The solar type II radio bursts of 7 March 2012: Detailed simulation analyses

J. M. Schmidt; Iver H. Cairns; V. V. Lobzin

摘要

Type II solar radio bursts are often indicators for impending space weather events at Earth. They are consequences of shock waves driven by coronal mass ejections (CMEs) that move outward from the Sun. We simulate such type II radio bursts by combining elaborate three-dimensional (3-D) magnetohydrodynamic (MHD) predictions of realistic CMEs near the Sun with an analytic kinetic radiation theory developed recently. The simulation approach includes the reconstruction of initial solar magnetic fields, the dimensioning of the initial flux rope of the CME with STEREO spacecraft data, and the launch of the CME into an empirical data-driven corona and solar wind. In this paper, we simulate a complicated double CME event (a very fast CME followed by a slower CME without interaction) and the related coronal and interplanetary type II radio bursts that occurred on 7 March 2012. We extend our previous work to show harmonic and interplanetary emission as well as the simulation’s surprising ability (for these events at least) for predicting emission for two closely spaced CMEs leaving the same active region. We demonstrate that the theory predicts well the observed fundamental and harmonic emission from ～20 MHz to 50 kHz or from the high corona to near 1 AU. Specifically, the theory predicts flux, frequency, and time variations that are consistent with the presence or absence of observed type II emissions when interfering emissions are absent and are not inconsistent with observations when interfering type III bursts are present. The predicted and observed type II emission is predominantly fundamental for these two events. Harmonic emission occurs for the second CME only for a short time interval, when an extended shock has developed that can drive flank emission. The coronal and interplanetary emission follow closely hyperbolic lines in frequency-time space, consisting of a succession of islands of emission with varying intensity. The islands develop due to competition between the shock moving through varying coronal and solar wind magnetic field structures (e.g., loops and streamers), growth of the driven radio source due to the spherical expansion of the shock, and movement of the active radio sources from the shock’s nose to its flanks.

机译：II型太阳射电爆发往往指标为即将到来的地球空间天气事件。冲击波由日冕的后果吗质量抛射(cme)的向外移动太阳。结合精心设计的三维(3 d)磁流体动力(磁流体动力)的预测现实的cme太阳附近的分析最近动态辐射理论的发展。模拟方法包括重建最初的太阳磁场的芝加哥商品交易所的初始通量绳的尺寸立体航天器的数据,和启动芝加哥商品交易所为实证数据驱动的电晕和太阳风。复杂的CME事件(非常快的CME的两倍其次是没有交互)和较慢的芝加哥商品交易所相关的日冕和星际II型2012年3月7日发生的无线电脉冲。显示谐波和扩展我们的以前的工作星际排放以及模拟(这些事件令人惊讶的能力至少)预测排放两个密切间隔的cme留下相同的活跃区域。证明了理论预测观察到的根本和谐波发射~ 20 MHz 50千赫或高日冕附近一个天文单位。频率和时间的变化符合的存在与否观察II型干扰时排放排放缺席,并不矛盾观察当干扰类型III爆发。II型排放主要是根本这两个事件。第二个CME只有很短的时间间隔,当一个震惊了,可以延长驱动侧发射。星际排放密切关注双曲线行频率时间空间,组成的连续发射不同的岛屿强度。通过不同冠冲击之间移动磁场和太阳风的结构(例如,循环和带),增长驱动的收音机由于球形扩张的来源冲击,运动的活跃的无线电来源从冲击的鼻子两翼。

The solar type II radio bursts of 7 March 2012: Detailed simulation analyses

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