活动区新浮磁流和暗条的激活

用数值计算方法探讨了新浮磁流驱动下暗条运动的基本规律。计算表明,活动区新浮磁流是驱动暗条运动导致暗条激活的有效机制之一,这个过程是通过暗条电流和背景磁场的相互作用来实现的。当选取不同强度的浮现磁流时,暗条可出现周期性振荡、激活上升和闪烁;此外,对同极性磁流浮现,当浮现强度足够强时,暗条一开始就会下沉。      

Emerging magnetic flux,flares and filaments — FBS interval 16–23 June 1980

17 emerging magnetic flux regions with arch filaments related to new sunspots were identified in Hale Active Region No. 16918 during the 7 day interval from 16–22 June. Most of the new flux regions were clustered around the filament channel between the old opposite polarity fields as were most of the flares. The two largest regions of new magnetic flux and a few of the smaller flux regions developed very near the end points of filaments. This suggests that the emergence of flux in existing active regions might be non-random in position along a filament channel as well as in distance from a filament channel.We have analyzed the positions of 88 flares to date during about half of each day. We find that slightly more than half (50%) of the flares, irrespective of their size, are centered within the new flux regions. About 1/5 (20%) were centered on the border between the new flux and the adjacent older magnetic field. Less than 1/3 occurred outside of the newly emerging flux regions but in many cases were very close to the newly emerging flux. We conclude that at least 2/3 of the flares are intimately related to the emerging flux regions while the remaining 1/3 might be either indirectly related or unrelated to the emerging flux.     

Magnetic flux expulsion as an acceleration mechanism for stellar winds

Observations of the Sun show that magnetic flux is emerging through the surface in small scales in rather copious amounts. In order to maintain a steady state field strength, this flux must either be locally dissipated or explelled or both. We believe that magnetic reconnection and subsequent flux explusion is the most effective manner in which to achieve this. If new flux emerges into an already preexisting coronal magnetic field, the ambient field must be pushed aside to allow room for the new flux. If the ambient field strength decreases outward with radial distance as is expected for all stars, it may pinch off the emerging flux through magnetic reconnection and expell it outward. The net force on an isolated diamagnetic plasmoid produced by this process is shown to assume a particularly simple form, depending only on the plasmoid's mass, its temperature, and the radial gradient of the logarithm of the undisturbed magnetic pressure. If a sufficient number of these magnetic elements are produced per unit time, this process translates to a net outward magnetic force on the coronal plasma which can be greater that the gas pressure force. Thus, a stellar wind can be produced by magnetic forces alone without the need for a high coronal gas pressure — a mechanism which could be effective in explaining why stars, such as the late-type giants, which possess cool coronae nevertheless exhibit vigorous coronal expansions.     

Solar magnetic feature detection and tracking for space weather monitoring

We present an automated system for detecting, tracking, and cataloging emerging active regions throughout their evolution and decay using SOHO Michelson Doppler Interferometer (MDI) magnetograms. The SolarMonitor Active Region Tracking (SMART) algorithm relies on consecutive image differencing to remove both quiet-Sun and transient magnetic features, and region-growing techniques to group flux concentrations into classifiable features. We determine magnetic properties such as region size, total flux, flux imbalance, flux emergence rate, Schrijver’s R-value, R^∗ (a modified version of R), and Falconer’s measurement of non-potentiality. A persistence algorithm is used to associate developed active regions with emerging flux regions in previous measurements, and to track regions beyond the limb through multiple solar rotations. We find that the total number and area of magnetic regions on disk vary with the sunspot cycle. While sunspot numbers are a proxy to the solar magnetic field, SMART offers a direct diagnostic of the surface magnetic field and its variation over timescale of hours to years. SMART will form the basis of the active region extraction and tracking algorithm for the Heliophysics Integrated Observatory (HELIO).     

Relationships of a growing magnetic flux region to flares

Some sites for solar flares are known to develop where new magnetic flux emerges and becomes abutted against opposite polarity pre-existing magnetic flux (review by Galzauskas/1/). We have identified and analyzed the evolution of such flare sites at the boundaries of a major new and growing magnetic flux region within a complex of active regions, Hale No. 16918. This analysis was done as a part of a continuing study of the circumstances associated with flares in Hale Region 16918, which was designated as an FBS target during the interval 18 – 23 June 1980. We studied the initiation and development of both major and minor flares in Hα images in relation to the identified potential flare sites at the boundaries of the growing flux region and to the general development of the new flux. This study lead to our recognition of a spectrum of possible relationships of growing flux regions to flares as follows: (1) intimate interaction with adjacent old flux — flare sites centered at new/old flux boundary, (2) forced or “intimidated” interaction in which new flux pushes old field having lower flux density towards a neighboring old polarity inversion line where a flare then takes place, (3) “influential” interaction — magnetic lines of force over an old polarity inversion line, typically containing a filament, reconnect to the new emerging flux; a flare occurs with erupting filament when the magnetic field overlying the filament becomes too weak to prevent its eruption, (4) inconsequential interaction — new flux region is too small or has wrong orientation for creating flare conditions, (5) incidental — flare occurs without any significant relationship to new flux regions.     

Numerical simulation of reconnection in an emerging magnetic flux region

The resistive MHD equations are numerically solved in two dimensions for an initial-boundary-value problem which simulates reconnection between an emerging magnetic flux region and an overlying coronal magnetic field. The solution involves both ideal-MHD and resistive-MHD processes, and the solution shows an evolution which is remarkably suggestive of the preflare, impulsive, and main phases of the flare-cycle.     

Diamagnetic aspects of the coronal transient phenomenon

If a magnetic structure emerges into the solar atmosphere containing a preexisting magnetic field, the preexisting field must be moved aside to allow space for the emerging flux. Under these conditions, provided the ambient field strength decreases outward with radial distance, the ambient field may tend to pinch off the emerging field through magnetic reconnection and expell it outward. Here, a model is developed to demonstrate this effect and to evaluate its relevance to the coronal transient phenomenon. In particular, we argue that, if magnetic reconnection can be initiated in such a configuration, the upward force produced by the ambient field is enhanced and, depending upon the internal conditions of the configuration, a coronal transient could be initiated in this manner.     

IUE observations of cataclysmic variables

The four years of IUE operation have revealed that the ultraviolet region of the spectrum contributes a dominant share of the emerging energy from cataclysmic variables and provides important clues to the physical nature of these systems. The implications of the continuum flux distributions and line spectra for the determination of the accretion rates and mass loss rates are considered.     

Cool luminous stars

A broad theme emerging from $\text{IUE}$ and $\text{Einstein}$ observations of cool stars is that magnetic fields control the structure and energy balance of the outer atmospheres of these stars. I summarize the phenomena associated with magnetic fields in the Sun and show that similar phenomena occur in cool luminous stars. High dispersion spectra are providing unique information concerning densities, atmospheric extension, and emission line widths. A recent unanticipated discovery is that the transition lines are redshifted (an antiwind) in β Dra (G2 Ib) and perhaps other stars, which I interpret as indicating downflows in closed magnetic flux tubes as are seen in the solar flux tubes above sunspots. Finally, I classify the G and K giants and supergiants into three groups — active stars, quiet stars, and hybrid stars — depending on whether their atmospheres are dominated by closed magnetic flux tubes, open field geometries, or a predominately open geometry with a few closed flux tubes embedded.     

A theoretical model for the magnetic helicity of solar active regions

Active regions on the solar surface are known to possess magnetic helicity, which is predominantly negative in the northern hemisphere and positive in the southern hemisphere. Choudhuri et al. [Choudhuri, A.R. On the connection between mean field dynamo theory and flux tubes. Solar Phys. 215, 31–55, 2003] proposed that the magnetic helicity arises due to the wrapping up of the poloidal field of the convection zone around rising flux tubes which form active regions. Choudhuri [Choudhuri, A.R., Chatterjee, P., Nandy, D. Helicity of solar active regions from a dynamo model. ApJ 615, L57–L60, 2004] used this idea to calculate magnetic helicity from their solar dynamo model. Apart from getting broad agreements with observational data, they also predict that the hemispheric helicity rule may be violated at the beginning of a solar cycle. Chatterjee et al. [Chatterjee, P., Choudhuri, A.R., Petrovay, K. Development of twist in an emerging magnetic flux tube by poloidal field accretion. A&A 449, 781–789, 2006] study the penetration of the wrapped poloidal field into the rising flux tube due to turbulent diffusion using a simple 1-d model. They find that the extent of penetration of the wrapped field will depend on how weak the magnetic field inside the rising flux tube becomes before its emergence. They conclude that more detailed observational data will throw light on the physical conditions of flux tubes just before their emergence to the photosphere.     

On the nature of coronal loops above the quiet sun network

The structure and dynamics of a box in a stellar corona can be modeled employing a 3D MHD model for different levels of magnetic activity. Depending on the magnetic flux through the surface the nature of the resulting coronal structures can be quite different. We investigate a model of an active region for two sunspots surrounded by magnetic field patches comparable in magnetic flux to the sunspots. The model results in emission from the model corona being concentrated in loop structures. In Gudiksen and Nordlund (2005) the loops seen in EUV and X-ray emission outline the magnetic field, following the general paradigm. However, in our model, where the magnetic field is far from a force-free state, the loops seen in X-ray emission do not follow the magnetic field lines. This result is of interest especially for loops as found in areas where the magnetic field emerging from active regions interacts with the surrounding network.     

The relation of solar flares to the evolution and proper motions of magnetic fields

The second Action Interval of the FBS coincided with an extended period of gradual evolution in a large complex of activity which served as the target for a coordinated space-ground study. The complex produced a multitude of subflares, half of which were clustered around just a few sites, each with a distinctive magnetic character. The essential flare-producing conditions at these preferred sites were preserved for many hours, even days, despite disruptions by flares and despite the eroding effects that accompany the disintegration of sunspot groups. Three preferred sites were active for the entire Interval, 22–27 May 1980. A comparison of flaring with non-flaring sites which also contained strong concentrations of flux demonstrates the importance of magnetic complexity, flux emergence, and motions at the photospheric level. The most energetic events by far, a chain of five closely homologous flares, erupted within 13 hours at a site where all these factors were conspicuously combined. The incessant activity preceding and during these flares of the fine chromospheric fibrils that covered and surrounded this particularly energetic site indicates reconfiguration of flux tubes in the chromosphere in a matter of minutes. These rapid (2–5 minutes), small (～10 arc-sec) changes are identified with emerging flux and with pores moving rapidly (≥200 m/s) very close to a magnetic neutral line.     

Numerical MHD modeling of the solar driver for the destabilization of a coronal helmet streamer

We investigate the forms of the solar driver which cause the destabilization of helmet streamers. Two forms of solar drivers are considered; (i) emergence of a flux-rope from sub-photospheric levels and (ii) application of a photospheric shear motion to a streamer-flux rope system. Numerical results showed that both cases exhibit the characteristics of commonly observed coronal mass ejections (CMEs), but the propagation speed of the CME is higher than the background solar wind speed when the solar driver is the emerging magnetic flux and is the same as the solar wind speed when the photospheric shear is used as the solar driver. The energy constraint allowing the magnetic field transition from a closed to an open configuration is also addressed.     

Driving major solar flares and eruptions: A review

This review focuses on the processes that energize and trigger M- and X-class solar flares and associated flux-rope destabilizations. Numerical modeling of specific solar regions is hampered by uncertain coronal-field reconstructions and by poorly understood magnetic reconnection; these limitations result in uncertain estimates of field topology, energy, and helicity. The primary advances in understanding field destabilizations therefore come from the combination of generic numerical experiments with interpretation of sets of observations. These suggest a critical role for the emergence of twisted flux ropes into pre-existing strong field for many, if not all, of the active regions that produce M- or X-class flares. The flux and internal twist of the emerging ropes appear to play as important a role in determining whether an eruption will develop predominantly as flare, confined eruption, or CME, as do the properties of the embedding field. Based on reviewed literature, I outline a scenario for major flares and eruptions that combines flux-rope emergence, mass draining, near-surface reconnection, and the interaction with the surrounding field. Whether deterministic forecasting is in principle possible remains to be seen: to date no reliable such forecasts can be made. Large-sample studies based on long-duration, comprehensive observations of active regions from their emergence through their flaring phase are needed to help us better understand these complex phenomena.     

Actors of the main activity in large complex centres during the 23 solar cycle maximum

During the maximum of Solar Cycle 23, large active regions had a long life, spanning several solar rotations, and produced large numbers of X-class flares and CMEs, some of them associated to magnetic clouds (MCs). This is the case for the Halloween active regions in 2003. The most geoeffective MC of the cycle (Dst = −457) had its source during the disk passage of one of these active regions (NOAA 10501) on 18 November 2003. Such an activity was presumably due to continuous emerging magnetic flux that was observed during this passage. Moreover, the region exhibited a complex topology with multiple domains of different magnetic helicities. The complexity was observed to reach such unprecedented levels that a detailed multi-wavelength analysis is necessary to precisely identify the solar sources of CMEs and MCs. Magnetic clouds are identified using in situ measurements and interplanetary scintillation (IPS) data. Results from these two different sets of data are also compared.     

中性电流片的形成和环形日冕瞬变

在双极背景场下,光球层反向磁通量的喷发将会在新老磁场之间形成中性电流片.本文从理想磁流体方程组出发,考虑磁场和日冕等离子体的相互作用,对上述电流片的形成过程进行了数值研究.结果表明,对亚音速喷发,将由里向外形成四个区域:(1)由喷发物质直接形成的低温,高密度日珥,位于最里层;(2)紧挨抛射日珥的低温稀疏区;(3)喷发物质和日冕物质向中性电流片集中形成的高温.高密度物质环;(４)在环的周围,由快磁声波形成的,密度略比日冕背景为高的前鞘区.上述结构与典型的环形日冕瞬变的观测特征相符.由此表明双极背景场下反向磁通量的喷发可能是触发这类瞬变的重要机制.      

低高度空间高能质子通量分布计算

介绍了AP-8模式、CRRESPRO模式和PSB97模式,并用这3种模式分别计算低高度空间300—1100km范围内的高能质子通量分布,由IDL软件绘出通量等值线图．AP-8模式通量主要受银河宇宙线调制,即受太阳活动直接影响,与太阳活动高年相比,太阳活动低年的质子通量较大;CRRESPRO模式中,因活动期和平静期的数据采集时间前后相差很短,从而使同一高度上两种环境条件下的通量分布相似．模式之间的比较结果表明,AP-8模式通量较小,CRRESFRO模式通量较大,PSB97模式通量介于二者之间,并与实测通量接近．PSB97是为低高度(1000km以下)定制的模式,在低高度上优于AP-8模式和CRRESPRO模式,能较好地计算当前条件下的低高度高能质子通量．     

CME productivity associated with Solar Flare peak X-ray emission flux

It is often noticed that the occurrence rate of Coronal Mass Ejections (CMEs) increases with increase in flare duration where peak flux too increase. However, there is no complete association between the duration and peak flux. Distinct characteristics have been reported for active regions (ARs) where flares and CMEs occur in contrast to ARs where flares alone occur. It is observed that peak flux of flares is higher when associated with CMEs compared to peak flux of flares with which CMEs are not associated. In other words, it is likely that flare duration and peak flux are independently affected by distinct active region dynamics. Hence, we examine the relative ability of flare duration and peak flux in enhancing the CME productivity. We report that CME productivity is distinctly higher in association with the enhancement of flare peak flux in comparison to corresponding enhancement of flare duration.     

氧-乙炔烧蚀试验中热流密度的计算

通过氧-乙炔烧蚀试验中改变氧气与乙炔气流量比值的一系列试验,研究了热流密度随其变化的规律,并利用一元线性回归方法,分区间拟合得到了热流密度与两种气体流量比值的数学关系式,经检验该关系式适用性较好,为防热复合材料在氧-乙炔烧蚀试验中热流密度的变化提供了可靠的计算依据.     

基于GM(1,1)与灰区间估计的SPE通量水平长期预测

太阳质子事件（SPE,Solar Proton Events）是干扰日地空间最主要的源,大规模质子事件会影响在轨空间站实验设备的可靠性,有时甚至会威胁空间站的安全运行.提出一种基于灰色GM（1,1）和区间估计太阳质子事件预测方法;首先对1976—2010年SPE通量水平数据进行预处理,分别建立以发生时间为序列的一般SPE通量序列与极端SPE通量序列;之后将灰色GM（1,1）与区间估计相结合建立预测方法,融合反映一般SPE通量水平随周期性波动的活跃性调节系数,建立SPE通量水平长期预测模型;然后叠加不同SPE类型所得结果合成预测年份的SPE通量水平,给出未来一年或几年间SPE通量水平的变化范围;最后选取1976—2010年太阳质子事件年均值数据,分多批次预测1996—1998年和1999—2001年等SPE通量均值区间,结果表明各年实际发生SPE的通量均值均位于预测区间内,并且多年预测区间偏差最大值小于26%,实验结果还表明单次预测时长以2~3年为宜.