Report of Geomagnetic Pulsation Indices for Space Weather Applications.

摘要

The phenomenon of ultra-low frequency (ULF) geomagnetic pulsations was first observed in the ground-based measurements of the 1859 Carrington Event (Stewart, 1861) and has been studied for over 100 years. Pulsation frequency is considered to be ultra low when it is lower than the natural frequencies of the plasma, such as the ion gyrofrequency. ULF pulsations are considered a source of noise in some geophysical analysis techniques, such as aeromagnetic surveys (Wanliss and Antoine, 1995) and transient electromagnetics, so it is critical to develop near real-time space weather products to monitor these geomagnetic pulsations. The proper spectral analysis of magnetometer data, such as using wavelet analysis techniques, can also be important to Geomagnetically Induced Current (GIC) risk assessment. The classification of ULF pulsations as Pc1, Pc2, Pc3, Pc4, and Pc5 for continuous pulsations and Pi1 and Pi2 for irregular pulsations is shown in table 1 (Jacobs and others, 1964). The sources of pulsations are different for each frequency band. Higher-frequency pulsations are caused by fluctuations and instabilities in the equatorial ionosphere and magnetosphere. Lower frequency pulsations are caused by other complicated phenomena, such as a local wave-particle instability or from coupling of wave energy propagating through the magnetosphere; they are produced either in the solar wind/magnetosheath or at the magnetopause/boundary layer (Anderson, 1993, 1994). Pulsations can be measured using ground-based magnetometers or space-based in-situ observations of magnetic and electric fields.