[1] Latitudinal and diurnal distributions of spectral power and spatial coherency parameters of the geomagnetic variations in the Pc5-6 (1-6 mHz) frequency range are analyzed using data of magnetometer stations in Antarctica. The available stations give the possibility to form a latitude chain along the geomagnetic meridian 40°E stretching from magnetic latitude 69°S to 86°S. Long-period ULF activity at polar cap latitudes is characterized by lower amplitudes and wider spectra with lower central frequencies as compared with typical auroral Pc5 pulsations. The meridional distribution of average Pc5-6 spectral power is nonmonotonic and has a minimum near 80°. In general, the low-frequency broadband ULF activities in the polar cap and at auroral latitudes seem to be decoupled. This long-period ULF activity in the polar cap could be an image of wave activity in the tail lobes or the manifestation of turbulent component of the ionospheric convection at very high latitudes, but this requires further investigation.
[1] The power spectra of remarkable events of long-period fluctuations of the geomagnetic field (as identified at a low-latitude station, L'Aquila, l % 36°) reveal a tendency for a repeated occurrence of power enhancements in the same frequency bands (f % 0.9-1.0, 1.2-1.4, 2.1-2.3, 2.5-2.7 mHz), often coincident with CMS frequencies. In four cases the data availability and the results of the spectral analysis allowed unambiguous conclusions on the correspondence between ground, magnetospheric, and solar wind fluctuations. For most wave packets, the comparative analysis reveals an unprecedented one-to-one correspondence in terms of frequency, onset, and duration; it suggests that geomagnetic fluctuations can be driven directly by fluctuations of the solar wind density at the same frequencies. On the other hand, the repeated occurrence in the same frequency bands and some evidence for amplification processes suggest additional contributions possibly related with cavity/waveguide resonances.Citation: Villante, U., P. Francia, M. Vellante, P. Di Giuseppe, A. Nubile, and M. Piersanti (2007), Long-period oscillations at discrete frequencies: A comparative analysis of ground, magnetospheric, and interplanetary observations,
Abstract.A statistical analysis of the geomagnetic field fluctuations in the Pc5 frequency range (1-5 mHz) at a low latitude station (L = 1.6) provides further evidence for daytime power peaks at discrete frequencies. The power enhancements, which become more pronounced during high solar wind pressure conditions, may be interpreted in terms of ground signatures of magnetospheric cavity/waveguide compressional modes driven by solar wind pressure pulses. In this sense, the much clearer statistical evidence for afternoon events can be related to corotating structures mainly impinging the postnoon magnetopause. A comparison with results obtained for the same time intervals from previous investigations at higher latitudes and in the Earth's magnetosphere confirms the global character of the observed modes.
We present a statistical analysis of Pc3–4 pulsations during 2005 at two polar cap stations (Terra Nova Bay and Dome C, Antarctica) and, for comparison, at a low‐latitude station (L'Aquila). The analysis technique allows to discriminate the signal component from the background noise in the power spectrum and to determine the frequency of such ULF signal, commonly associated to the upstream wave source. The comparison of data makes evident that the characteristics of the ULF pulsations are different at low and high latitudes, and significant differences emerge also between the two polar cap stations. At Dome C the ULF signals are observed during the whole day, while at Terra Nova Bay and at L'Aquila the signals are mainly observed in the dayside sector. The different cone angle dependence at L'Aquila and Dome C, the steeper slope in the frequency dependence on the interplanetary magnetic field strength at Dome C with respect to L'Aquila and Terra Nova Bay and the time dependence of the coherence between pulsations at the Antarctic stations suggest that at low‐latitude waves are transmitted to the ground from a region close to the subsolar bow shock, while near the geomagnetic pole waves are mainly transmitted through the magnetotail lobes. At Terra Nova Bay, where the local field lines approach the cusp around noon and are stretched into the magnetotail around midnight, the transmission path seems to be time dependent, with daytime and nighttime pulsations penetrating through the subsolar point and via the magnetotail lobes, respectively.
This study is focused to investigate the Pc5 geomagnetic pulsations in response to the solar wind forcing and their relationship with the relativistic electron flux at geostationary orbit. We analyzed the correlation of the Pc5 power in the magnetosphere and on the ground, at low and high latitude, with the solar wind speed and fluctuation power of the interplanetary magnetic field and solar wind dynamic pressure through the years 2006 to 2010, also examining the relative timing between pulsations and solar wind parameters. We found a very significant correlation of the Pc5 power with simultaneous solar wind pressure fluctuations and with the solar wind speed lagged by several hours; the relative amplitude of the two correlation peaks depending on the solar cycle phase and on the latitude. We also found a strong relationship between the Pc5 power and the >600 keV and >2 MeV electron flux at geosynchronous orbit. Clear evidence emerges that the electron flux follows the Pc5 power by about 2 days; the time delay is a bit longer for the higher energy electrons.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.