外辐射带区域新建地磁场经验模型的定量研究

准确的磁场模型对于辐射带粒子环境研究至关重要.本文利用美国Van Allen Probes（VAP）在2012至2018年期间测量的磁场数据和GOES15在2011至2017年期间测量的磁场数据，定量地评估了三个较新的外磁场经验模型（TS05、TA15和TA16）对外辐射带区域（3~6.6R_E）磁场的描述性能.本文选择预测效率（Prediction Efficiency，PE）作为评估指标，定量分析各模型在不同空间范围（Lm值）、不同地磁活动水平（Kp）以及不同磁地方时（MLT）下的性能表现，并且计算了观测磁场与模型磁场的夹角θ，以评估模型的磁场方向预测能力.结果表明：PE随Lm值增大，随地磁扰动增强而下降；θ随Lm值增大，随地磁扰动增强而增大.在Lm=5~6.5R_E范围内，PE呈现晨昏不对称性，MLT=12-21时的PE值小于MLT=0-9时的值，说明三个磁场模型可以较好地描述晨侧磁场的强度，但它们并不能很好地反映下午至昏侧磁场的大小；在地球同步轨道附近（Lm~6.6R_E），PE呈现昼夜不对称性，MLT=9-15时的PE值大于其他时区的值，说明三个磁场模型可以很好地反映昼侧磁场大小，但在夜侧可能存在较大的误差.θ在MLT=6-12时的值小于其他时区的值，呈现昼夜不对称性，说明三个磁场模型可以较好地描述昼侧磁力线的分布位型，但在夜侧存在较大的方向描述误差.在外辐射带3~6.5R_E内，TA16模型与VAP磁场观测数据最为接近，PE均大于0.7，θ均小于3°；在地球同步轨道高度（6.6R_E），TS05模型与GOES15卫星磁场观测数据最为接近，PE约为0.75，θ约为7°.相关的研究结果可以为我国星载高能粒子探测器探测数据的在轨交叉定标、辐射带高能粒子动态模型研究和相关的磁层环境理论/应用研究提供地磁场模型选择方面的参考.

Quantitative performance assessment of recent empirical geomagnetic field models in outer radiation belt zone

Accuracy of geomagnetic field model has key importance for the theoretical and operational studies about radiation belt. Using magnetic field data measured by Van Allen Probes (VAP) from 2012 to 2018 and GOES15 from 2011 to 2017, this paper quantitatively evaluates performances of three newer empirical external magnetic field models (TS05, TA15, and TA16) in the outer radiation belt (3~6.6R_E). The prediction efficiency (PE) is chosen as a measure to quantitatively assess models' performance in various spatial ranges (Lm), under different geomagnetic conditions (Kp), and along with magnetic local time (MLT). Also, θ (the angle between the observed and estimated magnetic field vector) is calculated to evaluate the model's ability to predict the direction of the magnetic field. The results show that with increasing Lm and disturbed level of geomagnetic field, the PE decreases and the θ increases. The PE at MLT=12-21 is smaller than MLT=0-9 in the range of Lm=5~6.5R_E, showing a dawn-dusk asymmetry and indicating that the three magnetic field models can describe the strength of the magnetic field in the dawn sector better than in the sector from afternoon to dusk ; at the geosynchronous orbit (Lm~6.6R_E), PE at MLT=9-15 is greater than at other local times, the day-night asymmetry indicates that the three magnetic field models can well estimate the magnitude of the magnetic field in the dayside, but they may have noticeable errors on the nightside. The θ at MLT=6-12 is smaller than at other local times, showing a day-night asymmetry and indicating that the three magnetic field models can better describe the geomagnetic field configuration in the dayside, but they may have noticeable errors in the nightside. Within the range of Lm~3~6.5R_E, the estimations of TA16 are the closest to the observations from VAP, with PE > 0.7 and θ < 3°; at the geosynchronous orbit (6.6R_E), the estimation of TS05 model is the closest to the observations from GOES15 with PE of about 0.75 and θ of about 7°. The relevant research results can provide references for the selection of geomagnetic field models for the on-orbit cross calibration of energetic particles for Chinese spaceborne energetic particle detectors, the study of the dynamic model of energetic particles in the radiation belt, and related theory/application research of the magnetospheric environment.