Improvement of satellite data main field modelling through a better separation of internal from external contributions

从卫星磁场测量确定地磁长期变化需要重复生成相隔约一个月的不同时期的主磁场模型。从连续场模型的高斯系数的变化中导出长期变化。这个过程对模型的质量提出了很高的要求，因为任何虚假的影响都可能模仿一个变化。随着2000年7月15日CHAMP卫星的发射，高度精确的磁场测量已经成为可能。由于设计寿命长，为5年，而且是低极轨道，这套数据对长期变化研究特别有用。为了充分利用主磁场建模的准确性，必须特别注意正确去除电离层电流中的磁场贡献。高纬度地区尤其具有挑战性。在这里，即使在夜晚和磁性安静的日子里，实质性的电流也在流动。过去，几乎没有采取任何措施来进一步改善这种状况。在本提案中，我们计划通过结合地面和空间观测来模拟极地地区的电离层电流。其目的是建立一个平静期电离层电流的描述，这是由地面和太阳风观测控制，并可用于校正的CHAMP磁场数据之前，主要场建模。

Determining the geomagnetic secular variation from satellite magnetic field measurements requires the repeated generation of main field models for different epochs separated by about a month. From the changes in the Gauss coefficients of successive field models the secular variation are derived. This procedure puts high demands on the quality of the models, since any spurious effect may mimic a variation. With the launch of the CHAMP satellite on 15th July 2000 highly accurate magnetic field measurements have become available. The long designed life-time of 5 years and the low polar orbit make this data set particularly useful for secular variation studies. In order to utilise the full accuracy for main field modelling special attention has to be paid to a correct removal of the magnetic contribution from ionospheric currents. Particulary challenging are the high latitudes. Here substantional currents are flowing even on the night side and during magnetically quiet days. In the past little has been done to further improve this situation. In this proposal we plan to model the ionospheric currents in the polar regions by combining ground-based and space-based observations. The aim is to construct a description of ionospheric currents for quiet periods, which is controlled by ground-based and solar wind observations and which can be used to correct the CHAMP magnetic field data prior to main field modelling.