Dynamics of the photospheric magnetic field in the vicinity of the solar equator

SOHO-MDI daily magnetic field synoptic data (a 14-year series of daily maps of the solar magnetic field intensity B available at the site ) have been used to analyze the dynamics of the photospheric magnetic field in the vicinity of the solar equator. The standard deviation s _B of the field B calculated over areas of tens of square degrees on the solar disk was taken as a basic index. An 11-year variation similar to that observed at higher latitudes is observed in the vicinity of the equator, and is similar for weak and strong fields; i.e., the solar cycle exists in the sunspot-free zone. New qualitative data support the idea that the weak background magnetic field increases toward the solar limb. This angular dependence suggests the existence of a transverse component of the background field. The magnetic fields in the vicinity of the equator were significantly different in the initial phases of Cycles 23 and 24. Annual variations of s _B were observed near the center of the solar disk. These variations are due to two factors: the annual variation of the distance from the equator to the disk center and the increase of s _B with with distance from the equator. Reliable detection of these variations is an evidence of high accuracy of the s _B estimates.     

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.     

Search for the general magnetic fields in late-type giants

Surface-averaged longitudinal magnetic-field components (by analogy with the Sun called the general magnetic field) have been measured for 15 late-type giants with an accuracy of several Gauss. Statistically significant fields were detected for nine of these stars. The magnetic-field values obtained suggest the existence of general magnetic fields in these giants.     

Localization of magnetic reconnection from the differential characteristics of magnetic fields

Magnetic reconnection for arbitrary magnetic fields without null points is analyzed in the absence of plasma. A potential model field for four sources is considered. A method for the localization of probable reconnection regions using computable differential characteristics of magnetic fields is proposed. Some separator properties are examined, and separator regions are found for the best-known reconnection conditions.     

A generalized polarity rule for solar magnetic fields

It is shown that, when all components of the large-scale solar magnetic field are longitudinally averaged, the N polarity and the eastward transverse component of the B _φ field associated with both local and large-scale fields over the Northern hemisphere are somewhat stronger and occupy a smaller area during odd cycles than does the field of opposite polarity. This behavior is reversed for even cycles or the Southern hemisphere. The regular Hale law is a particular form of the above rule. The nature of this asymmetry seems to be rooted in the dynamo mechanism itself, and should be important for fields on any scale.     

Horizontal magnetic fields in the solar photosphere

Two-dimensional simulations of time-dependent solar magnetogranulation are used to analyze the horizontal magnetic fields and the response of the synthesized Stokes profiles of the IR FeI λ1564.85 nm line to the magnetic fields. The 1.5-h series of MHD models used for the analyses reproduces a region of the magnetic network in the photosphere with an unsigned magnetic flux density of 192 G at the solar surface. According to the magnetic-field distribution obtained, the most probable absolute strength of the horizontal magnetic field at an optical depth of τ ₅ = 1(τ ₅ denotes τ at λ = 500 nm) is 50 G, while the mean value is 244 G. On average, the horizontal magnetic fields are stronger than the vertical fields to heights of about 400 km in the photosphere due to their higher density and the larger area they occupy. The maximum factor by which the horizontal fields are greater is 1.5. Strong horizontal magnetic flux tubes emerge at the surface as spots with field strengths of more than 500 G. These are smaller than granules in size, and have lifetimes of 3–6 min. They form in the photosphere due to the expulsion of magnetic fields by convective flows coming from deep subphotospheric layers. The data obtained qualitatively agree with observations with the Hinode space observatory.     

Effect of magnetic fields on leveling

Normally, the establishment of national leveling networks was for the purpose of supporting national mapping programs of engineering projects. They are also used as a base on which to establish national gravity networks. During recent years, much study and investigation have been done concerning the characteristics and capabilities of these networks to provide data for determining height velocity changes due to crustal movements.

In the early 1960's the use of automatic (compensator) leveling instruments became common for establishing precise geodetic leveling networks. In 1981, at FIG, Montreux, Professor W.E. Rumpt and Mr. H. Meurisch reported the influence of DC-AC magnetic fields on the line of sight of compensator instruments. As a result, several manufacturers modified their automatic leveling instruments to minimize the AC-DC magnetic effect. Wild Heerbrugg, whose unmodified NA-2 level was least affected by magnetic fields, further reduced the effect by shielding it's compensator.

At the very least, the impact of this discovery will cause national geodetic agencies to modify their existing automatic leveling equipment and possibly embark on a releveling or reanalysis of their existing network. When studying micro/macro earth crustal movements, the geodesist must take this new factor into account in analysing data.     

The electric fields of radio pulsars with asymmetric nondipolar magnetic fields

The effect of the curvature of open magnetic field lines on the generation of electric fields in radio pulsars is considered in the framework of a Goldreich-Julian model, for both a regime with a free outflow of electrons from the neutron-star surface and the case of a small thermoemission current. An expression for the electron thermoemission current in a strong magnetic field is derived. The electric field associated with the curvature of the magnetic flux tubes is comparable to the field generated by the relativistic dragging of the inertial frames.     

Electric and magnetic fields in the astrophysics of wormholes

We consider the properties of electric and magnetic fields in vacuum in the neighborhood of static, spherically symmetric wormholes. Although certain aspects of this problem have been considered before, some important features remained undiscovered. We study in detail the properties of electric and magnetic fields in the case of quasi-adiabatic motion of field sources near an Ellis-Bronnikov wormhole and the passage of such sources through the wormhole. An exact solution is found in closed form for a wormhole immersed in a magnetic field that is homogeneous at infinity, as well as an exact solution for a dipolar field without sources. The properties of electromagnetic fields are important for possible observational manifestations of wormholes in astrophysics.     

Meridional drift of large-scale solar magnetic fields

It is shown that the meridional drift of large-scale fields starts in the equatorial zone and continues over 15–16 yrs (16–17 according to another estimate), i.e., during three fourths of the 22-year cycle. There is an abrupt retardation of the drift at latitudes of 30°–50°, and a stagnation region where the drift rate does not exceed several meters per second arises. The drift becomes rapid again at higher latitudes. The stagnation region coincides with the area in which the radial gradient of the rotational velocity is close to zero in the convective zone. This drift is compared with helio-seismological data on the rotation in the convective zone. A model taking into account some elements of dynamo theory is proposed.     

A possible mechanism for natural graphite formation

By extrapolating the Arrhenius plots for carbonization and experimental thermal progressive graphitization, it is shown that carbonization can go to completion in nature (ΔH ≈ 65 kcal/mole), whereas progressive graphitization is thermodynamically improbable (ΔH ≈ 260 kcal/mole). The mechanism of formation of natural graphite has thus to be determined. Since the geothermal gradient is not strong enough for producing graphite, the existence of shear stresses has to be taken into account. Metamorphism and tectonics create suitable conditions for this transformation. Series of samples of increasing rank from anthracites to metaanthracites, semigraphite and graphite (some of them from the same parent rocks) were compared with carbon, heat-treated experimentally under pressure (5 kbar). Anthracites are microporous materials. Their pores are flattened parallel to the bedding by a pressure effect which is responsible for a long-range statistical preferred orientation. They are anisotropic in texture but only biperiodically crystallized (turbostratic). Metaanthracites differ from anthracites only by an increasing coalescence between adjacent pores. They are thus either mesoporous or even macroporous. They are still turbostratic. Semi-graphites are suddenly obtained as a new phase by an increase in temperature, pressure and shear stresses. They are formed by single macropores, i.e. hollow distorted polyhedral shells. They are partially graphitized. Graphite is suddenly produced by a second phase change also due to an increase in temperature, pressure and shear stresses. The lamellar shape represents the limit of a flattened macropore.     

Geometry of solar prominences and magnetic fields in the corona

The spatial location of the surface at which most of the prominence mass is concentrated is compared with the location of the “neutral surface” where B _r = 0 (B _r is the magnetic field) calculated in a potential approximation using photospheric data. More than fifty prominences (filaments) observed in 1999–2003 are studied. The vertical deviations of the prominences (predominantly toward the west) correspond well to the inclination of the neutral surface. The results provide evidence for the magnetic support of filaments of opposite polarities (the magnetic-rope model).     

Pulsations in the atmospheres of hot Jupiters possessing magnetic fields

The discovery of the possible existence of huge quasi-stationary envelopes around a number of hot Jupiters (i.e., with sizes appreciably exceeding their Roche lobes) and the need to correctly take into account their properties when interpreting observational data require a careful analysis of the main physical processes influencing their atmospheres. One important factor is the possibility that the planet has a magnetic field. It was shown earlier that the presence of even a modest dipolar magnetic field of a hot Jupiter (with a magnetic moment approximately 1/10 the magnetic moment of Jupiter) influences the properties of the planetary atmosphere, in particular, leading to expansion of the range of parameters for which a giant, quasi-closed envelope can form around the planet. It was also established that the presence of a planetary magnetic field reduced the mass-loss rate from the envelope, since matter flowing out from the inner Lagrange point moves perpendicular to the field lines. Three-dimensional magnetohydrodynamical (MHD) modeling on time scales appreciably exceeding the time for the formation of the envelope show that pulsations arise in the atmospheres of hot Jupiters possessing dipolar magnetic fields, with characteristic periods ~0.27P_orb. This behavior is easy to understand physically, since even in the case of a spherical atmosphere, the continuous expansion of the ionized atmsphere of a hot Jupiter can lead to the accumulation of matter in regions bounded by closed field lines, and to the periodic rupture of the atmosphere beyond the magnetic field. In the case considered, when the system contains a giant envelope fed by a stream of matter from the inner Lagrange point, the presence of such pulsations gives rise to appreciable variations in the gas-dynamical structure of the flow. In particular, pulsations of the atmosphere lead to tearing off of part of the flow and sharp fluctuations in the size of the envelope, leading to variations in the envelope’s observational properties.     

Solar magnetic fields and the intensity of the green coronal line

Synoptic maps of the intensity of the λ530.5 nm FeXIV green coronal line and maps of computed coronal magnetic fields for the period 1977–2001 are compared. For quantitative comparisons, the correlation coefficients r for the correlation between these two parameters at corresponding points of the synoptic maps are calculated. This coefficient exhibits cyclic variations in the spot-formation zone, ±30° and the zone above 30° and is in antiphase in these two zones. In the low-latitude zone, the correlation coefficient is always positive, reaches its maximum at activity minimum, and strongly decreases by activity maximum. Above 30°, r reaches maximum positive values at activity maximum and then gradually decreases, passing through zero near the beginning of the phase of activity minimum and becoming negative during this phase. A Fourier analysis of r as a function of time reveals a wavelike variation with a period close to 1.3 yr (known also from helioseismological data for the tachoclinic region of magnetic-field generation), as well as a pronounced wave with a period of about 5 yr. The latitude dependence of r seems to be related to variations in the contributions from local, large-scale, and global fields. Our analysis suggests an approach to studying the complex problem of mechanisms for coronal heating.     

The formation of hydrochemical indicators for the pay zones in the Surgut arch oil fields

The causes of the spatial variation in the hydrochemical indicators of groundwater in several oil fields in the Surgut arch of West Siberia are considered. On the basis of statistical processing of the database, including several thousand analyses of groundwater, histograms of the distribution of mineralization and concentrations of Ca²⁺ and HCO ₃ ^? ions through the main pay horizons of the fields are constructed. The influence of deep (hydrothermal) water inflow on the formation of the chemical composition of the stratum waters of oil fields, which is exhibited by an increasing content of HCO ₃ ^? ion with depth, is substantiated.     

The death lines of radio pulsars for dipolar and asymmetric magnetic fields

The effect of curvature of open magnetic-field tubes on the death lines of radio pulsars is studied. The solution is obtained in the framework of a Goldreich-Julian model for both dipolar and asymmetric magnetic fields. The tube-axis curvature can shift the death line appreciably toward either longer or shorter periods. If the field is dipolar and gamma rays are generated by the inverse Compton effect, the formation of secondary plasma is more efficient near the death line. In the case of an asymmetric magnetic field, the generation of radio emission beyond the tube of open field lines is possible.     

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.     

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.     

Stokes-meter observations of the solar mean magnetic field: Probable manifestations of strong small-scale magnetic fields

For many years, information on the solar mean magnetic field (SMMF) of the Sun—an important heliophysical and astrophysical parameter—was restricted to magnetographic measurements in only one spectral line, FeI λ525.02 nm. More informative observations of the Stokes-meter parameters of the SMMF were first initiated on a regular basis at the Sayan Solar Observatory. The availability of I and V data obtained simultaneously in several spectral lines has made it possible to study fundamentally new physical problems. In this paper, based on a comparison of SMMF observations in several spectral lines, we find high correlations in the data and important systematic differences in the magnetic-field strength B, which we interpret as a manifestation of kilogauss magnetic fields in fine-structure magnetic elements. Results of theoretical modeling of the SMMF strength ratios for the FeI λ525.02 nm-FeI λ524.70 nm and FeI λ630.15 nm-FeI λ630.25 nm lines are presented. The asymmetries of the V profiles of four lines near the FeI λ525.02 nm line are examined; these lines are important diagnostics for studies of small-scale dynamical processes. The Sayan Solar Observatory SMMF measurements are in good consistency with the Wilcox Solar Observatory data for 2003: for a comparison of N = 137 pairs of points in the two data sets, the correlation coefficient ρ is 0.92 for the linear regression between the datasets B_WSO = 0.03(±0.05) + 0.93(±0.03)B_SSO.