Kp Index Forecast Model Based on GBR Method
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摘要: 地磁Kp指数是空间天气预警的重要指标, 也是研究太阳风–磁层耦合的关键参数. 采用梯度提升回归(GBR)算法和随机森林(RF)两种机器学习方法, 构建了以太阳风、行星际磁场参数、历史Kp值和太阳黑子数据为输入的3 h 地磁 Kp指数预报模型. 预报结果表明, 两种方法均可提前1 h预报地磁Kp指数, 预测结果与观测值之间的相关系数为0.90, 其中GBR方法在均方根误差上表现出更好的效果, 均方根误差为0.56. Kp指数预报模型在太阳活动周不同相位的预测结果存在差异, 在活动周下降阶段模型预测结果与观测数据的相关系数更高. 比较了不同地磁扰动下模型的预测情况, 相比中等磁暴和超强磁暴, 模型对强磁暴(6≤Kp<7)的预报准确度最高.Abstract: The solar wind transports solar activity energy to interplanetary space, causing changes in the spatial structure of the Earth’s magnetosphere and causing disastrous space weather. The Kp index is an important indicator for space weather alerts and a key parameter for the coupling between solar wind and the magnetosphere. With the development of machine learning methods, more and more space weather forecasting works adopt this method. In this paper, two machine learning methods, Gradient Boosting Regression (GBR) algorithm and Random Forest (RF), are used to construct a 3-hour Kp index prediction model with solar wind, interplanetary magnetic field parameters, historical Kp values and sunspot data as inputs. The forecast results show that our methods can predict the Kp index one hour in advance and the correlation coefficient is 0.90 between the Kp index of the optimal case recommended by the model and the actual value. The GBR model performs better, the root Mean Square Error (Erms) is 0.56, and the Prediction Efficiency (P) is 0.81. The Kp index prediction model shows varying performances in different solar cycle phases, with better result during the cycle descending phase. The high-speed solar wind drive dominates the magnetospheric dynamics, and the model with solar wind as the main input parameter in the cycle descending phase has a better prediction effect. The model prediction situations under different geomagnetic disturbances have been compared. Compared with moderate and super severe magnetic storms, the model has the highest prediction accuracy for severe magnetic storms (6≤Kp<7). In this study, the results of different prediction models are compared and analyzed. The prediction model can not only provide early warning of severe space weather, but also better understand the relationship between geomagnetic index and solar wind input energy, which provides more methods and theoretical basis for the research work of solar wind-magnetosphere coupling.
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Key words:
- Kp index /
- Machine learning /
- Space weather forecast
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图 2 观测Kp值与GBR3和RF3模型的预测Kp值对比(红色虚线表示对角线, 蓝色虚线表示线性拟合直线相关系数为0.90)
Figure 2. Kp observations and predictions, with observed Kp values on the horizontal axis and predicted values on the vertical axis (The red dashed line represents the diagonal line, and the blue dashed line represents the linear fit result of the scatter, with a correlation coefficient of 0.90)
表 1 输入参数和3 h 地磁 Kp指数预测模型结果 (提前1 h)
Table 1. Data set variables and comparison of the prediction model results of 3-hour Kp index (predict 1 h)
模型名称 输入参数 C P Erms GBR1 vsw, Psw, Nsw, Bz, B, E 0.89 0.79 0.58 RF1 0.87 0.75 0.65 GBR2 vsw, Psw, Nsw, Bz, B, E, Kpt–3 0.90 0.81 0.56 RF2 0.89 0.79 0.59 GBR3 vw, Psw, Nsw, Bz, B, E, Kpt–3, Aall 0.90 0.81 0.56 RF3 0.90 0.80 0.58 注 Kpt–3 表示3 h 前Kp 指数. 表 2 3 h地磁 Kp指数GBR预测模型与现有模型结果对比
Table 2. Comparison of the GBR prediction model of 3-hour Kp index with the existing models
表 3 3 h模型在太阳活动周不同相位的预测结果相关系数
Table 3. Correlation coefficient during different solar cycle phase of the 3-hour prediction model
GBR1 RF1 GBR2 RF2 GBR3 RF3 上升阶段 0.89 0.88 0.89 0.88 0.89 0.88 极大期 0.88 0.87 0.89 0.88 0.89 0.88 下降阶段 0.89 0.89 0.90 0.89 0.90 0.90 表 4 不同地磁扰动情况下3 h地磁 Kp 指数预测结果
Table 4. Comparison of the prediction results of 3-hour Kp index under different geomagnetic disturbance
数据总数 预测次数 准确比例/(%) 5≤Kp<6 413 106 26 6≤Kp<7 104 36 35 Kp≥7 24 6 24 -
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