共查询到20条相似文献，搜索用时 15 毫秒
1.
Shadia Rifai Habbal 《Astrophysics and Space Science》1996,243(1):49-56
The temperature in the acceleration region of the solar wind remains one of the most elusive parameters to measure. Knowledge of the temperature as well as its gradient in the inner corona is fundamental for placing constraints on physical mechanisms thought to be responsible for the coronal heating process, as well as for understanding the flow properties of the solar wind. Estimates of the helium abundance is essential for understanding the puzzling behavior of heavier ions in the solar wind. As an illustration of the difficulties and uncertainties involved in the inferences of plasma parameters in the wolar wind acceleration region, The inference of electron temperature and helium abundance will be described. Prospects for future observations will be briefly discussed. 相似文献
2.
We present recent observations of the plasma parameters in coronal holes at the origin of the fast solar wind and in the interplanetary
medium. A model based on the heat conductivity law in a dilute plasma shows the coherency of the electron and proton temperature
observations from coronal holes to the interplanetary medium. These new observations are severe constraints for any model
of the expansion of the fast solar wind. We discuss why and how non-equilibrium multispecies Fokker-Planck approach must be
developed and present a generalized Grad's solution.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
The magnetic field of Mercury and the structure and dynamics of Mercury's magnetosphere, which will be studied by the spacecraft orbiting Mercury, are strongly influenced by the interaction of the solar wind with Mercury. In order to understand the internal magnetic field, it will be necessary to correct the observations of the external field for the distortions produced by the solar wind. Understanding of the solar wind interaction with Mercury is essential for understanding the structure and dynamics of the magnetosphere and phenomena such as magnetic storms. Helios 1 and 2 made a number of passes in the region traversed by the orbit of Mercury, and each pass provided a sample of the solar wind environment of Mercury. This paper reviews the plasma and magnetic field observations from Helios that provide a general basis for interpreting the observations of Mercury that will be made by orbiting spacecraft. The variables that govern the structure and dynamics of the magnetospheres of Mercury and Earth are approximately 5–10 times larger at Mercury than at Earth. Thus, the solar wind interaction with Mercury will be much stronger than the interaction with Earth. Moreover, the solar wind at Mercury is probably more variable than that at Earth. There is a clear need for measurements of the solar wind during the approach of spacecraft to Mercury and while they are in orbit around Mercury. 相似文献
4.
The flux rate of cosmic rays incident on the Earth’s upper atmosphere is modulated by the solar wind and the Earth’s magnetic
field. The amount of solar wind is not constant due to changes in solar activity in each solar cycle, and hence the level
of cosmic ray modulation varies with solar activity. In this context, we have investigated the variability and the relationship
of cosmic ray intensity with solar, interplanetary, and geophysical parameters from January 1982 through December 2008. Simultaneous
observations have been made to quantify the exact relationship between the cosmic ray intensity and those parameters during
the solar maxima and minima, respectively. It is found that the stronger the interplanetary magnetic field, solar wind plasma
velocity, and solar wind plasma temperature, the weaker the cosmic ray intensity. Hence, the lowest cosmic ray intensity has
good correlations with simultaneous solar parameters, while the highest cosmic ray intensity does not. Our results show that
higher solar activity is responsible for a higher geomagnetic effect and vice versa. 相似文献
5.
T. W. Garner T. L. Gaussiran II J. A. York D. M. Munton C. M. Slack III A. M. Mahrous 《Earth, Moon, and Planets》2009,104(1-4):227-235
The International Heliophysical Year (IHY) 2007 is an international scientific program designed to coordinate observations of the heliosphere, the region of space from the solar surface through the solar wind and various planetary magnetospheres to the planetary upper atmospheres. A particular emphasis is given to the development of long-term international collaborations that will study the external drivers to the space environment and climate. The Ionospheric Tomography Network of Egypt (ITNE) is one such collaboration. It is a new chain of ionospheric tomography receivers that will be deployed to investigate the equatorial regions of the Earth’s ionosphere. The distribution of plasma density within 20° of the magnetic equator is highly sensitive to forcing from the solar wind through a process known as the equatorial fountain. ITNE will provide new observations of the density structures associated with the equatorial fountain. 相似文献
6.
The numerical integration of hydrodynamics equations with an allowance for thermal conductivity was made using the temperature distribution in the corona situated above the active regions obtained from the damping time of solar radio bursts of Types III and V. It is essential that for the integration path serve the magnetic field lines along which exciters of bursts are moving and accelerated coronal plasma can move freely too.The main result is the discovery of such regions, where the high temperature gradient precludes the possibility of a continuous flow of coronal plasma. These regions, where intense heating and rapid acceleration of the coronal plasma take place, were situated at distances of about 2 R
from the Sun's center. They probably possess the character of weak detonation waves. The waves of cooling can also be present in these regions of discontinuity of the flow. The observations of bursts of Type V at distances up to 6.3 R
gives some evidence that discontinuities of flow of the solar wind of the same nature can possibly arise also in the more remote parts of the solar corona.It is important that the similar jumps of velocity and other parameters of coronal plasma were also discovered earlier in a quite independent way as a result of the interpretation of the solar radio echo data. It can be anticipated that the nonthermal heating of coronal plasma, which was postulated to remove discrepancies between the existing models and observations of solar wind, was localized mainly in these regions thus playing an important role in the formation of the fundamental properties of the interplanetary medium.The obtained results are of preliminary character since there are no reliable and homogeneous data on bursts of Types III and V especially at 20-10 MHz, where the work is difficult due to the man-made interference and also at still lower frequencies, observed by the cosmic probes. We can hope that the filling of this gap allows us to construct a realistic model of outflow of coronal plasma from active regions, which can be successfully compared with the results of direct measurement of parameters of solar wind. 相似文献
7.
《Planetary and Space Science》2006,54(13-14):1336-1343
The Venus Express mission is scheduled for launch in 2005. Among many other instruments, it carries a magnetometer to investigate the Venus plasma environment. Although Venus has no intrinsic magnetic moment, magnetic field measurements are essential in studying the solar wind interaction with Venus. Our current understanding of the solar wind interaction with Venus is mainly from the long lasting Pioneer Venus Orbiter (PVO) observations. In this paper, we briefly describe the magnetic field experiment of the Venus Express mission. We compare Venus Express mission with PVO mission with respect to the solar wind interaction with Venus. Then we discuss what we will achieve with the upcoming Venus Express mission. 相似文献
8.
During the previous years spacecraft observations of so-called Energetic Neutral Atoms (ENAs) have become an important remote-sensing
technique in planetary science for analyzing the solar wind plasma flow around the upper atmospheric environments of Solar
System bodies. ENAs are produced whenever solar- or stellar wind protons interact via charge exchange with a neutral particle
from a planetary atmosphere so that their signals constrain both, ion distributions and neutral gas densities. The observation
of ENAs which have been generated due to charge exchange with stellar wind plasma have been used for the indirect mass loss
and stellar wind property estimation of Sun-like stars by observing the interaction regions carved out by the collisions between
stellar winds and the interstellar medium. In this work we review ENA-observations and data interpretations at Solar System
planets and recent hydrogen-cloud observations in UV Lyman-α absorption around hydrogen-rich extra-solar gas giants. We discuss the production of stellar wind related hydrogen ENA-clouds
around close-in exoplanets and show how a detailed analysis of attenuation spectra obtained for transiting hydrogen-rich close-in
gas giants can be used for the study of the upper atmosphere structure, the planet’s magnetosphere and to obtain information
on stellar wind properties. Finally, we discuss how future hydrogen cloud observations around exoplanets by space observatories
like the Russia-led World Space Observatory-UV (WSO-UV) together with ESAs planned PLATO mission can be used for the reconstruction
of the solar wind history or the test of magnetosphere evolution hypotheses. 相似文献
9.
太阳风中的电磁离子回旋(Electromagnetic Ion Cyclotron, EMIC)波自报道以来,受到了广泛的关注和研究.由于波的频率接近质子的回旋频率, EMIC波可以通过回旋共振波粒相互作用将波能传递给离子,并在太阳风粒子加热和加速等能化现象中发挥重要作用.总结了太阳风中EMIC波的观测和理论研究进展,包括EMIC波在磁云内外、磁云和行星际日冕物质抛射鞘区中的观测研究得到的一系列结果以及基于观测进行波的激发机制所取得的研究进展,并展望未来研究太阳风中EMIC波的突破方向. 相似文献
10.
M. Dryer S. T. Wu G. Gislason S. M. Han Z. K. Smith J. F. Wang D. F. Smart M. A. Shea 《Astrophysics and Space Science》1984,105(1):187-208
A time-dependent, nonplanar, two-dimensional magnetohydrodynamic computer model is used to simulate a series, separately examined, of solar flare-generated shock waves and their subsequent disturbances in interplanetary space between the Sun and the Earth's magnetosphere. The ‘canonical’ or ansatz series of shock waves include initial velocities near the Sun over the range 500 to 3500 km s?1. The ambient solar wind, through which they propagate, is taken to be a steady-state homogeneous plasma (that is, independent of heliolongitude) with a representative set of plasma and magnetic field parameters. Complete sets of solar wind plasma and magnetic field parameters are presented and discussed. Particular attention is addressed to the MHD model's ability to address fundamental operational questions vis-à-vis the long-range forecasting of geomagnetic disturbances. These questions are: (i) will a disturbance (such as the present canonical series of solar flare shock waves) produce a magnetospheric and ionospheric disturbance, and, if so, (ii) when will it start, (iii) how severe will it be, and (iv) how long will it last? The model's output is used to compute various solar wind indices of current interest as a demonstration of the model's potential for providing ‘answers’ to these questions. 相似文献
11.
The discovery of the solar wind has been an outstanding achievement in heliophysics and space physics. The solar wind plays a crucial role in the processes taking place in the Solar System. In recent decades, it has been recognized as the main factor that controls the terrestrial effects of space weather. The solar wind is an unusual plasma laboratory of giant scale with a fantastic diversity of parameters and operating modes, and devoid of influence from the walls of laboratory plasma systems. It is also the only kind of stellar wind accessible for direct study. The history of this discovery is quite dramatic. Like many remarkable discoveries, it had several predecessors. However, the honor of a discovery usually belongs to a scientist who was able to more fully explain the phenomenon. Such a man is deservedly considered the US theorist Eugene Parker, who discovered the solar wind, as we know it today, almost “with the point of his pen”. In 2017, we will celebrate the 90th anniversary birthday of Eugene Parker. 相似文献
12.
The investigation of plasma tails of comets is an important part of comet research. Different classifications of plasma tails of comets are proposed. Plasma acceleration in the tails is investigated in sufficient detail. Several cometary forms are explained. Plasma tails of Mars and Venus were observed during the first studies of these planets. They are associated with the capture of ionized atoms and exosphere molecules by the solar wind magnetized plasma flow. Distinct plasma tails of Mars and Venus are caused by the mass loading of the solar wind with heavy ions. It was shown that the transverse dimension of the tails of Mars, Venus, and comets can be quite accurately determined by production rate of the obstacle to the solar wind flow. While plasma tails of Mars and Venus are investigated by in situ measurements from spacecraft, observations of comet tails from the Earth make it possible to see the entire object under study and to monitor changes in its structure. A certain similarity of cometary and planetary tails can be explained by the nonmagnetic nature of both types of bodies. Thus, it is reasonable to suppose that investigations of plasma tails of comets can supplement the information obtained by in situ methods of the study of the planets. In this paper, plasma tails of comets, presumably analogous to the plasma tails of Mars and Venus, have been identified on modern photographs of comets (more than 1500 photographs viewed). Only quasi-steady laminar tails are considered. They are divided into two types: double structures and outflows. The paper attempts to define the 3D structure of double structures and to determine certain characteristics of outflows. 相似文献
13.
J. &#x;afrnkov Z. N me
ek L. P&#x;ech A.A. Samsonov A. Koval K. Andreov 《Planetary and Space Science》2007,55(15):2324-2329
Fast forward interplanetary (IP) shocks have been identified as a source of large geomagnetic disturbances. However, the shocks can evolve in the solar wind, they are modified by interaction with the bow shock and during their propagation through the magnetosheath. A few previous papers refer the inclination and deceleration of the IP shock front in this region. Our contribution continues this effort and presents the study of an IP shock interaction with the bow shock. Since the bow shock is a reversed fast shock, the interaction of the IP shock and bow shock is a problem of interaction of two fast MHD shocks.
We compare profiles of magnetic field and plasma parameters observed by several spacecraft in the solar wind and magnetosheath with the profiles of the same parameters resulting from the MHD numerical model. The MHD model suggests that the interaction of an IP shock with the bow shock results in an inward bow shock displacement that is followed by its outward motion. Such motion will result in an indentation propagating along the bow shock surface. This scenario is confirmed by multipoint observations. Moreover, the model confirms also previous suggestions on the IP shock deceleration in the magnetosheath. 相似文献
14.
Roman M. Häberli Michael R. Combi Tamas I. Gombosi Darren L. De Zeeuw Kenneth G. Powell 《Icarus》1997,130(2):373-386
The observation of ions created by ionization of cometary gas, either by ground-based observations or byin situmeasurements can give us useful information about the gas production and composition of comets. However, due to the interaction of ions with the magnetized solar wind and their high chemical reactivity, it is not possible to relate measured ion densities (or column densities) directly to the parent gas densities. In order to quantitatively analyze measured ion abundances in cometary comae it is necessary to understand their dynamics and chemistry. We have developed a detailed ion–chemical network of cometary atmospheres. We include production of ions by photo- and electron impact-ionization of a background neutral atmosphere, charge exchange of solar wind ions with cometary atoms/molecules, reactions between ions and molecules, and dissociative recombination of molecular ions with thermal electrons. By combining the ion–chemical network with the three-dimensional plasma flow as computed by a new fully three-dimensional MHD model of cometary plasma environments (Gombosiet al.1996) we are able to compute the density of the major cometary ions everywhere in the coma. The input parameters for our model are the solar wind conditions (density, speed, temperature, magnetic field) and the composition and production rate of the gas. We applied our model to Comet P/Halley in early March 1986, for which the input parameters are reasonably well known. We compare the resulting column density of H2O+with ground-based observations of H2O+from DiSantiet al.(1990). The results of our model are in good agreement with both the spatial distribution and the absolute abundance of H2O+and with their variations with the changing overall water production rate between two days. The results are encouraging that it will be possible to obtain production rates of neutral cometary constituents from observations of their ion products. 相似文献
15.
在多年的太阳光谱观测中，通过观察各种天气条件的变化对光谱仪成像质量的影响，初步总结出使像质优良的几条规律1)在连续刮风过程中当风突然停止或减弱的短暂时间内像质明显变好；2)当夜间通宵有风而次日天气晴朗时像质变好；3)多云过后的短暂晴天成像优良；4)接连阴雨几天后的开始晴天像质较好。 相似文献
16.
A. Geranios 《Astrophysics and Space Science》1981,77(1):167-178
Plasma temperature observations in the solar wind at 1 AU show that very low temperatures of electrons and protons appear not only after interplanetary shock waves, but also after solar wind streams. It is generally believed that the region embedded by a fast preceding and a slower following solar wind is expanding. In this way, the plasma inside may become cooler. In this analysis, we use plasma measurements made aboard the VELA and IMP satellites. Due to the limitations of data, we only give a qualitative picture of the possibility that low temperature regions may be given to local expansions of the plasma. In addition, we assume that these regions are not magnetically closed and therefore not thermically isolated, but are open and connected with the hot corona along the interplanetary magnetic field lines. Therefore, these regions are heated from the corona due to the thermal conduction. In this analysis both the theoretically predicted and the experimentally measured conducted electron heat fluxes are considered. 相似文献
17.
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
18.
N.V. ErkaevH.K. Biernat 《Planetary and Space Science》2003,51(12):745-755
The magnetized solar wind carries a large amount of energy but only a small fraction of it enters the magnetosphere and powers its dynamics. Numerous observations show that the interplanetary magnetic field (IMF) is a key parameter regulating the solar wind-magnetosphere interaction. The main factor determining the amount of energy extracted from the solar wind flow by the magnetosphere is the plasma flow structure in the region adjacent to the sunward side of the magnetopause. While compared to the energy of the solar wind flow the IMF magnetic energy is relatively weak, it is considerably enhanced in a thin layer next to the dayside magnetopause variously called the plasma depletion layer or magnetic barrier. Important features of this barrier/layer are (i) a pile-up of the magnetic field with (ii) a concurrent decrease of density, (iii) enhancement of proton temperature anisotropy, (iv) asymmetry of plasma flow caused by magnetic field tension, and (v) characteristic wave emissions (ion cyclotron waves). Importantly, the magnetic barrier can be considered as an energy source for magnetic reconnection. While the steady-state magnetic barrier has been extensively examined, non-steady processes therein have only been addressed by a few authors. We discuss here two non-steady aspects related to variations of the magnetic barrier caused by (i) a north-to-south rotation of the IMF, and (ii) by pulses of magnetic field reconnection at the magnetopause. When the IMF rotates smoothly from north-to-south, a transition layer is shown to appear in the magnetosheath which evolves into a thin layer bounded by sharp gradients in the magnetic field and plasma quantities. For a given reconnection rate and calculated parameters of the magnetic barrier, we estimate the duration and length scale of a reconnection pulse as a function of the solar wind parameters. Considering a sudden decrease of the magnetic field near the magnetopause caused by the reconnection pulse, we study the relaxation process of the magnetic barrier. We find that the relaxation time is longer than the duration of the reconnection pulse for large Alfvén-Mach numbers. 相似文献
19.
The Sun affects physical phenomena on Earth in multiple ways.In particular,the material in interplanetary space comes from coronal expansion in the form of inhomogeneous plasma flow (solar wind),which is the primary source of the interplanetary medium.Ground-based Interplanetary Scintillation (IPS) observations are an important and effective method for measuring solar wind speed and the structures of small diameter radio sources.We discuss one mode of ground-based single-station observations: Single-Station Single-Frequency (SSSF) mode.To study the SSSF mode,a new system has been established at Urumqi Astronomical Observatory (UAO),China,and a series of experimental observations were successfully carried out from May to December,2008. 相似文献
20.
Close temporal correlation between high-frequency Langmuir waves and low-frequency electromagnetic whistler waves has been observed recently within magnetic holes of the solar wind. In order to account for these observations, a theory is formulated to describe the nonlinear coupling of Langmuir waves and whistler waves. It is shown that a Langmuir wave can interact nonlinearly with a whistler wave to produce either right-hand or left-hand circularly polarized electromagnetic waves. Nonlinear coupling of Langmuir waves and whistler waves may lead to the formation of modulated Langmuir wave packets as well as the generation of circularly polarized radio waves at the plasma frequency in the solar wind. Numerical examples of whistler frequency, nonlinear growth rate and modulation frequency for solar wind parameters are calculated. 相似文献