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To emphasize the relationship between the pre-seismic geomagnetic signals and Vrancea seismicity, in this work it is hypothesized that before an earthquake initiation, the high stress reached into seismogenic volume generates dehydration of the rocks and fracturing processes followed by release of electric charges along the faulting systems, which lead to resistivity changes. These changes were explored on September 2016 by the normalized function Bzn obtained from the geomagnetic data recorded in ULF range (0.001-0.0083 Hz). A statistical analysis was also performed to discriminate on the new Bzn* time series a pre-seismic signature related to the Mw5.7 earthquake. Significant anomalous behavior of Bzn* was identified on September 21, with 3 days prior to the onset of the seismic event. Similar information is provided by registrations of the magnetic and electron concentration variations in the ionosphere over the Vrancea zone, by Swarm satellites, 4 days and 1 day before the earthquake.
Content available remote Nonlinear plasma wave processes observed in the polar cusp
We present observations of electric and magnetic field variations from proton (about few Hz) to electron cyclotron frequencies (about few kHz) obtained by STAFF instrument on Cluster satellites during two cusp crossings, at ~6 RE altitude, in September 2002. The cusp was identified by the presence of intensive fluxes of counter streaming electrons with low energies and broadband wave activity which is typical for this region. Special attention is given for the interval of measurements when the wave-form of the magnetic field fluctuations was taken in this region by CLUSTER satellites. The wave has been processed using the wavelet and bispectral analysis. Results showing the cascade of turbulence and wave-wave interactions are presented in this paper. A three wave process can be responsible for the broadening of the wave spectra in the polar cusp.
Dayside magnetosphere is the place for various transient events, one class of which-called flux transfer events (FTEs) has been a subject of special importance for almost 20 years. Due to the magnetosphere-ionosphere coupling, phenomena at the dayside magnetopause should have signatures in the high-latitude ionosphere. A search for ground signatures of transient events at the dayside magnetopause is one of the goals of correlated multi-point studies. Ground signatures (if any) can provide additional arguments in the discussion on the nature of transient events. FTEs were chosen for the current study because they are easy to identify and are common in the high-apogee satellite observations. Most of previous studies focused on high-latitude observations themselves, which left the relation of the ionospheric peculiarities to FTEs unproved, if not ambiguous. This work, on the contrary, starts with the magnetopause observations by AMPTE-IRM and UKS satellites. For the events detected, ground magnetometer data are collected, in some cases supplied by AMPTE-CCE data. Observations of some of the events studied are presented. The signatures are discussed in the frame of current theoretical FTE models.
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