Oleksiy Agapitov — Page 2

arXiv2017

A reconstruction method of electron density distribution in the equatorial region of magnetosphere

A method for the estimation of electron density from the ratio of the wave magnetic and electric field amplitude of whistler waves is developed. Near the geomagnetic equator, whistler wave normals are mainly close to the direction of the background magnetic field. Dispersion relation of whistler wave in the parallel propagation approximation is used in this method. Signals registered by STAFF-SA instrument on board the Cluster spacecraft are used for electron density reconstruction. The Cluster spacecraft crossed the plasmasphere at all local times and in a wide range of latitudes over 10 years (2001-2010) covering well the frequency range of both plasmaspheric hiss and lower band chorus emissions in a vicinity of the geomagnetic equator. The proposed technique can be useful in allowing to supplement plasma density statistics obtained from recent probes (such as THEMIS or Van Allen Probes), as well as for reanalysis of statistics derived from continuous measurements of only one or two components of the wave magnetic and electric fields on board spacecraft covering equatorial regions of the magnetosphere.

physics.space-ph↗

arXiv2015

Magnetospheric ULF waves driven by external sources

The multi-spacecraft missions (Cluster and THEMIS) observations allowed to collect large data base for Ultra Low Frequency (ULF) waves properties, their localization, and sources. Mainly here we focused on these recent results. Studying of the source and characteristics of ULF waves can help in the understanding of the interaction and energy transport from solar wind to the magnetosphere. Here we present peculiarities of ULF waves generated by different solar wind phenomenon: surface magnetopause instability, magnetosphere cavity modes and solar wind dynamic pressure sudden impulses (SI) penetration into the magnetosphere. Permanent observations of ULF waves involve existence of the permanent source and, as the previous studies showed, the contributions to Pc4-Pc5 ULF wave power from the external sources are larger than the contribution from internal magnetosphere sources. The Kelvin-Helmholtz instability (KHI) can generate on the magnetosphere flanks classical ULF resonant waves with spatially localized amplitude maximum. As observations show the constraint satisfaction of KHI development is quite rare. SI in solar wind dynamic pressure generate ULF waves with different polarization and frequency close to the frequency of the local field line resonance (FLR). Wide range of temporal and amplitude characteristics of solar wind dynamics can generate magnetosphere cavity modes and magnetosonic perturbations which penetrate through the magnetosphere and can couple with the local FLR modes. The observed dependence of ULF waves properties on their localization are well correspond to these sources and their occurrence.

physics.space-ph↗