太阳风源区磁重联激发波动和加速粒子的研究

Alfvenic turbulence and superthermal particles are important energy source for solar wind acceleration and heating, but the generation mechanism remains unclear. It is believed that Alfven waves and superthermal particles generated in the solar wind source region, since both of them are propagating outward in the solar wind flux tube. Tu et al. (Science, 2005) suggested a new scenario of solar wind origin as driven by magnetic reconnection. This new scenario has attracted wide attention from the community and been basically accepted by the community.Our recent simulation shows that the magnetic reconnection as a result of supergranular advection indeed feeds the mass to the nascent solar wind. However, the effect after reconnection has not been exploited intensively. It is believed that the waves and superthermal particles in the high-speed streams are in fact generated in the source region of solar wind, where reconnection may play the crucial role. This project will focus on the wave excitation and particle acceleration via magnetic reconnection. (1) We will diagnose the wave modes as excited, analyze the wave power distribution in the space of frequency and wavevector, and thus study the proportion of wave energy in the total energy transformed due to reconnection. To investigate the solar wind heating due to wave dissipation, we will look at the wave mode conversion as well as turbulence formation. (2) We plan to test the acceleration of different species in the chromospheric reconnection environment, comparing the acceleration difference for different species. Moreover, we will simulate the escape of accelerated particle along the expanding open field as well as the scattering by the stimulated waves and turbulence. Hopefully, based on this project, the scenario of solar wind origin driven by magnetic reconnection will be improved, a breakthrough will be envisioned on the generation of waves and superthermal particles in the interplanetary space.

太阳风高速流中的阿尔芬湍流和超热粒子为太阳风加速加热提供了重要的能量，但是其产生机制尚未清楚。阿尔芬波和超热粒子大都沿太阳风磁流管传播，也应该是在太阳风源区产生的。Tu et al.(Science，2005)提出的磁重联驱动太阳风起源的新概念引起学术界的广泛关注和引用。我们的模拟表明超米粒对流驱动的磁重联确实能为太阳风初始外流提供所需的物质。本项目将通过观测分析和数值模拟研究太阳风源区磁重联对波动的激发和粒子的加速。(1)我们将诊断激发产生的波模成分、研究波动能量占磁重联能量转换的比例；(2)考察上传波动的波模转换和反射下传混合形成湍流，评估能量耗散对初始太阳风的加热作用；(3)将揭示不同种类粒子在色球磁重联中的加速过程，进一步模拟粒子加速后沿开放膨胀磁场逃逸并受波动湍流散射的过程。基于本研究，磁重联驱动太阳风起源的新图像将得到完善，行星际中波动湍流和超热粒子来源的研究将获得突破性进展。

背景：.磁重联和波湍动被认为是太阳风起源的两个关键供能机制。但是磁重联和波湍动在太阳风中是如何耗散供能一直未解。..内容：.本项目着眼于如下问题：磁重联如何驱动太阳风的初始外流？磁重联能否激发波动进行远距离长时间供能？磁重联能否产生行星际空间的超热电子？波湍动里怎样形成有利于磁重联的电流/间断面结构？这些电流/间断面结构处的加热效应如何？间断面结构在统计上如何影响湍流的各向异性特征？..结果：.（一）模拟指出源区磁重联能有效激发波动上传和并加速粒子流出或逃逸。（1.1）水平对流的闭合磁圈能与网络交汇处的开放场发生磁重联，为开放场提供初始加速和加热的太阳风初始外流；（1.2）色球磁重联能驱动产生源区色球海葵状喷流和慢激波，并且发现磁重联激发的慢激波无明显抬升过渡区；（1.3）高磁雷诺数的日冕磁重联能有次级磁岛的不稳定性，导致磁岛间歇撞击开放场同时激发三种磁流体力学波；（1.4）太阳风源区的磁重联电场能有效加速产生逃逸超热电子，形成行星际空间看到的晕外电子。（二）模拟和观测报告了波湍动演化中能形成有利于磁重联的电流片/切向间断面，并且能导致有效的加热并改变湍流的各向异性特征。（2.1）发现旋转间断面是由于阿尔芬波的陡化产生，而湍流中磁力线管的挤压及分离导致切向间断面的形成和瓦解；（2.2）发现切向间断面可引起垂直和平行温度的明显增加，而旋转间断面则没有，且切向间断面的个数要远少于旋转间断面；（2.3）发现多尺度压力平衡结构可在磁流体湍流中形成，其产生机制可有斜传慢波驱动。（2.4）发现去除间歇后垂直谱变陡，各向异性减弱。（2.5）发现多尺度压力平衡结构的产生机制可与斜传慢波在阿尔芬湍流中的被动垂直串级有关。..意义：.研究成果给出了太阳风源区中的磁重联能量转换的丰富过程，为太阳风源区的遥感诊断提供理论依据。研究成果给出了阿尔芬性波湍动能自洽形成有利于磁重联的间断面间歇性结构，加深了对湍动间歇本质及其效应的认识。