镜模波识别方法研究及其在火星磁鞘中的应用

镜模波是温度各向异性等离子体中的一种波动结构，根据磁场和离子分布及波动特性可以进行识别.本文对比了只使用磁场数据与同时使用磁场及离子数据两种识别方法，分析了两类方法的特点.只使用磁场数据的方法基于磁场强度变化大、方向沿背景磁场的特征，通常使用磁场强度的波动幅度ΔB/|B|以及磁场变化方向与背景磁场的夹角θ_min，θ_max作为参数；同时使用磁场及粒子数据的方法利用的是磁场纵波特性、总压平衡和波动在等离子体坐标系下静止的特征.使用两种方法对MAVEN卫星在火星磁鞘内的数据进行识别，结果表明在某些情况下，只使用磁场数据会导致对镜模波的误判.通过研究改变上述参数阈值时识别结果的变化，发现当θ_min> 40°，θ_max < 40°，ΔB/|B|> 80%时，只用磁场数据可取得较好的识别效果. 

Mirror-mode Wave Identification Methods and Their Application to Martian Magnetosheath

Mirror-mode waves are structures usually seen in plasma with temperature anisotropy, identifiable through features in magnetic field and particle distribution and fluctuation. Two identification methods are analyzed and compared in this paper. Method A uses magnetic field data only, while Method B combines magnetic field and particle data. Method A is based mainly on features of magnetic field variation such as large amplitude fluctuation along background field direction, using magnitude of magnetic field fluctuation ΔB/|B| and angles between background field and maximum/minimum variation direction θ_max, θ_min as criteria. Method B is based on features such as wave compression, total pressure balance and zero velocity in plasma frame. Identification using data from MAVEN probe in the Martian magnetosheath shows that Method A can cause misidentification under certain circumstances, e.g. magneto-sonic waves. Results of identification using Method A with varying criteria ΔB/|B| and θ_min/θ_max are studied in the Martian magnetosheath, suggesting threshold values: θ_min> 40°, θ_max< 40° and ΔB/|B| > 80% can yield satisfying results.