The solar 10.7 cm radio flux,F_(10.7),a measure of the solar radio flux per unit frequency at a wavelength of 10.7 cm,is a key and serviceable index for monitoring solar activities.The accurate prediction of F_(10.7) is of significant importance for short-term or long-term space weather forecasting.In this study,we apply Back Propagation(BP)neural network technique to forecast the daily F_(10.7)based on the trial data set of F_(10.7) from 1980 to 2001.Results show that this technique is better than the other prediction techniques for short-term forecasting,such as Support Vector Regression method.
Based on the multipoint magnetic observations of Cluster from 2001 to 2004,the magnetic field structure in magnetotail Neutral Sheet(NS) is statistically surveyed.The results are as follows.In NS,a cubic function is selected to reveal the relation between y(GSM) and positional parameter z.The relation between y and magnetic field values indicates that the magnetic field is weak at midnight region and strengthens gradually at the duskside and dawnside.The relation between y and curvature radius is expressed by a quadratic function.And R_c of flattened CS is less than that of the normal CS.B_y determines the orientation of MFLs' configuration.The polar angle of the curvature vector is affected by the NS configuration.In addition,the correlation between the polar angle of the curvature vector and z is higher.The polar angle of the normal of the osculating plane is uncertain in the center area.The relation between the azimuthal angles of the curvature vector(the normal of the osculating plane) and y is negatively correlated.An empirical model applied to yz plane of the three-dimensional structure of the magnetic field lines in the NS are developed,and it is represented as a function of the positional parameter y.Finally,the current density is also statistically surveyed.
XIAO ChaoSHEN ChaoCHENG GuoshengZHANG HuaZHANG TingCARR C M
Comparing the ESP/EVE/SDO flux data of 2011 Feb 6, with the counterparts of XRS/GOES and SEM/SOHO, we find that there is an enhancement that is not apparent in the two latter datasets. The enhancement, possibly regarded as a flare at first glimpse, nevertheless, does not involve an energy-release from the Sun. Based on the enhancement, we combine data from SXI/GOES 15 into a synthesized analysis, and concluded that it arises from a particle-associated enhancement in the channel that measures XUV radiation. Paradoxically, it seems to be somewhat of a particle-avalanching process. Prior to the event, a moderate geomagnetic storm took place. Subsequently, while the event is proceeding, a geomagnetic substorm is simultaneously observed. Therefore, the particles, though unidentified, are probably energetic electrons induced by substorm injection.
本文基于自己开发的全球三维磁层模型,模拟研究了IMF(Interplanetary Magnetic Field)北向并且By分量较大(时钟角为60°)时磁层顶三维结构及其重联图像.结果发现,IMF By为正时,在北极隙区附近尾-昏侧存在IMF与地磁场之间稳定持续的重联现象;参与重联的地球磁场既有闭合磁力线也有开放磁力线;IMF在北极隙区与地球闭合磁力重联后一端与南磁极相连的磁力线在尾向运动时还可能与北尾瓣的开放磁力线重联而重新闭合,这种重联与磁力线循环过程不同于同一条IMF磁力线分别在南北半球与地磁场重联的模型.南极隙区的重联发生在尾-晨侧,其动力学过程与北极隙区情形类似.我们的模拟结果表明,IMF By较大时不可能发生IMF同一条磁力线分别在南北极隙区重联的情形,也不会因此而减少尾瓣的开放磁力线.
A new method for determining the central axial orientation of a two-dimensional coherent magnetic flux rope(MFR)via multipoint analysis of the magnetic-field structure is developed. The method is devised under the following geometrical assumptions:(1) on its cross section, the structure is left-right symmetric;(2) the projected structure velocity is vertical to the line of symmetry. The two conditions can be naturally satisfied for cylindrical MFRs and are expected to be satisfied for MFRs that are flattened within current sheets. The model test demonstrates that, for determining the axial orientation of such structures, the new method is more efficient and reliable than traditional techniques such as minimum-variance analysis of the magnetic field,Grad-Shafranov(GS) reconstruction, and the more recent method based on the cylindrically symmetric assumption. A total of five flux transfer events observed by Cluster are studied using the proposed approach, and the application results indicate that the observed structures, regardless of their actual physical properties, fit the assumed geometrical model well. For these events, the inferred axial orientations are all in excellent agreement with those obtained using the multi-GS reconstruction technique.
基于全球三维磁层MHD(Magnetohydrodynamics)模拟模型,研究了行星际磁场(Interplanetary Magnetic Field,IMF)北向与南向时磁尾横断面(X=18 RE)的结构及等离子片的粒子注入机制.模拟结果很好地符合一些已知的观测数据和经验模型.从向阳面磁层顶IMF及重联后磁力线尾向运动过程的角度,对磁尾横断面粒子热压力分布、磁力线投影、等离子片或电流片旋转、粒子流场分布等结构进行了合理的解释.根据模拟得到的磁尾横断面结构,及IMF北向与南向时磁力线投影显著不同的位形,可以通过E×B漂移很好地说明不同IMF条件下,太阳风粒子对磁尾等离子片的不同注入特性.另外,还通过磁尾横断面磁场梯度的计算,说明了太阳风向等离子片粒子注入的晨-昏不对称性.
A long-standing mystery in the study of Field-Aligned Currents(FACs) has been that: how the currents are generated and why they appear to be much stronger at high altitudes than in the ionosphere. Here we present two events of magnetotail FACs observed by the Magnetospheric Multiscale Spacecraft(MMS) on 1 st July and 14 th July 2016, to show how the Substorm Current Wedges(SCW) were formed. The results show that particles were transferred heading towards the Earth during the expansion phase of substorms.The azimuthal flow formed clockwise(counter-clockwise) vortex-like motion, and then generated downward(upward) FACs on the tailward/poleward side of the distorted field with opposite vorticity on their Earthward/equatorward side. We also analyzed the Region 1 FACs observed by the Earth Explorer Swarm spacecraft on 1 st July 2016 and found that they were associated with FACs observed by MMS, although differing by a factor of 10. This difference suggests that either there was the closure of the currents at altitudes above 500 km or the currents were not strictly parallel to B and closed at longitudes away from where they were generated.
ZHANG CSHEN CYANG Y YDUNLOP M WTI SRUSSELL C TLüHR HBURCH J LLINDQVIST P ATORBERT R BFRIIS-CHRISTENSEN E
