Specific features of explosive plasma flows in the near-earth space

The analytical expressions for determining the deceleration region of plasma, produced during large-scale geophysical experiments of explosion type, and taking into account the effect of the rarefied ionosphere and geomagnetic field have been obtained. The possibility of the magnetosphere braking by plasma produced by a powerful explosion is analyzed. The simplified set of equations used to analyze the linear and non-linear stages of flute instability of explosive plasma expanding into the magnetic field has been obtained. The mass overflow between flutes and the viscous force is taken into account. The experimental studies of flute instability during laser plasma expansion into the magnetic field are theoretically substantiated. The mechanism explaining the formation of a jet stream and the main jet inclination of 11° with respect to the axis of symmetry has been proposed.     

The main features of solar wind plasma correlations of importance to space weather strategy

In this work solar wind measurements from several spacecraft were used to investigate the correlations of solar wind plasma parameters. These results provide a test of the concept of predicting space weather by monitoring the condition of the solar wind at a large distance (up to 230R_e, the L1 point) upstream from the Earth.We compared the ion flux and bulk velocity time behavior measured by widely-separated spacecraft: the spacecraft pairs INTERBALL-1 and IMP 8 (separations up to 30R_e), INTERBALL-1 and WIND, and IMP 8 and WIND (both with separations up to 250R_e). The average value of the ion flux correlation coefficient is about 0.73. But in some cases the plasma parameters from two spacecraft are very different in both behavior and value, so correlations are very poor.The technique of multifactorial analysis was used to obtain the physical dependences of the correlations on the spacecraft separation and on different plasma and magnetic field parameters. We found that the correlation values have a weak but significant dependence on the separation perpendicular to the Sun–Earth line (YZ_se-separations up to 90R_e).The most important factors influencing the correlation level are density (or ion flux) variability, the direction of the IMF vector to the Sun–Earth line (cone angle), and the solar wind bulk velocity.     

Kinetic features of bursty bulk flows and dipolarization fronts

正Bursty bulk flows(BBFs)and dipolarization fronts(DFs)are two important phenomena responsible for the transport of energy,mass and magnetic flux from the Earth's magnetotail to the inner magnetosphere during magnetosphere substorms.The BBFs are defined as the high-speed flows of several hundred km/s in the central plasma sheet lasting about 10 minutes,while DFs are defined as,with much shorter time scale of several seconds,sharp increases in the northward magnetic field component in the plasma sheet.These two phenomena     

Spectral features of long-period volcanic signals: Klyuchevskoi Volcano

This study is concerned with spectral features in the long-period volcanic signals observed on Klyuchevskoi Volcano during the period 2000–2007. The results were obtained from digital records made at seven seismic stations communicating via radio telemetry; they were deployed on the slope of and close to Klyuchevskoi. It is shown that the spectral content of long-period volcanic signals changed toward lower frequencies during the period from mid 2003 to the end of 2007. The change in the spectra is here related to the volcano’s activity, which increased at the end of 2003 and was accompanied by numerous explosions and the outflow of lava from the crater.     

Development of solar flares and features of the fine structure of solar radio emission

The reason for the occurrence of different elements of the fine structure of solar radio bursts in the decimeter and centimeter wavelength ranges has been determined based on all available data from terrestrial and satellite observations. In some phenomena, fast pulsations, a zebra structre, fiber bursts, and spikes have been observed almost simultaneously. Two phenomena have been selected to show that the pulsations of radio emission are caused by particles accelerated in the magnetic reconnection region and that the zebra structure is excited in a source, such as a magnetic trap for fast particles. The complex combination of unusual fiber bursts, zebra structure, and spikes in the phenomenon on December 1, 2004, is associated with a single source, a magnetic island formed after a coronal mass ejection.     

Propagating plasma patch and associated neutral stream flows

Plasma patches are regions of enhanced ionization that are created in the dayside cusp or equatorward of the cusp in the sunlit hemisphere during northward interplanetary magnetic field. After formation, and a change to a southward interplanetary magnetic field, they drift across the polar cap with the prevailing convection speed. As a plasma patch propagates, charge exchange reactions occur, which lead to the production of both ion and neutral particles throughout the patch. In the region directly above the patch, an upward jet of H⁺ and O⁺ forms. This ion jet, in turn, acts to produce an upward flux of neutral H and O stream particles because of charge exchange reactions between the ion jet and the background neutral atmosphere. A three-dimensional, time-dependent model of the ion and neutral polar winds was used in order to study the evolution of the neutral stream particles that are produced in a ‘representative’ propagating plasma patch, with the anticipation that the neutral stream particles produced by the ion jet would display a distinct signature. However, the outflow of neutral H atoms above a patch is only slightly visible in the simulation due to a continuous outflow flux of H (∼10⁹ cm⁻² s⁻¹) across the entire polar cap. On the other hand, the upward flux of neutral O from the patch is more dependent on both the state of the ionosphere and the amount of heating, with increased upward fluxes over areas where the heating is high. Typically, the upward neutral O streams are predominantly located in the pre-midnight auroral oval.     

Axisymmetric equilibria of a gravitating plasma with incompressible flows

Abstract

It is found that the ideal magnetohydrodynamic equilibrium of an axisymmetric gravitating magnetically confined plasma with incompressible flows is governed by a second-order elliptic differential equation for the poloidal magnetic flux function containing five flux functions coupled with a Poisson equation for the gravitation potential, and an algebraic relation for the pressure. This set of equations is amenable to analytic solutions. As an application, the magnetic-dipole static axisymmetric equilibria with vanishing poloidal plasma currents derived recently by Krasheninnikov et al. (1999) are extended to plasmas with finite poloidal currents, subject to gravitating forces from a massive body (a star or black hole) and inertial forces due to incompressible sheared flows. Explicit solutions are obtained in two regimes: (a) in the low-energy regime β₀ ≈ γ₀ ≈ δ₀ ≈ ε₀ ? 1, where β₀, γ₀, δ₀, and ε₀ are related to the thermal, poloidal-current, flow and gravitating energies normalized to the poloidal-magnetic-field energy, respectively, and (b) in the high-energy regime β₀ ≈ γ₀ ≈ δ₀ ≈ ε₀ ? 1. It turns out that in the high-energy regime all four forces, pressure-gradient, toroidal-magnetic-field, inertial, and gravitating contribute equally to the formation of magnetic surfaces very extended and localized about the symmetry plane such that the resulting equilibria resemble the accretion disks in astrophysics.     

Spectral features of geomagnetic low point displacement and its mechanism

In this paper,Changli station in Hebei Province was taken as an example,in which the minute data of geomagnetic Z component was used to analyze the spectral values of its main frequencies during normal time,geomagnetic storm time and low point displacement time interval respectively. After fitting of ten high spectral values to loga-rithmic functions,it is found that,by using same length of data,the spectral values at geomagnetic storm time in-crease apparently compared with those at normal time,especially at the high frequency segment. While low point displacement occurred,the spectral values at high frequency are approximate to those at normal time,but at period above 4 hours they are mostly lower than those at normal time. Comparison of accumulating of some FFT results at low point displacement and normal time shows that,spectral values at periods of 8.5 and 13.7 hours increase at low point displacement time relative to those at normal time. Compared with the images of Ne observed at DE-METER satellite,it is illustrated that the occurrence of geomagnetic low point displacement is well corresponding with the increase of Ne in ionosphere. Finally it was discussed about those spectral features and the occurrence mechanism of geomagnetic low point displacement.     

Steady flows in solar magnetic solutions structures-a class of exact MHD solutions

Abstract

A class of exact solutions to the steady, two-dimensional magnetohydrodynamic equations ina cylindrical geometry is presented. These may model both closed and open magnetic structures found in the solar atmosphere. For closed structures, it is found that increasing the flow speed causes the summit of the arcade of closed magnetic fieldlines to rise. Parameter ranges also exist where the solution has regions of open and closed field, and so the solutions may be relevant for modelling flows in solar magnetic structures such as coronal streamers, X-ray bright points coronal plumes and coronal holes.     

Certain features of UHF propagation during solar proton events

Results of the experimental reception of the UHF signal from geostationary satellite, visible at a low elevation angle from the receiving point, have been considered. It has been noted that the fluctuation intensity considerably increases during powerful solar proton events. The observed effect can be caused by interference between direct and secondary rays related to tropospheric irregularities. The hypothesis explaining obtained results based on the optical model of solar-tropospheric coupling is proposed.     

地磁低点位移频谱特征及机理探讨

以河北省昌黎地震台为例,使用该台地磁Z分量的分钟值数据,分别对比了正常时段、磁暴发生时段、 低点位移时段的主要频率谱值变化特征. 通过多频点功率谱对数拟合,发现在数据长度相等的情况下,相对于正常时段而言磁暴时段各频率的能量明显增强,特别是高频端尤其明显; 而当大范围低点位移发生时,高频端的能量基本与正常时段持平,但4个小时以上的周期功率谱大部分要低于正常段. 通过对多日低点位移时段的FFT累加与正常时段对比后发现,低点位移发生时,8.5小时和13.7小时周期的频谱值增加. 通过与DE-METER卫星观测的电子密度数据空间图象进行对比,发现地磁低点位移的发生与空间Ne的增加有很好的对应性. 最后对这些变化特征及低点位移可能产生的机制进行了探讨.      

Polarization of compressible turbulent fluctuations in the solar wind plasma

Compressible fluctuations in solar wind plasma are analyzed on the basis of the 1995–2010 WIND and Advanced Composition Explorer (ACE) spacecraft data. In the low-speed solar wind (V ₀ < 430 km/s), correlations between fluctuations in the magnetic field direction and plasma density, as well as between velocity fluctuations and plasma density, are found. The covariance functions of these parameters calculated as functions of the local magnetic field direction are axially symmetric relative to the axis, which is oriented nearly along the regular magnetic field of the heliosphere (the Parker spiral). Fluctuations in the magnetic field and velocity are polarized in the plane that is orthogonal to the axis of symmetry. Plasma oscillations of these properties can be caused by fast magnetosonic waves propagating from the Sun along the Parker spiral.     

Hard X-ray generation in the turbulent plasma of solar flares

The influence of scattering of accelerated electrons in the turbulent plasma on the transformation of their distribution function is studied. The turbulence is connected with the emergence of magnetic inhomogeneities and ion-sound mode. The level of ion-sound turbulence is specified by the ratio W ^s/nk _B T _e = 10^?3, while the value of magnetic fluctuations is δB/B = 10^–3. Different initial angular distributions of the function of accelerated-electron source are regarded: from isotropic to narrow directional distributions. For the chosen energy-density values of the ion-sound turbulence and the level of magnetic fluctuations, it is shown that both types of turbulence lead to a qualitative change in the hard X-ray brightness along the loop, moreover their influence was found to be different. Models with magnetic fluctuations and the ion sound can be distinguished not only by the difference in the hard X-ray distribution along the loop but also by the photon spectrum.     

乌梁素海沉水植物群落光谱特征及冠层水深影响分析

沉水植物对于改善富营养化水体和重建水生生态系统起着至关重要的作用.应用遥感技术可以实时、大面积监测沉水植物的分布和生长情况,而冠层水深直接影响沉水植物在湖泊、河流中的准确遥感解译.本研究基于实测光谱数据,分析了乌梁素海沉水植物光谱特征,并研究了冠层水深对乌梁素海沉水植物反射光谱的影响,建立了乌梁素海沉水植物冠层水深反演模型.结果表明:1)挺水植物在短波红外1662 nm和2223 nm附近分别有一个反射峰,这是挺水植物区别于沉水植物和漂浮藻类的重要波段; 0深度沉水植物(WDC=0)与漂浮藻类的光谱反射率非常接近,但是在绿波段(550～690 nm)有明显差异,因此,可以利用绿波段和短波红外波段的光谱特征来区分挺水植物、沉水植物和漂浮藻类.2)沉水植物群落的光谱反射率随冠层水深的增加而降低,在700～900 nm波段范围内变化最为明显,且在700～735 nm波段附近,沉水植物群落光谱反射率与冠层水深呈显著负相关.3)在建立的单波段/波段比沉水植物冠层水深反演模型中,波段比反演模型要优于单波段反演模型,波段比反演模型的决定系数R2> 0.70,均方根误差<13.70 cm,...     

Effects of solar eclipses in the ionosphere: Doppler sounding results: 2. Spectral analysis

The results of a spectral analysis of time variations in the Doppler frequency shift which accompanied solar eclipses in 1999?C2008 and calculations and estimates of disturbances in signal parameters are presented. Parameters of the ionosphere and its irregular structure are estimated on the basis of observational data. The calculation results correspond to the results of observations.     

Spectral attenuation of solar radiation in Patagonian fjord and coastal waters and implications for algal photobiology

The spectral attenuation of solar irradiation was measured during summer in two types of coastal waters in southern Chile, a north Patagonian fjord (Seno Reloncaví) and open coast (Valdivia). In order to relate the light availability with the light requirements of upper subtidal seaweeds, the saturating irradiance for photosynthesis (E_k) from P–I curves was measured. In addition the UV risk was assessed. Based on the z_1% of PAR, the lower limit of the euphotic zone in the studied systems averaged 21 m (K_d 0.24 m^?1) in Seno Reloncaví and 18 m (K_d 0.27 m^?1) in the coast of Valdivia. Photosynthesis of the studied seaweeds was saturated at markedly lower irradiances than found in their natural depths at the time of the study. Solar radiation penetrating into these depths at both locations largely supports the light requirements for the photosynthesis of subtidal species: 50–160 μmol m^?2 s^?1 for seaweeds from Seno Reloncaví (7 m tidal range) and 20–115 μmol m^?2 s^?1 for Valdivia assemblages (2 m tidal range). Optimal light conditions to saturate photosynthesis (E_k) were present at 10–16 m water depth. The attenuation of solar irradiation did not vary significantly between the fjord and coastal sites of this study. However, the underwater light climates to which seaweeds are exposed in these sites vary significantly because of the stronger influence of tidal range affecting the fjord system as compared with the open coastal site. The patterns of UV-B penetration in these water bodies suggest that seaweeds living in upper littoral zones such as the intertidal and shallow subtidal (<3 m) may be at risk.     

A search for north-south asymmetry of interplanetary magnetic field and solar plasma

An analysis of interplanetary magnetic field (IMF) and plasma data taken near 1 AU during solar activity cycle 21 reveals the following. 1. The yearly averaged spiral angle shows a solar cycle dependence. 2. The spiral angle north of the current sheet is 2.4○ higher than south of it during both epochs of positive and negative polarities. 3. The included angle is 4.8○ higher during the epoch of positive polarity than during the epoch of negative polarity. 4. The asymmetries in the number of away and toward IMF days are correlated with the asymmetries in solar activity. 5. The solar plasma north of the current sheet is hotter, faster and less dense than south of it during the epoch of negative polarity. 6. An asymmetry in the averaged filed magnitude is absent for solar cycle 21.