World Data Centre for Geomagnetism, Copenhagen

The WDC has a FTP-server to distribute the PCN index derived from the geomagnetic observatory Qaanaaq (THL) and the Kp-index data products derived at the geomagnetic observatory Niemegk (NGK). The WDC is also holding extensive archives of magnetograms and other geomagnetic observatory data products that predate the introduction of digital data recording. The material is in analogue form such as film or microfiche. The Polar Cap index (abbreviation PC index) consists of the Polar Cap North (PCN) and the Polar Cap South (PCS) index, which are derived from magnetic measurements taken at the geomagnetic observatories Qaanaaq (THL, Greenland, +85o magnetic latitude) and Vostok (VOS, Antarctica, -83o magnetic latitude), respectively. The idea behind these indices is 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 antisunward plasma flow (and related Hall current) which can be monitored at the Qaanaaq and Vostok magnetic observatories. PC aims at 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 PC is given in units of mV/m as for the electric field. In August 2013, the International Association of Geomagnetism and Aeronomy (IAGA) endorsed the PC index. The endorsed PC index is accessible at pcindex.org or through WDC Copenhagen.

世界数据中心（WDC）设有FTP服务器，用于分发由地磁观测站Qaanaaq（THL）提取的PCN指数以及在地磁观测站Niemegk（NGK）生成的Kp指数数据产品。此外，WDC还保存了大量的磁图及其他地磁观测站数据产品的档案，这些档案早于数字数据记录技术的引入。这些材料以模拟形式存在，如胶片或缩微胶片。极冠指数（简称PC指数）包括极冠北（PCN）和极冠南（PCS）指数，分别由地磁观测站Qaanaaq（THL，位于格陵兰，磁纬+85o）和沃斯托克（VOS，位于南极，磁纬-83o）的磁测量得出。这些指数背后的理念是估算极冠中反太阳方向等离子体对流的强度。这种对流与电霍尔电流相关，并导致与反太阳方向等离子体流动（及相关霍尔电流）垂直的磁场变化，这些变化可以在Qaanaaq和沃斯托克地磁观测站进行监测。PC指数旨在监测太阳风对磁层的能量输入（即加载活动）。该指数的构建方式使其与磁层边缘的合并电场呈线性关系；因此，PC指数以mV/m为单位，与电场单位相同。2013年8月，国际地磁与大气协会（IAGA）批准了PC指数。批准的PC指数可通过pcindex.org或通过哥本哈根的世界数据中心获取。