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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 28, issue 9
Ann. Geophys., 28, 1761–1775, 2010
© Author(s) 2010. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 28, 1761–1775, 2010
© Author(s) 2010. This work is distributed under
the Creative Commons Attribution 3.0 License.

  28 Sep 2010

28 Sep 2010

Spatial distribution of spectral parameters of high latitude geomagnetic disturbances in the Pc5/Pi3 frequency range

N. V. Yagova1, V. A. Pilipenko1,2, L. N. Baransky1, and M. J. Engebretson3 N. V. Yagova et al.
  • 1Institute of the Physics of the Earth, Moscow 123995, Russia
  • 2Space Research Institute, Moscow 117997, Russia
  • 3Augsburg College, Minneapolis, MN 55454, USA

Abstract. We analyze spectral parameters of the geomagnetic disturbances within the 1–4 mHz (Pc5/Pi3) frequency range for 29 observatories from polar to auroral latitudes. The main object of this study is the broadband (noise) background under quiet and moderately disturbed conditions. To obtain a quantitative description of background high-latitude long period ULF activity the log-log dependence of the spectral power on frequency is expanded over Legendre polynomials, and the coefficients of this expansion (spectral moments) are used to describe the most common features of these spectra. Not only the spectral power, but also the spectral slope and higher spectral moments, averaged over relatively long time intervals, demonstrate a systematic dependence on corrected geomagnetic (CGM) latitude, Φ, and magnetic local time, MLT. The 2-D distributions of the spectral moments in Φ-MLT coordinates are characterized by existence of structures, narrow in latitude and extended in MLT, which can be attributed to the projections of different magnetospheric domains. Spatio-temporal distributions of spectral power of elliptically (P-component) and randomly (N-component) polarized signal are similar, but not identical. The N-component contribution to the total signal becomes non-negligible in regions with a high local activity, such as the auroral oval and dayside polar cusp. The spectral slope indicates a larger relative contribution of higher frequencies upon the latitude decrease, probably, as a result of the resonant effects in the ULF noise. The higher spectral moments are also controlled mostly by CGM latitude and MLT and are fundamentally different for the polarized and non-polarized components. This study is a step towards the construction of an empirical model of the ULF wave power in Earth's magnetosphere.

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