Time filter

Source Type

North Billerica, MA, United States

Sobisevich L.E.,Russian Academy of Sciences | Kanonidi K.K.,Radio Waves | Sobisevich A.L.,Russian Academy of Sciences
Doklady Earth Sciences | Year: 2010

Analysis of experimental observations of the Earth's magnetic field variations recorded by the scientific instruments at the Northern Caucasus Geophysical Observatory of the Institute of Physics of the Earth, Russian Academy of Sciences, in the period 2007-2009 was performed. It was found that the characteristic ultra-low-frequency (ULF) waveforms of the geomagnetic disturbances were distinguished in the structure of the observed variations that reflect the process of preparation and development of a tsunamigenic earthquake. © 2010 Pleiades Publishing, Ltd. Source

Golubkov G.V.,RAS Semenov Institute of Chemical Physics | Manzhelii M.I.,RAS Semenov Institute of Chemical Physics | Karpov I.V.,Radio Waves
Russian Journal of Physical Chemistry B | Year: 2013

In periods of high solar activity and the formation of geomagnetic storms, additional background incoherent ultrahigh frequency (UHF) radiation with decimeter to millimeter wavelengths in the high E and D layers of the Earth's ionosphere is generated. This emission is produced by transitions between Rydberg states of atoms and molecules of atmospheric gases, which are excited by electrons and are surrounded by a neutral species of the medium. At present, there is no reliable information on the integrated intensity of UHF radiation in this wavelength range. This problem can be solved on knowledge of the dynamics of collisional and radiative quenching of Rydberg states and of the kinetics of their population in the lower ionosphere. An analysis of the available experimental data shows that the radiation is generated in an atmospheric layer located at altitudes between 50 and 110 km. The current theory is discussed and the ways of its further improvement connected with the development of more rigorous theoretical methods for describing the effect of neutral particles of medium on the collisional and radiative quenching dynamics, including the elementary processes with participation of the nitrogen and oxygen molecules, are suggested. For quantitatively estimates the influence of excited particles on the incoherent UHF radiation of the atmosphere, it is necessary carrying out of the preliminary calculations the potential energy surfaces and dynamics of nonadiabatic transitions between Rydberg states, construction the electronic wave functions, and determination the dipole moments of the allowed transitions and the emission line shapes. Obtained results can be included into the general kinetic scheme which defines of the UHF radiation intensity versus the density and temperature of the atmosphere. Accompanying its infrared (IR) radiation can be used to define of Rydberg states. © 2013 Pleiades Publishing, Ltd. Source

Cannon P.D.,Lancaster University | Honary F.,Lancaster University | Borisov N.,Radio Waves
Journal of Geophysical Research A: Space Physics | Year: 2016

Experiments in the illumination of the F region of the ionosphere via radio frequency waves polarized in the ordinary mode (O-mode) have revealed that the magnitude of artificial heating-induced effects depends strongly on the inclination angle of the pump beam, with a greater modification to the plasma observed when the heating beam is directed close to or along the magnetic zenith direction. Numerical simulations performed using a recently developed finite-difference time-domain (FDTD) code are used to investigate the contribution of the O-mode to Z-mode conversion process to this effect. The aspect angle dependence and angular size of the radio window for which conversion of an O-mode pump wave to the Z-mode occurs is simulated for a variety of plasma density profiles including 2-D linear gradients representative of large-scale plasma depletions, density-depleted plasma ducts, and periodic field-aligned irregularities. The angular shape of the conversion window is found to be strongly influenced by the background plasma profile. If the Z-mode wave is reflected, it can propagate back toward the O-mode reflection region leading to resonant enhancement of the electric field in this region. Simulation results presented in this paper demonstrate that this process can make a significant contribution to the magnitude of electron density depletion and temperature enhancement around the resonance height and contributes to a strong dependence of the magnitude of plasma perturbation with the direction of the pump wave. © 2016. American Geophysical Union. All Rights Reserved. Source

Borisov N.,Radio Waves | Franz M.,Max Planck Institute for Solar System Research
Nonlinear Processes in Geophysics | Year: 2011

We show that the slow magnetosonic (SM) perturbations generated in the vicinity of the magnetopause, due to the excitation of the Kelvin-Helmholtz (K.-H.) instability in the case of a supersonic flow velocity, are transformed into fast magnetosonic (FM) waves which can propagate into the magnetosheath. Under the conditions discussed in this paper, the FM wave has negative energy in the stationary (magnetospheric) coordinate frame. Due to this the outgoing FM wave increases the growth rate of the K.-H. instability excited at the magnetopause. Within the linear theory, we investigate the influence of the excited FM wave on the growth rate of the K.-H. instability. Simultaneously we predict the transformation of the SM mode into kinetic Alfvén (KA) mode. Thus, in general, two types of waves with different polarizations (the KA wave and the FM wave) should appear in the magnetosheath due to the excitation of the K.-H. instability. At the same time, the SM perturbations are only present in the localized region where the K.-H. instability is excited. To correctly describe the excitation of waves, we use two-fluid (for electrons and ions) magnetohydrodynamics. This approach is more general than the ideal magnetohydrodynamics and allows us to take into account the effects associated with the finite Larmor radius of ions. Also it can be used to investigate the K.-H. instability in a multi-component plasma, or in the case where the frequency of perturbations is of the order of the gyrofrequency of oxygen ions which may occur, for example, at the magnetosheath of Mars. Source

Puchkov V.A.,Radio Waves
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2013

Powerful electromagnetic waves illuminating the ionospheric plasma generate small-scale density irregularities elongated in the direction of the geomagnetic field. Stochastic motion of these irregularities results in fluctuations of HF radio signals backscattered by the illuminated region. Observations of the full wave form of the radio signals make it possible to reconstruct the distribution function of the irregularities over their velocities. An experiment with such a reconstruction is proposed. © 2013 Elsevier B.V. All rights reserved. Source

Discover hidden collaborations