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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 transfer of wave energy to plasma energy is a very crucial issue in coronal holes and helmet streamer regions. Mixed mode
Alfvén waves, also known as kinetic Alfvén wave (KAW) can play an important role in the energization of the plasma particles
because of their potential ability to heat and accelerate the plasma particles via Landau damping. This paper presents an
investigation of the growth of a Gaussian perturbation on a non-uniform kinetic Alfvén wave having Gaussian wave front. The
effect of the nonlinear coupling between the main KAW and the perturbation has been studied. The dynamical equations for the
field of the main KAW and the perturbation have been established and their semi-analytical solution has been obtained in the
low (β≪ me/mi≪ 1) and the high (β≫ me/mi≪ 1) β cases. The critical field of the main KAW and the perturbation has been evaluated. Nonlinear evolution of the main
KAW and the perturbation into the filamentary structures and its dependence on various parameters of the solar wind and the
solar corona have been investigated in detail. These filamentary structures can act as a source for the particle acceleration
by wave particle interaction because the KAWs are mixed modes and Landau damping is possible. Especially, in the solar corona,
the low β and the high β cases could correspond to the coronal holes and the helmet streamer. The presence of the primary
and the secondary filaments of the perturbation may change the spectrum of the Alfvénic turbulence in the solar wind. 相似文献
3.
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
4.
In this paper we have investigated the beat wave excitation of an ion-acoustic wave at the difference frequency of two kinetic
(or shear) Alfvén waves propagating in a magnetized plasma with β<1 (β=8π
n
e0
T
e/B
0
2
, where n
e0 is the unperturbed electron number density, T
e is the electron temperature, and B
0 is the external magnetic field). On account of the interaction between two kinetic Alfvén waves of frequencies ω
1 and ω
2, the ponderomotive force at the difference frequency ω
1−ω
2 leads to the generation of an ion-acoustic wave. Also because of the filamentation of the Alfvén waves, magnetic-field-aligned
density dips are observed. In this paper we propose that the ion-acoustic wave generated by this mechanism may be one of the
possible mechanisms for the heating and acceleration of solar wind particles. 相似文献
5.
Starting with a large number (N=100) of Wind magnetic clouds (MCs) and applying necessary restrictions, we find a proper set of N=29 to investigate the average ecliptic plane projection of the upstream magnetosheath thickness as a function of the longitude
of the solar source of the MCs, for those cases of MCs having upstream shock waves. A few of the obvious restrictions on the
full set of MCs are the need for there to exist a driven upstream shock wave, knowledge of the MC’s solar source, and restriction
to only MCs of low axial latitudes. The analysis required splitting this set into two subsets according to average magnetosheath
speed: slow/average (300 – 500 km s−1) and fast (500 – 1100 km s−1) speeds. Only the fast set gives plausible results, where the estimated magnetosheath thickness (ΔS) goes from 0.042 to 0.079 AU (at 1 AU) over the longitude sector of 0° (adjusted source-center longitude of the average magnetic
cloud) to 40° off center (East or West), based on N=11 appropriate cases. These estimates are well determined with a sigma (σ) for the fit of 0.0055 AU, where σ is effectively the same as
(chi-squared) for the appropriate quadratic fit. The associated linear correlation coefficient for ΔS versus |Longitude| was very good (c.c.=0.93) for the fast range, and ΔS at 60° longitude is extrapolated to be 2.7 times the value at 0°. For the slower speeds we obtain the surprising result that
ΔS is typically more-or-less constant at 0.040±0.013 AU at all longitudes, indicating that the MC as a driver, when moving close
to the normal solar wind speed, has little influence on magnetosheath thickness. In some cases, the correct choice between
two candidate solar-source longitudes for a fast MC might be made by noting the value of the observed ΔS just upstream of the MC. Also, we point out that, for the 29 events, the average sheath speed was well correlated with the
quantity ΔV[=(〈V
MC〉−〈V
UPSTREAM〉)], and also with both 〈V
MC〉 and 〈V
MC,T〉, where 〈V
MC〉 is the first one-hour average of the MC speed, 〈V
MC,T〉 is the average MC speed across the full MC, and 〈V
UPSTREAM〉 is a five-hour average of the solar wind speed just upstream of the shock. 相似文献
6.
Electromagnetic instabilities in high-β plasmas, where β is the ratio of the kinetic plasma energy to the magnetic energy, have a broad range of astrophysical applications. The presence
of temperature anisotropies T
∥
/T
⊥
>1 (where ∥ and ⊥ denote directions relative to the background magnetic field) in solar flares and the solar wind is sustained by the observations
and robust acceleration mechanisms that heat plasma particles in the parallel direction. The surplus of parallel kinetic energy
can excite either the Weibel-like instability (WI) of the ordinary mode perpendicular to the magnetic field or the firehose
instability (FHI) of the circularly polarized waves at parallel propagation. The interplay of these two instabilities is examined.
The growth rates and the thresholds provided by the kinetic Vlasov – Maxwell theory are compared. The WI is the fastest growing
one with a growth rate that is several orders of magnitude larger than that of the FHI. These instabilities are however inhibited
by the ambient magnetic field by introducing a temperature anisotropy threshold. The WI admits a larger anisotropy threshold,
so that, under this threshold, the FHI remains the principal mechanism of relaxation. The criteria provided here by describing
the interplay of the WI and FHI are relevant for the existence of these two instabilities in any space plasma system characterized
by an excess of parallel kinetic energy. 相似文献
7.
I. Sabbah 《Solar physics》2007,245(1):207-217
Neutron monitor data observed at Climax (CL) and Huancayo/Haleakala (HU/HAL) have been used to calculate the amplitude A of the 27-day variation of galactic cosmic rays (CRs). The median primary rigidity of response, R
m, for these detectors encompasses the range 18 ≤R
m≤46 GV and the threshold rigidity R
0 covers the range 2.97≤R
0≤12.9 GV. The daily average values of CR counts have been harmonically analyzed for each Bartels solar rotation (SR) during
the period 1953 – 2001. The amplitude of the 27-day CR variation is cross-correlated to solar activity as measured by the
sunspot number R, the interplanetary magnetic field (IMF) strength B, the z-component B
z
of the IMF vector, and the tilt angle ψ of the heliospheric current sheet (HCS). It is anticorrelated to the solar coronal
hole area (CHA) index as well as to the solar wind speed V. The wind speed V leads the amplitude by 24 SRs. The amplitude of the 27-day CR variation is better correlated to each of the these parameters
during positive solar polarity (A>0) than during negative solar polarity (A<0) periods. The CR modulation differs during A>0 from that during A<0 owing to the contribution of the z-component of the IMF. It differs during A
1>0 (1971 – 1980) from that during A
2>0 (1992 – 2001) owing to solar wind speed. 相似文献
8.
This paper presents the model equations governing the nonlinear interaction between dispersive Alfvén wave (DAW) and magnetosonic
wave in the low-β plasmas (β≪m
e/m
i; known as inertial Alfvén waves (IAWs); here
\upbeta = 8pn0T /B02\upbeta = 8\pi n_{0}T /B_{0}^{2} is thermal to magnetic pressure, n
0 is unperturbed plasma number density, T(=T
e≈T
i) represents the plasma temperature, and m
e(m
i) is the mass of electron (ion)). This nonlinear dynamical system may be considered as the modified Zakharov system of equations
(MZSE). These model equations are solved numerically by using a pseudo-spectral method to study the nonlinear evolution of
density cavities driven by IAW. We observed the nonlinear evolution of IAW magnetic field structures having chaotic behavior
accompanied by density cavities associated with the magnetosonic wave. The relevance of these investigations to low-β plasmas
in solar corona and auroral ionospheric plasmas has been pointed out. For the auroral ionosphere, we observed the density
fluctuations of ∼ 0.07n
0, consistent with the FAST observation reported by Chaston et al. (Phys. Scr.
T84, 64, 2000). The heating of the solar corona observed by Yohkoh and SOHO may be produced by the coupling of IAW and magnetosonic wave via filamentation process as discussed here. 相似文献
9.
Statistical Comparison of Magnetic Clouds with Interplanetary Coronal Mass Ejections for Solar Cycle 23 总被引：1，自引：0，他引：1
We compare the number and characteristics of interplanetary coronal mass ejections (ICMEs) to those of magnetic clouds (MCs)
by using in-situ solar wind plasma and magnetic field observations made at 1 AU during solar cycle 23. We found that ≈ 28% of ICMEs appear
to contain MCs, since 103 magnetic clouds (MCs) occurred during 1995 – 2006, and 307 ICMEs occurred during 1996 – 2006. For
the period between 1996 and 2006, 85 MCs are identified as part of ICMEs, and six MCs are not associated with ICMEs, which
conflicts with the idea that MCs are usually a subset of ICMEs. It was also found that solar wind conditions inside MCs and
ICMEs are usually similar, but the linear correlation between geomagnetic storm intensity (Dst
min ) and relevant solar wind parameters is better for MCs than for ICMEs. The differences between average event duration (Δt) and average proton plasma β (〈β〉) are two of the major differences between MCs and ICMEs: i) the average duration of ICMEs (29.6 h) is 44% longer than for MCs (20.6 hours), and ii) the average of 〈β〉 is 0.01 for MCs and 0.24 for ICMEs. The difference between the definition of a MC and that for an ICME is one of the major
reasons for these average characteristics being different (i.e., listed above as items i) and ii)), and it is the reason for the frequency of their occurrences being different. 相似文献
10.
Comet outburst activity and the structure of solar wind streams were compared on the basis of Pioneer 10, 11, Vela 3 and IMP
7, 8 measurements at the heliocentric distance r ≈ 1–6 AU. It is shown that the solar wind velocity waves which are evolving into corotating shock waves beyond the Earth
orbit may be responsible for comet outburst activity. The correlation between variations of comet outburst activity with heliocentric
distance and the behavior of the solar wind velocity waves is established. The closeness of the characteristic times for the
velocity waves and comet outburst activity (7–8 days at r = 1 AU) as well as the simultaneous growth of both the characteristic times with r are noted. The observed distribution of the comet outburst activity parameters during the 11-year cycle is also in good agreement
with the phase distributions during the 11-year cycle of variations of the coronal hole areas and the rate of change of the
sunspot area δS
p. 相似文献
11.
T.S. Bastian 《Astrophysics and Space Science》2001,277(1-2):107-116
Radio wave propagation through an inhomogeneous, random plasma produces a variety of observable phenomena – group delay, Faraday
rotation, refraction, angular broadening, spectral broadening, and scintillations in phase, amplitude, and frequency. These
may be exploited to constrain the mean and fluctuating properties of the medium through a variety of remote sensing techniques.
In the case of the solar corona and the solar wind, the mean density, magnetic field, solar wind speed, and the spatial spectrum
of the density fluctuation scan all be constrained in regions that are inaccessible to in situmeasurements.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
A technique for determining the effective temperature T
eff
and the acceleration of gravity log g of F and G supergiants is discussed using four bright stars as examples, specifically two F supergiants, α Lep(F0 Ib) and
π Sgr (F2 II), and two G supergiants, β Aqr (G0 Ib) and α Aqr (G2 Ib). In all four cases the parameter log g was derived from the high precision parallaxes recently obtained by van Leeuwen in a new reduction of data from Hipparcos.
Because of this, the accuracy of the determinations of log g is much greater than before. Estimates of the parameter T
eff
were checked using accurate values of T
eff
obtained previously by the infrared flux method (IRFM). In the case of the early F supergiants, this method confirms the
good accuracy of the T
eff
values derived from the Balmer lines and the β-index. Measurements of the Balmer lines for the G supergiants are difficult
because of strong blending, so the indices [c
1] and β serve as indicators of T
eff
. It is shown that the indices [c
1] and β yield a systematic difference in the values of T
eff
; the IRFM confirms that deriving T
eff
from the index [c
1] is more accurate. Based on the values of T
eff
and log g that have been found here, with the aid of the evolutionary tracks, we estimate the mass M and age t of each star. The Fe II lines, which are insensitive to departures from LTE, have been used to determine the microturbulence
parameter V
t
and the iron abundance. The latter is close to the solar iron abundance. Some problems concerning the chemical composition
of these stars are discussed using the supergiant α Lep as an example.
Translated from Astrofizika, Vol. 52, No. 2, pp. 237–257 (May 2009). 相似文献
13.
We analyze the relationship between the coronal hole (CH) area/position and physical characteristics of the associated corotating
high-speed stream (HSS) in the solar wind at 1 AU. For the analysis we utilize the data in the period DOY 25 – 125 of 2005,
characterized by a very low coronal mass ejection (CME) activity. Distinct correlations between the daily averaged CH parameters
and the solar wind characteristics are found, which allows us to forecast the solar wind velocity v, proton temperature T, proton density n, and magnetic field strength B, several days in advance in periods of low CME activity. The forecast is based on monitoring fractional areas A, covered by CHs in the meridional slices embracing the central meridian distance ranges [−40°,−20°], [−10°,10°], and [20°,40°].
On average, the peaks in the daily values of n, B, T, and v appear delayed by 1, 2, 3, and 4 days, respectively, after the area A attains its maximum in the central-meridian slice. The peak values of the solar wind parameters are correlated to the peak
values of A, which provides also forecasting of the peak values of n, B, T, and v. The most accurate prediction can be obtained for the solar wind velocity, for which the average relative difference between
the calculated and the observed peak values amounts to
%. The forecast reliability is somewhat lower in the case of T, B, and n (
, 30, and 40%, respectively). The space weather implications are discussed, including the perspectives for advancing the real-time
calculation of the Sun – Earth transit times of coronal mass ejections and interplanetary shocks, by including more realistic
real-time estimates of the solar wind characteristics. 相似文献
14.
P. K. Manoharan 《Solar physics》2006,235(1-2):345-368
Knowledge of the radial evolution of the coronal mass ejection (CME) is important for the understanding of its arrival at
the near-Earth space and of its interaction with the disturbed/ambient solar wind in the course of its travel to 1 AU and
further. In this paper, the radial evolution of 30 large CMEs (angular width > 150∘, i.e., halo and partial halo CMEs) has been investigated between the Sun and the Earth using (i) the white-light images of
the near-Sun region from the Large Angle Spectroscopic Coronagraph (LASCO) onboard SOHO mission and (ii) the interplanetary scintillation (IPS) images of the inner heliosphere obtained from the Ooty Radio Telescope (ORT). In the LASCO field of view at heliocentric
distances R≤30 solar radii (R⊙), these CMEs cover an order of magnitude range of initial speeds, VCME≈260–2600 km s−1. Following results have been obtained from the speed evolution of these CMEs in the Sun–Earth distance range: (1) the speed
profile of the CME shows dependence on its initial speed; (2) the propagation of the CME goes through continuous changes,
which depend on the interaction of the CME with the surrounding solar wind encountered on the way; (3) the radial-speed profiles
obtained by combining the LASCO and IPS images yield the factual view of the propagation of CMEs in the inner heliosphere
and transit times and speeds at 1 AU computed from these profiles are in good agreement with the actual measurements; (4)
the mean travel time curve for different initial speeds and the shape of the radial-speed profiles suggest that up to a distance
of ∼80 R⊙, the internal energy of the CME (or the expansion of the CME) dominates and however, at larger distances, the CME's interaction
with the solar wind controls the propagation; (5) most of the CMEs tend to attain the speed of the ambient flow at 1 AU or
further out of the Earth's orbit. The results of this study are useful to quantify the drag force imposed on a CME by the
interaction with the ambient solar wind and it is essential in modeling the CME propagation. This study also has a great importance
in understanding the prediction of CME-associated space weather at the near-Earth environment. 相似文献
15.
The comparison of the brightness and area of coronal holes (CH) to the solar wind speed, which was started by Obridko et al. (Solar Phys.
260, 191, 2009a) has been continued. While the previous work was dealing with a relatively short time interval 2000 – 2006, here we have
analyzed the data on coronal holes observed in the Sun throughout activity Cycle 23. A catalog of equatorial coronal holes
has been compiled, and their brightness and area variations during the cycle have been analyzed. It is shown that CH is not
merely an undisturbed zone between the active regions. The corona heating mechanism in CH seems to be essentially the same
as in the regions of higher activity. The reduced brightness is the result of a specific structure with the magnetic field
being quasi-radial at as low an altitude as 1.1R
⊙ or a bit higher. The plasma outflow decreases the measure of emission from CH. With an adequate choice of the photometric
boundaries, the CH area and brightness indices display a fairly high correlation (0.6 – 0.8) with the solar wind velocity
throughout the cycle, except for two years, which deviate dramatically – 2001 and 2007, i.e., the maximum and the minimum of the cycle. The mean brightness of the darkest part of CH, where the field lines are nearly
radial at low altitudes, is of the order of 18 – 20% of the solar brightness, while the brightness of the other parts of the
CH is 30 – 40%. The solar wind streams originate at the base of the coronal hole, which acts as an ejecting nozzle. The solar
wind parameters in CH are determined at the level where the field lines are radial. 相似文献
16.
L. K. Jian C. T. Russell J. G. Luhmann R. M. Skoug J. T. Steinberg 《Solar physics》2008,250(2):375-402
We have performed a survey of the characteristics of two types of large spatial-scale solar-wind structures, stream interaction
regions (SIRs), and interplanetary coronal mass ejections (ICMEs), near 5.3 AU, using solar-wind observations from Ulysses. Our study is confined to the three aphelion passes of Ulysses, and also within ± 10° of the solar ecliptic plane, covering a part of 1992, 1997 – 1998, and 2003 – 2005, representing three
slices of different phases of the solar activity cycle. Overall, there are 54 SIRs and 60 ICMEs in the survey. Many are merged
in hybrid events, suggesting that they have undergone multiple interactions prior to reaching Jovian orbit. About 91% of SIRs
occur with shocks, with 47% of such shocks being forward – reverse shock pairs. The solar-wind velocity sometimes stays constant
or even decreases within the interaction region near 5.3 AU, in contrast with the gradual velocity increase during SIRs at
1 AU. Shocks are driven by 58% of ICMEs, with 94% of them being forward shocks. Some ICMEs seem to have multiple small flux
ropes with different scales and properties. We quantitatively compare various properties of SIRs and ICMEs at 5.3 AU, and
study their statistical distributions and variations with solar activity. The width, maximum dynamic pressure, and peak perpendicular
pressure of SIRs all become larger than ICMEs. Dynamic pressure (P
dyn) is expected to be important for Jovian magnetospheric activity. We have examined the distributions of P
dyn of SIRs, ICMEs, and general solar wind, but these cannot explain the observed bimodal distribution of the location of the
Jovian magnetopause. By comparing the properties of SIRs and ICMEs at 0.72, 1, and 5.3 AU, we find that the ICME expansion
slows down significantly between 1 and 5.3 AU. Some transient and small streams in the inner heliosphere have merged into
a single interaction region.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
17.
P.A. Dalin G.N. Zastenker K.I. Paularena J.D. Richardson 《Astrophysics and Space Science》2001,277(1-2):323-324
Solar wind measurements on board several spacecraft were used to study the two-points correlations of the solar wind plasma
structures. The factor shaving the most influence on the correlation level are the density variability and IMF cone angle.
The characteristic length of large solar wind structures is estimated at 500–1000 R
E.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
Astrometric observations at different zenith distances have been performed in Dresden in an area centered atNGC 6791 where there are some stars with reliable color information (widely dispersed spectral types in the MK systemand color indices BT – VT) as well as with accurate positions from Tycho‐2 catalog. The results are used to estimate how significant improvements in stellar positions may be when accurate corrections for color refraction are taken into account. We have treated two cases for refraction calculations: (1) a photometric case for color indices and (2) a spectral case for spectral types and luminosity classes. To calculate refraction we use Stone's modified computer code (Malyuto & Meinel 2000). To treat the photometric case we have calculated the synthetic color indices for the spectral energy distributions of Sviderskiene (1988). The positional improvements due to including color refraction corrections are significant and slightly larger in the spectral case. An improvement of about 15% is reached at a zenith distance of 65°. Our basic conclusion is that color refraction should be taken into account for obtaining accurate stellar positions from ground based observations at larger zenith distances. Reliable refraction corrections may be calculated from spectral and/or photometric data. 相似文献
19.
Recent numerical investigations of wave propagation near coronal magnetic null points (McLaughlin and Hood: Astron. Astrophys.
459, 641, 2006) have indicated how a fast MHD wave partially converts into a slow MHD wave as the disturbance passes from a low-β plasma to a high-β plasma. This is a complex process and a clear understanding of the conversion mechanism requires the detailed investigation
of a simpler model. An investigation of mode conversion in a stratified, isothermal atmosphere with a uniform, vertical magnetic
field is carried out, both numerically and analytically. In contrast to previous investigations of upward-propagating waves
(Zhugzhda and Dzhalilov: Astron. Astrophys.
112, 16, 1982a; Cally: Astrophys. J.
548, 473, 2001), this paper studies the downward propagation of waves from a low-β to high-β environment. A simple expression for the amplitude of the transmitted wave is compared with the numerical solution. 相似文献
20.
The perihelion advance of the orbit of Mercury has long been one of the observational cornerstones for testing General Relativity
(G.R.).The main goal of this paper is to discuss how, presently, observational and theoretical constraints may challenge Einstein's
theory of gravitation characterized by β=γ=1. To achieve this purpose, we will first recall the experimental constraints upon
the Eddington-Robertson parameters γ,β and the observational bounds for the perihelion advance of Mercury, Δωobs. A second point will address the values given, up to now, to the solar quadrupole moment by several authors. Then, we will
briefly comment why we use a recent theoretical determination of the solar quadrupole moment, J
2=(2.0 ± 0.4) 10-7, which takes into account both surfacic and internal differential rotation, in order to compute the solar contribution to
Mercury's perihelion advance. Further on, combining bounds on γ and J
2 contributions, and taking into account the observational data range for Δωobs,we will be able to give a range of values for β. Alternatively, taking into account the observed value of Δωobs, one can deduce a dynamical estimation of J
2 in the setting of G.R. This point is important as it provides a solar model independent estimation that can be confronted
with other determinations of J
2 based upon solar theory and solar observations (oscillation data, oblateness...). Finally, a glimpse at future satellite
experiments will help us to understand how stronger constraints upon the parameter space (γω J
2) as well as a separation of the two contributions (from the quadrupole moment, J
2, or purely relativistic, 2α2+2αγ–β) might be expected in the future.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献