The Polar Cap North (PCN) index

The Polar Cap (PC) index consists of the Polar Cap North (PCN) and the Polar Cap South (PCS) indices, which are derived from magnetic measurements taken at the geomagnetic observatories in Qaanaaq (THL, Greenland, +85o magnetic latitude) and Vostok (VOS, Antarctica, -83o magnetic latitude), respectively. These indices are used to estimate the intensity of anti-sunward plasma convection in the polar caps. This convection is associated with electric Hall currents and consequent magnetic field variations perpendicular to the anti-sunward plasma flow (and related Hall current). These magnetic field variations are monitored at the Qaanaaq and Vostok magnetic observatories. The PC index aids in monitoring the energy input from solar wind to the magnetosphere (loading activity). The index is constructed in such a way that it has a linear relationship with the merging Electric Field at the magnetopause; consequently, the PC index is given in units of mV/m as for the electric field.极盖（Polar Cap, PC）指数包含北极盖（Polar Cap North, PCN）指数与南极盖（Polar Cap South, PCS）指数，二者分别基于格陵兰岛卡纳克（Qaanaaq, THL，地磁纬度+85°）地磁台站与南极沃斯托克（Vostok, VOS，地磁纬度-83°）地磁台站的磁测量数据计算得到。此类指数可用于估算极盖区内逆日向等离子体对流的强度。该对流与霍尔电流及垂直于逆日向等离子体流（及相关霍尔电流）的磁场扰动密切相关，上述磁场扰动可通过卡纳克与沃斯托克地磁台站进行监测。极盖指数有助于监测太阳风向磁层的能量输入（即加载活动）。该指数的构建逻辑使其与磁层顶处的合并电场呈线性关系，因此极盖指数采用与电场一致的单位：毫伏每米（mV/m）。