Bulg. J. Phys. vol.34 no.2 (2007), pp. 136-148

ULF Wave Index and Its Possible Applications in Space Physics

N. Romanova1, V. Pilipenko2, N. Crosby3, O. Khabarova2
1Institute of the Physics of the Earth, Russia
2Space Research Institute, Russia
3Belgian Institute of Aeronomy, Belgium
Abstract. The solar wind-magnetosphere interaction has a turbulent character, which is not accounted for by commonly used geomagnetic indices and OMNI parameters. To quantify the level of low-frequency turbulence/variability of the geomagnetic field, IMF, and solar wind plasma, we have introduced ULF wave power indices. These simple hourly indices are based on the integrated spectral power in the band 2-7 mHz or wavelet power with time scales ~10-100 min. The ground wave index has been produced from the data of global magnetometer arrays in the northern hemisphere. The interplanetary and geostationary wave indices have been calculated using magnetometer and plasma data from interplanetary and geosynchronous satellites. These indices have turned out to be useful for statistical analysis of various space weather problems. These indices enables one to examine easily the statistical correspondence between the ULF activity and interplanetary conditions. For example, the enhancements of relativistic electrons at the geosynchronous orbit were not directly related to the intensity of magnetic storms, but they correlated well with intervals of elevated ground ULF wave index. This fact confirmed the importance of magnetospheric ULF turbulence in energizing electrons up to relativistic energies. The interplanetary index has revealed statistically the role of the interplanetary turbulence in driving the magnetosphere by the IMF/solar wind. The application of this index to the analysis of conditions in the solar wind before magnetic storm onsets has shown that a weak irregular increase of the solar wind density is observed on average 2 days prior to storm commencement. The ULF index database for the period since 1991 is freely available via anonymous FTP for all interested researchers for further validation and statistical studies.

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