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

Abstract

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, , and magnetic local time, MLT. The 2-D distributions of the spectral moments in -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 (Ncomponent) 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.Correspondence to: N. V. Yagova (nyagova@yandex.ru)

Climatology of rapid geomagnetic variations at high latitudes over two solar cycles

“…4). Since large dH /dt values are obviously related to high frequencies, the results by Yagova et al (2010) at least qualitatively support our findings from a different viewpoint.…”

“…Although Kataoka and Pulkkinen (2008) did not study auroral latitudes, we may speculate a similar behaviour there. Yagova et al (2010) consider spectral parameters of high latitude geomagnetic disturbances in the Pc5/Pi3 frequency range (periods of about 250-1000 s). Their Fig.…”

Non-triggered auroral substorms and long-period (1–4 mHz) geomagnetic and auroral luminosity pulsations in the polar cap

“…Processes in the geomagnetic tail, which may be related to any pre-substorm signatures, are reflected mostly in broadband, high-latitude, long-period ULF fluctuations. Such "geomagnetic noise" requires a quantitative analysis technique, such as that developed by Yagova et al (2010Yagova et al ( , 2015. Yagova et al (2010) found that the spectral content of high-latitude geomagnetic pulsations in the 1-5 mHz (Pc5/Pi3) frequency range is characterized by regular diurnal variation and irregular day-to-day variation.…”

“…Such "geomagnetic noise" requires a quantitative analysis technique, such as that developed by Yagova et al (2010Yagova et al ( , 2015. Yagova et al (2010) found that the spectral content of high-latitude geomagnetic pulsations in the 1-5 mHz (Pc5/Pi3) frequency range is characterized by regular diurnal variation and irregular day-to-day variation. The regular fraction is controlled by geomagnetic latitude and magnetic local time (MLT), while the irregular variations of Pc5/Pi3 spectral parameters are controlled by the space weather conditions, both in the solar wind and in the magnetosheath-magnetosphere system.…”

“…PSDs, and the magnetic-auroral cross spectra (in both square coherence and phase difference) are calculated for the two horizontal components of the magnetic field and the 557.7 nm MSP channel. In addition to the cross-spectral analysis, a quantitative description of broad-band pulsations is carried out using the methods described in Yagova et al (2010Yagova et al ( , 2015 and the reader is directed to those papers for a more detailed description. Briefly, the technique is based upon an expansion into Legendre polynomials of a log-log spectrum with the resulting coefficients providing a quantitative description of ULF wave activity.…”