Study of Cross Polar Cap Potential Behavior During Storms and Superstorms Using Defense Meteorological Satellite Program (DMSP) Data

太阳风与磁层和磁层与电离层耦合的关键特征之一是施加在极帽上的电势下降。这种电势下降及其在极地电离层中的相关电势分布模式可以作为太阳风与磁层耦合的代理测量。最近的研究表明，在极端太阳风条件下，极地电离层的行为与在平静时期和中等磁暴期间的行为不同，极端太阳风条件下会产生非常大的磁暴，即超级磁暴。似乎无论太阳风所携带的电场有多强，极帽电位下降都会在一个固定的水平上达到饱和。此外，在这些饱和电位条件下，极帽本身的大小似乎停止了膨胀。了解极帽电位的行为和极帽本身的大小，以及它们如何响应太阳风驱动因素（太阳风电场和太阳风冲击压力）以及电离层电导率的变化，是理解这一现象的潜在物理原理和开发准确可靠的地球空间环境模型的关键。这个为期三年的项目将使用DMSP航天器的极地电离层参数数据库来探索极地电离层对常规风暴和极端超级风暴的反应。该项目将开发一个关于极帽大小作为极帽潜力大小和各种太阳风输入的函数的经验模型。将检查太阳风电场中至高值的周期，以确定开始出现势饱和的过渡区域。该项目还将比较Hill-Siscoe模型得出的电离层Pedersen电导率与AMIE模型得出的电导率

One of the key features in the coupling of the solar wind to the magnetosphere and the magnetosphere to the ionosphere coupling is the electric potential drop imposed across the polar cap. This potential drop and its associated potential distribution pattern in the polar ionosphere serves as a proxy measurement of the coupling between the solar wind and the magnetosphere. Recent work has shown that the polar ionosphere behaves differently under the extreme solar wind conditions that produce the very large magnetic storms known as superstorms as compared with the behavior during quiet times and moderate magnetic storms. It appears that the polar cap potential drop saturates at a set level no matter how strong the system is driven by the electric field carried by the solar wind. In addition the size of the polar cap itself appears to stop expanding under these saturated potential conditions. Understanding the behavior of the polar cap potential and the size of the polar cap itself and how they respond to solar wind drivers (the solar wind electric field and the solar wind ram pressure) as well as to the changes in the conductivity in the ionosphere are key to understanding the underlying physics of the phenomenon and in developing accurate and reliable models of the geospace environment. This three-year project will use the database of polar ionospheric parameters from the DMSP spacecraft to explore the polar ionosphere's response to regular storms and to the extreme superstorms. The project will develop an empirical model of the size of the polar cap as a function of the magnitude of the polar cap potential and various solar wind inputs. Periods of medium to high values of the solar wind electric field will be examined to determine the transition region where the saturation of the potential begins to appear. The project will also compare the ionospheric Pedersen conductivity derived from the Hill-Siscoe model with the value derived using the AMIE