共查询到19条相似文献，搜索用时 218 毫秒
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太阳风是日地空间的主要物质来源,太阳风的观测对日地空间环境及地球物理的研究具有重要意义。地基行星际闪烁观测是监测太阳风风速,测量太阳风等离子体不规则结构,研究遥远致密射电源角径的重要且有效的方法。介绍了行星际闪烁地基观测的单站单频模式的基本理论,针对单站单频模式观测的数据处理及自编软件。本文的工作是为行星际闪烁单站双频系统数据分析处理作前期准备。 相似文献
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太阳风研究的新进展：略谈“尤里西斯”观测藻间由太阳向外“吹”出的电子和离子组成的等离子体在局部行星际介质中占据一个巨大的腔。这些等离子体称为太阳风。它起源于具有百万度高温的太阳外层大气─—日冕。由于日冕温度很高，太阳风等离子体在克服太阳引力，以３００... 相似文献
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本文综述80年代以来,行星际空间和地球磁层研究方面的进展。 在行星际物理方面,太阳风的加速机制、太阳风高速流与低速流之间的相互作用、耀斑激波在行星际空间传播等问题都有长足进展,特别是行星际磁云结构的存在,表明行星际有大小尺度的复杂结构,它们都与日冕和太阳风相关而且都对磁层有不同影响。 相似文献
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本文以行星际空烁为主，综述了通过电波传播的观测来研究太阳风的方法及近３０年的观测结果。概述了这种方法的优缺点，基本假设和基础理论，讨论了这种方法所得到的太阳风电子密度谱，太阳风三维结构以及与太阳活动周的关系，特别是肯定了闪烁测量在研究太阳风加速区问题中的作用。并且结合当前的国际日地物理计划指出了９０年代的研究重点。最后，简述了北京天文台密云站射电天文设备用于行星际闪烁观测的可能性及特点。 相似文献
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由磁绳结构主导、平均尺度约二、三十个小时的行星际磁云是日冕物质抛射在行星际膨胀、传播的体现。最近，Moldwin等人报道在太阳风中还观测到一些尺度在几十分钟的小尺度磁绳结构，并认为太阳风中的磁绳结构在尺度分布上可能具有双峰特征，在全面检视了WIND卫星(1995年-2000年)和ACE卫星(1998年-2000年)的观测资料后，发现了在行星际太阳风中一些尺度为几个小时的中尺度磁绳结构，利用初步整理的其中28个中尺度磁绳结构事件，认为太阳风中的磁绳结构在尺度分布上可能是连续的，这对行星际太阳风中磁绳结构物理起源的研究可能提出重要的物理限制。 相似文献
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借助于弱散射理论和模式拟合方法，单站行星际闪烁观测可以诊断太阳风速度，本文讨论了太阳风参数和射电源角尺度对闪烁谱的影响，以及太阳风速度的积分效应，结果表明，闪烁谱的特征是与视线上距太阳最近处的太阳风速度直接相关的。 相似文献
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等离子体天体物理学是研究宇宙间最广泛存在的物质状态规律的科学。太阳最外层大气日冕的温度约达到一二百万度,高温下的太阳物质呈现高温等离子体状态;地球电离层是处于温度相对较低的等离子体状态。人造地球卫星以及太阳系深空探测表明,行星际空间并非真空,而是存在着来自日冕的连续微粒辐射——太阳风,它是因日冕膨胀而形成的连续向外发出的、伸向遥远的太阳系空间的等离子体流。等离子体物理过程在许多日地物理现象中,诸如太阳耀斑、黑子、日冕物质抛射、日珥、太阳风等研究中起重要作用,探索日地空间物理过程的规律是认识与之有关的空间现象的关键。 相似文献
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1976年的太阳风流速行星际闪烁测量显示了一个期待的风速空间变化趋势,即在高的太阳纬度上或在大的角距离(相对于由日冕观测导出的行星际电流片)上出现高的太阳风速。仔细考察电流片偏离太阳赤道地区的风速变化,发现太阳风速相对于太阳赤道的空间分布并不对称,极小风速出现在行星际电流片附近。在1976年,平均风速u随离电流片的角距离λ变化为 u(λ)=800sio~2λ 350(公里/秒),|λ|≤35° u(λ)=600(公里/秒),|λ|>35° 相似文献
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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
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The Air Force/NASA Solar Mass Ejection Imager (SMEI) will provide two-dimensional images of the sky in visible light with high (0.1%) photometric precision, and unprecedented sky coverage and cadence. To optimize the information available from these images they must be interpreted in three dimensions. We have developed a Computer Assisted Tomography (CAT) technique that fits a three-dimensional kinematic heliospheric model to remotely-sensed Thomson scattering observations. This technique is designed specifically to determine the corotating background solar wind component from data provided by instruments like SMEI. Here, we present results from this technique applied to the Helios spacecraft photometer observations. The tomography program iterates to a least-squares solution of observed brightnesses using solar rotation, spacecraft motion and solar wind outflow to provide perspective views of each point in space covered by the observations. The corotational tomography described here is essentially the same as used by Jackson et al. (1998) for the analysis of interplanetary scintillation (IPS) observations. While IPS observations are related indirectly to the solar wind density through an assumed (and uncertain) relationship between small-scale density fluctuations and density, Thomson scattering physics is more straightforward, i.e., the observed brightness depends linearly on the solar wind density everywhere in the heliosphere. Consequently, Thomson scattering tomography can use a more direct density-convergence criterion to match observed Helios photometer brightness to brightness calculated from the model density. The general similarities between results based on IPS and Thomson scattering tomography validate both techniques and confirm that both observe the same type of solar wind structures. We show results for Carrington rotation 1653 near solar minimum. We find that longitudinally segmented dense structures corotate with the Sun and emanate from near the solar equator. We discuss the locations of these dense structures with respect to the heliospheric current sheet and regions of activity on the solar surface. 相似文献
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S. Ananthakrishnan 《Journal of Astrophysics and Astronomy》2000,21(3-4):439-444
The ground-based radio astronomy method of interplanetary scintillations (IPS) and spacecraft observations have shown, in
the past 25 years, that while coronal holes give rise to stable, reclining high speed solar wind streams during the minimum
of the solar activity cycle, the slow speed wind seen more during the solar maximum activity is better associated with the
closed field regions, which also give rise to solar flares and coronal mass ejections (CME’s). The latter events
increase significantly, as the cycle maximum takes place. We have recently shown that in the case of energetic flares one
may be able to track the associated disturbances almost on a one to one basis from a distance of 0.2 to 1 AU using IPS methods.
Time dependent 3D MHD models which are constrained by IPS observations are being developed. These models are able to simulate
general features of the solar-generated disturbances. Advances in this direction may lead to prediction of heliospheric propagation
of these disturbances throughout the solar system. 相似文献
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S. A. Hardwick M. M. Bisi J. A. Davies A. R. Breen R. A. Fallows R. A. Harrison C. J. Davis 《Solar physics》2013,285(1-2):111-126
The technique of interplanetary scintillation (IPS) is the observation of rapid fluctuations of the radio signal from an astronomical compact source as the signal passes through the ever-changing density of the solar wind. Cross-correlation of simultaneous observations of IPS from a single radio source, received at multiple sites of the European Incoherent SCATter (EISCAT) radio antenna network, is used to determine the velocity of the solar wind material passing over the lines of sight of the antennas. Calculated velocities reveal the slow solar wind to contain rapid velocity variations when viewed on a time-scale of several minutes. Solar TErrestrial RElations Observatory (STEREO) Heliospheric Imager (HI) observations of white-light intensity have been compared with EISCAT observations of IPS to identify common density structures that may relate to the rapid velocity variations in the slow solar wind. We have surveyed a one-year period, starting in April 2007, of the EISCAT IPS observing campaigns beginning shortly after the commencement of full science operations of the STEREO mission in a bid to identify common density structures in both EISCAT and STEREO HI datasets. We provide a detailed investigation and presentation of joint IPS/HI observations from two specific intervals on 23 April 2007 and 19 May 2007 for which the IPS P-Point (point of closest approach of the line of sight to the Sun) was between 72 and 87 solar radii out from the Sun’s centre. During the 23 April interval, a meso-scale (of the order of 105 km or larger) transient structure was observed by HI-1A to pass over the IPS ray path near the P-Point; the observations of IPS showed a micro-scale structure (of the order of 102 km) within the meso-scale transient. Observations of IPS from the second interval, on 19 May, revealed similar micro-scale velocity changes, however, no transient structures were detected by the HIs during that period. We also pose some fundamental thoughts on the slow solar wind structure itself. 相似文献
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Scattering of radio waves by density fluctuations in the solar wind leads to rapid variation in the intensity of compact radio sources. This phenomenon, known as Interplanetary Scintillation (IPS), provides a simple method to study interplanetary activity in the inner heliosphere. During the solar maximum of cycle 22, we carried out extensive, high-time-resolution IPS observations of fast moving interplanetary plasma clouds (IPCs). The observations were done using the Ooty Radio Telescope (ORT) and covered the region between 0.2 AU and 0.8 AU around the Sun. We detected 33 IPCs having velocities of 600 to 1400 km s–1. A two-component model of scattering by time-varying solar wind was developed to analyse these IPCs. The model enabled us to estimate the mass, energy and geometry of each disturbance and to associate them with solar-geomagnetic activity.Detailed analysis suggests that these IPCs were interplanetary signatures of massive and energetic Solar Mass Ejections (SMEs). The SMEs were found to have average mass and kinetic energy of 5.3×1016 g, 2.4×1032 ergs. The average span and width of the SME was found to be 42° and 8×106 km. Association of these disturbances with solar-geomagnetic activity shows that about 80% of them are associated with Long-Duration X-ray Events (LDXE) and Solar Mass Ejections (SMEs). Only 50% of the events were associated with geomagnetic activity. The present experiment has demonstrated that continuous IPS monitoring is an effective technique to detect mass ejections in the interplanetary medium and to study their evolution through the inner heliosphere. 相似文献
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We use dual-site radio observations of interplanetary scintillation (IPS) with extremely long baselines (ELB) to examine meridional flow characteristics of the ambient fast solar wind at plane-of-sky heliocentric distances of 24?–?85 solar radii (R ⊙). Our results demonstrate an equatorwards deviation of 3?–?4° in the bulk fast solar wind flow direction over both northern and southern solar hemispheres during different times in the declining phase of Solar Cycle 23. 相似文献
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This paper reports on the first combination of results from in-situ plasma measurements at Venus, using data from Venus Express, and remote sensing data from observations of interplanetary scintillation (IPS). In so doing, we demonstrate the value of combining remote sensing and in-situ techniques for the purpose of investigating interaction between solar wind, under several different conditions, and the Venusian magnetosphere. The ion mass analyser instrument (IMA) is used to investigate solar wind interaction with the Venusian magnetosphere in the presence of two different solar wind phenomena; a co-rotating interaction region (CIR) and a coronal mass ejection (CME). The CIR, detected with IPS and sampled in-situ at Venus is found to dramatically affect upstream solar wind conditions. These case studies demonstrate how combining results from these different data sources can be of considerable value when investigating such phenomena. 相似文献
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Rajendra Shelke 《Journal of Astrophysics and Astronomy》2006,27(2-3):101-112
Coronal holes and interplanetary disturbances are important aspects of the physics of the Sun and heliosphere. Interplanetary
disturbances are identified as an increase in the density turbulence compared with the ambient solar wind. Erupting stream
disturbances are transient large-scale structures of enhanced density turbulence in the interplanetary medium driven by the
high-speed flows of low-density plasma trailing behind for several days. Here, an attempt has been made to investigate the
solar cause of erupting stream disturbances, mapped by Hewish & Bravo (1986) from interplanetary scintillation (IPS) measurements
made between August 1978 and August 1979 at 81.5 MHz. The position of the sources of 68 erupting stream disturbances on the
solar disk has been compared with the locations of newborn coronal holes and/or the areas that have been coronal holes previously.
It is found that the occurrence of erupting stream disturbances is linked to the emergence of new coronal holes at the eruption
site on the solar disk.
A coronal hole is indicative of a radial magnetic field of a predominant magnetic polarity. The newborn coronal hole emerges
on the Sun, owing to the changes in magnetic field configuration leading to the opening of closed magnetic structure into
the corona. The fundamental activity for the onset of an erupting stream seems to be a transient opening of pre-existing closed
magnetic structures into a new coronal hole, which can support highspeed flow trailing behind the compression zone of the
erupting stream for several days. 相似文献
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We have carried out a program of continuous Interplanetary Scintillation (IPS) monitoring of the interplanetary activity using Ooty Radio Telescope (ORT). From May 1990 to March 1991, during the 22nd, solar maximum, a few radio sources were monitored to provide long stretches of IPS data with a high-time resolution of few minutes. These observations covered 0.3 to 0.8 AU region (12° to 70° elongations) around the sun at several heliographic latitudes. During the observation, we detected 33 short-time scale IPS events which had significant variation in the scintillation index and solar wind velocity. These were considered to be due to travelling interplanetary disturbances.A multi-component model of plasma density enhancement was developed to estimate the geometry and physical properties of these IPS events. Detailed analysis of 20 of these events suggests, 1. fast IPS events were interplanetary signatures of Coronal Mass Ejections (CMEs), 2. the average mass and energy of these events was 1016 gm and 1033 erg respectively,3. 80% of IPS events were associated with X-ray flares on the sun and 50% were associated with geomagnetic activity at earth. Detailed study of the multicomponent model suggests IPS observations at smaller elongations (hence at higher radio frequencies) are more suited to detect fast-moving interplanetary disturbances such as produced by CMEs. 相似文献