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1.
Synoptic maps of white-light coronal brightness from SOHO/LASCO C2 and distributions of solar wind velocity obtained from
interplanetary scintillation are studied. Regions with velocity V≈300 – 450 km s−1 and increased density N>10 cm−3, typical of the “slow” solar wind originating from the belt and chains of streamers, are shown to exist at Earth’s orbit,
between the fast solar wind flows (with a maximum velocity V
max ≈450 – 800 km s−1). The belt and chains of streamers are the main sources of the “slow” solar wind. As the sources of “slow” solar wind, the
contribution from the chains of streamers may be comparable to that from the streamer belt. 相似文献
2.
The variation with position and view direction of heliospheric H-L scattered intensity seen by a L detector in the heliosphere is re-examined. Here, a frequency- and angle-dependent multiscattering calculation (Scherer, 1994; Scherer and Fahr, 1995) is used that takes into account the local thermodynamical conditions of the scattering agent, such as temperature, density and bulk velocity of the neutral interplanetary hydrogen, as given in a recent model by Osterbart and Fahr (1992). The calculated intensity patterns show strongly pronounced dependencies of the direction of the line of sight which are explained by effects of the Doppler shift in the resonance absorption and the dipole-phase function used in the multiscattering calculation. The theoretical results obtained with these computations nicely fit the intensities measured byPrognoz 5/6 probe (Lallement, Bertaux, and Dalaudier, 1985; Bertauxet al., 1985) without, however, assuming a latitude dependence of the solar wind mass outflow. This expresses the fact that, using an adequate radiation transport calculation, it is possible to explain thePrognoz andGalileo data without the need to specify anisotropic solar wind mass outflow from the corona preferred by several authors (Lallement, Bertaux, and Dalaudier, 1985; Lallement, 1989; Broadfoot and Kumar, 1978; Bertauxet al., 1985; Ajelloet al., 1994). In view of forthcomingUlysses solar wind measurements at polar latitudes this might be of importance to know. 相似文献
3.
Michael Schulz 《Astrophysics and Space Science》1973,24(2):371-383
The magnetohydrodynamics of solar-wind flow lead logically to the formation of one warped annular neutral surface that apparently
extends from ≈ 2r
⊙ (solar radii) to the boundary of the heliosphere. The most likely asymptotic configuration for this neutral sheet intersects
the heliomagnetic equatorial plane along four corotating arcs. The observer sees a reversal of magnetic polarity on each crossing
of the neutral surface, and so interprets each reversal as the crossing of a sector boundary. 相似文献
4.
Ultra-high resolution hydrodynamic simulations using 10243 grid points are performed of early supernova burst in a forming galaxy, with properties similar to those inferred for Lyman
α emitters (LAEs) and Lyman Break Galaxies (LBGs). We show that, at the earliest stages of less than 300 Myr, continual supernova
explosions produce multitudinous hot bubbles and cooled H(I) shells in-between. The H(I) shells radiate intense Lyman α (Lyα) emission like LAEs. We found that the bubbly structures produced are quite similar to the observed features in the Lyα surface brightness distribution of the extended LAEs. After 1 Gyr, the galaxies are dominated by stellar continuum radiation
and then resemble the LBGs. At this point, the abundance of heavy elements appears to be solar. After 13 Gyr, these galaxies
resemble present-day ellipticals. 相似文献
5.
J. L. Bertaux E. Quémerais R. Lallement E. Kyrölä W. Schmidt T. Summanen J. P. Goutail M. Berthé J. Costa T. Holzer 《Solar physics》1997,175(2):737-770
After one year of almost flawless operation on board the SOHO spacecraft poised at L1 Lagrange point, we report the main features
of SWAN observations. SWAN is mainly dedicated to the monitoring of the latitude distribution of the solar wind by the Lα
method. Maps of sky Lα emissions were recorded througout the year. The region of maximum emission, located in the upwind hemisphere,
deviates strongly from the pattern that could be expected from a solar wind constant with latitude. It is divided into two
lobes by a depression aligned with the solar equatorial plane called the Lyα groove already noted in 1976 Prognoz data. The
north lobe is much brighter than the south lobe. These two characteristics can be explained qualitatively by an enhanced ionization
along the neutral sheet where the slow solar wind is concentrated, which results from the higher low-latitude solar wind mass
flux as measured by Ulysses. The groove is the direct imprint on the sky of the enhanced carving by the slow solar wind, at
this time of solar minimum, when the tilt angle of the neutral sheet is small. The question is still pending to predict what
will happen with the ascending phase of the solar cycle. Observations of comets are briefly mentioned, with the ability of
SWAN to monitor the H2O production of many comets. Operations of the instrument are briefly described, including some instrumental problems which
could be solved by software modifications sent to the instrument.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1004979605559 相似文献
6.
We search for persistent and quasi-periodic release events of streamer blobs during 2007 with the Large Angle Spectrometric Coronagraph on the Solar and Heliospheric Observatory and assess the velocity of the slow solar wind along the plasma sheet above the corresponding streamer by measuring the dynamic
parameters of blobs. We find ten quasi-periodic release events of streamer blobs lasting for three to four days. In each day
of these events, we observe three – five blobs. The results are in line with previous studies using data observed near the
last solar minimum. Using the measured blob velocity as a proxy for that of the mean flow, we suggest that the velocity of
the background slow solar wind near the Sun can vary significantly within a few hours. This provides an observational manifestation
of the large velocity variability of the slow solar wind near the Sun. 相似文献
7.
An analysis and interpretation of reflected solar Lyman α intensity data acquired with the Hubble Space Telescope (HST) implies
an equatorially confined atmosphere with SO2 column densities ∼ 1–2 × 1016 cm-2. Poleward of 30° the SO2 density must decrease sharply reaching an asymptotic polar value of < 1015 cm-2 at 45° to achieve the observed 2 kR intensity peaks. The corresponding surface reflectivities must be either a constant 0.047
for higher equatorial SO2 or a variable reflectivity of 0.027 with lower SO2 densities at the equator increasing to a polar value of ∼ 0.05. The average residence time for an atmospheric SO2 molecule is ∼ 2–3 days for the canonical mass loading rate of the Io plasma torus = 1030 amu s-1. With atomic hydrogen in the atmosphere and corona constrained by the HST observations, it is estimated that a pickup proton
density ratio of 0.25–0.4% can be sustained by a supply of Io plasma torus protons neutralized in Io's atmosphere/exosphere,
if protons constitute 7% of the total torus ion density, which is close to the Chust et al. (1999) pickup proton density ratio and under the widely quoted 10% proton content of the torus.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
It is well known that the interaction of an interplanetary coronal mass ejection (ICME) with the solar wind leads to an equalisation
of the ICME and solar wind velocities at 1 AU. This can be understood in terms of an aerodynamic drag force per unit mass
of the form F
D/M=−(ρe
AC
D/M)(V
i−V
e)∣V
i−V
e∣, where A and M are the ICME cross-section and sum of the mass and virtual mass, V
i and V
e the speed of the ICME and solar wind, ρe the solar wind density, C
D a dimensionless drag coefficient, and the inverse deceleration length γ=ρe
A/M. The optimal radial parameterisation of γ and C
D beyond approximately 15 solar radii is calculated. Magnetohydrodynamic simulations show that for dense ICMEs, C
D varies slowly between the Sun and 1 AU, and is of order unity. When the ICME and solar wind densities are similar, C
D is larger (between 3 and 10), but remains approximately constant with radial distance. For tenuous ICMEs, the ICME and solar
wind velocities equalise rapidly due to the very effective drag force. For ICMEs denser that the ambient solar wind, both
approaches show that γ is approximately independent of radius, while for tenuous ICMEs, γ falls off linearly with distance.
When the ICME density is similar to or less than that in the solar wind, inclusion of virtual mass effects is essential. 相似文献
9.
An investigation of the fine ray structure of the coronal streamer belt using LASCO data 总被引：3，自引：0，他引：3
It is shown that within R>3–4 Rfrom the solar center the coronal streamer belt consists in a sequence of radial brightness rays. A minimum angular size of the individual ray d2.0°–2.5°, which is about the same in the directions normal to and along the streamer-belt, is independent of the distance from the Sun at R=4–6 R. The lifetime of the rays can exceed 10 days. From time to time, inhomogeneities of material inside the rays begin to move in the antisunward direction. Plots of increase in their velocity with the distance from the Sun are similar to those obtained by Sheeley et al. (1997) for inhomogeneities that are carried by a quasi-stationary solar wind in streamers. It is concluded that the phenomena discussed in this paper and by Sheeley et al. (1997) share a common origin. It is suggested that a different origin of solar wind flows in streamers and in coronal holes may be associated with a different character of flows in microtubes of the magnetic field comprising a total solar wind flow. These tubes are observed as brightness rays in streamer belts and plumes in coronal holes. 相似文献
10.
Unipolar streamers (also known as pseudo-streamers) are coronal structures that, at least in coronagraph images, and when
viewed at the correct orientation, are often indistinguishable from dipolar (or “standard”) streamers. When interpreted with
the aid of a coronal magnetic field model, however, they are shown to consist of a pair of loop arcades. Whereas dipolar streamers
separate coronal holes of the opposite polarity and whose cusp is the origin of the heliospheric current sheet, unipolar streamers
separate coronal holes of the same polarity and are therefore not associated with a current sheet. In this study, we investigate
the interplanetary signatures of unipolar streamers. Using a global MHD model of the solar corona driven by the observed photospheric
magnetic field for Carrington rotation 2060, we map the ACE trajectory back to the Sun. The results suggest that ACE fortuitously
traversed through a large and well-defined unipolar streamer. We also compare heliospheric model results at 1 AU with ACE
in-situ measurements for Carrington rotation 2060. The results strongly suggest that the solar wind associated with unipolar streamers
is slow. We also compare predictions using the original Wang–Sheeley (WS) empirically determined inverse relationship between
solar wind speed and expansion factor. Because of the very low expansion factors associated with unipolar streamers, the WS
model predicts high speeds, in disagreement with the observations. We discuss the implications of these results in terms of
theories for the origin of the slow solar wind. Specifically, premises relying on the expansion factor of coronal flux tubes
to modulate the properties of the plasma (and speed, in particular) must address the issue that while the coronal expansion
factors are significantly different at dipolar and unipolar streamers, the properties of the measured solar wind are, at least
qualitatively, very similar. 相似文献
11.
B. V. Jackson J. A. Boyer P. P. Hick A. Buffington M. M. Bisi D. H. Crider 《Solar physics》2007,241(2):385-396
Interplanetary Scintillation (IPS) allows observation of the inner heliospheric response to corotating solar structures and
coronal mass ejections (CMEs) in scintillation level and velocity. With colleagues at STELab, Nagoya University, Japan, we
have developed near-real-time access of STELab IPS data for use in space-weather forecasting. We use a 3D reconstruction technique
that produces perspective views from solar corotating plasma and outward-flowing solar wind as observed from Earth by iteratively
fitting a kinematic solar wind model to IPS observations. This 3D modeling technique permits reconstruction of the density
and velocity structure of CMEs and other interplanetary transients at a relatively coarse resolution: a solar rotational cadence
and 10° latitudinal and longitudinal resolution for the corotational model and a one-day cadence and 20° latitudinal and longitudinal
heliographic resolution for the time-dependent model. This technique is used to determine solar-wind pressure (“ram” pressure)
at Mars. Results are compared with ram-pressure observations derived from Mars Global Surveyor magnetometer data (Crider et al.
2003, J. Geophys. Res.
108(A12), 1461) for the years 1999 through 2004. We identified 47 independent in situ pressure-pulse events above 3.5 nPa in the Mars Global Surveyor data in this time period where sufficient IPS data were available. We detail the large pressure pulse observed at Mars in
association with a CME that erupted from the Sun on 27 May 2003, which was a halo CME as viewed from Earth. We also detail
the response of a series of West-limb CME events and compare their response observed at Mars about 160° west of the Sun – Earth
line by the Mars Global Surveyor with the response derived from the IPS 3D reconstructions. 相似文献
12.
As known for a long time, interstellar wind neutral helium atoms deeply penetrate into the inner heliosphere and, when passing through the solar gravity field, form a strongly pronounced helium density cone in the downwind direction. Helium atoms are photoionized and picked-up by the solar wind magnetic field, but as pick-up ions they are not simply convected outwards with the solar wind in radial directions as assumed in earlier publications. Rather they undergo a complicated diffusion-convection process described here by an appropriate kinetic transport equation taking into account adiabatic cooling and focusing, pitch angle scattering and energy diffusion. In this paper, we solve this equation for He+pick-up ions which are injected into the solar wind mainly in the region of the helium cone. We show the resulting He+pick-up ion density profile along the orbit of the Earth in many respects differs from the density profile of the neutral helium cone: depending on solar-wind-entrained Alfvénic turbulence levels, the density maximum when looking from the Earth to the Sun is shifted towards the right side of the cone, the ratio of peak-densities to wing-densities varies and a left-to-right asymmetry of the He+-density profile is pronounced. Derivation of interstellar helium parameters from these He+-structures, such as the local interstellar medium (LISM) wind direction, LISM velocity and LISM temperature, are very much impeded. In addition, the pitch-angle spectrum of He+pick-up ions systematically becomes more anisotropic when passing from the left to the right wing of the cone structure. All effects mentioned are more strongly pronounced in high velocity solar wind compared to the low velocity solar wind. 相似文献
13.
Increasing the effective spatial resolution when analyzing LASCO-C2/SOHO data helped to reveal the existence of double-ray
structure in the streamer belt, both in the absence and presence of belt bends. Streamer-belt rays located in the plane of
the sky are demonstrated to deviate poleward (north- and southward, respectively, in the N and S hemispheres) at distances
R < 4{–}5R⊙ from the Sun center. These new results concerning streamer belt structure are important as the basis for checking a theory
claiming to adequately describe physical processes in the corona. 相似文献
14.
S.R. Prabhakaran Nayar V. Sanalkumaran Nair V.N. Radhika K. Revathy 《Solar physics》2001,201(2):405-417
The solar wind plasma exhibits many features of the solar surface passed on to the interplanetary medium as temporal variations
due to the solar rotation. The yearly average values of solar wind velocity, and geomagnetic index A
p during 1965–1999 were found to exhibit long period evolution. They were found to peak around the declining phase of each
solar cycle. While the solar wind velocity peaks around the second half of the declining phase, the IMF field strength increases
around the first half of the declining phase of each solar cycle. The power spectrum of these parameters shows peaks around
37-day, 30-day, 27-day, 13.5-day, 9-day, and 7-day periods. The temporal evolution of the power spectrum of the solar wind
plasma parameters and the geomagnetic activity index A
p are also studied in detail and presented with the help of contour graphs. These studies indicate that the strength of the
quasi-periodicities in the interplanetary medium evolves with time. 相似文献
15.
A technique is proposed for separating the rays of the streamer belt with quasi-stationary and non-stationary solar wind (SW) flows. It is shown that the lifetime of rays with a quasi-stationary SW can exceed 20 days. A new method has been developed for measuring the relative density distribution of a quasi-stationary slow SW flowing along the streamer belt's ray of increased brightness, based on the LASCO/SOHO data. It is shown that the density n for such SW flows varies with the radius R according to the relationship nR
–, where =13.3–3.9 within 4 R
0 R 6 R
0 (here R
0 is the solar radius), and decreases gradually further away. It is also shown that the V(R)-profiles in some rays of the streamer belt differ little from each other, although the value of the mass flow density, j
E, at the Earth's orbit in them can vary more than by a factor of 4. This distinguishes in a crucial respect a slow SW in the streamer belt's rays from a fast SW originating in coronal holes, for which j
Econstant and the dependences V(R) in different fast flows can differ greatly. 相似文献
16.
Observations of interplanetary magnetic field polarity, solar wind speed, and geomagnetic disturbance index (C9) during the years 1962–1975 are compared in a 27-day pictorial format that emphasizes their associated variations during the sunspot cycle. This display accentuates graphically several recently reported features of solar wind streams including the fact that the streams were faster, wider, and longer-lived during 1962–1964 and 1973–1975 in the declining phase of the sunspot cycle than during intervening years (Bame et al., 1976; Gosling et al., 1976). The display reveals strikingly that these high-speed streams were associated with the major, recurrent patterns of geomagnetic activity that are characteristic of the declining phase of the sunspot cycle. Finally, the display shows that during 1962–1975 the association between long-lived solar wind streams and recurrent geomagnetic disturbances was modulated by the annual variation (Burch, 1973) of the response of the geomagnetic field to solar wind conditions. The phase of this annual variation depends on the polarity of the interplanetary magnetic field in the sense that negative sectors of the interplanetary field have their greatest geomagnetic effect in northern hemisphere spring, and positive sectors have their greatest effect in the fall. During 1965–1972 when the solar wind streams were relatively slow (500 km s-1), the annual variation strongly influenced the visibility of the corresponding geomagnetic disturbance patterns.Visiting Scientist, Kitt Peak National Observatory, Tucson, Arizona.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. 相似文献
17.
The model of the solar wind interaction with interstellar medium suggested by Baranovet al. (1970) is developed. In this model (TSM) the presence of two shock waves is assumed, through which the solar wind and interstellar gas pass, the latter moving relative to the Sun at supersonic speed (20 km s–1).The distance between shocks was considered earlier (Baranovet al., 1970; Baranov and Krasnobaev, 1971) to be small compared with their distance from the Sun, due to the hypersonic character of the flow. The structure of the subsonic flow portion may not be taken into account.In the present paper the distribution of the gas parameters in the region between shocks is calculated which, in particular, allows us to estimate the possibility of its experimental detection, observing radio-scintillation on interstellar irregularities (Baranovet al., 1975).The possible influence on the model of galactic hydrogen neutral atoms penetrating into interplanetary medium is estimated. 相似文献
18.
It is shown on the basis of analyzing the LASCO/SOHO data that the main quasi-stationary solar wind (SW), with a typical lifetime of up to 10 days, flows in the rays of the streamer belt. Depending on R, its velocity increases gradually from V3 km s–1 at R1.3 R
to V170 km s–1 at R15 R
. We have detected and investigated the movement of the leading edge of the main solar wind at the stage when it occupied the ray, i.e., at the formative stage of a quasi-stationary plasma flow in the ray. It is shown that the width of the leading edge of the main SW increases almost linearly with its distance from the Sun. It is further shown that the initial velocity of the inhomogeneities (`blobs') that travel in the streamer belt rays increases with the distance from the Sun at which they originate, and is approximately equal to the velocity of the main solar wind which carries them away. The characteristic width of the leading edge of the `blob' R
, and remains almost unchanging as it moves away from the Sun. Estimates indicate that the main SW in the brightest rays of the streamer belt to within distances at least of order R3 R
represents a flow of collisional magnetized plasma along a radial magnetic field. 相似文献
19.
Eric Quémerais Bill R. Sandel J.L. Bertaux R. Lallement 《Astrophysics and Space Science》2000,274(1-2):123-132
We present the Lyman α sky background data obtained by the UV spectrometers on the Voyager 1 and 2 spacecraft between 1993
and early 1998. These data which consist of special maneuvers dedicated to the study of the Lyα pattern in the outer heliosphere
represent a unique opportunity to constrain the hydrogen distribution in the outer heliosphere.A first analysis of the data
is presented. This consists of a comparison with a Hot Model of the hydrogen distribution combined with a radiative transfer
calculation in the hypothesis of Complete Frequency Redistribution. We confirm previous measurements showing the existence
of an excess in Lyα background in the upwind direction. The radial variation of the upwind intensity measurements found from
the two Voyager data sets are different. The Voyager 1 data show a radial decrease following r
-1.4 whereas the Voyager 2 data yield r
-0.79. These values have been derived after correction for solar flux variations using the SOLSTICE/UARS data set.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
20.
A. H. Gabriel 《Solar physics》1971,21(2):392-400
As a result of a collaborative rocket experiment carried out during the solar eclipse on 7 March, 1970, measurements have been made of the brightness of Lyman from the corona, at heights between 5 × 104 and 5 × 105 km above the limb. The emission is shown to occur primarily through the resonance scattering of chromospheric Lyman from the residual neutral hydrogen in the corona. Both the absolute value and radial fall-off of the brightness agree well with calculations based on solar density models. The Lyman emission has similar variations around the limb to the white light corona, showing in particular an equatorial enhancement. 相似文献