Spatiotemporal sunspot impulses and reversal of the polar magnetic field on the sun

The spatiotemporal organization of sunspots in the form of activity impulses (according to Gnevyshev’s terminology) is considered as a source of poleward magnetic surges of new polarity. Polar fields in the northern and southern hemispheres have been reconstructed from 1875 to 2012. An increase in the tilt angle of magnetic bipoles with latitude is a crucial parameter in the proposed model to reverse the polar field on the Sun. The role of the surface meridional flow forming magnetic surges of new and old polarities is discussed. It is shown that the velocity and the latitudinal profile of the flow influence the modeled polar field.     

Magneto-acoustic-gravity waves in the horizontal magnetic field

Abstract

In this paper we consider the propagation of magneto-acoustic-gravity waves in a compressible, conducting isothermal atmosphere permeated by a uniform horizontal magnetic field. The singular levels, arising in a horizontal magnetic field, are considered in their most general form. Exact analytical solutions for a number of particular cases of wave propagation are obtained. The wave transformation is analyzed for all these cases using the solutions obtained.

Based on the theory of wave propagation across a magnetic field, low-frequency wave trapping in a chromospheric resonator is explained, and some properties of running penumbral waves are discussed.     

Effectiveness of fast electron retention in the magnetic cavern during disturbance of the magnetic field azimuthal symmetry

The loss rate of fast electrons (with an energy much higher than the energy of the plasma electron thermal motion), when they leave a magnetic cavern during a disturbance of the magnetic field azimuthal symmetry, is studied. The cases of point and volume sources of fast particles have been considered. The plasma density in the cavern is supposed to be low, so that collisions of fast electrons with plasma particles can be neglected. The effect of the electric field on particle motion is neglected because it is assumed that the electric charge particles outgoing from the cavern is compensated by the counter current of plasma conductivity electrons. The dependence of the loss value on the harmonic number and the amplitude of the cavern boundary radius disturbance has been obtained.     

亚暴期间等离子体对流速度及热层纬向风速度变化的统计学分析

本文利用2001年至2005年间CHAMP卫星及DMSP(F13,F15)卫星观测数据,对亚暴发生前后,亚暴初始位置所在磁地方时(Magnetic Local Time, MLT)东侧2 h(+2 h,MLT)至西侧4 h(-4 h,MLT)范围内等离子体对流速度(Vy)及热层纬向风速度(Uy)的变化进行了统计学分析.研究发现在亚暴发生后的1.5 h内,所有MLT区间的Vy均明显增大,且峰值位置的地磁纬度向赤道侧移动,1.5 h后,Vy减小,峰值的纬度向极区移动,表明亚暴的发生能显著增强等离子体对流速度;在亚暴发生位置的西侧0~2 h内,Vy增幅最大,这表明亚暴对热层的影响主要在西侧,影响最大的区域是西侧0~2 h MLT区间;Uy在亚暴发生后3 h持续增大,其对亚暴的响应相较于Vy有1.5 h的延迟.     

Auroral electrojet dynamics during magnetic storms, connection with plasma precipitation and large-scale structure of the magnetospheric magnetic field

Effect of the equatorward shift of the eastward and westward electrojets during magnetic storms main phase is analyzed based on the meridional chains of magnetic observatories EISCAT and IMAGE and several Russian observatories (geomagnetic longitude ≈110°, corrected geomagnetic latitudes 74°>φ>51°.) Magnetic storms of various Dst index intensity where the main phase falls on 1000 UT - 2400 UT interval were selected so that one of the observatory chains was located in the afternoon - near midnight sector of MLT. The eastward electrojet center shifts equatorward with Dst intensity increase: when Dst ≈ −50 nT the electrojet center is located at φ ≈ 62°, when Dst ≈ −300 nT it is placed at φ ≈ 54°. The westward electrojet center during magnetic storms main phase for intervals between substorms shifts equatorward with Dst increase: at φ ≈ 62° when Dst ≈ −100 nT and at φ ≈ 55° when Dst ≈ −300 nT. During substorms within the magnetic storms intervals the westward electrojet widens poleward covering latitudes φ ≈ 64°–65°. DMSP (F08, F10 and F11) satellite observations of auroral energy plasma precipitations at upper atmosphere altitudes were used to determine precipitation region structure and location of boundaries of various plasma domains during magnetic storms on May 10–11, 1992, February 5–7 and February 21–22, 1994. Interrelationships between center location, poleward and equatorward boundaries of electrojets and characteristic plasma regions are discussed. The electrojet center, poleward and equatorward boundaries along the magnetic observatories meridional chain were mapped to the magnetosphere using the geomagnetic field paraboloid model. The location of auroral energy oxygen ion regions in the night and evening magnetosphere is determined. Considerations are presented on the mechanism causing the appearance in the inner magnetosphere during active intervals of magnetic storms of ions with energy of tens KeV. In the framework of the magnetospheric magnetic field paraboloid model the influence of the ring current and magnetospheric tail plasma sheet currents on large-scale magnetosphere structure is considered.     

Induction at short periods in the horizontal field variations in the Indian peninsula

A study of the horizontal components of certain short-period magnetic-fluctuation events, viz., storm sudden commencements and bays, shows appreciable anomalies at two of the five magnetic observatories in peninsular India. The electric current patterns deduced from the magnetic horizontal induced variations imply channelling of induced currents through the Palk Straits and around the southern tip of the Indian peninsula. An interesting feature of these anomalies is that while the induced magnetic vertical variations are strongly correlated with the horizontal northward magnetic field, the electric current concentrations flow parallel to the coast; southwest, near Annamalainagar, and north near Trivandrum. The observations are interpreted in terms of a regional, east-west, induced electric current pattern which is perturbed in the vicinity of the two observatories by the Indian peninsula.     

Gravity and magnetic field interpretation based on transformations of horizontal gradients in the VECTOR system

A method of potential field processing based on the transformation of vectors of the total horizontal gradient in windows of various sizes is considered. The gradients are calculated at the centers of triangles, whose vertices are points of observations, as a rule, of gravity and magnetic fields. Averaging of horizontal gradients of the field rather than initial values of the field is the main distinction of this approach from the known methods. This procedure, referred to in this paper as vector scanning of the field, makes it possible to obtain layer distributions of field sources in a 3-D diagram that is a quasi-density model of the study medium within the framework of certain model concepts. The paper presents a model example demonstrating the possibility of separating the fields produced by two sources located on a vertical line and an example illustrating the application of this method to the interpretation of the gravity field in the zone of the geodynamic influence of the Urals.     

Diagnosis of dominant forcing factors for large-scale vertical velocities during active and break phases of the monsoon

An attempt to diagnose the dominant forcings which drive the large-scale vertical velocities over the monsoon region has been made by computing the forcings like diabatic heating fields,etc. and the large-scale vertical velocities driven by these forcings for the contrasting periods of active and break monsoon situations; in order to understand the rainfall variability associated with them. Computation of diabatic heating fields show us that among different components of diabatic heating it is the convective heating that dominates at mid-tropospheric levels during an active monsoon period; whereas it is the sensible heating at the surface that is important during a break period. From vertical velocity calculations we infer that the prime differences in the large-scale vertical velocities seen throughout the depth of the atmosphere are due to the differences in the orders of convective heating; the maximum rate of latent heating being more than 10 degrees Kelvin per day during an active monsoon period; whereas during a break monsoon period it is of the order of 2 degrees Kelvin per day at mid-tropospheric levels. At low levels of the atmosphere, computations show that there is large-scale ascent occurring over a large spatial region, driven only by the dynamic forcing associated with vorticity and temperature advection during an active monsoon period. However, during a break monsoon period such large-scale spatial organization in rising motion is not seen. It is speculated that these differences in the low-level large-scale ascent might be causing differences in convective heating because the weaker the low level ascent, the lesser the convective instability which produces deep cumulus clouds and hence lesser the associated latent heat release. The forcings due to other components of diabatic heating, namely, the sensible heating and long wave radiative cooling do not influence the large-scale vertical velocities significantly.     

正交水平磁偶源的电磁场分布规律

正交水平磁偶源是模拟天然场源的较好人工源,可以方便地实现可控源高频大地电磁张量测量.正交水平磁偶源的电磁场分布规律是野外工作布置的理论基础,为此计算了均匀大地模型正交水平磁偶源的电磁场.计算结果表明:电磁场水平分量在各个象限都有一相对低值带,对应的标量视电阻率形成了畸变带,但张量视电阻率畸变带消失;张量视电阻率曲线形态显示出近区的低阻、过渡区的高阻隆起和远区趋于真值的规律.通过野外试验验证理论计算结果,在无法准确确定地下介质电阻率参数的情况下,以天然电磁场计算的电阻率为参照对比研究了正交水平磁偶源电磁场的分布规律.试验结果表明:正交水平磁偶源与电偶源的电磁场同样的存在近区、过渡区和远区;在远区,正交水平磁偶源与测点的相对位置对张量测量结果几乎没有影响,即在远区可以在任何方位测量;正交水平磁偶源的布置要考虑收发距的影响,保证测量在远区进行.     

Determination of rock magnetization in a horizontal layer from the external magnetic field

The inverse problem of magnetometry is solved for a horizontal layer. Model masses are magnetized nonuniformly. The magnetization vector is a function of two horizontal coordinates. The components of this vector are determined from data on the external magnetic field.     

Seismic velocities and thickness of horizontal and dipping subsurface layers

Summary A new approach to the determination of the interval and average seismic velocities and thickness of arbitrarily dipping subsurface rock layers from surface travel time measurement is presented. The method is referred to as thegeometric recursion. Its derivation is based upon the geometry of the seismic ray paths between a shotpoint and a geophone, and is basically an extension of Gardner's equation of dip correction. Travel time measurements at and distance between the shotpoint and the geophone and apparent dip angles of the layers are needed in using the techniques. The values determined with the new method are compared with those from two existing methods that are applicable only for the horizontal layers. The accuracy and shortcomings of these methods are then analyzed and discussed with real examples as illustrations. The main computing technique used in the method is the iterative approximation of the undetermined but interrelated subsurface parameters in common loops. The method is practical to use, particularly when the travel time measurements in an area are not redundant. Its efficiency is dependent primarily upon the accuracy of the travel time measurements as well as the effective control of the shortcomings of the method.     

Intermittency analysis and spatial dependence of magnetic field disturbances in the fast solar wind

Based on Helios measurements, seven quantities of normalized PDF (Probability Distribution Function) associated with magnetic field and its disturbances are utilized to characterize the intermittency in the fast solar wind using Castaing distributions and the idea of “Flatness”. The magnetic field fluctuations are found to be more intermittent at farther distances from the sun. The “Flatness” decreases with increasing time scales, with the corresponding PDF eventually approaching Gaussian distributions. Such a transition occurs at a relatively small time scale for the perpendicular component of perturbed field. The increase in “Flatness” with decreasing time scale is more apparent farther from the sun. By examining how the relative energy density of magnetic disturbances at various time scales changes with the mean field, our study supports the idea that the perturbed fields in the fast solar wind in the frequency range considered are consistent with cross-scale redistribution of wave energy favoring larger scales.     

地磁场H、D受HVDC输电干扰特征分析

以受宁东线高压直流（HVDC）输电干扰相对严重的11个地磁台站为主要研究对象,以蒙城台为干扰幅度量取的参考台站,研究了地磁场水平分量H、磁偏角D受HVDC输电的干扰特征.发现H和D受HVDC输电干扰具有同步性和偏向性;同一HVDC输电线路两侧H和D干扰幅度具有线性关系,但线性关系明显弱于垂直分量Z干扰幅度的比例关系;接地极附近台站各自的Z、H、D干扰幅度具有线性关系.之后对H和D干扰产生的机理进行了深入的定性分析.根据得到的干扰特征的结论,提出了以红山台Z、H、D为输入的本研究相关台站的Z、H、D为输出的自动计算方法.经过误差分析,本方法平均误差水平低于国家地磁学科中心当前使用算法误差水平,最高降幅达42.9%.     

Evidence of more efficient whistler-mode transmission during periods of increased magnetic activity

In a previous study it was reported that whistler- mode signals received at Faraday, Antarctica (65°S,64°W) and Dunedin, New Zealand (46°S, 171°E) with entry regions in Pacific longitudes (typically from the VLF transmitter NLK, Seattle, USA) showed an increase in transmission of wave energy as magnetic activity increased. However, signals with entry regions in Atlantic longitudes (typically from the NSS transmitter, Annapolis, USA) did not appear to show such a relationship. This paper reports the results of a study of the same two longitude ranges but with the opposite transmitter providing additional whistler-mode signal information, with L-values in the range 1.8–2.6. Transmissions from NLK once again indicate a relationship between the transmission of wave energy and magnetic activity even though the signals were propagating in Atlantic longitudes, not Pacific. Any trend in NSS events observed at Dunedin was obscured by a limited range of magnetic activity, and duct exit regions so close to the receiver that small-scale excitation effects appeared to be occurring. However, by combining data from both longitudes, i.e Pacific and Atlantic, and using only ducts with exit regions that were > 500 km from the receiver, NSS events were found to show the same trend as NLK events. No significant longitude-dependent or transmitter-dependent variations in duct efficiency could be detected. Duct efficiency increases by a factor of about 30 with K_p = 2–8 and this result is discussed in terms of changes in wave-particle interactions and duct size.     

Latitude-time evolution of the large-scale magnetic field in the 21st and 22nd cycles of solar activity

Using the observational data of the Stanford observatory on photospheric magnetic fields for 1976?C2001, we separate open and closed configurations of the magnetic field with a filter of a specified spatial scale and demonstrate that the 11-year solar cycle passes two significantly different phases.     

Beginning of the new solar cycle (cycle 24) in the large-scale open solar magnetic field

It is proposed to determined minimums of the 11-year solar cycles based on a minimal flux of the large-scale open solar magnetic field. The minimal fluxes before the finished cycle 23 (Carrington rotation CR 1904) and the started cycle 24 (CR 2054, April 2007) were equal to 1.8 × 10²² and 1.2 × 10²² μs, respectively. The long-term tendency toward an approach to a deep minimum of solar activity is confirmed. On the assumption that magnetic flux variations from minimums to maximums are proportional to each other, the anticipated value of the maximal Wolf number during cycle 24 is estimated as W _max = 80.     

经验和抛物面模式模拟暴时磁场的误差特性研究

利用两种不同的磁场模式,协同GOES10/12、Polar及Geotail的实测资料,本文对3种不同强度磁暴的磁层磁场进行了详细分析,从而检验了两种不同磁场模式的可靠性,给出了模式间的性能对比.我们采用Tsyganenko经验模式及Alexeev抛物面模式,分别模拟了2004年4月、7月和11月的磁暴,3个磁暴过程中最强Dst指数分别达到-110 nT,-150 nT以及-289 nT.结果发现:T01模式对于中等磁暴时磁场模拟准确,而由于建立模式的数据库中强磁暴资料少,模式中不包含亚暴效应,T01对于强磁暴磁场模拟的误差增大,磁场分量远远偏离观测值;A2000模式缺少部分环电流及Ⅱ区场向电流,模式对于近地点Polar轨道上的磁场扰动模拟不足,对强磁暴时亚暴效应的过高模拟使其模拟的磁场分量偏高;T01模式对于中等磁暴时磁场的模拟效果明显好于A2000模式,随着磁层扰动的增强,T01与A2000模式的总体性能相当.     

Linear stability of a non-constantly stratified horizontal layer penetrated by an azimuthal magnetic field

Summary The convection in a rapidly rotating, electrically conducting, horizontal fluid layer, non-constantly stratified and penetrated by an inhomogeneous magnetic field, is studied. The convection is investigated for various ratios of the thickness of the stable and unstable stratified part of the layer. The thermal model of the layer, as well as the analysis of the results have been treated with regard to the physical conditions in the liquid core of the Earth.

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日面方位磁场扰动和行星际磁场螺旋结构

文采用球坐标下2.5维理想MHD模型,对日球子午面内方位磁场扰动的传播进行数值模拟,重点分析它对行星际磁场螺旋角的影响. 本文认为,观测到的行星际磁场螺旋角大于Parker模型的预言值,是太阳表面不断向行星际发出同向方位磁场扰动的结果;太阳较差自转在太阳内部产生的方位磁场为这类扰动提供了源头. 模拟结果表明,采用持续时间等于周期的十分之一、扰动幅度为103nT量级的正向方位磁场扰动,就可使1 AU处行星际磁场的螺旋角增加2°左右,与有关观测结果相符. 模拟结果还表明,上述方位磁场扰动对日球子午面内的太阳风特性和磁场位形的影响基本上可以忽略.