China
Africa
Explore chapters and articles related to this topic
Mitigation of Negative Geomagnetic Disturbance Impacts on Power Systems
Published in Olga Sokolova, Nikolay Korovkin, Masashi Hayakawa, Geomagnetic Disturbances Impacts on Power Systems, 2021
Olga Sokolova, Nikolay Korovkin, Masashi Hayakawa
Many industrial sectors affected by space weather would like to receive the forecast on Bz amplitude within the 24 hours before the event. Moderate and severe events are also of interest to the customers, not only extreme. After the initial eruption, forecasters can map the event to Earth-arrival using a procedure shown in Fig. 5.4. Achieving this is associated with the set of difficulties. The main one is the orientation of the magnetic vectors within CMEs. A south directed solar wind magnetic field is more likely to heat the Earth's magnetosphere, causing the field lines to break and reconnect while releasing energy and causing geomagnetic storms [52]. Magnetic reconnection allows energy to enter the magnetosphere on the day-side, consequently, energy is stored and explosively released on the nightside. A model capable of predicting magnetic vectors with a lead time of more than 24 h is described in [75]. The other difficulty is that aforementioned SOHO and STEREO satellites are scientific missions, therefore scientific measurements and investigations have the higher priority. SWPC specialists control on GOES and DISCOVR satellites.
Radio Emission from Stellar Objects
Published in Ronald L. Snell, Stanley E. Kurtz, Jonathan M. Marr, Fundamentals of Radio Astronomy, 2019
Ronald L. Snell, Stanley E. Kurtz, Jonathan M. Marr
Solar radio emission!radio burstsIt was the occurrence of a radio burst at meter wavelengths associated with a large sunspot group that caused the jamming of the English radar in 1942 that we alluded to in Section 7.1. The radio burst emission follows the appearance of solar flares at optical wavelengths. These radio bursts occur over a range of wavelengths from centimeters to decameters and vary in duration from a few minutes to nearly an hour. In solar flares, which are a result of the intense magnetic fields in sunspots, magnetic reconnection can cause a sudden re-arrangement of the magnetic field lines into a lower energy configuration. Magnetic energy is released in the process and transferred to the surrounding plasma, heating the gas.
Extreme Environment Electronics in NASA’s Heliophysics Vision
Published in John D. Cressler, H. Alan Mantooth, Extreme Environment Electronics, 2017
The sun behaves as a magnetic dipole with strong magnetic field lines. During a minimum in solar activity, the magnetic field lines are aligned. High solar activity occurs when the sun’s dipole is in the process of changing polarity, and the associated field lines invert relative to their starting points (see Figure 3.1). Since similar field lines repel each other, tangled magnetic field lines result is high solar activity. During times of high solar activity, there are releases of energy and/or mass, called solar flares and corona mass ejections (CMEs), respectively (see Figures 3.2 and 3.3). The flares and CMEs spurt energy and matter into the heliosphere, and these eruptions have directionality. Streamers from the flares and CMEs may loop back into the sun, and when the loops return to the sun’s surface, it is called magnetic reconnection.
An exact threshold for separator bifurcation
Published in Geophysical & Astrophysical Fluid Dynamics, 2022
Magnetic reconnection, the process whereby magnetic field lines change their connectivity within regions of intense electric current, is a fundamental plasma process that underpins many astrophysical phenomena (Priest and Forbes 2000). Although a great deal of effort has been dedicated to understanding reconnection in two dimensions (2D) (e.g.Zweibel and Yamada 2009), in many scenarios, the three-dimensional (3D) nature of reconnection cannot be ignored and in fact in 3D reconnection is fundamentally different from 2D, occurring continuously throughout the volume of a current sheet (Hesse and Schindler 1988, Hornig and Priest 2003, Wyper and Hesse 2015). The key to understanding reconnection in three dimensions is understanding the 3D topological features of a magnetic field where current sheets naturally form; 3D null points, separators and Quasi-Separatrix Layers (e.g. Aulanier et al.2005, Parnell et al.2008, Priest and Pontin 2009), and how they evolve in response to reconnection within these current layers.
Experimental investigation of a partial collapse during the sawtooth instability in EAST
Published in Radiation Effects and Defects in Solids, 2021
Azam Hussain, Jinlin Xie, Wandong Liu
Magnetic reconnection is a fundamental process in which topology of the magnetic field is reorganized and the field energy is converted into plasma kinetic and thermal energy. Magnetized plasmas are found to be sensitive to several kinds of macroscopic MHD instabilities in fusion plasma devices, which can degrade plasma confinement and plasma energy. Sawtooth activity is one of the typical examples of such macroscopic MHD perturbations in the core region of a tokamak. It is activated by internal kink modes, which has an m/n = 1/1 structure defining an inversion radius, whereas m, n are poloidal and toroidal mode numbers, respectively (1). The sawtooth instability is associated with the topological feature of the magnetic field and is observed when the safety factor q0 < 1 on the magnetic axis. However, during the collapse process of sawtooth, the estimation of magnetic field topology and q profile is a challenging task both experimentally and theoretically. Experimentally, two kinds of collapses are observed: the full sawtooth collapse in which hot core dissipates, while the in partial collapse, the hot core survives. However, the partial collapse is detected during the crash time when q0 < 1 as well as after crash time when q0 ≥ 1.
An Open Boundary Condition for High-order Solutions of Magnetohydrodynamics on Unstructured Grids
Published in International Journal of Computational Fluid Dynamics, 2020
Xiaoliang Zhang, Chunlei Liang
Magnetic reconnections occur in highly conducting plasmas where the magnetic topology breaks down and rearranges resulting in the conversion of magnetic energy to kinetic energy, thermal energy, and particle acceleration. It is normally an explosive event after a slow and gradual build-up process. Magnetic reconnection is thought to play a crucial role in eruptive solar events such as solar flares, coronal mass ejections, etc.