Detection of a cyclotron line in the radio spectrum of a solar active region and its interpretation

Observations of the active region AR 7962 obtained at 2–32 cm on the RATAN-600 radio telescope on May 10–12, 1996, are presented. The high-resolution measurements detected a narrow feature near 8.5 cm against the background of the smooth spectrum of the local source associated with sunspots. This narrow-band emission is identified with a bright, pointlike, high-frequency source at 1.7 cm recorded on maps made using the Nobeyama radio telescope. The characteristics of the observed line (lifetime 3 days, brightness temperature of the order of several million Kelvin, relative width of about 10%) suggest that it can be explained as thermal cyclotron radiation at the third harmonic of the electron gyrofrequency from a compact source containing a dense, hot plasma; the corresponding higher frequency emission could be due to thermal Bremsstrahlung. Analysis of the RATAN-600 and Nobeyama data can be used to probe the magnetic field, kinetic temperature, and electron density in the radiation source in the corona.     

MHD simulations of current-sheet formation over a bipolar active region

We present the results of numerical simulations of the development of a current sheet in the solar corona over a bipolar region during the emergence of two new sunspots arranged collinearly with older spots. Two fronts of increased plasma density form at the boundary of the rising new magnetic flux. One of these is due to the generation of a current sheet, whose magnetic field accumulates energy for a flare. The other front is a branch of the density perturbation, and separates the old and new magnetic fluxes in a region where the magnetic field lines have the same direction on both sides of the boundary. The development of this perturbation is not associated with the energy accumulation in the corona, and hinders observation of the preflare state and complicates analysis of the results. This second front can be interpreted as the eruption of a filament before the onset of the flare. A scheme conservative with respect to magnetic flux was introduced in the Peresvet code that solves the MHD equations, in order to suppress numerical instabilities in regions of large magnetic-field gradients.     

Small-amplitude oscillations in solar filaments

The temporal and spatial properties of small-amplitude oscillations have been studied using spectral observations of motions in solar filaments carried out at the Sayan Solar Observatory (Institute of Solar-Terrestrial Physics, Russian Academy of Sciences). Oscillations with different periods and spatial scales exist simultaneously in filaments. Swaying motions of filaments in the plane of the sky have been detected. The character of these oscillatory motions is compared with oscillations in the Doppler velocity at the same filament sites.     

Pre-flare changes in the turbulence regime for the photospheric magnetic field in a solar active region

Observations of the total magnetic field in the active region NOAA 6757 have been used to study the turbulence regime from 2.5 h before the onset of a 2B/X1.5 flare until two minutes after its maximum. The curvature of the exponent ζ(q) for the structure functions of the B _z field increases monotonically before the flare (i.e., the multifractal character of the B _z field becomes more complex) but straightens at the flare maximum and coincides with a linear Kolmogorov dependence (implying a monofractal structure for the B _z field). The observed deviations of ζ(q) from a Kolmogorov line can be used for short-term forecasting of strong flares. Analysis of the power spectra of the B _z field and the dissipation of magnetic-energy fluctuations shows that the beginning of the flare is associated with the onset of a new turbulence regime, which is closer to a classical Kolmogorov regime. The scaling parameter (cancellation index) of the current helicity of the magnetic field, k _h , remains at a high level right up until the last recording of the field just before the flare but decreases considerably at the flare maximum. The variations detected in the statistical characteristics of the turbulence can be explained by the formation and amplification of small-scale flux tubes with strong fields before the flare. The dissipation of magnetic energy before the flare is primarily due to reconnection at tangential discontinuities of the field, while the dissipation after the flare maximum is due to the anomalous plasma resistance. Thus, the flare represents an avalanche dissipation of tangential discontinuities.     

Magnetic flux in an active solar region and its correlation with flares

The correlation between the magnetic flux in an active solar region and associated powerful solar flares is studied. The behavior of the active regions AR 10486 and AR 10365 is considered. These regions produced a series of class X flares as they crossed the solar disk. The flares appeared when the magnetic flux exceeded 10²² Mx. The magnetic flux remained constant during all the flares except for one. During this flare, the flux decreased by about 10%; this impulsive decrease of the flux was also recorded in the absence of flares. No energy flux from the photosphere to the corona at the time of the flare was observed. The behavior of the photospheric field in AR 10486 and AR 10365 is consistent with a slow accumulation of energy in the corona and the explosive release of energy stored in the magnetic field of a current sheet above an active region during the flare.     

Some properties of the joining of solar filaments

Some possibilities for the reconnection of magnetic-field lines of solar filaments that approach when the photospheric polarity inversion lines change their positions, are discussed. The interaction between filaments depends on their internal properties, which are determined by the filament chirality, or the sign of the helicity of the filament magnetic field. In quadrupolar magnetic configurations, filaments with the same chirality can exchange their halves. Filaments with opposite chirality rupture after the reconnection of the polarity inversion lines, since the two fragments of the different filaments cannot be connected continuously. The morphology and connectivity of the filaments are analyzed using daily Hα filtergrams obtained over the period of maximum activity of the 23rd solar cycle. Examples of alterations of the filament connectivity occuring during the evolution of photospheric fields are presented.     

Morphological indictors of the chirality of solar filaments

There is no doubt that the structural features of filaments reflect properties of their magnetic fields, such as chirality and helicity. However, the interpretation of some morphological features can lead to incorrect conclusions when the observing time is limited and the spatial resolution is insufficiently high. In spite of the relative constancy of their overall shapes, filaments are dynamical formations with inhomogeneities moving along the threads making them up. Therefore, it is possible to observe material concentrated not only in magnetic traps, but also along curved arcs. Difficulties often arise in determining the chirality of filaments with anomalous “barbs”; i.e., those whose jagged side is located on the opposite side of the axis compared to most (“normal”) filaments. A simple model is used to show that anomalous barbs can exist in an ordinary magnetic flux rope, with the threads of its fine structure oriented nearly perpendicular to its length. A careful analysis of images with the maximum available spatial resolution and with information about temporal dynamics, together with comparisons with observations in various spectral lines, can enable a correct determination of the chirality of filaments.     

The structure of solar filaments. Prominences in the corona free from external magnetic field

The new approach to the modeling of quiescent solar prominences is proposed. We solve the inverse magnetohydrostatic problem, when the pressure, density and temperature of plasma in the filament are calculated from the equilibrium equations using the given magnetic structure (magnetic flux function is proposed to be known). The new exact nonlinear solutions for dense (n ≈ (2?3) × 10¹¹ cm^?3) and cold (T ≈ (5?10) × 10³ K) filaments, embedded in the plan, vertically stratified atmosphere (hot solar corona) free of magnetic field, are derived. The filaments are stretched along the horizontal axisy(the translational symmetry is assumed: ?/?y = 0) and located parallel to and above a photospheric, magnetic polarity reversal line. The magnetic field lines have a structure of magnetic flux rope with helical field lines in three-dimensional space; the strength of magnetic field falls rapidly with distance from a rope axis. No external longitudinal magnetic field is needed to equilibrate the prominence. The net electric current along the filament is equal to zero. The model of magnetic arcade with the deflection (sag) on the top, proposed by Pikelner (1971) as a basic form of normal prominence, is calculated also using the method proposed. It is shown that such magnetic arcade, having the magnetic field strength of few gauss only, can effectively maintain the equilibrium of cool dense filament at the heights about 50–60 Mm.     

Late Paleozoic faults of the Altai region, Central Asia: tectonic pattern and model of formation

The present kinematic and dynamic analysis of large-scale strike-slip faults, which enabled the formation of a collage of Altai terranes as a result of two collisional events. The Late Devonian–Early Carboniferous collision of the Gondwana-derived Altai-Mongolian terrane and the Siberian continent resulted in the formation of the Charysh–Terekta system of dextral strike-slip faults and later the Kurai and Kuznetsk–Teletsk–Bashkauss sinistral strike-slip faults. The Late Carboniferous–Permian collision of the Siberian and Kazakhstan continents resulted in the formation of the Chara, Irtysh and North-East sinistral strike-slip zones. The age of deformation of both collisional events becomes younger toward the inner areas of the Siberian continent. In the same direction the amount of displacement of strike-slip faulting decreases from several thousand to several hundred kilometers. The width of the Late Paleozoic zone of deformation reaches 1500 km. These events deformed the accretion-collision continental margins and their primary paleogeographic pattern.     

The active region Orion KL in polarized emission in the Orion

The fine structure of the active region in the Orion KL gas-dust complex has been measured in polarized H₂O maser emission (epoch December 12, 1998) with an angular resolution of 0.15 mas, or 0.07 AU, and a velocity resolution of 0.05 km/s. The maser emission is concentrated in a line with ΔV = 0.45 km/s, V _LSR = 7.65 km/s, and a flux density of F = 2.1 MJy. The structure consists of a compact source (ejector), highly collimated bipolar outflow, and a toroidal component. The brightness temperature of the ejector is T _b = 2 × 10¹⁶ K, and its degree of linear polarization reaches m ≈ 20%. The variation of the polarization angle across the profile is dX/dV = ?23°/(km/s), which considerably exceeds the Faraday rotation in the HII region foreground to the molecular cloud. The observed “rotation” is explained as an effect of different orientations for the polarization of the ejected outflows. The brightness temperature of the bipolar outflow is T _b ≈ 10¹⁴ K, while that of individual components is T _b ≈ 10¹⁵ K. The degree of polarization in the components exceeds that of the ejector and reaches m ≈ 50%. The position angle of the polarization is X ≈ 45° relative to the outflow. The torus, which is observed edge-on, has a diameter of 0.38 AU and a thickness of 0.08 AU. The brightness temperature of the tangential directions in the torus is T _b ≈ 5 × 10¹⁵ K, and the rotational velocity is V _rot ≈ 0.02 km/s. The degree of polarization is m ≈ 40%, and its position angle relative to the azimuthal plane is X ≈ 43°. The relative deviations of the polarization plane in the bipolar outflow and torus relative to the pumping direction are nearly the same and are determined by Faraday rotation within the HII region.     

Resonance-centrifugal effects as a factor in the formation of solar magnetic arcades

The development of magnetohydrodynamical centrifugal instability is considered as a possible mechanism for the formation of solar magnetic arcades. The computations show that the plasma in a cylindrical, magnetized, rotating layer can develop two families of waveguide-resonance instability modes. These are gyroscopic resonance modes of the rotating, cylindrical layer and harmonics of fast magnetoacoustic waves that propagate along the forming cylindrical layer and initiate resonance instability in the layer. The joint action of these two mechanisms is able to produce the observed morphology of solar magnetic arcades.     

下扬子区新生代断陷盆地的构造与形成

为了揭示下扬子海陆全区新生代断陷盆地的构造特征,进而探讨盆地的形成机理,故对研究区的地震、钻井和地质资料进行系统分析,梳理区内的主要构造地质证据,并在时空上进行对比。垂直盆地走向的区域大剖面构造解析显示,下扬子区由陆至海,盆地范围逐步扩大,断陷充填厚度逐渐增厚,结构趋于复杂,表明盆地的拉伸量和伸展强度自西向东呈增大趋势。受下扬子块体近似楔形几何形状与东部侧向挤压的边界条件约束,块体近南北向侧向扩展,块体内区域伸展,前新生代的基底先存断裂复活,诱发区域张裂作用和盆地沉降,断陷盆地形成受基底应力两个基本因素制约。下扬子新生代块体的伸展与郯庐断裂的右旋走滑,均为下扬子块体构造形变的地质响应,其动力学机制可用太平洋板块北西向俯冲进行解释。     

Dynamics of the hard X-ray,gamma-ray,and microwave emission of solar flares produced by the active region NOAA 0069 in August 2002

Regularities have been searched for in the dynamics of characteristics of flare solar radiation during the development of the active region NOAA 0069 in the interval of August 14–24, 2002. The SONG (Solar Neutrons and Gamma rays) instrument onboard the Russian CORONAS-F Solar Observatory recorded hard X-ray and gamma-ray radiation in nine of the 30 flares of class above C5 in this active region within the indicated time interval. It was obtained that, in accordance with the development of the active region, the X- and gamma-ray flux tended to increase at the flare maxima while the hard X-ray spectral index tended to decrease; flares with a harder radiation spectrum occurred in the sunspot umbra, i.e., in the region with the strongest magnetic fields.     

Twist of magnetic fields in solar active regions

We study the twist properties of photospheric magnetic fields in solar active regions using magnetographic data on 422 active regions obtained at the Huairou Solar Observing Station in 1988–1997. We calculate the mean twist (force-free field α_f) of the active regions and compare it with the mean current-helicity density of these same active regions, h _c =B _∥·(?×B)_∥. The latitude and longitude distributions and time dependence of these quantities is analyzed. These parameters represent two different tracers of the α effect in dynamo theory, so we might expect them to possess similar properties. However, apart from differences in their definitions, they also display differences associated with the technique used to recalculate the magnetographic data and with their different physical meanings. The distributions of the mean α_f and h _c both show hemispherical asymmetry—negative (positive) values in the northern (southern) hemisphere—although this tendency is stronger for h _c. One reason for these differences may be the averaging procedure, when twists of opposite sign in regions with weak fields make a small contribution to the mean current-helicity density. Such transequatorial regularity is in agreement with the expectations of dynamo theory. In some active regions, the average α_f and h _c do not obey this transequatorial rule. As a whole, the mean twist of the magnetic fields α_f of active regions does not vary significantly with the solar cycle. Active regions that do not follow the general behavior for α_f do not show any appreciable tendency to cluster at certain longitudes, in contrast to results for h _c noted in previous studies. We analyze similarities and differences in the distributions of these two quantities. We conclude that using only one of these tracers, such as α_f, to search for signatures of the α effect can have disadvantages, which should be taken into account in future studies.     

The Lar Dam; an example of infrastructural development in a geologically active karstic region

The problems associated with the construction of the Lar Dam, Iran, provide a classic example of problems that can result from infrastructural development in an active geological terrain which includes the regional carbonate units. The Lar Dam lies in a heavily faulted and fractured region close to the active Damavand volcano. The fracturing has enhanced the production of karst and sinkholes in the limestone below the dam, and acidic ground-water run-off from the Damavand volcano increases the dissolution of the carbonate beds along the fractures to produce sinkholes below the dam. The initial problem of building the dam in such a region is compounded by the relationship between water loss due to enhanced sinkhole development and the remedial measures being taken to lessen this leakage. Drainage of the sub-reservoir caverns through leakage along fractures can lead to loss of hydrostatic support for the developing sub-reservoir caverns, and their consequent collapse. Furthermore, rapid changes in subterranean water levels would lead to rock-shattering hammer effects particularly during rapid rises in water level.     

Bipolar outflow in the active region orion KL

The fine structure of the region of formation of a protostar in the dense molecular cloud OMC-1 of the Orion Nebula was studied during a period of enhanced activity in 1998–1999, with an angular resolution of 50 μas and a velocity resolution of Δv = 0.053 km/s. Inclusions of ice granules in the bipolar outflow were detected and identified. The velocity of the outflow reaches ∼50 km/s, while that of the granules is <5 km/s. The outflow sublimates and accelerates H₂O molecules, thereby exciting the maser emission. As a result, their relative velocity and, accordingly, pumping level decrease. The maser emission of the outflow is observed at distances out to ρ < 3 mas, or <1.5 AU. However, in the distant part (ρ > 5 mas), bullets corresponding to maser emission excited by the outflow in the surrounding medium are observed. The emission is amplified by the external medium at a velocity of v _LSR = 7.65 km/s in the bandwidth Δ _v ≈ 0.5 km/s. The sources of pumping are clusters of infrared sources. The bipolar outflow is inclined at a small angle to the plane of the sky. The acceleration of the maser inclusions also increases the longitudinal component of the velocity, reducing amplification of the emission. The brightness temperature of the components decreases: T _b ∼ ρ ^−0.8±0.1. The activity terminates with the exponential decline of the maser emission, F ∼ exp(−0.5t ²); in the saturated mode this is determined by a decrease in the optical depth, τ ∼ t ². The material of the surrounding space, including the ice granules, is drawn into the disk, moves along spirals toward the nozzle, and is ejected as a highly collimated bipolar flow. The density of material in the outflow exceeds the surrounding density by three to four orders of magnitude. The accretion of the surrounding material and ejection of the bipolar outflow are a unified process accompanying the initial phase of formation of protostars. The counter motion of material at the center stimulates the formation of a central massive object, whose gravitational field accelerates the process and stabilizes the system. The ratio of the durations of periods of high and low activity is determined by the rates of ejection and disk replenishment, and is ∼1:10. The rotating bipolar flow is self-focused.     

Investigation of magnetic fields in solar active regions

The magnetic-field structure in solar active regions outside spots is studied. The line-of-sight fields were measured using the new Crimean digital magnetograph in three spectral lines—Fe I 5253 Å, Fe II 5234 Å, and Ti I 5193 Å. Observations in the Fe II 5234 Å line indicate systematically higher field strengths than those in the Fe I 5253 Å line. The magnetic fluxes in 2″ elements are ～4.3×10¹⁸ Mx, ～4.6×10¹⁸ Mx, and ～6.2×10¹⁸ Mx according to the Fe I 5253 Å, Ti I 5193 Å, and FeII 5234 Å observations, respectively. Elements 2″–8″ in size make the largest contribution to the magnetic fluxes of active regions outside spots.     

Volcanic sequence and magma formation in the Oslo region

The Permian activity in the Oslo region started with lava effusions. Monzonitic rhomb porphyry flows predominate, with basaltic flows inbetween. Then a number of basalt volcanoes formed. This phase ended in explosive volcanism, producing ignimbrites, and the explosive activity is considered the primary cause for formation of at least four large and a few smaller cauldrons (or calderas). Below the lava surface monzonitic magma and associated syenitic and granitic magmas crystallized to larvikite, nordmarkitic and granitic rocks. These magmas are assumed to be formed by local melting of portions of the lower crust. The mode of emplacement is stoping.     

Propagation of a fast magnetoacoustic shock wave in the magnetosphere of an active region

The propagation of a fast magnetoacoustic shock wave the magnetosphere of a solar active region is considered the nonlinear geometrical acoustics approximation. The magnetic field is modeled as a subphotospheric magnetic dipole embedded in the radial field of the quiet corona. The initial parameters of the wave are specified at a spherical surface in the depths of the active region. The wave propagates asymmetrically and is reflected from regions of the strong magnetic field, which results in the radiation of the wave energy predominantly upwards. Substantial gradients in the Alfvén speed facilitate appreciable growth in the wave intensity. Non-linear damping of the wave and divergence of the wave front lead to the opposite effect. Analysis of the joint action of these factors shows that a fast magnetoacoustic perturbation outgoing from an active region can correspond to a shock wave of moderate intensity. This supports the scenario in which the primary source of the coronal wave is an eruptive filament that impulsively expands in the magnetosphere of an active region.     

Evolution of a filament due to magnetic-field variations in a complex active region

The complex active region NOAA 9672 is studied when it was near the central meridian, from October 21–26, 2001. At that time, there was an emergence of new magnetic flux, with the ongoing formation of a filament. The dynamics of the magnetic field are studied in order to search for their possible manifestations in the filament structure, using SOHO MDI magnetograms, SOHO EIT and TRACE filtergrams in the 171 Å line, and Hα filtergrams available via the Internet. Our earlier conclusion that filaments form at the boundaries of supergranules near polarity-inversion lines is confirmed. The conclusion of Chae that sinistral filaments have positive magnetic helicity is also confirmed. New information about magnetic-field decay processes is obtained. The direction of motion of the magnetic poles and their relative positions suggest that the axial field of a filament forms as a result of either reconnection of cancelling magnetic poles, or emergence of horizontal magnetic-flux tubes.