26 research outputs found
Nonstationary Pearl Pulsations as a Signature of Magnetospheric Disturbances
. We analyse long-lasting (several hours) Pc1 pearl pulsations with decreasing, increasing or constant central frequency. We show that nonstationary pearl events (those with either decreasing or increasing central frequency) are observed simultaneously with increasing auroral magnetic activity at the nightside magnetosphere while the stationary events (constant central frequency) correspond to quiet magnetic conditions. Events with decreasing central frequency are observed mostly in the late morning and daytime whereas events with increasing central frequency appear either early in the morning or in the afternoon. We explain the diurnal distribution of the nonstationary pearl pulsations in terms of proton drifts depending on magnetic activity, and evaluate the magnetospheric electric field based on the variation of the central frequency of pearl pulsations. Key words. Magnetospheric physics, geomagnetic pulsations.
Dust grain dynamics due to nonuniform and nonstationary high-frequency radiations in cold magnetoplasmas
A general nonlinear theory for low-frequency
electromagnetic field generation due to high-frequency nonuniform and
nonstationary electromagnetic radiations in cold, uniform, multicomponent,
dusty magnetoplasmas is developed. This theory permits us to consider the
nonlinear action of all waves that can exist in such plasmas. The equations
are derived for the dust grain velocities in the low-frequency nonlinear
electric fields arising due to the presence of electromagnetic cyclotron
waves travelling along the background magnetic field. The dust grains are
considered to be magnetized as well as unmagnetized. Different regimes for
the dust particle dynamics, depending on the spatio-temporal change of the
wave amplitudes and plasma parameters, are discussed. It is shown that
induced nonlinear electric fields can have both an electrostatic and
electromagnetic nature. Conditions for maximum dust acceleration are found.
The results obtained may be useful for understanding the possible mechanisms
of dust grain dynamics in astrophysical, cosmic and laboratory plasmas under
the action of nonuniform and nonstationary electromagnetic waves
An effect of the ionospheric Alfvén resonator on multiband Pc1 pulsations
On 2 December 1999, the magnetometer stations in northern Finland registered structured Pc1 activity simultaneously in three distinct frequency bands. Using simultaneous EISCAT radar measurements of the high-latitude ionosphere, we have studied the ionospheric resonator properties during this multiband Pc1 event. The frequencies of the three structured Pc1 bands were found to closely correspond to the second, third and fourth harmonic of the calculated fundamental frequency of the ionospheric Alfvén resonator (IAR). In addition, those frequencies of the three pearl bands that were closest to the exact IAR harmonics were found to have the strongest intensities. The results demonstrate that the resonator can have an important role on ground-based Pc1 activity over a notably large frequency range, favoring transmission of waves with frequencies close to the resonator's eigenfrequencies. Since the frequencies of all three bands correspond to the maximum rather than the minimum of the transmission coefficient, the traditional bouncing wave packet model needs to be revised.<br><br> <b>Key words.</b> Ionosphere (auroral ionosphere; ionosphere magnetosphere interactions; wave propagation
Coherent multiple Pc1 pulsation bands: possible evidence for the ionospheric Alfvén resonator
A fair fraction of Pc1 pulsation events
observed on the ground includes more than one simultaneous pulsation band. In
most such multiband events the bands display different characteristics and,
therefore, come from different source regions via horizontal ducting in the
ionosphere. However, in this report we identify a new "coherent"
subclass of multiband Pc1 events where the pearls of the simultaneous bands have
the same group velocities (repetition rates) as well as dispersion and other
properties, thus implying that the bands are produced by the same source.
Studying one example of such a coherent multiband event in more detail, we argue
that these events defy an explanation in terms of band splitting by
magnetospheric heavy ions because the observed frequency gap between the bands
is smaller than would result in such a case. We interpret these events to be due
to the frequency dependence of the ionospheric reflection coefficient of Alfvén
waves. An oscillatory frequency dependence of the coefficient is a natural
consequence of the idea that the ionosphere acts as a resonator for Alfvén
waves. We also discuss other predictions of this interpretation
Coherent multiple Pc1 pulsation bands: possible evidence for the ionospheric Alfvén resonator
A fair fraction of Pc1 pulsation events observed on the ground includes more than one simultaneous pulsation band. In most such multiband events the bands display different characteristics and, therefore, come from different source regions via horizontal ducting in the ionosphere. However, in this report we identify a new &quot;coherent&quot; subclass of multiband Pc1 events where the pearls of the simultaneous bands have the same group velocities (repetition rates) as well as dispersion and other properties, thus implying that the bands are produced by the same source. Studying one example of such a coherent multiband event in more detail, we argue that these events defy an explanation in terms of band splitting by magnetospheric heavy ions because the observed frequency gap between the bands is smaller than would result in such a case. We interpret these events to be due to the frequency dependence of the ionospheric reflection coefficient of Alfvén waves. An oscillatory frequency dependence of the coefficient is a natural consequence of the idea that the ionosphere acts as a resonator for Alfvén waves. We also discuss other predictions of this interpretation