-region sources when the open flux was from a strong field region with no corresponding coronal hole in the NSO He 10830 Å synoptic coronal-hole maps. Here, we present a detailed investigation of several of these active-region sources using ACE and Ulysses solar wind data, potential field models of the corona, and solar imaging data. We find that the solar wind from these active-region sources has distinct signatures, e.g., it generally has a higher oxygen charge state than wind associated with helium-10830 Å coronal-hole sources, indicating a hotter source region, consistent with the active region source interpretation. We compare the magnetic topology of the open field lines of these active-region sources with images of the hot corona to search for corresponding features in EUV and soft X-ray images. In most, but not all, cases, a dark area is seen in the EUV and soft X-ray image as for familiar coronal-hole sources. However, in one case no dark area was evident in the soft X-ray images: the magnetic model showed a double dipole coronal structure consistent with the images, both indicating that the footpoints of the open field lines, rooted deep within the active region, lay near the separatrix between loops connecting to two different opposite polarity regions. 相似文献
14.
The Grad–Shafranov reconstruction is a method of estimating the orientation (invariant axis) and cross section of magnetic
flux ropes using the data from a single spacecraft. It can be applied to various magnetic structures such as magnetic clouds
(MCs) and flux ropes embedded in the magnetopause and in the solar wind. We develop a number of improvements of this technique
and show some examples of the reconstruction procedure of interplanetary coronal mass ejections (ICMEs) observed at 1 AU by
the STEREO, Wind, and ACE spacecraft during the minimum following Solar Cycle 23. The analysis is conducted not only for ideal localized ICME
events but also for non-trivial cases of magnetic clouds in fast solar wind. The Grad–Shafranov reconstruction gives reasonable
results for the sample events, although it possesses certain limitations, which need to be taken into account during the interpretation
of the model results. 相似文献
15.
The solar magnetic field maps every point in the corona to a corresponding place on the solar surface. Identifying the magnetic
connection map is difficult at low latitudes near the heliospheric current sheet, but remarkably simple in coronal hole interiors.
We present a simple analytic magnetic model (‘pseudocurrent extrapolation’) that reproduces the global structure of the corona,
with significant physical advantages over other nearly analytic models such as source-surface potential field extrapolation.
We use the model to demonstrate that local horizontal structure is preserved across altitude in the central portions of solar
coronal holes, up to at least 30 Rs, in agreement with observations. We argue that the preserved horizontal structure may be used to track the magnetic footpoint
associated with the location of a hypothetical spacecraft traveling through the solar corona, to relate in situ measurements of the young solar wind at ∼10–30 Rs to particular source regions at the solar surface. Further, we discuss the relationship between readily observable geometrical
distortions and physical parameters of interest such as the field-aligned current density. 相似文献
16.
An extended Ulysses interplanetary coronal mass ejections (ICMEs) list is used to statistically study the occurrence rate of ICMEs, the interaction
of ICMEs with solar wind, and the magnetic field properties in ICMEs. About 43% of the ICMEs are identified as magnetic clouds
(MCs). It is found that the occurrence rate of ICMEs approximately follows the solar activity level, except for the second
solar orbit; the rate is higher in the southern heliolatitude than in the northern heliolatitude; and it roughly decreases
with the increase of ICME speeds. Our results show that the speed difference between the ICME and the solar wind in front
of it shows a slight decrease with increasing heliocentric distance for ICMEs preceded by a shock, whereas no such dependence
is found for the ICMEs without shock association. It is also found that approximately 23% of the ICMEs are associated with
radial field events, in which the interplanetary magnetic field with near-radial direction lasts for many hours, in the Ulysses detected range, and these associated events are not necessarily confined to fast ICMEs or the trailing portions of ICMEs.
Nearly all these associated events occur during the period of declining solar wind speed and most of them occur at low heliolatitudes. 相似文献
17.
R.G. Marsden 《Astrophysics and Space Science》2001,277(1-2):337-347
Launched in October 1990, the ESA-NASA Ulysses mission has conducted the very first survey of the heliosphere within 5 AU
of the Sun over the full range of heliolatitudes. With polar passes taking place in 1994 and 1995, the timing of the mission
has enabled Ulysses to characterise the global structure of the heliosphere at solar minimum, when the corona adopts its simplest
configuration. The most important findings to date include a confirmation of the uniform nature of the high-speed (∼ 750 km/s)solar
wind flow from the polar coronal holes, filling two-thirds of the volume of the inner heliosphere; the sharp boundary, existing
from the chromosphere through the corona, between fast and slow solar wind streams; the latitude independence of theradial
component of the heliospheric magnetic field; the lower-than-expected latitude gradient of galactic and anomalous cosmic rays;
the continued existence of recurrent increases in the flux of low-energy ions and electrons up to the highest latitudes. Without
doubt, the Ulysses mission has provided a unique set of observations of the heliosphere at solar minimum, resulting in a good
understanding of many aspects of its behaviour. In this review, we will highlight some of the key findings to date, and also
look ahead to the challenges that await as Ulysses returns to high latitudes to explore the heliosphere at solar maximum and
beyond. Finally, a brief summary is given of the prospects for heliospheric research in the post-Ulysses era.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
Analysis of the green line corona for the interval 1947–1970 suggests the existence of largescale organization of the emission. The green line emission at high northern latitudes (≈ 40°–60°) is correlated with the emission at high southern latitudes 6, 15 and 24 days later, while the low latitude green corona seems to be correlated on both sides of the equator with no time lag. These coronal features are recurrent with a 27-day period at all latitudes between ± 60 °, and we associate these large-scale structures with the solar magnetic sector structure. The high correlation between northern and southern high-latitude emission at 15 days time lag is explained as a signature of a two-sector structure, while four sectors are associated with the 6 and 24 day peaks. 相似文献
19.
Employing the synoptic maps of the photospheric magnetic fields from the beginning of solar cycle 21 to the end of 23, we
first build up a time – longitude stackplot at each latitude between ±35°. On each stackplot there are many tilted magnetic
structures clearly reflecting the rotation rates, and we adopt a cross-correlation technique to explore the rotation rates
from these tilted structures. Our new method avoids artificially choosing magnetic tracers, and it is convenient for investigating
the rotation rates of the positive and negative fields by omitting one kind of field on the stackplots. We have obtained the
following results. i) The rotation rates of the positive and negative fields (or the leader and follower polarities, depending on the hemispheres
and solar cycles) between latitudes ±35° during solar cycles 21–23 are derived. The reversal times of the leader and follower
polarities are usually not consistent with the years of the solar minimum, nevertheless, at latitudes ±16°, the reversal times
are almost simultaneous with them. ii) The rotation rates of the three solar cycles averaged over each cycle are calculated separately for the positive, negative
and total fields. The latitude profiles of rotation of the positive and negative fields exhibit equatorial symmetries with
each other, and those of the total fields lie between them. iii) The differences in rotation rates between the leader and follower polarities are obtained. They are very small near the
equator, and increase as latitude increases. In the latitude range of 5° – 20°, these differences reach 0.05 deg day−1, and the mean difference for solar cycle 22 is somewhat smaller than cycles 21 and 23 in these latitude regions. Then, the
differences reduce again at latitudes higher than 20°. 相似文献
20.
Identifying co-rotating structures in solar wind enables us to predict solar wind variation at the Earth and, hence, geomagnetic disturbances. However, co-rotating structures during solar maximum are sometimes difficult to see. We correlated solar wind data obtained by two spacecraft, Nozomi heading towards Mars and ACE at the L1 point, from late 1999 through early 2002. There were intervals when the solar wind showed specific co-rotating structures even in the midst of the solar maximum, whereas no correlation was found during the other intervals. The coefficient was generally higher between Nozomi and ACE than for the 27-day recurrence at ACE, while there was some correlation, especially when the difference in longitude between the two spacecraft was less than 120°. Although frequency of occurrence of CMEs is partly responsible for the correlation, the results can be interpreted in terms of rapid changes in co-rotating high-speed streams from near-equatorial coronal holes at the solar maximum. 相似文献