太阳过渡区里网络喷流的观测研究

The solar transition region is the interface between the relatively cool chromosphere and the million-degree corona. The dominant structure in this region is the network, which is the upward extension of the supergranular boundary. High-resolution observations by IRIS reveal numerous small-scale jet-like features with speeds of 80-250 km/s from the network. The ubiquitous presence of these high-reaching (often larger than 10 Mm) jets suggests that they may play a crucial role in the mass and energy budgets of the corona and solar wind. We propose the first comprehensive investigation of the detailed origin, heating and behavior of these network jets using data obtained by the IRIS, SDO/AIA, Hinode/EIS, Hinode/SOT and NST instruments. The proposed investigation will determine the role of these jets in coronal heating and solar wind origin. It will also provide detailed constraints on the jet generation mechanisms, and greatly improve our understanding of magnetic reconnection in partially ionized plasma...The proposed investigation is divided into three parts: (1) Using existing and planned observations, we will obtain a large sample of network jets in quiet Sun and coronal holes, both at the disk center and near the limb. Using the slit-jaw images of IRIS, we will quantify the speed, acceleration, lifetime and length of these jets. Using the IRIS spectra, we will determine the electron densities and measure the amplitudes of small-scale Alfvenic waves associated with the jets. (2) We will investigate the generation mechanisms of these high-speed network jets. We will quantify the brightness increase at the footpoints, and quantify how many jets show an inverted "Y"-shape structure. We will also use the magnetic field measured by HINODE/SOT and NST to investigate the possible correlation between the magnetic field evolution (e.g., flux emergence, flux cancelation) and the creation of network jets, and the possible dependence of the network jets on the magnetic field strength and complexity (e.g., the flux imbalance). (3) We will evaluate the contribution of network jets to coronal heating and solar wind origin.Using combined imaging and spectroscopic observations by IRIS, our preliminary study has clearly shown that many network jets reach at least 0.1 MK. We plan to investigate how many jets can be further heated to coronal temperatures with coordinated observations from SDO/AIA and HINODE/EIS. The mass and energy supply to the corona and solar wind by these jets will be carefully evaluated.

太阳过渡区是低温色球与高温日冕之间的过渡层次。最近，IRIS卫星的高分辨率观测发现，在过渡区中强磁场的网络组织中普遍存在速度高达80-250 km/s的喷流。我们计划对网络喷流的特征、起源和加热进行详细的统计研究，从而确定其对日冕加热和太阳风起源的贡献，并增进对部分电离的等离子体中磁重联的理解。我们将从三个方面进行研究：（1）利用IRIS的大量数据，测量网络喷流的传播时间、距离、速度、密度以及伴随喷流的阿尔芬波振幅，研究这些参数在开放磁场和闭合磁场区域的异同。（2）研究网络喷流的产生机制。利用IRIS的数据，量化喷流足点辐射的变化，统计多少喷流具有倒Y形结构。结合HINODE/SOT和NST等仪器的磁场数据，分析喷流产生前后的磁场演化特征。（3）结合IRIS和HINODE/EIS、SDO/AIA等日冕观测仪器的数据，研究网络喷流的加热过程，评估其对高温日冕和太阳风的物质和能量供应的贡献。

过渡区网络喷流是IRIS卫星于2014年发现的一类普遍性的喷流活动。作为太阳过渡区最主要的动态结构，这些网络喷流被认为跟色球针状物的加热有重要联系。本项目的研究内容包括三个部分：（1）统计分析这些喷流在不同区域里的特征；（2）研究这些喷流的产生机制；（3）研究这些喷流对高温日冕的贡献。在本项目的支持下，我们主要利用IRIS卫星、大熊湖天文台GST望远镜以及云南天文台NVST望远镜的观测，在如上三个方面均取得了重要的研究结果。主要结果总结如下：（1）我们对冕洞和宁静区的网络喷流特征进行了统计研究，发现冕洞中的喷流速度更快，传播的距离更大。（2）通过分析紫外光谱数据和红外谱线的偏振观测，我们发现这些喷流至少有一部分是由磁重联产生的。（3）我们发现在太阳宁静区，这些喷流被普遍加热到百万度的高温。这些研究结果表明，太阳低层大气中的普遍性喷流在日冕加热过程中起到了关键的作用。