The vorticity of Solar photospheric flows on the scale of granulation

We employ time sequences of images observed with a G-band filter (λ4305Å) by the Solar Optical Telescope (SOT) on board of Hinode spacecraft at different latitude along solar central meridian to study vorticity of granular flows in quiet Sun areas during deep minimum of solar activity. Using a feature correlation tracking (FCT) technique, we calculate the vorticity of granular-scale flows. Assuming the known pattern of vertical flows (upward in granules and downward in intergranular lanes), we infer the sign of kinetic helicity of these flows. We show that the kinetic helicity of granular flows and intergranular vortices exhibits a weak hemispheric preference, which is in agreement with the action of the Coriolis force. This slight hemispheric sign asymmetry, however, is not statistically significant given large scatter in the average vorticity. The sign of the current helicity density of network magnetic fields computed using full disk vector magnetograms from the Synoptic Optical Long-term Investigations of the Sun (SOLIS) does not show any hemispheric preference. The combination of these two findings suggests that the photospheric dynamo operating on the scale of granular flows is non-helical in nature.     

特大地磁暴的一种行星际源:多重磁云

2001年3月31日观测到的大的多重磁云(Multi MC)事件造成了第23周太阳峰年(2000～2001)最大的地磁暴(Dst=-387nT). 通过分析ACE飞船的观测数据, 描述了这个多重磁云在1AU处的磁场和等离子体特征. 并且根据SOHO和GOES卫星的观测资料, 认证了它的太阳源. 在这次事件中, 由于多重磁云内部异常增强的南向磁场, 使之地磁效应变得更强, 它大大的延长了地磁暴的持续时间. 观测结果与理论分析表明, 多重磁云中子磁云的相互挤压使磁云内的磁场强度及其南向分量增强数倍, 从而加强了地磁效应. 因此, 研究认为多重磁云中子磁云之间的相互压缩是造成特大地磁暴的一种机制. 此外, 研究发现形成多重磁云的日冕物质抛射(CMEs)并不一定要来自同一太阳活动区.     

Origin and structures of solar eruptions Ⅱ: Magnetic modeling

The topology and dynamics of the three-dimensional magnetic field in the solar atmosphere govern various solar eruptive phenomena and activities, such as flares, coronal mass ejections, and filaments/prominences. We have to observe and model the vector magnetic field to understand the structures and physical mechanisms of these solar activities. Vector magnetic fields on the photosphere are routinely observed via the polarized light, and inferred with the inversion of Stokes profiles. To analyze these vector magnetic fields, we need first to remove the 180° ambiguity of the transverse components and correct the projection effect. Then, the vector magnetic field can be served as the boundary conditions for a force-free field modeling after a proper preprocessing. The photospheric velocity field can also be derived from a time sequence of vector magnetic fields.Three-dimensional magnetic field could be derived and studied with theoretical force-free field models, numerical nonlinear force-free field models, magnetohydrostatic models, and magnetohydrodynamic models. Magnetic energy can be computed with three-dimensional magnetic field models or a time series of vector magnetic field. The magnetic topology is analyzed by pinpointing the positions of magnetic null points, bald patches, and quasi-separatrix layers. As a well conserved physical quantity,magnetic helicity can be computed with various methods, such as the finite volume method, discrete flux tube method, and helicity flux integration method. This quantity serves as a promising parameter characterizing the activity level of solar active regions.     

Development of substorm bulges during storms of different interplanetary origins

Different solar wind structures are observed: magnetic clouds (MC), recurrent streams (RS), and regions of their interaction with undisturbed solar wind (Sheath and CIR). Three of these structures, Sheath, CIR, MC, are the sources of geomagnetic storms. We have searched for distinctions in the development of substorm bulges occurring during geomagnetic storms connected with the MC, Sheath and CIR. Solar wind parameters were taken from the Wind spacecraft and the auroral bulge parameters were obtained from the Ultra Violet Imager onboard Polar spacecraft. We determined the dimensions of the auroral bulges, the poleward aurora propagation, and the onset latitude of auroral bulges. It is shown that auroral bulges “geometry” is different for the examined types of storms. In consequence, the ratio between longitudinal and latitudinal sizes is also different.     

太阳高能粒子(SEP)传播数值模拟中的太阳风背景场研究

太阳高能粒子(SEP)事件是一类重要的空间天气灾害性事件,如能准确预报SEP事件,人们便可以采取必要的防护措施,保障卫星、星载设备以及航天员的安全,尽可能地降低经济损失.因此,其数值预报研究在空间天气预报研究中占有很重要的地位.SEP事件中的高能粒子在不同的时间尺度内被耀斑过程或者CME驱动的激波加速,并且在被扰动后的行星际太阳风中传输,这些过程都紧紧依赖于太阳风背景场.因此获取更加接近物理真实的太阳风背景场是模拟SEP事件的重要部分,也是提高SEP物理模式的关键因素之一.我们目前的工作基于张明等发展的SEP在行星际空间传播的模型,尝试将Parker太阳风速度解及WIND飞船观测的磁场实时数据融入模型中,研究不同的太阳风速度以及真实磁场分布对SEP在行星际空间中传播的影响.通过求解聚焦传输方程,我们的模拟结果表明:(1)快太阳风条件下,绝热冷却效应项发挥了更大的作用,使粒子能量衰减的更快,而慢太阳风对粒子的通量变化没有显著影响;(2)加入观测的磁场数据时,粒子的全向通量剖面发生了比较明显的变化,具体表现在:通量峰值推迟到达、出现多峰结构、各向异性也发生一些改变.分析表明真实磁场的极性对粒子在行星际空间中传播有着重要的影响.     

The solar magnetic flux mid-term periodicities and the solar dynamo

We investigate here the fluctuations in the total, open and closed solar magnetic flux (SMF) for the period 1971–1999 by means of the maximum entropy method in the frequency range 5×10⁻⁹–10⁻⁷ Hz (6 yr to 120 days). We use monthly data for the total, open and closed magnetic solar fluxes. Periodicities found in the series are similar showing that there is some relationship between the fluxes. The most important finding of this work is the existence of fluctuations at around 1.3 and 1.7 yr in the SMF with alternating importance during consecutive even and odd solar cycles. These fluctuations are directly related with variations present in cosmic rays, solar wind parameters and geomagnetic activity indexes. A quasi-triennial periodicity previously found in sunspots and other solar phenomena is also of importance. The SMF is generated by the action of the solar dynamo; therefore, it is through the magnetic flux that the solar dynamo influences several heliospheric phenomena.     

太阳活动区磁场与CMEs和太阳质子事件

文中选了５ 个典型活动区, 分析了这些活动区的磁场, 与活动区相应的ＣＭＥｓ, 太阳爆发事件和太阳质子事件我们发现, 对于Ｅ ≥１０ｍｅＶ 的太阳质子事件有相应的源活动区, 源耀斑和ＣＭＥ; 活动区矢量磁场有剪切, 磁场剪切越强质子事件越强; 多数在质子耀斑发生前出现磁流浮现; 太阳１０ｃｍ 射电爆发持续时间长文中结果还佐证了Ｓｈｅａｌｙ 等的结果： Ｘ 射线耀斑的长持续时间与ＣＭＥ 的发生正相关另外,在５ 个活动区中, 有三个大耀斑发生前没有明显的磁剪切作为它们的先兆, 它们是非质子源耀斑这是Ｍｏｏｒｅ, Ｈａｇｙａｒｄ 和Ｄａｖｉｓ 的磁场强剪切是耀斑产生的必要条件的反例     

Analytical configurations of a force-free magnetic cylinder in the solar wind

The problem of a smooth field configuration, which should be an initial configuration in modeling (using the method of coarse particles) the problem of a stationary solar wind flow around a magnetic cloud in the case of a spatially two-dimensional statement (when a magnetic cloud is considered as a force-free magnetic cylinder with a finite radius) is considered. It has been indicated that such a statement is possible only when the magnetic field in the solar wind is parallel to the cylinder axis. The method for finding the magnetic field of a force-free cylinder with a finite radius, when some field component is specified and another component is determined based on this one (which makes it possible to construct fields with preassigned properties), has been proposed. The variant for constructing the initial field configuration in the transition region around a cylinder has been proposed. This variant makes it possible to gradually pass from homogeneous crossed fields in the solar wind to a force-free magnetic and zero electric fields within a cylinder, an electric field being potential and orthogonal to a magnetic field (in the reference system related to a magnetic cloud).     

太阳磁场方向变化对于地球大气温度异常变化的意义

本文根据苏黎世天文台太阳黑子11年周期资料和太阳黑子磁场磁性变化周期特征,构建了太阳黑子磁场磁性指数MI(Magnetic Index)时间序列.分析表明：太阳活动磁性周期平均长度为222年,但是每个周期长度是不相等的;多数情况周期短时磁性指数较大,对应太阳活动水平强;周期变长时磁性指数较小,对应太阳活动水平较弱;太阳黑子磁场磁性指数序列也具有80～90年的世纪周期. 进一步研究指出,太阳黑子磁场磁性指数曲线由极小值升至极大值时期,太阳磁场南向,行星际磁场磁力线与地磁场磁力线重联,此时磁层为开磁层,太阳风将携带大量等离子体从向阳面进入地球磁层,从而使输入的动量、能量和物质大幅度增加,与北半球对流层增温时期对应;太阳黑子磁场磁性指数曲线由极大值下降至极小值时期,太阳磁场北向,与磁层顶地磁场同向,行星际磁场不会与地磁场发生重联,此时磁层为闭磁层,这种情况下,只有少数带电粒子能够穿越磁力线进入地球磁层,与北半球对流层降温时期对应.     

Small-Scale Magnetic Helicity and Nonlinear Stabilization of the Dynamo

According to present-day ideas, nonlinear saturation of the astrophysical dynamo and, in particular, the solar dynamo, are based on the consideration of the magnetic helicity balance, to which the helicities of the large-scale magnetic field and small-scale field related to it contributed. We show that, in a mirrorasymmetric medium, the small-scale magnetic field generated by the small-scale dynamo also has a nonzero magnetic helicity, which also should be taken into account in the magnetic helicity balance.     

一次日食电离层效应模拟研究

用120°E经度链附近台站电离层垂测资料和一个二维低纬电离层理论模式探讨1995年10月24日日食电离层效应．在日食条件下只考虑日食区计算太阳EUV辐射减少．模式结果显示：（1）日食期间较低高度电离层光食效应显著,电子浓度跟随食分迅速变化,在食甚后浓度减少达到最大。较高高度电离层对日食响应延迟.（2）低纬地区日食日f₀.F₂比控制日低,而h_mF₂比控制日高．在低纬度地区日食带来的影响相对较大·（3）赤道附近h_mF₂食甚后有一突变,出现日食F₁.5层。（4）食甚后海口纬度附近F层受日食影响持久,而f₀F₂在赤道附近出现第2次下降．最后对低纬日食电离层效应的动力学因素进行了初步的讨论．     

Comparative outline of the region of interaction of the solar wind with the Ionosphere of Venus and Mars

The general features of the region of interaction of the solar wind with the ionosphere of Venus and Mars are compared using data obtained with the Mariner 5 and the Pioneer Venus Orbiter (PVO) spacecraft for Venus and with the Phobos II, the Mars Global Surveyor (MGS) and the Mars Express spacecraft for Mars. Despite the overall weak intrinsic global magnetic field that is present in both planets there are significant differences in the manner in which the interplanetary magnetic field accumulates and is organized around and within their ionosphere. Such differences are unrelated to the crustal magnetic field remnants inferred from the MGS measurements around Mars. In fact, while in Venus and Mars there is a region in which the magnetic field becomes enhanced as it piles up in their plasma environment it is shown that such a region exhibits different regimes with respect to changes in the ion composition measured outside and within the ionosphere. At Venus the region of enhanced magnetic field intensity occurs in general above the ionopause which represents the boundary across which there is a change in the ion composition with dominant solar wind protons above and planetary O⁺ ions below. At Mars the region of enhanced magnetic field is located below a magnetic pileup boundary across which there is also a comparable change in the ion composition (solar wind protons above and planetary O⁺ ions below). It is argued that this difference in the relative position of the region of enhanced magnetic field with respect to that of a plasma boundary that separates different ion populations results from the peculiar response of the ionosphere of each planet to the oncoming solar wind dynamic pressure. While at Venus the peak ionospheric thermal pressure is in general sufficient to withhold the incident solar wind kinetic pressure there is a different response in Mars where the peak ionospheric thermal pressure is in general not large enough to deviate the solar wind. In this latter case the ionosphere is unable to force the solar wind to move around the ionosphere and as a result the oncoming electron population can reach low altitudes where it is influenced by neutral atmospheric particles (the solar wind proton population is replaced at the magnetic pileup boundary which marks the upper extent of the region where the interplanetary magnetic field becomes enhanced). Peculiar conditions are expected near the magnetic polar regions and over the terminator plane where the solar wind is directed along the sides of the planet.     

地球磁尾中不同类型磁结构的磁螺度演化特征

在二维三分量MHD数值模拟的基础上 ,对地球磁尾不同类型磁结构的形成作磁螺度分析 .研究表明 ,对于由晨昏电场产生的磁尾驱动重联过程 ,通过系统边界输运的磁螺度通量是引起系统总磁螺度变化的直接原因 .不同的初始磁螺度密度分布和磁螺度通量输运 ,可以引起中性片区域磁螺度密度分布的不同演化 ,从而导致具有不同拓扑位形磁结构的形成 .     

Submillimeter-wave and observations of the event on 28 November, 2001

We present a detailed study of a 1B/M6.9 impulsive flare combining high time resolution (1 ms) and instantaneous emission source localization observations at submillimeter frequencies (212 GHz), obtained with the solar submillimeter telescope (SST), and Hα data from the Hα solar telescope for argentina (HASTA). The flare, starting at 16:34 UT, occurred in active region (AR) 9715 (NOAA number) on November 28, 2001, and was followed by an Hα surge. We complement our data with magnetograms from the Michelson Doppler Imager (SOHO/MDI). SST observed a short impulsive burst at 212 GHz, presenting a weak bulk emission (of about 90 sfu) composed of a few shorter duration structures. The integrated Hα and the 212 GHz light curves present a remarkable agreement during the impulsive phase of the event. The delay between both curves stays below 12 s (the time resolution of the Hα telescope). The flare as well as the surge are linked to new flux emergence very close to the main AR bipole. Taking into account the AR magnetic field evolution, we infer that magnetic field reconnection, occurring at low coronal levels, could have been at the origin of the flare; while in the case of surge this would happen at the chromospheric level.     

Effects of the Sun on the Earth's environment

Solar disturbances are observed to have significant effects in near-Earth space. Over the past half-century of observation, a relatively clear picture has developed of how and why the typical solar wind — as well as the most extreme solar events — drive geospace responses. It is clear that magnetospheric substorms, geomagnetic storms (both recurrent and aperiodic events), and even certain atmospheric chemical changes have their origins in the solar–terrestrial coupling arena. High-speed solar wind streams and fast coronal mass ejections (CMEs) can often have strong interplanetary shock waves and southward magnetic fields which can initiate strong storm responses. We demonstrate in this review that available modern space-observing platforms and ground facilities allow us to trace drivers from the Sun to the Earth's atmosphere. This allows us to assess quantitatively the energy transport that occurs throughout the Sun–Earth system during both typical and extreme conditions. Hence, we are continuously improving our understanding of “space weather” and its effects on human society.     

孤立磁拱的约束平衡位形

本文讨论分层大气中孤立约束磁通量拱的二维静平衡位形．通量拱中的磁场初步假定为无力场，通过利用有限元计算方法，得到这个非线性自由边界问题的数值解．结果清楚地表明磁拱的内外场的耦合关系，并讨论了大气压力分布，尤其是大气标高对通量拱位形的影响．     

Spectral features of solar plasma flows

Research to the identification of plasma flows in the Solar wind by spectral characteristics of solar plasma flows in the range of magnetohydrodynamics is devoted. To do this, the wavelet skeleton pattern of Solar wind parameters recorded on Earth orbit by patrol spacecraft and then executed their neural network classification differentiated by bandwidths is carry out. This analysis of spectral features of Solar plasma flows in the form of magnetic clouds (MC), corotating interaction regions (CIR), shock waves (Shocks) and highspeed streams from coronal holes (HSS) was made. The proposed data processing and the original correlation-spectral method for processing information about the Solar wind flows for further classification as online monitoring of near space can be used. This approach will allow on early stages in the Solar wind flow detect geoeffective structure to predict global geomagnetic disturbances.     

Solar particle events seen by the MOPITT instrument

This paper reports on Device Single Events (DSEs) occurring in the Measurements Of Pollution In The Troposphere (MOPITT) space instrument piezoelectric accelerometers. It is found that DSEs correlate with the radiation environment, solar activity and high intensity Solar Proton Events.     

Writhe in the stretch-twist-fold dynamo

This article looks at the influence of writhe in the stretch-twist-fold dynamo. We consider a thin flux tube distorted by simple stretch, twist, and fold motions and calculate the helicity and energy spectra. The writhe number assists in the calculations, as it tells us how much the internal twist changes as the tube is distorted. In addition it provides a valuable diagnostic for the degree of distortion. Non mirror-symmetric dynamos typically generate magnetic helicity of one sign on large-scales and the opposite sign on small scales. The calculations presented here confirm the hypothesis that the large-scale helicity corresponds to writhe and the small scale corresponds to twist. In addition, the writhe helicity spectrum exhibits an interesting oscillatory behavior. The technique of calculating Fourier spectra for the writhe helicity may be useful in other areas of research, for example, the study of highly coiled molecules.