Dynamic Characteristics of Area Variations of Small and Large Sunspots and Quasi-Biennial Oscillations in Solar Activity

The spatiotemporal and chaotic dynamics of variations in area of sunspot groups related conventionally to small (area <50 Msh) and large (area >50 Msh) populations is analyzed. The Greenwich Observatory–Marshall Space Flight Center data were used. The results show that both sunspot populations have a single initial source, which is a magnetic flux generated by the dynamo process (presumably at the bottom of the convective zone) and is responsible for the 11—22-year periodicity of solar activity. A possible explanation of the revealed different behavior of the considered populations is that the magnetic flux is partially involved in another process responsible for the shaping of primarily very large sunspot groups. This process develops presumably in the upper layer of the convective zone with an unstable amplitude and a period varying within 1–2 years. The analysis of power spectrum of the Wolf number time series has indicated the difference between dynamic characteristics of the two studied processes.     

Unique solar flare of September 22, 2011: The suction effect

The specific features in the development of an X1 solar flare, which occurred on September 22, 2011, and was registered with the Atmospheric Imaging Assembly (AIA) device onboard the Solar Dynamics Observatory (SDO) in the UV line (λ = 304 Å, He II), are analyzed. During the flare, which lasted about 12 h, cold plasma was sucked up with an increasing velocity from a very distant region into the low-lying hot region of flare energy release along a flat helical trajectory. This phenomenon fundamentally differs from a surge ejection, when matter previously ejected from the flare region returns to the flare hot zone under the action of gravity. Suction of cold plasma “from outside” into the hot flare region is interpreted in the scope of the rope flare mechanism, according to which an extremely inhomogeneous plasma density distribution in the cross-section originates in an emerging magnetic rope. In the region with a sharply decreased density (which is the suction region), the drift velocity in the current chanel can reach the ion thermal velocity, which inevitably results in the excitation of plasma turbulence and anomalous resistance, i.e., in the development of a flare.     

2001年4月2日太阳耀斑及其太阳质子事件的观测结果研究

2001年4月2日, 太阳爆发了一个近年来X射线通量最大的一次耀斑并伴有质子事件, 利用“资源一号”卫星星内粒子探测器和神舟二号飞船X射线探测器的观测资料, 对这一事件的高能粒子响应进行了特例研究. “资源一号”卫星运行于太阳同步轨道, 高度约800km, 和宁静时期的统计结果对比, 这次耀斑后, 星内粒子探测器在地球极盖区（地球开磁场区）观测到耀斑粒子的出现, 这是宁静时期没有的; 神舟二号飞船轨道高度400km, 倾角为42°, X射线探测器在42°中高纬地区也观测到高能电子通量比宁静时明显的增加, 这表明, 太阳耀斑引起的近地空间辐射环境的变化遍及纬度约40°以上的区域, 甚至在40°N附近400 km左右的高度上仍然有响应. 但是, 中高纬度、极光带和极盖区的粒子来源, 加速机制和响应方式却不一定相同, 需要分别讨论. 资料分析和对比还表明, 质子事件的强度并不一定和耀斑的X射线通量成正比, 因此, 近地空间高能粒子对耀斑的响应也不是完全决定于X射线强度.     

The influence of a fluid-porous interface on solar pond stability

The linear instability of the gradient zone of a solar pond containing a fluid-porous interface is investigated. It is found that the gradient zone can retain the same stability for lower values of the solute Rayleigh number with the introduction of a porous material compared with a purely fluid layer, whilst maintaining the same lower convective zone temperature.Interestingly, it is also shown that for certain parameter values the penetration of a porous medium into the gradient zone can cause the temperature of the lower convective zone to rise. However, for certain parameter ranges, when the fluid-porous interface is towards the top of the gradient zone, the solar pond can become highly unstable.     

Crustal splitting and the emplacement of Pyrenean lherzolites and granulites

Pyrenean lherzolites representing fragments of the upper mantle are embedded in Mesozoic sediments along the 500-km-long, 20-km-wide “North Pyrenean Zone”. These ultramafics and the nearby occurrence of granulites, the presence of undersaturated rocks intrusive in the Cretaceous, and the development of a narrow elongate zone of “Pyrenean metamorphism”, confer a fundamental orogenic and geodynamic significance to this zone. These phenomena and the emplacement of the lherzolites may be attributed to an important phase of crustal thinning followed by a succession of compressive stages. The crustal thinning involved in the North Pyrenean Zone is possibly related to a transcurrent movement mainly during Albian and Senonian times, indicating a transform zone [24]. The ascent and emplacement of lherzolites in Albian sediments may have occurred in response to alternating tensional and compressional stresses operating in transcurrent zones. The Pyrenean metamorphism in Mesozoic sediments may be related to convective (emplacement of lherzolites) as well as conductive (thermal anomaly in connection with the rifting) processes. This model is compared with existing transform domains. Finally, it is suggested that crustal thinning may permit the incorporation of lower crust-upper mantle associations in the upper levels of the crust during subsequent compressive stages.     

Relationship between nonthermal and gasdynamic processes in powerful solar flares

The relationship between gas-dynamic processes and particle acceleration is illustrated using three examples. For the flare of July 6, 2006, observations show that explosive evaporation of the chromosphere occurs in the pulse phase. In addition, the coronal mass emission (CME) related to this flare reflects the primary energy release. In the strong limb flare of July 14, 2005, the CME observed in the external layers of the corona seems to be a consequence of repeated energy releases and plasma emissions. Apparently, this is indicated by the additional emission in the decimeter range, which is typical of posteruptive processes. An example of a weak flare during the decay phase of the strong event of April 15, 2001, was also accompanied by a decimeter burst.     

Helicity–vorticity turbulent pumping of magnetic fields in the solar convection zone

We study the effect of turbulent drift of a large-scale magnetic field that results from the interaction of helical convective motions and differential rotation in the solar convection zone. The principal direction of the drift corresponds to the direction of the large-scale vorticity vector. Thus, the effect produces a latitudinal transport of the large-scale magnetic field in the convective zone wherever the angular velocity has a strong radial gradient. The direction of the drift depends on the sign of helicity and it is defined by the Parker–Yoshimura rule. The analytic calculations are done within the framework of mean-field magnetohydrodynamics using the minimal τ-approximation. We estimate the magnitude of the drift velocity and find that it can be a few m/s near the base of the solar convection zone. The implications of this effect for the solar dynamo are illustrated on the basis of an axisymmetric mean-field dynamo model with a subsurface shear layer. The model shows that near the bottom of the convection zone the helicity–vorticity pumping results mostly from the kinetic helicity contributions. We find that the magnetic helicity contributions to the pumping effect are dominant at the subsurface shear layer. There the magnitude of the drift velocity is found to be a few cm/s. We find that the helicity–vorticity pumping effect can have an influence on the features of the sunspot time–latitude diagram, producing a fast drift of the sunspot activity maximum at the rise phase of the cycle and a slow drift at the decay phase of the cycle.     

The Effect of Heat Conduction on the Formation of Coronal Condensations in the Solar Atmosphere

Geomagnetism and Aeronomy - In this work, the evolution of oscillation instability in large-scale magnetic fields in the upper layers of the Sun’s convective zone is studied. The nonlinear...     

流变边界层及其对华北克拉通热/地震岩石圈底界差异的意义

二维热传导/对流数值模型显示,纯传导的固体岩石圈与纯对流的流体软流圈之间存在一过渡层,即流变边界层,其间传导与对流共同作用来传递热量.流变边界层厚度主要由软流圈黏性系数（η）控制,而受固体岩石圈厚度及热状态影响很小.随着η从1×10²¹Pa·s降低至1×10¹⁹ Pa·s,流变边界层也随之减薄,流变边界层的厚度与lg（η）成正比. 流变边界层的存在是造成热岩石圈与地震岩石圈厚度差异的重要因素. 全球典型克拉通岩石圈的对比结果表明,地震岩石圈厚度普遍大于热岩石圈厚度,二者的差异多数在70~90 km,很好地验证了流变边界层的存在. 研究发现二者的差异在华北克拉通自西向东逐渐减小：由西部鄂尔多斯的约80 km减少至渤海湾盆地的约20 km. 反映出华北克拉通岩石圈下部流变边界层厚度自西向东减薄,意味着软流圈黏性系数自西向东逐渐降低.这可能与中生代太平洋俯冲脱水形成的低黏大地幔楔有关,从一侧面印证了太平洋俯冲对华北克拉通破坏的影响.     

The flux ejection dynamo effect

Abstract

The mean-field effects of cyclonic convection become increasingly complex when the cyclonic rotation exceeds ½-π. Net helicity is not required, with negative turbulent diffusion, for instance, appearing in mirror symmetric turbulence. This paper points out a new dynamo effect arising in convective cells with strong asymmetry in the rotation of updrafts as against downdrafts. The creation of new magnetic flux arises from the ejection of reserve flux through the open boundary of the dynamo region. It is unlike the familiar α-effect in that individual components of the field may be amplified independently. Several formal examples are provided to illustrate the effect. Occurrence in nature depends upon the existence of fluid rotations of the order of π in the convective updrafts. The flux ejection dynamo may possibly contribute to the generation of field in the convective core of Earth and in the convective zone of the sun and other stars.     

白天混合层顶部夹卷层厚度的特征研究

本文首先对Deardorff的一阶模型给予解释，在此基础上分析对流边界层湍流动能方程，分析机械湍流和对流湍流对边界层发展的贡献，提出一个新的速度尺度，混合层顶速度尺度，定义了全理查森数，给出夹卷层厚度的参数化方案，并用Boers和Elotanta的雷达观测数据进行验证。参数化方案与实验数据符合得很好。当夹卷层厚度表示为夹卷速度或夹卷理查森数的函数时，该函数曲线随边界层发展通常表现为磁滞回线形状现象，利用本文的理论进行了解释。     

Observing Convective Aggregation

Convective self-aggregation, the spontaneous organization of initially scattered convection into isolated convective clusters despite spatially homogeneous boundary conditions and forcing, was first recognized and studied in idealized numerical simulations. While there is a rich history of observational work on convective clustering and organization, there have been only a few studies that have analyzed observations to look specifically for processes related to self-aggregation in models. Here we review observational work in both of these categories and motivate the need for more of this work. We acknowledge that self-aggregation may appear to be far-removed from observed convective organization in terms of time scales, initial conditions, initiation processes, and mean state extremes, but we argue that these differences vary greatly across the diverse range of model simulations in the literature and that these comparisons are already offering important insights into real tropical phenomena. Some preliminary new findings are presented, including results showing that a self-aggregation simulation with square geometry has too broad distribution of humidity and is too dry in the driest regions when compared with radiosonde records from Nauru, while an elongated channel simulation has realistic representations of atmospheric humidity and its variability. We discuss recent work increasing our understanding of how organized convection and climate change may interact, and how model discrepancies related to this question are prompting interest in observational comparisons. We also propose possible future directions for observational work related to convective aggregation, including novel satellite approaches and a ground-based observational network.     

海南岛海风雷暴结构的数值模拟

本文利用高分辨率WRF模式对2012年7月20日发生在海南地区的一次海风雷暴过程进行模拟,探讨了海南岛复杂地形下海风雷暴的结构、发展演变过程及其触发机制.结果表明,海南岛北部向内陆传播的海风与南部受地形阻挡的海风相遇后会形成海风辐合带,辐合带能影响当地的散度和涡旋特征,为雷暴的发生发展提供有利的动力和热力学条件.海南岛受热带海洋的影响较大,当地的水汽条件和对流潜势长期保持着有利于对流发展的状态,自由对流高度始终处于较低的位置,一旦海风辐合带来的抬升运动克服对流抑制到达自由对流高度后,对流就能自主地发展起来,所以单纯的海风辐合也常常能触发当地的强雷暴.雷暴发生发展过程中对流参数存在明显的变化,其演变曲线的突变位置对雷暴的发生有一定的指示作用.海南岛的海风雷暴过程与当地的复杂地形密切相关,地形的动力阻挡作用影响着低层海风的辐合以及对流的发展.     

Structure and development of the spotless flare on March 16, 1981

The morphological peculiarities of the 1N (N09W22) two-ribbon spotless flare on March 16, 1981, as well as its connection with a magnetic field, have been considered. In contrast to major flares of the active region, this spotless flare is characterized by a large-scale development process, a large distance from the magnetic neutral line, and the absence of the spread of the ribbons. The development of the flare had four periods. At the beginning of each period, a sharp increase in the brightness of the flare was observed along with a simultaneous decrease in the area of the flare ribbons. The areas of the ribbons varied synchronously during all of the periods. However, the situation changed abruptly near the maximum: the area of one of the ribbons increased, whereas the area of the other ribbon decreased. In our opinion, this behavior is a manifestation of real physical processes in the flare source and was a precursor of the beginning of the flare decay. The magnetic field and its topology, as well as the cellular structure of the chromosphere, were primarily responsible for the evolution of the flare. Almost all of the mottles and bright parts of the flare were localized in the immediate vicinity of magnetic hills with field intensities from 80 to 250 G. The main structural elements of the flare have been identified. A phenomenon called the tunnel effect has been revealed: the flare progresses inside a tunnel formed by the system of dark arch structures (filaments). The results indicate that spotless flares apparently constitute a specific class of flare phenomena and the study of them is of great interest for understanding of the origin of solar flares.     

Effects of shear in the convective boundary layer: analysis of the turbulent kinetic energy budget

Effects of convective and mechanical turbulence at the entrainment zone are studied through the use of systematic Large-Eddy Simulation (LES) experiments. Five LES experiments with different shear characteristics in the quasi-steady barotropic boundary layer were conducted by increasing the value of the constant geostrophic wind by 5 m s^-1 until the geostrophic wind was equal to 20 m s^-1. The main result of this sensitivity analysis is that the convective boundary layer deepens with increasing wind speed due to the enhancement of the entrainment heat flux by the presence of shear. Regarding the evolution of the turbulence kinetic energy (TKE) budget for the studied cases, the following conclusions are drawn: (i) dissipation increases with shear, (ii) the transport and pressure terms decrease with increasing shear and can become a destruction term at the entrainment zone, and (iii) the time tendency of TKE remains small in all analyzed cases. Convective and local scaling arguments are applied to parameterize the TKE budget terms. Depending on the physical properties of each TKE budget contribution, two types of scaling parameters have been identified. For the processes influenced by mixed-layer properties, boundary layer depth and convective velocity have been used as scaling variables. On the contrary, if the physical processes are restricted to the entrainment zone, the inversion layer depth, the modulus of the horizontal velocity jump and the momentum fluxes at the inversion appear to be the natural choices for scaling these processes. A good fit of the TKE budget terms is obtained with the scaling, especially for shear contribution.     

基于CloudSat资料的北上江淮气旋暴雪云系结构特征

2007年3月3-5日和2013年11月24-25日,受江淮气旋北上影响,我国北方大部地区遭遇罕见暴风雪天气,2次暴雪过程有很多相似之处.利用常规观测、CloudSat卫星云廓线雷达的探测资料和NECP/NCAR再分析资料,分析了这2次暴雪过程江淮气旋云系结构和微物理特征.结果表明：（1）北上江淮气旋的冷锋云系较窄,以深厚对流云为主,回波核心在2~7 km,其结构在气旋发展的不同阶段变化不大;（2）逗点头云系范围宽广,在气旋的不同发展阶段,结构和强度有显著差异.气旋初始锋面波动和锋面断裂阶段,逗点头云系有两个降水区：北部为由多个单体组成的大范围层状云区,强回波从地表向上伸展,上空有高空对流泡,建立了播撒云-供水云机制,有利于下部冰晶粒子长大;南部有对流云柱发展.逗点头西部的冷输送带云系主要集中在6 km以下,强度弱,冰粒子含量少;（3）气旋暖锋后弯阶段,干侵入加强,冷锋后部的无云区或少云区范围扩大,逗点头云系南北范围收缩、变窄,云系的高度、强度和含水量减弱,冷锋云系也减弱;（4）气旋冷锋云系和逗点头南部的对流云柱以降雨为主,位于高纬度陆地上的逗点头云系以降雪为主,当逗点头云系处于海上有对流不稳定发展,以降雨为主.冷锋云系北部和逗点头云系南部均有由层积云或高积云组成的低云,以毛毛雨为主.冷锋云系和逗点头云系北部100-200 km的范围为随高度和距离逐渐变薄的高层云,无降水对应.     

Magnetic field dynamics based on SOHO/MDI data in the region of flares related to halo coronal mass ejections

Variations in the photospheric magnetic field in the region of solar flares, related to halo coronal mass ejections (HCMEs) with velocities V > 1500, 1000 < V < 1500, and V < 650 km/s, have been studied based on SOHO/MDI data. Using data with a time resolution of 96 min, it has been indicated that on average the ??B _L?? and ??|B _L|?? field characteristics increase nonmonotonically during 1?C1.5 days before a flare and decrease during 0.5?C1 days after a flare for groups of ejections with V > 1000 km/s for all considered HCME groups. Angle brackets designate averaging of the measured B _L magnetic field component and its magnitude |B _L| within an area with specified dimensions and the center coincident with the projection onto the region where the flare center field is measured. It has been established that a solar flare related to an HCME originates when the ??B _L?? and ??|B _L|?? values are larger than the boundary values in the flare region. Based on 1-min data, it has been found for several HCMEs with V > 1500 km/s that the beginning of powerful flares related to ejections is accompanied by rapid impulsive or stepped variations in ??B _L?? and ??|B _L|?? near the center of a flare with a size of approximately 4.5°. It has been established that the HCME velocity positively correlates with the |??B _L??| value at the flare onset.     

Flare forecasting based on sunspot-groups characteristics

Our comprehension of solar flares is still lacking in many aspects and the possibility of observing active regions during the first phases of flare occurrence is limited by our capability of doing accurate flare forecasting. In order to give a contribution to this aspect, we focused our attention on the characteristics that must be fulfilled by sunspot-groups in order to be flare-productive. We addressed this problem using a statistical approach: first, we analyzed sunspot-groups parameters (i.e., Zürich class, magnetic configuration, area, morphology of the penumbra) and evolution; then, we performed a flare forecasting campaign, based on the results obtained in the first phase and on real-time observations. The results obtained by comparing the flare forecasting probability with the number of flares that have actually occurred are quite encouraging; we plan to improve this procedure by including a bigger statistical sampling.     

Extremely strong geomagnetic storm of September 2–3, 1859, according to the archived data of observations at the Russian network

A retrospective analysis of the Russian magnetic observations of the Carrington event that occurred on September 2–3, 1859, has been performed. The conclusion has been made that this event was caused by the series of three recurrent eruptive solar flares during ～40 h. The characteristics of the geomagnetic crochet, related to a considerable flux of the ionizing electromagnetic radiation during this flare, have been studied. The value and direction of a magnetic field disturbance, registered during the maximum of the geomagnetic storm of September 2, unambiguously indicate that all Russian stations were in the auroral oval zone, which was strongly expanded southward from its average position. The disturbance dependence on the station longitude—the absence of magnetometer pinning in Nerchinsk—is interpreted as the possible manifestation of a strong asymmetry in the effective contour of the current system, which was connected to the heliosphere and covered the disturbed magnetosphere and ionosphere during the short period that lasted only 1–3 h.