Solar Wind Plasma Fluctuations Research Articles

Relationship between geomagnetic storm development and the solar wind parameter ß

We have analyzed the dynamics of solar wind and interplanetary magnetic field (IMF) parameters during the development of 933 isolated geomagnetic storms, observed over the period from 1964 to 2010. The analysis was carried out using the epoch superposition method at intervals of 48 hrs before and 168 hrs after the moment of Dst minimum. The geomagnetic storms were selected by the type of storm commencement (sudden or gradual) and by intensity (weak, moderate, and strong). The dynamics of the solar wind and IMF parameters was compared with that of the Dst index, which is an indicator of the development of geomagnetic storms. The largest number of storms in the solar activity cycle is shown to occur in the years of minimum average values (close in magnitude to 1) of the solar wind parameter β (β is the ratio of plasma pressure to magnetic pressure). We have revealed that the dynamics of the Dst index is similar to that of the β parameter. The duration of the storm recovery phase follows the characteristic recovery time of the β parameter. We have found out that during the storm main phase the β parameter is close to 1, which reflects the maximum turbulence of solar wind plasma fluctuations. In the recovery phase, β returns to background values β~2‒3.5. We assume that the solar wind plasma turbulence, characterized by the β parameter, can play a significant role in the development of geomagnetic storms.

Связь развития геомагнитных бурь с параметром ß солнечного ветра

We have analyzed the dynamics of solar wind and interplanetary magnetic field (IMF) parameters during the development of 933 isolated geomagnetic storms, observed over the period from 1964 to 2010. The analysis was carried out using the epoch superposition method at intervals of 48 hrs before and 168 hrs after the moment of Dst minimum. The geomagnetic storms were selected by the type of storm commencement (sudden or gradual) and by intensity (weak, moderate, and strong). The dynamics of the solar wind and IMF parameters was compared with that of the Dst index, which is an indicator of the development of geomagnetic storms. The largest number of storms in the solar activity cycle is shown to occur in the years of minimum average values (close in magnitude to 1) of the solar wind parameter β (β is the ratio of plasma pressure to magnetic pressure). We have revealed that the dynamics of the Dst index is similar to that of the β parameter. The duration of the storm recovery phase follows the characteristic recovery time of the β parameter. We have found out that during the storm main phase the β parameter is close to 1, which reflects the maximum turbulence of solar wind plasma fluctuations. In the recovery phase, β returns to background values β~2‒3.5. We assume that the solar wind plasma turbulence, characterized by the β parameter, can play a significant role in the development of geomagnetic storms.

Dynamic properties of small-scale solar wind plasma fluctuations.

The paper presents the latest results of the studies of small-scale fluctuations in a turbulent flow of solar wind (SW) using measurements with extremely high temporal resolution (up to 0.03 s) of the bright monitor of SW (BMSW) plasma spectrometer operating on astrophysical SPECTR-R spacecraft at distances up to 350,000 km from the Earth. The spectra of SW ion flux fluctuations in the range of scales between 0.03 and 100 s are systematically analysed. The difference of slopes in low- and high-frequency parts of spectra and the frequency of the break point between these two characteristic slopes was analysed for different conditions in the SW. The statistical properties of the SW ion flux fluctuations were thoroughly analysed on scales less than 10 s. A high level of intermittency is demonstrated. The extended self-similarity of SW ion flux turbulent flow is constantly observed. The approximation of non-Gaussian probability distribution function of ion flux fluctuations by the Tsallis statistics shows the non-extensive character of SW fluctuations. Statistical characteristics of ion flux fluctuations are compared with the predictions of a log-Poisson model. The log-Poisson parametrization of the structure function scaling has shown that well-defined filament-like plasma structures are, as a rule, observed in the turbulent SW flows.

Polarization of compressible turbulent fluctuations in the solar wind plasma

Compressible fluctuations in solar wind plasma are analyzed on the basis of the 1995–2010 WIND and Advanced Composition Explorer (ACE) spacecraft data. In the low-speed solar wind (V0 < 430 km/s), correlations between fluctuations in the magnetic field direction and plasma density, as well as between velocity fluctuations and plasma density, are found. The covariance functions of these parameters calculated as functions of the local magnetic field direction are axially symmetric relative to the axis, which is oriented nearly along the regular magnetic field of the heliosphere (the Parker spiral). Fluctuations in the magnetic field and velocity are polarized in the plane that is orthogonal to the axis of symmetry. Plasma oscillations of these properties can be caused by fast magnetosonic waves propagating from the Sun along the Parker spiral.

Whistler wave cascades in solar wind plasma

Non-linear, three-dimensional, time-dependent fluid simulations of whistler wave turbulence are performed to investigate role of whistler waves in solar wind plasma turbulence in which characteristic turbulent fluctuations are characterized typically by the frequency and length-scales that are, respectively, bigger than ion gyrofrequency and smaller than ion gyroradius. The electron inertial length is an intrinsic length-scale in whistler wave turbulence that distinguishably divides the high-frequency solar wind turbulent spectra into scales smaller and bigger than the electron inertial length. Our simulations find that the dispersive whistler modes evolve entirely differently in the two regimes. While the dispersive whistler wave effects are stronger in the large-scale regime, they do not influence the spectral cascades which are describable by a Kolmogorov-like k−7/3 spectrum. By contrast, the small-scale turbulent fluctuations exhibit a Navier–Stokes-like evolution where characteristic turbulent eddies exhibit a typical k−5/3 hydrodynamic turbulent spectrum. By virtue of equipartition between the wave velocity and magnetic fields, we quantify the role of whistler waves in the solar wind plasma fluctuations.

Study of energetic particle anisotropy in weak and strong foreshocks

In this paper, we continue our recent statistical studies of solar wind plasma fluctuations in the Earth’s foreshock and their relationship to measurements of energetic ion (∼25, 50, 110 keV energy channels) fluxes under different solar wind and interplanetary magnetic field conditions, based on the INTERBALL–1 data obtained during 1995–2000. We discuss spatial and temporal characteristics of the energetic particle interaction with the foreshock plasma. We compare the intervals of upstream observations inside the foreshock of different strengths and relate plasma fluctuations to observed energetic particle pitch-angle distributions, anisotropy, and spectra at different distances to the bow shock. We discuss possible physical explanations of observed phenomena.

INTERBALL-1 observations of plasma and energetic particle fluxes upstream of the Earth's bow shock

In this paper, we follow our recent statistical examinations of solar wind plasma fluctuations in the Earth's foreshock and their relationship to measurements of energetic ion ( ∼ 25 keV) fluxes under different solar wind and interplanetary magnetic field conditions, based on the INTERBALL-1 data obtained during 1995–2000. We study in detail the influence of more energetic particles ( ∼ 50 and 110 keV energy channels) and their energetic and angular distributions. We compare the intervals of upstream observations outside the foreshock and inside the foreshock of different strengths and relate plasma fluctuations to observed energetic particle spectra and anisotropy at different distances to the bow shock. We discuss possible physical explanations of observed phenomena.

Lognormal distributions and spectra of solar wind plasma fluctuations: Wind 1995–1998

The fluctuations in the hour averages of the speedV, densityN, and proton temperatureTat 1 AU are large, intermittent, and spiky on a scale of a year. The lognormal distribution is a good model for the distribution of measurements of these variables made at 1 AU during 1996, 1997, and 1998, near solar minimum, and during the rising phase of the solar cycle. The lognormal distribution is less satisfactory as a model for the data obtained during 1995, when corotating streams were present. For that year the distributions ofV,N, andTwere double‐peaked; nevertheless, the number of observations associated with the fast wind distribution was only 12–17%. Shocks, corotating streams, interaction regions, signatures of the sources of the streams, and the heliospheric plasma sheet are present in the data, but each of these features has its own variability. Taken together, these components and their interactions result in episodic signals and distribution functions with large tails. There remains a need for dynamical models of the solar wind that incorporate and describe both deterministic and statistical properties of the solar wind.