Solar Wind Irregularities Research Articles

Amplitude fluctuations for optical waves propagation through non-Kolmogorov coronal solar wind turbulence channels.

Optical communication has a great potential for the future deep space communication, while the amplitude fluctuations caused by the coronal solar wind irregularities has been a challenging topic during superior solar conjunction. In this paper, a closed-form amplitude fluctuations expression for optical waves propagation through non-Kolmogorov solar wind turbulence is derived by establishing a generalized coronal turbulence spectrum model. The profound impact of the coronal parameters on the bit error rate (BER) performance of the free space optical system is also investigated based on the derived amplitude fluctuations model. The derived expression allows easy analysis of the evolution of the amplitude fluctuations and, in particular, an understanding of the imposed effects caused by the parameters during the waves propagation. The combined effect of the optical wavelength, non-Kolmogorov spectral index, turbulence outer scale, relative solar wind density fluctuation factor, and link distance on amplitude fluctuations are evaluated. Numerical calculations show that these parameters produce obvious effects on the amplitude fluctuations and the BER. The large optical wavelength can mitigate the influence of the coronal turbulence. Our results have potential applications for evaluating the link performance of the future deep space communication.

Phase fluctuations model for EM wave propagation through solar scintillation at superior solar conjunction

Traveling solar wind disturbances have a significant influence on radio wave characteristics during the superior solar conjunction communication. This paper considers the impact of solar scintillation on phase fluctuations of electromagnetic (EM) wave propagation during the superior solar conjunction. Based on the Geometric Optics approximation, the close-form approximation model for phase fluctuations is developed. Both effects of anisotropic temporal variations function of plasma irregularities and their power spectrum are presented and analyzed numerically. It is found that phase fluctuations rapidly decrease with increasing Sun–Earth–Probe angle and decrease with increasing frequency at the rate of 1/f2. Moreover, the role of various features of the solar wind irregularities and their influence on the EM wave characteristic parameters is studied and discussed. Finally, we study the phase fluctuations of typical cases in order to better understand the impact of phase fluctuations in future deep space communication scenarios during solar conjunction periods.

Solar wind-induced atmospheric erosion at Mars: first results from ASPERA-3 on Mars Express.

The Analyzer of Space Plasma and Energetic Atoms (ASPERA) on board the Mars Express spacecraft found that solar wind plasma and accelerated ionospheric ions may be observed all the way down to the Mars Express pericenter of 270 kilometers above the dayside planetary surface. This is very deep in the ionosphere, implying direct exposure of the martian topside atmosphere to solar wind plasma forcing. The low-altitude penetration of solar wind plasma and the energization of ionospheric plasma may be due to solar wind irregularities or perturbations, to magnetic anomalies at Mars, or both.

Analysis of the VLBI-System Response to the Emission from a Radio Source, Propagated through the Circumsolar Plasma

In this paper, we analyze solar-corona and solar-wind irregularities by the method of radio sounding using a very-long-baseline interferometer. The coronal plasma disturbs the radiation field propagated from the source to the receiving stations of the interferometer along different paths. Analysis of the output signal of the radio interferometer allows one to get information on physical characteristics of the propagation medium in cases where monochromatic signals from spacecraft or noise emission from natural radio sources are observed. In this paper, we calculate for the first time the theoretical power spectrum of interferometric response to the emission from a radio source propagated through a turbulent medium. The results obtained using the description of field fluctuations by the geometric-optical and smooth-variation methods are compared. Mathematical modeling of experiments on coronal-plasma sounding shows good agreement between the actual observations and the theoretical calculations.

Three-Dimensional Simulation Study of Plasmoid Injection into Magnetized Plasma

Resent observations suggest that, during solar flares, plasmoids are injected into the interplanetary medium (Stewart et al., 1982). It has also been pointed out that solar wind irregularities modeled as plasmoids are penetrated into the magnetosphere (Lemaire, 1977). These plasmoid injections are considered to be an important process because they transfer mass, momentum, and energy into such magnetized plasma regions. Our objective is to investigate the dynamics of a plasmoid, which is injected into a magnetized plasma region and to reveal mechanisms to transfer them. To achieve this, we carried out three-dimensional magnetohydrodynamic (MHD) simulations.

A study for the interaction between solar wind irregularities and the magnetosphere through three-dimensional simulations

In order to understand the interaction between solar wind irregularities and the closed magnetosphere, three-dimensional (3-D) computer simulations for ideal magnetohydrodynamical (MHD) equations are performed. This paper considers only the situation in which the initial interstellar magnetic field is either parallel or antiparallel to the magnetospheric magnetic field. The irregularity is modeled as a ball, which initially moves toward the magnetosphere. The penetration of the irregularity in the 3-D model is found to be less efficient than in a two-dimensional (2-D) model. Through a comparison of the present results from 3-D simulations, not much difference has been found in the efficiency for the irregularity to penetrate into the magnetosphere between two situations in which the interstellar field is parallel or antiparallel to the magnetospheric field.

Detection of wave phenomena in the solar corona using radio occultation methods

Solar wind irregularities modulate the radio waves propagating in the solar corona and supercorona. The magnitude of the fluctuations is determined by the intensity of electron density irregularities and their characteristic period by the irregularities velocity. Detailed analysis shows however that the velocity registered in radio occultation experiments is actually a combination of two velocities, namely the velocity of plasma flows and that of the magnetohydrodynamic waves. This feature may manifest itself in several maxima in the correlation functions of the frequency fluctuations in signals registered at several ground stations. The interaction of plasma flows with the magnetosonic waves propagating from and toward the Sun results correspondingly in higher and lower apparent velocity of the irregularities. It was proved in radio occultation data obtained using spacecraft Venera-15,-16, Viking and Voyager.

A simulation study of impulsive penetration of solar wind irregularities into the magnetosphere at the dayside magnetopause

A two‐dimensional magnetohydrodynamic code is used to study impulsive penetration processes that occur when a plasma irregularity in the magnetosheath, modeled as a field‐aligned filament, impinges on the day side magnetopause. If the magnetic fields in the magnetosheath and magnetosphere are parallel or antiparallel, then a filament in the magnetosheath can always penetrate into the magnetosphere. However, if the fields in the magnetosheath and magnetosphere are not aligned, then a filament can only penetrate into the magnetosphere when its initial kinetic energy density exceeds the magnetic energy density attributed to the transverse component of the magnetic field by a factor of 50. In this case, the magnetospheric field lines reconnect behind the filament, thereby trapping it within the magnetosphere. Otherwise, the increasing magnetic stress in front of the filament will eventually stop the filament from further penetration. For typical parameters found at the dayside magnetopause, the threshold condition obtained from this two‐dimensional model predicts that penetration is possible only when the angle between the fields is within approximately 5° of parallel or antiparallel. During the penetration process, velocity vortices are observed both inside the filament and in the external plasma. Either increased β within the magnetosphere, or the larger plasma density at the magnetopause associated with antiparallel magnetic fields, will act to reduce the penetration velocity.

Analytic solution for the two‐frequency mutual coherence function for spherical wave propagation

The quadratic approximation for the phase structure function is used to obtain the two‐frequency mutual coherence function Γ(Δρ, Δω) for spherical wave propagation through a finite slab with transmitter and receiver located in free space on opposite sides of the slab. General analytic solutions are derived for two cases. In the first case the random slab is represented by a one‐dimensional power spectrum of electron density fluctuations corresponding to propagation through elongated irregularities as would occur for an equatorial satellite link to a ground station. In the second case the random slab consists of isotropic ionization irregularities. Both cases taken together represent the extremes of the range of results to be expected for propagation through ionospheric fluctuations, solar wind irregularities, or ionization irregularities caused by barium cloud instabilities. For both cases the complex general analytic results are simplified by use of the thin phase screen approximation to obtain useful analytic expressions for Γ as well as the resulting impulse response function. It is shown that the impulse response to a transmitted power delta function reduces to an exponential form in the limit of strong diffraction and to a Gaussian form in the geometrical optics limit. The Gaussian form corresponds to pulse wander while the exponential form corresponds to diffractive spreading produced by multipath effects. The relationship between the generalized power spectrum and the impulse response function is given, and results are presented for the mean time delay and time delay jitter. The accuracy of the thin phase screen calculation of these quantities is investigated in detail.

Control of impulsive penetration of solar wind irregularities into the magnetosphere by the interplanetary magnetic field direction

Impulsive penetration of a solar wind filament into the magnetosphere is possible when the plasma element has an excess momentum density with respect to the background medium. This first condition is satisfied when the density is larger inside than outside the plasma inhomogeneity. In this paper we discuss the second condition which must be satisfied for such a plasma element to be captured by the magnetosphere: the magnetization vector ( M) carried by this plasma must have a positive component along the direction of B 0, the magnetic field where the element penetrates through the magnetopause. On the contrary, when M · B 0 < 0 , the filament is stopped at the surface of the magnetopause. Thus the outcome of the interaction of the filament with the magnetosphere depends upon the orientation of the Interplanetary Magnetic Field. For instance, penetration and capture in the frontside magnetosphere implies that B sw, the Interplanetary Magnetic Field, has a southward, or a small northward, component. Penetration and capture in the northern lobe of the magnetotail is favoured for an IMF pointing away from the Sun; in the southern lobe B sw must be directed towards the Sun for capture. Finally, for capture in the vicinity of the polar cusps the magnetospheric field ( B 0) assumes a wider range of orientations. Therefore, near the neutral points, it is easier to find a place where the condition M · B 0 > 0 is satisfied than elsewhere. As a consequence, the penetration and capture of solar wind irregularities in the cleft regions is possible for almost any orientation of the interplanetary magnetic field direction. All observations made to date support these theoretical conclusions.