M-I Coupling: An Observational and Modeling Study Under Conditions of Extreme Forcing

研究人员将通过对施加大极帽电势对M-I系统的影响进行协调观测和建模，研究磁层-电离层的耦合。重点将放在非常大的风暴上，即表现出极不寻常的电动力学行为的超级风暴。系统的演化和能量的耗散是理解耦合系统如何从高能量状态返回平衡的核心。先前的研究在对超级风暴的详细事件研究中揭示，观测到的1区和2区场向电流(FAC)、电导和粒子沉淀提供了许多惊喜：区域2 FAC是迄今在电离层观测到的最大的电离层之一，但地面上几乎没有磁特征；电导比预测的大许多倍；测量到的沉淀电子通量完全由低能(E200 EV)粒子组成。类似的行为在其他超级风暴期间也很明显，这些超级风暴发生在最近的太阳高峰期。显然，在超级风暴期间表现出的行为领域超出了目前对M-I耦合的理解。研究人员将研究一系列超级风暴，以便定性和定量地描述极帽电势分布异常大的条件下电离层的电动力学性质。他们将通过对等离子体漂移、粒子沉淀和磁扰动的直接观测，确定几次超级风暴过程中电场、场向电流和电导的演变。他们将通过使用全球数据驱动的电离层模型来扩展观测到的等离子体和磁测量的数据库。他们还将使用简化版本的赖斯对流模型来考虑施加的极帽电势对磁层对流的影响。在磁层-电离层耦合模型的指导下，对耦合电流和场的观测将提供在超级风暴期间工作的电动力过程的时间和空间演变的统一图景。DMSP在840公里高度对等离子体和磁场的观测仅限于卫星采样的当地时间，大约为06-18LT和09-21LT。虽然太阳同步轨道允许对这些当地时间区段进行持续监测，但缺乏关于其他当地时间和高度的信息。调查人员将用极端强迫条件下的电离层全球模型来补充DMSP的观测结果。这项研究将有助于更好地理解M-I耦合过程，特别是对电离层施加的大极帽电势的影响。它将给出电场、FAC、电导和粒子沉淀的定量范围，这些都从未被系统地报道过磁暴。这些参数对于研究大型磁活动开始后M-I系统演化的任何详细模型都是必不可少的。这项研究将对能量平衡和耗散的建模、这些过程的轨迹和时间尺度具有重要意义，所有这些都是M-I耦合问题的核心。

The investigators will study magnetosphere-ionosphere coupling through coordinated observational and modeling of the effects of the imposition of large polar-cap electric potentials on the M-I system. The focus will be on very large storms, i.e. superstorms, which exhibit highly unusual electrodynamic behavior. The evolution of the system and dissipation of energy are central to an understanding of how the coupled system proceeds from a highly energized state back to equilibrium. Previous studies have revealed during a detailed event study of a superstorm, that the observed Region 1 and 2 field-aligned currents (FACs), conductances and particle precipitation provided many surprises: the Region 2 FACs were amongst the largest ever observed in the ionosphere yet there was little magnetic signature on the ground; the conductances were many times larger than that predicted, and the measured precipitating electron flux consisted entirely of low-energy (E200eV) particles. Similar behavior was manifest during other superstorms, which occurred during the recent solar maximum period. It is clear that the realm of behavior demonstrated during superstorms is beyond current understanding of M-I coupling. The investigators will study a series of superstorms in order to develop a qualitative and quantitative description of the electrodynamic properties of the ionosphere under conditions of unusually large polar-cap potential distributions. They will determine the evolution of electric fields, field-aligned currents and conductances during the course of several superstorms through direct observations of the plasma drifts, particle precipitation and magnetic perturbations. They will extend the database of observed plasma and magnetic measurements by using a global data-driven model of the ionosphere. They will also use a simplified version of the Rice Convection Model to consider the effect of the imposed polar-cap potential on magnetospheric convection. Guided by a model for magnetosphere-ionosphere coupling, the observations of the coupling currents and fields will provide a unified picture of the temporal and spatial evolution of the electrodynamic processes at work during the superstorm. Observations of plasmas and magnetic fields made by DMSP at 840 km altitude are limited to the local times sampled by the satellites, which are approximately 06-18 LT and 09-21 LT. While the sun-synchronous orbits allow continuous monitoring of these local time sectors, information on other local times and altitudes is lacking. Investigators will supplement the DMSP observations with global modeling of the ionosphere under conditions of extreme forcing. This research will lead to an improved understanding of M-I coupling processes, in particular the effects of large polar-cap potentials imposed on the ionosphere. It will yield quantitative ranges for electric fields, FACs, conductances and particle precipitation, which have never been reported systematically for magnetic storms. These parameters are essential for any detailed model of the evolution of the M-I system after the commencement of large magnetic activity. The study will be significant in modeling of energy balance and dissipation, the loci and time scales for these processes, all of which are central to the problem of M-I coupling.