共查询到20条相似文献,搜索用时 31 毫秒
1.
Guhathakurta Madhullika Sittler Ed Fisher Richard Kucera Theresa Gibson Sarah McComas Dave Skoug Ruth 《Space Science Reviews》2001,97(1-4):45-50
The large-scale coronal magnetic fields of the Sun are believed to play an important role in organizing the coronal plasma
and channeling the high and low speed solar wind along the open magnetic field lines of the polar coronal holes and the rapidly
diverging field lines close to the current sheet regions, as has been observed by the instruments aboard the Ulysses spacecraft from March 1992 to March 1997. We have performed a study of this phenomena within the framework of a semi-empirical
model of the coronal expansion and solar wind using Spartan, SOHO, and Ulysses observations during the quiescent phase of the solar cycle. Key to this understanding is the demonstration that the white
light coronagraph data can be used to trace out the topology of the coronal magnetic field and then using the Ulysses data to fix the strength of the surface magnetic field of the Sun. As a consequence, it is possible to utilize this semi-empirical
model with remote sensing observation of the shape and density of the solar corona and in situ data of magnetic field and
mass flux to predict values of the solar wind at all latitudes through out the solar system. We have applied this technique
to the observations of Spartan 201-05 on 1–2 November, 1998, SOHO and Ulysses during the rising phase of this solar cycle and speculate on what solar wind velocities Ulysses will observe during its polar passes over the south and the north poles during September of 2000 and 2001. In order to do
this the model has been generalized to include multiple streamer belts and co-located current sheets. The model shows some
interesting new results.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
2.
We present observations of energetic (0.34–8 MeV) ions from the Ulysses spacecraft during its second ascent to southern high latitude regions of the heliosphere. We cover the period from January
1999 until mid-2000 as Ulysses moved from 5.2 AU and 18° S to 3.5 AU and 55° S. In contrast to the long-lived and well-defined ∼26-day recurrences that
were observed throughout Ulysses‘ first southern pass, energetic ion fluxes during the first portion of the Ulysses’ second polar orbit are highly irregular. Although corotating interaction regions (CIRs) are clearly present in solar wind
and magnetic field data throughout the first half of 1999, their effects on energetic ion intensities are quite different
from what they were in 1992–1993. No dominant strictly recurrent ion flux increases are observed in association with the arrival
of these CIRs. Correspondingly, there is no stable structure of large polar coronal holes during the same period. Isolated
transient solar energetic particle (SEP) events are observed at low and high latitudes. We compare energetic ion observations
from the ACE and Ulysses spacecraft during the first half of 1999 to determine the influence of these SEP events in the observed recurrent CIR structure.
Such SEP events occurred only occasionally during 1992–1993, but when they occurred, they obscured the recurrences in a manner
similar to that observed in 1999–2000. We therefore conclude that the basic differences in the behavior of energetic ion events
between the first and second southern passes are due to the short life of the corotating structure and the higher frequency
of SEP events occurring in 1999–2000.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
We have identified 20 coronal mass ejections, or CMEs, in the solar wind in the Ulysses data obtained between S30° and S75° during the second polar orbit. Unlike CME-driven disturbances observed at high latitudes
during Ulysses’ first polar orbit, these disturbances had plasma and magnetic field characteristics similar to those observed in the ecliptic
plane near 1 AU when one allows for evolution with heliocentric distance. Here we provide a brief overview of CME observations
at high latitudes both close to and far from the Sun, with emphasis on the recent Ulysses measurements on the rising portion of solar cycle 23.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
4.
We discuss the underlying direction of the heliospheric magnetic field measured by Ulysses in the latitude range 6° S-65° S by examining distributions of the magnetic field azimuthal angle with respect to the simple
Parker spiral model. During the first Ulysses traversal of this latitude range in 1992–1994, while solar activity was declining, the shape of the distributions obtained
at high latitudes in the fast solar wind differed from that at lower latitudes. In the present data set, obtained during rising
solar activity, both field polarities are present at all latitudes and the peaks of the distributions agree with the predicted
spiral direction to first approximation. However, compared to the first orbit, a significantly greater percentage of the observed
field vectors have large deviations from the spiral direction.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
5.
O. Moullard R.G. Marsden T.R. Sanderson C. Tranquille R.J. Forsyth B.E. Goldstein 《Space Science Reviews》2001,97(1-4):289-292
We present and compare observations of energetic protons during the two first transits of the Ulysses spacecraft from low to high latitudes in the southern heliosphere. Protons in the energy range 1.8–3.8 MeV from the COSPIN
experiment are studied for global trends and in relation to some ambient structures in the solar wind (corotating interaction
region, forward/reverse shock). The global trends show the large dependence on the heliospheric condition and solar activity,
including indications of a larger ambient particle population during the rising phase of solar activity and more efficient
solar wind particle accelerators during the declining phase. More enhancements in the proton flux intensity are time associated
with forward shocks than reverse contrary to first pass. Recurrent structures are found even during the second transit. Some
latitude dependent periodicities are observed that could relate to the differential solar rotation.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
6.
During the years 1996–2000 solar activity has been gradually rising and is now close to maximum. At the same time the Ulysses spacecraft has performed a north to south traverse of the low latitude regions of the heliosphere and is now once again travelling
through high southerly latitudes. We show some examples and report on the occurence rates of transient solar wind disturbances
which have been identified by their magnetic field signatures. ‘Magnetic clouds’ remain more common at low (compared to high)
latitudes despite the rise in solar activity. However, more events were observed at high latitudes than at solar minimum.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
7.
W. Pryor I. Stewart K. Simmons M. Witte J. Ajello K. Toskiba D. McComas D. Hall 《Space Science Reviews》2001,97(1-4):393-399
We model interplanetary H Lyman-α (Lα) observations from Galileo UVS (Ultraviolet Spectrometer) and EUVS (Extreme Ultraviolet Spectrometer) (Hord et al., 1992) and the Ulysses interstellar neutral gas (GAS) instrument (Witte et al., 1992). EUVS measurements near solar maximum (max) in 1990–1992 have a peaked brightness maximum upwind due to a rather isotropic
solar wind charge-exchange ionization pattern (A=0–0.25). GAS measurements from solar minimum (min) in 1997 have a plateau in the upwind direction that we model using Ulysses
SWOOPS (solar wind plasma experiment) solar min data on solar wind density and velocity at different heliographic latitudes.
The isotropic ionization pattern deduced from EUVS at solar max may be consistent with recent SWOOPS results (McComas et al., 2000b, c) that high speed solar wind is absent at high latitudes during solar max. Galileo and Ulysses Lα data favor higher H temperatures (15 000–18 000 K) than previous models.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
8.
With Ulysses approaching the south solar polar latitudes during a period of high solar activity, it is for the first time possible to
study the distribution of solar energetic particles (SEPs) in solar latitude as well as in radius and longitude. From July
1997 to August 2000, Ulysses moved from near the solar equator at ∼5 AU to ∼67° S latitude at ∼3 AU. Using observations of >∼30 MeV protons from Ulysses and IMP-8 at Earth we find good correlation between large SEP increases observed at IMP and Ulysses, almost regardless of the relative locations of the spacecraft. The observations show that within a few days after injection
of SEPs, the flux in the inner heliosphere is often almost uniform, depending only weakly on the position of the observer.
No clear effect of the increasing solar latitude of Ulysses is evident. Since the typical latitudinal extent of CMEs, which most likely accelerate the SEPs, is only ∼30°, this suggests
that the enhanced cross-field propagation for cosmic rays and CIR-accelerated particles deduced from Ulysses’ high latitude studies near solar minimum is also true for SEPs near solar maximum.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
9.
Walter D. Gonzalez Ezequiel Echer Bruce T. Tsurutani Alicia L. Clúa de Gonzalez Alisson Dal Lago 《Space Science Reviews》2011,158(1):69-89
We present a review on the interplanetary causes of intense geomagnetic storms (Dst≤−100 nT), that occurred during solar cycle 23 (1997–2005). It was reported that the most common interplanetary structures
leading to the development of intense storms were: magnetic clouds, sheath fields, sheath fields followed by a magnetic cloud
and corotating interaction regions at the leading fronts of high speed streams. However, the relative importance of each of
those driving structures has been shown to vary with the solar cycle phase. Superintense storms (Dst≤−250 nT) have been also studied in more detail for solar cycle 23, confirming initial studies done about their main interplanetary
causes. The storms are associated with magnetic clouds and sheath fields following interplanetary shocks, although they frequently
involve consecutive and complex ICME structures. Concerning extreme storms (Dst≤−400 nT), due to the poor statistics of their occurrence during the space era, only some indications about their main interplanetary
causes are known. For the most extreme events, we review the Carrington event and also discuss the distribution of historical
and space era extreme events in the context of the sunspot and Gleissberg solar activity cycles, highlighting a discussion
about the eventual occurrence of more Carrington-type storms. 相似文献
10.
Issautier Karine Hoang Sang Moncuquet Michel Meyer-Vernet Nicole 《Space Science Reviews》2001,97(1-4):105-108
The Ulysses spacecraft is reaching high heliolatitudes during the approach to solar maximum. We show preliminary in situ electron observations
from the URAP experiment, using thermal noise spectroscopy. This method is especially suited to measure accurately the electron
density and thermal temperature. The data acquired in the period June–September 2000 are compared to those obtained at similar
heliolatitudes near solar activity minimum and in the ecliptic plane near both solar maximum and minimum.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
11.
Alexeev Igor I. Belenkaya Elena S. Bobrovnikov Sergey Yu. Kalegaev Vladimir V. 《Space Science Reviews》2003,107(1-2):7-26
A magnetohydrodynamic model of the solar wind flow is constructed using a kinematic approach. It is shown that a phenomenological
conductivity of the solar wind plasma plays a key role in the forming of the interplanetary magnetic field (IMF) component
normal to the ecliptic plane. This component is mostly important for the magnetospheric dynamics which is controlled by the
solar wind electric field. A simple analytical solution for the problem of the solar wind flow past the magnetosphere is presented.
In this approach the magnetopause and the Earth's bow shock are approximated by the paraboloids of revolution. Superposition
of the effects of the bulk solar wind plasma motion and the magnetic field diffusion results in an incomplete screening of
the IMF by the magnetopause. It is shown that the normal to the magnetopause component of the solar wind magnetic field and
the tangential component of the electric field penetrated into the magnetosphere are determined by the quarter square of the
magnetic Reynolds number. In final, a dynamic model of the magnetospheric magnetic field is constructed. This model can describe
the magnetosphere in the course of the severe magnetic storm. The conditions under which the magnetospheric magnetic flux
structure is unstable and can drive the magnetospheric substorm are discussed. The model calculations are compared with the
observational data for September 24–26, 1998 magnetic storm (Dst
min=−205 nT) and substorm occurred at 02:30 UT on January 10, 1997.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
12.
The Anisotropy Telescopes (ATs) instrument, part of the COSPIN experiment on board Ulysses, measures fluxes and anisotropies of protons in the MeV range. We survey data from this instrument throughout the Ulysses mission, with particular emphasis on solar maximum, when large particle intensities were measured. The only significant fluxes
detected by the ATs during solar minimum are those associated with corotating interaction regions. We focus on events characterised
by very large first-order anisotropies, indicating beam-like streaming along the magnetic field lines, and also on times of
unusually low and constant anisotropies. We describe the parameters associated with these events and put forward possible
physical explanations of the extreme anisotropies observed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
13.
The modulation of galactic cosmic rays in the heliosphere seems to be dominated by four major mechanisms: convection, diffusion,
drifts (gradient, curvature and current sheet), and adiabatic energy losses. In this regard the global structure of the solar
wind, the heliospheric magnetic field (HMF), the current sheet (HCS), and that of the heliosphere itself play major roles.
Individually, the four mechanisms are well understood, but in combination, the complexity increases significantly especially
their evolvement with time - as a function of solar activity. The Ulysses observations contributed significantly during the past solar minimum modulation period to establish the relative importance
of these major mechanisms, leading to renewed interest in developing more sophisticated numerical models, and in the underlying
physics, e.g., what determines the diffusion tensor. With increased solar activity, the relative contributions of the mentioned
mechanisms change, but how they change and what causes these changes over an 11-year solar cycle is not well understood. It
can therefore be expected that present and forthcoming observations during solar maximum activity will again produce very
important insights into the causes of long-term modulation. In this paper the basic theory of solar modulation is reviewed
for galactic cosmic rays. The influence of the Ulysses observations on the development of the basic theory and numerical models are discussed, especially those that have challenged
the theory and models. Model-based predictions are shown for what might be encountered during the next solar minimum. Lastly,
modulation theory and modelling are discussed for periods of maximum solar activity when a global reorganization of the HMF,
and the HCS, occurs.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
14.
Lario D. Haggerty D.K. Roelof E.C. Tappin S.J. Forsyth R.J. Gosling J.T. 《Space Science Reviews》2001,97(1-4):277-280
On day 49 of 1999 a strong interplanetary shock was observed by the ACE spacecraft located at 1 AU from the Sun. This shock
was followed 10 hours later by a magnetic cloud (MC). A large solar energetic particle (SEP) event was observed in association
with the arrival of the shock and the MC at ACE. The Ulysses spacecraft, located at 22° S heliolatitude and nearly the same
ecliptic longitude as ACE, observed a large SEP event beginning on day 54 that peaked with the arrival of a solar wind and
magnetic field disturbance on day 61. A magnetic cloud was observed by Ulysses on days 63–64. We suggest a scenario in which both spacecraft intercepted the same MC, although sampling different regions
of it. We describe the effects that the MC produced on the streaming of energetic particles at both spacecraft.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
15.
Radio occultation, ultraviolet, and white-light measurements have expanded our knowledge of the morphology of density and
velocity in polar coronal holes, and made it possible to carry out the first systematic comparisons between the Ulysses solar wind measurements and quantitative white-light observations of the solar corona. This paper summarizes the rationale
and salient features of this new approach which has been used to relate the solar wind observed by Ulysses in 1993–1995 to the inner corona. The statistical characteristics (average, standard deviation, and autocorrelation function)
of the Ulysses density measurements of the fast wind are found to be mirrored in those of polarized brightness measurements of path-integrated
density made by the High Altitude Observatory (HAO) Mauna Loa K-coronagraph at 1.15 R
⊙. These results reinforce the conclusions from comparisons between measurements of the outer and inner corona. They show that
the polar coronal hole extends radially into the solar wind, and that sources of the fast wind are not limited to coronal
holes.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
16.
We have performed a joint survey of anisotropic ≳40 keV electron events from August 1997 to September 2000 using the matched
detectors on the Ulysses (ULS)/HI-SCALE and the ACE/EPAM instruments. A computer algorithm selected events with strong, statistically significant
pitch-angle anisotropies. Electron pitch-angle distributions at ACE (∼1 AU) are often ‘beams’ that are strongly collimated
along the local interplanetary magnetic field (IMF). These flare-associated impulsive injections can display rapid rise times
(∼15 min) and slower decays, or more irregular intensity histories. At ULS, the electron intensities are lower and the time
histories smoother, but strong anisotropies are still observable, indicating direct, nearly field-aligned propagation outward
from the Sun. We focus on four event periods, selected from the survey, during times when the angle between the footpoints
of the IMF lines intersecting ACE and ULS is small. These events span three full years and cover a wide range of distances
and heliographic latitudes. We found one reasonably good association between impulsive electron events at ACE and ULS, and
two events with small field-aligned gradients.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
17.
We examine the occurrence and intensity of Langmuir wave activity (electrostatic waves at the electron plasma frequency) during
the solar minimum and solar maximum orbits of Ulysses. At high latitudes during the solar minimum orbit, occurrences of Langmuir waves in magnetic holes were frequent; in the
second orbit, they were less common. This difference, in comparison with observations from the first Ulysses fast heliolatitude scan, suggests that Langmuir wave activity in magnetic holes is enhanced in solar wind from polar coronal
holes.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
18.
Using a survey of anisotropic electron events in the energy range of ~40–300 keV observed by HI-SCALE on Ulysses, we have selected several time intervals during 1999 when Ulysses traveled from about 20° S at 5.2 AU (January 1999) to 42° S at 4.2 AU (January 2000). We compare these events with observations at ~1 AU using the nearly identical instrument, EPAM on ACE. In order to study the solar origins of these electrons using the imaging Nançay Radioheliograph, we further restricted the list of events to those in which interplanetary magnetic field lines with origins on the visible solar disk, intersected Ulysses. We find that not all the anisotropic electron events are observed by both spacecraft and there exists a strong dependence on the spacecraft's magnetic connection back to the Sun. We have identified the solar origin for five electron events using radio observations, and correlate these with interplanetary type-III radio emissions using the WIND/WAVES experiment. 相似文献
19.
The three-dimensional structure of the solar maximum modulation of cosmic rays in the heliosphere can be studied for the first
time by comparing observations from Ulysses at high solar latitudes to those from in-ecliptic spacecraft, such as IMP-8. Observations through mid-2000 show that changes
in modulation remain well correlated at Earth and Ulysses up to latitudes of ∼60° south. The observed changes seem to be best correlated with changes in the inclination of the heliospheric
current sheet. The spectral index of the proton spectra at energies <100 MeV in the ecliptic and at high latitudes remain
roughly consistent with the T
+1 spectrum expected from modulation models, while the spectral index of the helium spectrum at both locations has changed smoothly
from the flat or even negative index spectra characteristic of anomalous component fluxes toward the T
+1 galactic spectrum with increasing modulation. Intensities near the equator and at high latitude remain nearly equal, and
latitudinal gradients for nucleonic cosmic rays thus remain small (<1% deg−1) at solar maximum. In the most recent data fluxes of protons and helium with energies less than ∼100 MeV nucl−1 measured by Ulysses are smaller than those measured at IMP-8, suggesting that the gradients may have switched to become negative toward the poles
even before a clear reversal of polarity for the solar magnetic dipole has been completed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
20.
Ulysses observed well-defined stream interaction regions, SIRs, associated with solar wind stream structure up to a latitude of S65°
and shocks to at least a latitude of S71° during the second polar orbit. These SIRs and shocks produced a substantial heliospheric
processing of the solar wind. Only a subset of the SIRs recurred on successive solar rotations and only about half of the
well-defined SIRs observed poleward of S9.8° were bounded by forward-reverse shock pairs. The majority of the SIRs had local
magnetic topologies and azimuthal orientations similar to, but meridional tilts different from, those observed in the first
polar orbit when most SIRs corotated with the Sun. The irregular meridional tilts presumably were a consequence of a complex
coronal geometry and the temporally evolving nature of the solar wind flow at this time. A lack of reverse shocks poleward
of S54° (with one exception) and a lack of well defined SIRs poleward of S65° is evidence that SIRs develop more slowly with
distance at high latitudes.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献