Empirical model of the Earth's cusp at low-altitudes
-
摘要: 地球极尖区是太阳风等离子体进入内磁层和电离层的一个重要“窗口”，但其总体结构长期以来尚未确定. 2008年3月8日两个连续亚暴期间，太阳风的整体变化范围较大，基于全球三维数值模拟我们建立了一个由行星际磁场（interplanetary magnetic field, IMF）BY、BZ控制的低高度（1.1个地球半径高度）极尖区的预报模式. 该模式由椭圆函数构造而成，拟合函数由极尖区位置和宽度控制并取决于IMF BY和BZ. 极尖区地磁纬度（geomagnetic latitude, MLAT）随着向北IMF BZ的增加而增加，随着向南IMF BZ的增加而明显降低. 当BY=0时，磁地方时（magnetic local time, MLT）接近12，当IMF为东向（西向）时，极尖区中心将位于北半球下午（上午）侧. MLAT宽度随IMF BZ从北转南而减小，MLT宽度随IMF BZ从北转南而增大. 通过与DMSP卫星观测结果的比较分析，验证了该模型的有效性. 基于低高度极尖区预报模式，将进一步建立极尖区三维预报模式，这将有助于空间天气预报.Abstract: The Earth's cusp is a critical "window" for the solar wind plasma to enterthe low-altitude magnetosphere and ionosphere. However, the overall configuration of cusp has not been established. Based on the simulation of two successive substorms on 8 March 2008, we propose a 2D model of low-altitude (1.1 RE) cusp modulated by the interplanetary magnetic field (IMF) BY and BZ. This model is constructed from curve fitting of low-altitude cusp with an elliptic function controlled by the cusp center and width, which is dependent on IMF BY and BZ. The plasma thermal pressure PT derived from the simulation data is used to extract the cusp center on the sphere surface with a radius of 6 RE. The cusp center is defined as where PT reaches the maximum, and the cusp boundary is identified as where PT decreases to 68% of that at the cusp center. After the high-altitude cusp has been determined, the low-altitude (0.1 RE altitude in the ionosphere) cusp can be obtained from mapping the high-altitude cusp along the magnetic field lines. The coordinate system of the low-altitude cusp used throughout this paper is the magnetic coordinate. The low-altitude cusp extracted from simulations is fitted with the elliptic function controlled by cusp location and width. The cusp geomagnetic latitude (MLAT) increases gradually with northward IMF BZ but decreases significantly with southward IMF BZ. The local magnetic time (MLT) is nearly 12 when BY = 0, corresponding to the observation results. When IMF BY is duskward (dawnward), the cusp center will locate at the post-noon (pre-noon) sector in the northern hemisphere. The MLAT width decreases as IMF BZ swings from north to south, and the MLT width is the opposite. This model is validated by comparing with observations from DMSP satellites during this concerning time interval. Based on this 2D model of low-altitude cusp, the 3D cusp could be obtained further, which would help to space weather prediction.
-
Key words:
- cusp /
- empirical model /
- solar wind /
- MHD simulation
-
图 1 2008年3月8日连续两次亚暴的概述. AU：虚线；AL：点线
Figure 1. The overview of two successive substorm on 8 March 2008
图 2 北半球热压的空间分布. （a）西向IMF BY和南向BZ；（b）东向IMF BY和北向 BZ. 菱形表示极尖区中心，实线表示极尖区边界. BS：南向BZ，BN：北向BZ，P：热压
Figure 2. The spatial distribution of P on the northern hemispheric surface derived from the simulation data. The left panel shows that at 12:00 UT under dawnward IMF BY and southward BZ and the right panel shows that at 14:20 UT under duskward IMF BY and northward BZ. The cusp centers are denoted by diamonds, and the cusp boundaries are represents by solid lines
图 3 北向（上）和南向（下）IMF时，判断得到的极尖区边界（菱形）和拟合结果（直线）
Figure 3. Two identified cusp boundaries (diamonds) and the corresponding curve fitting results (line) under northward and southward IMF
图 4 事件期间极尖区拟合的相关系数分布，阈值由垂直虚线表示. mean：平均值，median：中值
Figure 4. The correlation coefficient distribution of the cusp fitting during the event. The threshold value is denoted by the vertical dashed line
图 6 MLAT宽度和MLT宽度随IMF BZ的变化
Figure 6. The relation of MLAT width and MLT width with IMF BZ. The red lines are the fitting Results
图 7 IMF BZ（a）和IMF BY（b）变化时，模式计算得到的极尖区边界
Figure 7. The cusp boundaries calculated from our 2-D cusp model under different IMF BZ (a) and IMF BY (b)
图 8 （a, b）从DMSP观测到的沉降电子能量通量和观测到的极尖区（菱形）；（c, d）极尖区模式结果和对应观测结果（菱形）的比较. eeflx：下行电子能量通量
Figure 8. (a, b) Time variation of the downward electron energy flux (line) and observed cusps (diamond) from the DMSP observations; (c, d) The comparison of the observed cusp (diamond) and predicted cusp (line) for the corresponding comment
-
[1] Burch J L. 1972. Precipitation of low-energy electrons at high latitudes: Effects of interplanetary magnetic field and dipole tilt angle[J]. Journal of Geophysical Research, 77 (34): 6696-6707 doi: 10.1029/JA077i034p06696 [2] Burch J L. 1973. Rate of erosion of dayside magnetic flux based on a quantitative study of the dependence of polar cusp latitude on the interplanetary magnetic field[J]. Journal of Geophysical Research, 8 (1): 955-961 [3] Carbary J F, Meng C I. 1986. Correlation of cusp latitude with BZ and AE (12) using nearly one year's data[J]. Journal of Geophysical Research: Space Physics, 91: 10047-10054 doi: 10.1029/JA091iA09p10047 [4] Crooker N U, Burke W J. 1991. The cusp/cleft[J]. Reviews of Geophysics, 29 (S2): 1017-1027. [5] Escoubet C, Bosqued J M. 1989. The influence of IMF-BZ and/or ae on the polar cusp: An overview of observations from the aureol-3 satellite[J]. Planetary and Space Science, 37 (5): 609-626 doi: 10.1016/0032-0633(89)90100-1 [6] Fenrich F R, Luhmann J G, Fedder J A, et al. 2001. A global mhd and empirical magnetic field model investigation of the magnetospheric cusp[J]. Journal of Geophysical Research: Space Physics, 106 (A9): 18789 doi: 10.1029/2001JA900040 [7] Guo J G, Shi J K, Cheng Z W, et al. 2013. Variation of dependence of the cusp location at different altitude on the dipole tilt[J]. Chinese Science Bulletin, 58(28-29): 3541-3545. doi: 10.1007/s11434-013-5831-1 [8] Hu Y Q, Guo X C, Li G Q, et al. 2005. Oscillation of quasi-steady Earth's magnetosphere[J]. Chinese Physics Letters, 22(10): 2723 doi: 10.1088/0256-307X/22/10/073 [9] Hu Y Q, Guo X C, Wang C. 2007. On the ionospheric and reconnection potentials of the Earth: Results from global MHD simulations[J]. Journal of Geophysical Research: Space Physics, 112 (A7): A07215 [10] Kan J R, Lee L C. 1979. Energy coupling function and solar wind-magnetosphere dynamo[J]. Geophysical Research Letters, 6: 577-580 doi: 10.1029/GL006i007p00577 [11] Li H, Wang C, Zhang B. 2012. Variation characteristics of cusp configuration based on T96 model[J]. Chinese Journal of Space Science, 32 (4): 461-468. [12] Luhmann J G, Walker R J, Russell C T, et al. 1984. Patterns of potential magnetic field merging sites on the dayside magnetopause[J]. Journal of Geophysical Research: Space Physics, 89 (A3): 1739-1742 doi: 10.1029/JA089iA03p01739 [13] Merka J, Safrankova J, Nemecek Z. 2002. Cusp-like plasma in high altitudes: A statistical study of the width and location of the cusp from magion-4[J]. Annales Geophysicae, 20 (3): 311-320. doi: 10.5194/angeo-20-311-2002 [14] Newell P T, Meng C I. 1988. The cusp and the cleft/boundary layer: Low-altitude identification and statistical local time variation[J]. Journal of Geophysical Research: Space Physics, 93 (A12): 14549-14556 doi: 10.1029/JA093iA12p14549 [15] Newell P T, Meng C I, Sibeck D G, et al. 1989. Some low-altitude cusp dependencies on the interplanetary magnetic field[J]. Journal of Geophysical Research: Space Physics, 94 (A7): 8921-8927 doi: 10.1029/JA094iA07p08921 [16] Newell PT, Sotirelis T, Liou K, et al. 2006. Cusp latitude and the optimal solar wind coupling function[J]. Journal of Geophysical Research: Space Physics, 111 (A9): A09207. [17] Palmroth M, Janhunen P, Pulkkinen T I, et al. 2001a. Cusp and magnetopause locations in global MHD simulation[J]. Journal of Geophysical Research: Space Physics, 106 (A12): 29435 doi: 10.1029/2001JA900132 [18] Palmroth M, Laakso H, Pulkkinen T I. 2001b. Location of highaltitude cusp during steady solar wind conditions[J]. Journal of Geophysical Research: Space Physics, 106 (A10): 21109–21122. doi: 10.1029/2001JA900073 [19] Perreault P, Akasofu S I. 1978. A study of geomagnetic storms[J]. Geophysical Journal, 54: 547–573. doi: 10.1111/j.1365-246X.1978.tb05494.x [20] Peterson W K, Trattner K J. 2012. Sources of plasma in the high altitude cusp[J]. Journal of Atmospheric and Solar-Terrestrial Physics, 87-88: 1–10. doi: 10.1016/j.jastp.2011.07.001 [21] Pitout F, Escoubet C P, Klecker B, et al. 2006. Cluster survey of the mid-altitude cusp: 1. Size, location, and dynamics[J]. Annales Geophysicae, 24: 3011–3026 doi: 10.5194/angeo-24-3011-2006 [22] Qiu H-X, Han D-S, Zhang H-D, et al. 2022. A comparative study on the factors controlling the cusp auroral intensity between the northern and southern hemispheres[J]. Journal of Geophysical Research: Space Physics, 127(4): e30216 [23] Reiff P H, Hill T W, Burch J L. 1977. Solar wind plasma injection at the dayside magnetospheric cusp[J]. Journal of Geophysical Research, 82 (4): 479-491 doi: 10.1029/JA082i004p00479 [24] Rosenbauer H, Grunwaldt H, Montgomery M D, et al. 1975. Heos 2 plasma observations in the distant polar magnetosphere: The plasma mantle[J]. Journal of Geophysical Research, 80 (19): 2723-2737 doi: 10.1029/JA080i019p02723 [25] Siscoe G, Crooker N, Siebert K, et al. 2005. Cusp geometry in MHD simulations[J]. Surveys in Geophysics, 26 (1-3): 387-407 doi: 10.1007/s10712-005-1902-4 [26] Trattner K J, Fuselier S A, Yeoman T K, et al. 2005. Spatial and temporal cusp structures observed by multiple spacecraft and ground based observations[J]. Surveys in Geophysics, 26: 281-305 doi: 10.1007/s10712-005-1883-3 [27] Tsyganenko N A, Stern D P. 1996. Modeling the global magnetic field of the large-scale birkeland current systems[J]. Journal of Geophysical Research: Space Physics, 101 (A12): 27187-27198. doi: 10.1029/96JA02735 [28] Xiao C, Liu W, Shen C, et al. 2018. Study on the curvature and gradient of the magnetic field in Earth's cusp region based on the magnetic curvature analysis method[J]. Journal of Geophysical Research: Space Physics, 123(5): 3794-3805. doi: 10.1029/2017JA025028 [29] 徐佳莹, 吕建永, 王明, 等. 2018. 行星际磁场对极尖区位形变化的统计研究[J]. 地球物理学报, 61 （9 ）: 3526-3535, doi: 10 . 6038/ cjg2018M0118.Xu J Y, Lü J Y, Wang M, et al. 2018. Cusp location dependence on IMF: Cluster statistical study[J]. Chinese Journal of Geophysics, 61(9): 3526-3535 (in Chinese). doi: 10.6038/cjg2018M0118. [30] Zhang B, Brambles O, Lotko W, et al. 2013. Predicting the location of polar cusp in the lyon-fedder-mobarry global magnetosphere simulation[J]. Journal of Geophysical Research: Space Physics, 118 (10): 6327-6337 doi: 10.1002/jgra.50565 [31] Zhou XW, Russell CT. 1997. The location of the high-latitude polar cusp and the shape of the surrounding magnetopause[J]. Journal of Geophysical Research: Atmospheres, 102 (A1): 105 doi: 10.1029/96JA02702 [32] Zhou X W, Russell C T, Le G, et al. 1999. The polar cusp location and its dependence on dipole tilt[J]. Geophysical Research Letters, 26 (3): 429-432 doi: 10.1029/1998GL900312 [33] Zhou X W, Russell C T, Le G, et al. 2000. Solar wind control of the polar cusp at high altitude[J]. Journal of Geophysical Research: Space Physics, 105 (A1): 245. doi: 10.1029/1999JA900412 -
下载:
点击查看大图
计量
- 文章访问数: 367
- HTML全文浏览量: 213
- PDF下载量: 44
- 被引次数: 0
