Seasonal and diurnal variations in AMPERE observations of the Birkeland currents compared to modeled results
Seasonal and diurnal variations in AMPERE observations of the Birkeland currents compared to modeled results
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DOI：
10.1002/2015ja022050
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发表时间：
2016-05-01
影响因子：
2.8
通讯作者：
Korth, H.
中科院分区：
文献类型：
--
作者：
Coxon, J. C.;Milan, S. E.;Korth, H.
我们减少了活动磁层和行星电动力学响应实验(Ampere)所做的测量，得到了在月箱和小时箱中在两个半球流动的总伯克兰(场向)电流。我们利用6a(2010-2015)的数据对这些数据进行了分析，首次考察了太阳天顶角度驱动的两个半球同时流动的总Birkland电流的变化。在总的Birkland流中发现了日变化，这与太阳天顶角的变化是一致的。在北半球(南半球)的Bartels旋转过程中，北半球(南半球)的海流也有明显的季节变化。在接近春分的几个月里，北半球发现了更多的洋流，这与我们的预期相反。我们还对米兰(2013)估计Birkland电流幅度的模型进行了第一次测试，根据观测到的Birkland电流随季节和一天中时间的变化进行了修改，以考虑太阳对电离层电导的贡献。修正后的模型采用Bartels旋转的平均值(D)(按1.7标度)，与观测到的安培电流一致，相关系数在北半球为0.87，在南半球为0.86。改进了与日边重联率的相关性，是对模型的显著改进。残差的相关性被发现与北半球流动的更多洋流相一致。这一新观测到的北半球系统性较大的海流是在先前结果的背景下讨论的，这些结果表明，北半球可能比南半球对白天重联的反应更强烈。
We reduce measurements made by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) to give the total Birkeland (field-aligned) current flowing in both hemispheres in monthly and hourly bins. We analyze these totals using 6years of data (2010-2015) to examine solar zenith angle-driven variations in the total Birkeland current flowing in both hemispheres, simultaneously, for the first time. A diurnal variation is identified in the total Birkeland current flowing, consistent with variations in the solar zenith angle. A seasonal variation is also identified, with more current flowing in the Northern (Southern) Hemisphere during Bartels rotations in northern (southern) summer. For months close to equinox, more current is found to flow in the Northern Hemisphere, contrary to our expectations. We also conduct the first test of the Milan (2013) model for estimating Birkeland current magnitudes, with modifications made to account for solar contributions to ionospheric conductance based on the observed variation of the Birkeland currents with season and time of day. The modified model, using the value of (D) averaged by Bartels rotation (scaled by 1.7), is found to agree with the observed AMPERE currents, with a correlation of 0.87 in the Northern Hemisphere and 0.86 in the Southern Hemisphere. The improvement over the correlation with dayside reconnection rate is demonstrated to be a significant improvement to the model. The correlation of the residuals is found to be consistent with more current flowing in the Northern Hemisphere. This new observation of systematically larger current flowing in the Northern Hemisphere is discussed in the context of previous results which suggest that the Northern Hemisphere may react more strongly to dayside reconnection than the Southern Hemisphere.