Geomagnetic variations in the frequency range 2.5–12 Hz in the ionospheric F layer as measured by SWARM satellites

We have analyzed geomagnetic variations in the 2.5–12 Hz frequency range in the ionospheric F layer above the electron density maximum, using data from two SWARM satellites. The analysis is based on the data obtained under weak and moderate magnetic activity for 12 days in September and December 2016. To separate spatial inhomogeneities from time variations of the magnetic field, we analyzed signal waveforms and cross-spectra in a 2.56 s sliding window. A maximum in the occurrence and power spectral density of the variations was found at latitudes above the polar boundary of the auroral oval, which correspond to the magnetospheric input layers and dayside polar cusp/cleft. Typical waveforms of the high-latitude variations are the wave packets lasting for 5–10 periods, recorded with a short time delay by two satellites spaced by 40–100 km. These variations might be the ionospheric manifestation of the electromagnetic ion-cyclotron waves generated at the non-equatorial magnetosphere near the polar cusp. The waveforms and cross-spectra of the variations are examined in more details for two cases with different spatial distributions of the magnetic field in the ionosphere. For the ionospheric conditions corresponding to event 1 (September 17, 80° geomagnetic latitude, afternoon sector), spatial distributions of wave magnetic field in the ionosphere and on Earth are estimated using a model of Alfvén beam with a finite radius incident on the ionosphere [Fedorov et al., 2018]

About possibility to locate an EQ epicenter using parameters of ELF/ULF preseismic emission

A relation between parameters of preseismic ULF/ELF emissions and EQ is studied. The magnetic data measured at Karymshino station (Kamchatka, Russia) along with data on local seismic activity during eight years of observations (2001–2008) are taken for the analysis. Source azimuth is detected in different techniques, based on the analysis of the total field and its polarized pulsed component. The latter technique shows a better accuracy in the source azimuth detection. The errors of the method are associated with existence of non-seismic sources and with use of one-point observation. The second error can be eliminated by development of multi-point observations

Hydromagnetic spectroscopy of the magnetosphere with Pc3 geomagnetic pulsations along the 210° meridian

Analysis of Pc3 observational data along the 210° magnetic meridian showed a complicated frequency-latitude structure at middle latitudes. The observed period-latitude distributions vary between events with a "noisy source": the D component has a colored-noise spectrum, while the spectrum of <i>H</i> component exhibits regular peaks that vary with latitude, and events with a "band-limited source": the spectral power density of the <i>D</i> component is enhanced at certain frequencies throughout the network. For most ULF events a local gap of the <i>H</i> component amplitude has been exhibited at both conjugate stations at <i>L </i><u>~</u> 2.1. A quantitative interpretation has been given assuming that band-limited MHD emission from an extra-magnetospheric source is distorted by local field line resonances. Resonant frequencies had been singled out with the use of the asymmetry between spectra of <i>H</i> and <i>D</i> components. Additionally, a local resonant frequency at <i>L </i><u>~</u> 1.6 was determined by the quasi-gradient method using the data from nearly conjugate stations. The experimentally determined local resonance frequencies agree satisfactorily with those obtained from a numerical model of the Alfven resonator with the equatorial plasma density taken by extrapolation of Carpenter-Anderson model. We demonstrate how simple methods of hydromagnetic spectroscopy enable us to monitor simultaneously both the magnitude of the IMF and the magnetospheric plasma density from ULF data.<br><br><b>Key words. </b>Magnetospheric physics (Magnetosphere-ionosphere interactions; MHD waves and instabilities; plasmasphere

Control of high latitude geomagnetic fluctuations by interplanetary parameters: the role of suprathermal ions

We examine the statistical relationships between the interplanetary parameters and spectral power of the geomagnetic fluctuations in the 1&ndash;4 mHz frequency band at high latitude stations in two hemispheres. For that, we use a cross-correlative analysis of different combinations of parameters to identify a factor contributing most to the ULF power and to choose (whenever possible) the cross-related keynote controlling parameters. Along with the well-known dependencies of the high latitude pulsation power on the solar wind velocity and variations of the SW dynamical pressure and an additional factor &ndash; the flux of solar suprathermal ions with energies about several keV, has been established

Nighttime Pc3 pulsations : MM100 and MAGDAS observations

A poorly known type of ULF waves - nighttime Pc3 pulsations are analyzed on the ground from auroral to equatorial latitudes. These oscillations have turned out to be a typical nightside wave phenomenon at middle and equatorial geomagnetic latitudes. Nighttime Pc3s can be divided into two classes. Pc3 pulsations of the first class are the ”tails” of the LT distribution of morning Pc3 pulsations. They have the highest occurrence rate at pre-morning hours and at the same geomagnetic latitudes as typical dayside Pc3 pulsations. The night signatures of dayside Pc3 waves are observed during the periods of fast solar wind (> 600 km/s). The mechanism of this type of nighttime Pc3 pulsations is probably related to the refraction of a fast compressional wave incident on the dayside inner magnetosphere. The second type is the specific nighttime Pc3 pulsations. They are observed under moderate solar wind velocities and are localized at middle latitudes in the nightMLT sector. This type of nightside Pc3 pulsations is probably driven by a bursty magnetotail activity, similarly to quite-time Pi2 pulsations. The wave energy transfer from the magnetotail to the ground is to be performed via the fast magnetosonic wave. This conjecture is supported by high correlation of the occurrence rate of the specific nighttime Pc3s with the AE index of auroral activity