Empirically modelled Pc3 activity based on solar wind parameters
Empirically modelled Pc3 activity based on solar wind parameters
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基于太阳风参数的经验模型 Pc3 活动
DOI：
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发表时间：
2010
期刊：
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通讯作者：
T. Raita
中科院分区：
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作者：
B. Heilig;S. Lotz;J. Vero;P. Sutcliffe;J. Reda;K. Pajunpää;T. Raita
抽象。已知在某些太阳风（SW）/行星际磁场（IMF）条件下（例如高SW速度，低锥角），更可能发生地面Pc 3 -4脉动。在本文中，我们表明，在异常低的SW粒子密度的情况下，Pc 3活动是非常低的，无论其他有利的SW速度和锥角。我们重新调查SW控制的Pc 3脉动活动，通过统计分析和两个经验模型，强调SW密度对Pc 3活动的影响。我们利用OMNI项目的SW和IMF测量以及MM 100阵列的地基磁强计测量，将SW和IMF测量与Pc 3活动的发生联系起来。在迭代过程中使用多元线性回归和人工神经网络模型，以确定基于SW的输入参数集，这些参数集最佳地再现了一组Pc 3活性数据。在参数集中包含SW密度显著改进了模型。不仅密度本身，而且其他与密度相关的参数，如SW的动态压力，或磁层顶的间隔距离在模型中同样适用。根据现有的上游波理论，低密度事件期间Pc 3s的消失至少有四个原因：1。暂停在没有质子的情况下产生上游超低频波的离子回旋共振，2。弓形激波的减弱意味着反射效率的降低。西南部变得亚阿尔夫文，因此无法扫回以阿尔夫文速度向上游传播的波，和4。磁层顶（和弓形激波）的间隔距离的增加。虽然该模型不能解释缺乏Pc 3的间隔时，SW密度极低，由此产生的最佳模型输入组支持中纬度Pc 3活动主要是通过上游波的产生。
Abstract. It is known that under certain solar wind (SW)/interplanetary magnetic field (IMF) conditions (e.g. high SW speed, low cone angle) the occurrence of ground-level Pc3–4 pulsations is more likely. In this paper we demonstrate that in the event of anomalously low SW particle density, Pc3 activity is extremely low regardless of otherwise favourable SW speed and cone angle. We re-investigate the SW control of Pc3 pulsation activity through a statistical analysis and two empirical models with emphasis on the influence of SW density on Pc3 activity. We utilise SW and IMF measurements from the OMNI project and ground-based magnetometer measurements from the MM100 array to relate SW and IMF measurements to the occurrence of Pc3 activity. Multiple linear regression and artificial neural network models are used in iterative processes in order to identify sets of SW-based input parameters, which optimally reproduce a set of Pc3 activity data. The inclusion of SW density in the parameter set significantly improves the models. Not only the density itself, but other density related parameters, such as the dynamic pressure of the SW, or the standoff distance of the magnetopause work equally well in the model. The disappearance of Pc3s during low-density events can have at least four reasons according to the existing upstream wave theory: 1. Pausing the ion-cyclotron resonance that generates the upstream ultra low frequency waves in the absence of protons, 2. Weakening of the bow shock that implies less efficient reflection, 3. The SW becomes sub-Alfvenic and hence it is not able to sweep back the waves propagating upstream with the Alfven-speed, and 4. The increase of the standoff distance of the magnetopause (and of the bow shock). Although the models cannot account for the lack of Pc3s during intervals when the SW density is extremely low, the resulting sets of optimal model inputs support the generation of mid latitude Pc3 activity predominantly through upstream waves.