Mapping the Polar Ionospheric Conductivities

摘要提出的活动探索创造性和潜在的变革概念，以解决在极地地区获得足够的电导率图的基本问题。这些信息是我们关于磁层-电离层耦合的知识中缺失的一环，它阻碍了这一前沿领域的进展。所提出的努力为社区后续的全球建模研究奠定了基础，有可能显著推进知识，甚至可能引发我们对地球空间电动力学耦合的理解的突破。提案者计划通过利用最近和正在进行的卫星任务和地面仪器测量的磁场、电场和电流的大数据集，创建一个极区高度积分电导率的最先进的经验模型。经验模型的一个新特征将是能够首次产生高度积分的电导率模式，作为太阳EUV辐照度的函数，地球磁偶极子相对于太阳的倾斜和行星际磁场方向-所有这些都是已知的组织电导率的空间和时间行为及其大小。这一点尤其重要，因为电离层的导电性使磁层和太阳风之间相互作用产生的电流有可能通过上层大气关闭。这也是决定这些电流的能量如何沉积的关键因素。尽管电导率在驱动地球空间的行为中起着至关重要的作用，但它仍然是最不为人所知的量之一，因为直接测量极其困难，而且对其全球特征的直接观察尚不可能。该项目为研究生提供培训，从而为未来的科学劳动力做出贡献。地球空间系统内部耦合知识的进步可能会导致模型的改进，并最终实现对社会有价值的更好的空间天气预测。计算电离层高度积分电导率的方法需要现有经验模型（将得到改进）提供的电场、地面磁强计数据反演得到的无发散电流和卫星磁强计得到的无旋流电流。无旋流分量本质上是磁层场向电流通过电离层的闭合电流。如果磁力线近似垂直，就像在极区一样，由磁场对准和无旋流电流形成的电流环在地面上不产生磁信号；因此需要对无旋流电流的磁场特征进行卫星观测。如果电离层电导率是均匀的，则无旋流电流就是彼得森电流，无散度电流本质上就是霍尔电流，这可以通过在地面上观察到的磁场扰动来检测。

AbstractThe proposed activities explore creative and potentially transformative concepts to solve the fundamental problem of obtaining adequate conductivity maps in the polar region. This information is a missing link in our knowledge of magnetosphere-ionosphere coupling, which is hindering progress on this frontier. The proposed effort, which lays the groundwork for follow-on global modeling studies in the community, has the potential to significantly advance knowledge possibly even triggering a breakthrough in our understanding of Geospace electrodynamic coupling. The proposers plan to create a state-of-the-art empirical model of height-integrated electrical conductivities in the polar region by taking advantage of large datasets of magnetic field, electric field, and electric current measurements from recent and ongoing satellite missions and ground-based instrumentation. A new feature of the empirical model will be the ability to produce, for the first time, height-integrated electrical conductivity patterns as a function of solar EUV irradiance, the tilt of the Earth's magnetic dipole with respect to the Sun and the interplanetary magnetic field orientation - all of which are known to organize the spatial and temporal behavior of the conductivity as well as its magnitude. This is particularly important because ionospheric conductivity makes possible the closure through the upper atmosphere of currents that are generated by the interaction between the magnetosphere and the solar wind. It is also a key factor in determining how energy from these currents is deposited. Despite the critical role of the conductivity in driving the behavior of Geospace, it is still one of the most poorly known quantities because direct measurements are extremely difficult to make and direct observations of its global features have not yet been possible. The project provides training for a graduate student thus contributing to the future scientific workforce. The advances in knowledge about coupling within the Geospace system will likely lead to improved models and ultimately to better space weather predictions of value to society. The method for deriving ionospheric height-integrated conductivity requires electric fields supplied by an existing empirical model (which will be improved), divergence-free currents obtained from inversion of ground-based magnetometer data and curl-free currents obtained from satellite magnetometers. The curl-free current component is essentially the closing current through the ionosphere for magnetospheric field-aligned currents. If field lines are approximately vertical as in the polar regions, the current loop formed by the field-aligned and curl-free current produces no magnetic signature at the ground; hence the need for satellite observations of the magnetic field signature of the curl-free current. If the ionospheric conductivity is uniform, the curl-free current is the Pedersen current and the divergence-free current is essentially the Hall current, which can be detected through magnetic field perturbations observed on the ground.