Solar Wind Shock Wave Research Articles

DETERMINATION OF MAGNETIC RECONNECTION IN A LOW AND A HIGH ACTIVITY YEAR

When there is a temporary disturbance of earth's magnetosphere, then a geomagnetic storm (or solar storm) has occurred. It is caused by a solar wind shock wave and/or cloud of a magnetic field that interacts with the Earth's magnetic fields. The interaction of Interplanetary Magnetic Fields (IMF) of the sun [1] with the earth's magnetic fields in opposite directions is known as magnetic reconnection. Magnetic reconnection (often referred as is the breaking and reconnecting of oppositely directed magnetic field lines in plasma at a neutral point which leads to converting the magnetic field energy into plasma kinetic and thermal energy. It occurs either in the daytime (day reconnection) where the sunward convection near the polar cusps allows energized particles to be transmitted earthward or night-time (tail reconnection) where particles are injected into the magnetosphere, thus releasing stored energy in the form of auroral substorms. A geostorm can be determined by changes in the Disturbance-storm time (Dst) Sokolov [2]. However not all geomagnetic storms have an initial phase and not all sudden increases in Dst Original Research Article Ojerheghan and Adimula; IAARJ, 2(4): 30-47, 2020; Article no.IAARJ.62999 31 or SYM-H are followed by a geomagnetic storm. This paper attempts to determine when the magnetic reconnection occurs in the solar cycle 24 considering a low activity year 2009 and a high activity year 2012. We analysed 39 and 202 geomagnetic storms in 2009 and 2012 respectively considering the Dst indices and IMF Bz values of each month obtained from the OMNIWeb database. Our results showed that storms were frequent and intense at high levels of solar activity due to the frequent occurrence of CMEs and ICMEs in the year 2012 than in the year 2009 which occurred in 10% and 45% of days in the year 2009 and 2012 respectively. This study also revealed that negative Bz occurrences were 47.54% and 52.18% of Bz occurrences in 2009 and 2012 respectively. Thus, the more intense the geostorms, the more Bz would go south and the more magnetic reconnection and subsequently auroral substorms which can increase radiation doses for occupants of transpolar flights, disruption of shortwave radio communications, distortion of compass readings in polar regions, failure of electrical transmission lines, increased corrosion in long pipelines, anomalies in the operations of communications satellites, and potentially lethal doses of radiation for astronauts in interplanetary spacecraft.

Features in the Behavior of the Solar Wind behind the Bow Shock Front near the Boundary of the Earth’s Magnetosphere

Macroscopic discontinuous structures observed in the solar wind are considered in the framework of magnetic hydrodynamics. The interaction of strong discontinuities is studied based on the solution of the generalized Riemann–Kochin problem. The appearance of discontinuities inside the magnetosheath after the collision of the solar wind shock wave with the bow shock front is taken into account. The propagation of secondary waves appearing in the magnetosheath is considered in the approximation of one-dimensional ideal magnetohydrodynamics. The appearance of a compression wave reflected from the magnetopause is indicated. The wave can nonlinearly break with the formation of a backward shock wave and cause the motion of the bow shock towards the Sun. The interaction between shock waves is considered with the well-known trial calculation method. It is assumed that the velocity of discontinuities in the magnetosheath in the first approximation is constant on the average. All reasonings and calculations correspond to consideration of a flow region with a velocity less than the magnetosonic speed near the Earth–Sun line. It is indicated that the results agree with the data from observations carried out on the WIND and Cluster spacecrafts.

On the reason for the kink in the rigidity spectra of cosmic-ray protons and helium nuclei near 230 GV

A three-component phenomenological model describing the specific features of the spectrum of cosmic-ray protons and helium nuclei in the rigidity range of 30–2×105 GV is proposed. The first component corresponds to the constant background; the second, to the variable “soft” (30–500 GV) heliospheric source; and the third, to the variable “hard” (0.5–200 TV) source located inside a local bubble. The existence and variability of both sources are provided by the corresponding “surfatron accelerators,” whose operation requires the presence of an extended region with an almost uniform (in both magnitude and direction) magnetic field, orthogonally (or obliquely) to which electromagnetic waves propagate. The maximum energy to which cosmic rays can be accelerated is determined by the source size. The soft source with a size of ∼100 AU is located at the periphery of the heliosphere, behind the front of the solar wind shock wave. The hard source with a size of >0.1 pc is located near the boundary of an interstellar cloud at a distance of ∼0.01 pc from the Sun. The presence of a kink in the rigidity spectra of p and He near 230 GV is related to the variability of the physical conditions in the acceleration region and depends on the relation between the amplitudes and power-law exponents in the dependences of the background, soft heliospheric source, and hard near galactic source. The ultrarelativistic acceleration of p and He by an electromagnetic wave propagating in space plasma across the external magnetic field is numerically analyzed. Conditions for particle trapping by the wave and the dynamics of the particle velocity and momentum components are considered. The calculations show that, in contrast to electrons and positrons (e+), the trapped protons relatively rapidly escape from the effective potential well and cease to accelerate. Due to this effect, the p and He spectra are softer than that of e+. The possibility that the spectra of accelerated protons deviate from standard power-law dependences due to the surfatron mechanism is discussed.

Collision of a solar wind shock wave with the Earth’s bow shock. Wave flow pattern

The wave pattern of the flow developed when a solar wind shock wave propagates along the surface of the Earth's bow shock is studied. The investigation is carried out in the three-dimensional non-plane-polarized formulation within the framework of the ideal magneto- hydrodynamic model in which the medium is assumed to be inviscid and non-heat-conducting and to have the infinite conductivity. The global three-dimensional pattern of the interaction which is a function of the latitude and longitude of elements on the surface of the bow shock is constructed as a mosaic of solutions to the problem of breakdown of a discontinuity developed between the states behind the impinging and bow shocks on the moving curve of intersection of their fronts. The investigation is carried out for typical solar wind parameters and interplanetary magnetic field strength in the Earth's orbit and for several Mach numbers of the interplanetary shock wave, which makes it possible to trace the evolution of the flow developed as a function of the intensity of the shock perturbation of the solar wind. The solution obtained is necessary for interpreting measurements carried out by spacecraft located in the neighborhood of the Lagrange point and the Earth's magnetosphere. At present, spacecraft located in the solar wind in the neighborhood of the Lagrange point L1 at distances of approximately 250 Earth's radii RE from the Earth (Wind, SOHO, and ACE) and groups of spacecraft in the neighborhood of the Earth's bow shock, in the magnetosheath, and in the outer magnetosphere (THEMIS, Cluster, and Double Star) are measuring the state of the interplanetary medium and magnetic field and transferring the data to the Earth. The measurements are used to identify sharp jumpwise changes occurring in the solar wind and related to shock waves, rotational and tangential discontinuities, and their manifestations recorded on spacecraft in the neighborhood of the Earth with the aim to forecast the cosmic weather in the form of sudden storm commencements, magnetic substorms, and sudden impulses in the Earth's magnetosphere (1-4). The results of numerical MHD simulations carried out by means of various methods (2-6) are used in analyzing the events. However, the simulations have insufficient spatial resolution, and due to this fact several MHD waves merge with one another and can hardly be identified; for example, slow or Alfven waves are unified with the contact discontinuity (5). For the correct interpretation of measurements it is necessary to use the exact solutions to the problem of interaction between a solar wind discontinuity and the Earth's bow shock Sb (7-11). The quasi-steady-state method of finding them within the framework of magnetohydrodynamics of an ideally conducting medium was first proposed in (7, 8) as the solution to the problem of breakdown of a discontinuity between the states behind the interacting waves on the moving curve of intersection of their fronts. The wave flow pattern and the dependences of the physical parameters of the medium and the magnetic field were first obtained as functions of the angle of inclination of Sb to the solar wind velocity Vsw in the

Three-dimensional magnetohydrodynamic description of the process of collision of a solar wind shock wave and the Earth’s bow shock

The propagation of a solar wind shock wave along the surface of the Earth’s bow shock is investigated within the framework of an ideal magnetohydrodynamic model in the three-dimensional non-plane-polarized formulation. The most characteristic values of the solar wind parameters and the interplanetary magnetic field strength are considered for the plane front of a solar wind shock wave moving at various velocities along the Sun-Earth radius. The global three-dimensional pattern of the interaction is constructed as a function of the angle of inclination of the surface of the bow shock to the solar wind velocity and the azimuthal angle along the curve of intersection of the fronts of the interacting shock waves. The evolution of the flow developed in the neighborhood of the bow shock is investigated and the parameters of the medium and magnetic field are calculated.

Effect of the solar-wind shock wave on the polar ionosphere according to the radio occultation data on satellite-to-satellite paths

The polar lower ionosphere is distinguished by its variability due to various effects of solar activity. They result in the appearance of sporadic E S structures, in excitation of the broad spectrum of plasma inhomogeneities, and in variations of the electron concentration. The goal of the present study is to reveal regularities in the variations of the night-side polar lower ionosphere on the basis of radio wave measurements on links from navigation GPS satellites to CHAMP satellite. These ionosphere variations are stipulated by the effect of the flare solar activity. To this end, it was necessary to determine the altitude profiles of the electron concentration N e ( h ) and to find the characteristics of both sporadic E S structures and plasma inhomogeneities. We used the data of 327 radio occultation events of the night side polar ionosphere in regions of latitudes higher than 65° N for the time period from October 25 to November 9, 2003, when particularly strong solar activity was observed. In the radio occultation events of the ionosphere, we have registered the amplitude E and the increments of the phase path ψ for two coherent signals with the frequencies of f 1 = 1.5 GHz and f 2 = 1.2 GHz [1‐3]. In order to determine the excitation degree for small-scale inhomogeneity of the ionosphere plasma, we analyzed random fluctuations of the radio-wave amplitude δ E . These fluctuations were subjected to the standard procedure of statistical processing in order to obtain the root-mean-square amplitude deviation σ . The fluctuations δ E are caused mostly by plasma inhomogeneities located in the ionosphere F region at altitudes h ≈ 200–300 km. The analysis of these fluctuations has shown that the quantity σ is subjected to variations with the minimum values being σ min ≈ 1 .5% and with the maximum fluctuation level attaining 20%. In Fig. 1, dots indicate values of root-mean-square deviations σ for the fluctuations of the amplitude E , which were registered within the period of October 26 to November 9, 2003 (measurement dates are indicated at the horizontal axis). In the beginning of this period, the fluctuation intensity attained σ ≈ 2%, whereas later, on October 27, an increase in the fluctuations was observed. The maximum of the field-intensity fluctuations took place on October 29, 30, and 31 when σ attained 10‐14%. Starting from November 1, the fluctuation intensity began to decrease, and on November 4, elevated values of σ were recorded again. In order to determine the amplitude fluctuations σ A more objectively, we have excluded the slight effect of continually present small fluctuations with σ min = 1.5%. We have used here the relationship = σ 2 – and have realized smoothing the dependence as a function of time by the sliding mean technique with time interval 6-hour.

Magnetohydrodynamic description of the process of collision of a solar wind shock perturbation with the bow shock

The interaction of the solar wind oblique shock wave with the bow shock front ahead of the earth's magnetosphere is considered in an ideal MHD approximation. It is shown that as the impinging shock wave propagates along the bow front, the pattern of the emerging flow is qualitatively and quantitatively modified, being asymmetrical on the flanks. The effect of the interplanetary magnetic field orientation and the obliqueness of the arriving solar wind shock wave on this process is studied. It is shown that sharp nonlinear restructurings may occur, with neighboring, oppositely poled current layers emerging somewhere on the flanks. Alfven discontinuities and slow waves play a significant part in this process. The emerging current layers may account for the fact that only some solar wind shock waves are geoeffective.

Cosmic ray variations and turbulent flow systems: 0.3–1.0 AU; 1977–1980

Relations among the relative counting rates of cosmic ray protons and the magnetic fields and flows observed by Helios 1 between 0.3 AU and 1 AU in the period January 1977 to August 1980 are discussed. Isolated corotating or transient flows are associated with short‐term depressions in cosmic ray intensity, but the effects are localized in longitude. Systems of corotating streams do not produce a long‐term modulation effect, although temporary, short‐term depressions in cosmic ray intensity are associated with individual streams and interaction regions. Spectra of fluctuations of the magnetic field and magnetic helicity for systems of corotating flows often do not have the form f−5/3 at frequencies ≥10−5 Hz, and accordingly, the hydromagnetic fluctuations in corotating streams near the sun do not appear to represent fully developed turbulence at low frequencies. Systems of transient streams containing shocks that might encircle the sun are associated with long‐lasting decreases in cosmic ray intensity. The magnetic field fluctuations in such flow systems are often turbulent, with f−5/3 spectra extending from below 10−5 Hz to the Nyquist frequency of the data. The turbulence is likely to be confined to sheets with thicknesses of the order of 0.1 AU, possibly associated with shocks. We conclude that long‐term modulation of cosmic rays inside 1 AU is associated with turbulence in transient disturbances that probably encompass a large longitudinal extent around the sun. In mixed flow systems the effects are intermediate between those of corotating and transient systems. The net modulation may be relatively small, with large short‐term variations associated with individual streams.

Interaction of non-perpendicular/parallel solar wind shock waves with the earth's magnetosphere

The interaction of travelling interplanetary shock waves with the bow shock-magnetosphere system is considered. We consider the general case when the interplanetary magnetic field is oblique to the Sun-planetary axis, thus, the interplanetary shock is neither parallel nor perpendicular. We find that an ensemble of shocks are produced after the interaction for a representative range of shock Mach numbers. First, we find that the system S + R − CS − S + appears after the collision of travelling fast shock waves S + (Mach number M = 2 to 7) with the bow shock. Here, S − and R − represent the slow shock wave and slow rarefaction wave, and C represents the contact surface. It is shown that in the presence of an interplanetary field that is inclined by 45° to the radial solar wind velocity vector, the waves R − and S − are weak waves and, to the first degree of approximation, the situation is similar to the previously studied normal perpendicular case. The configuration, R + C m S − S + or R + C m R − S + where C m is the magnetopause, appears as the result of the fast shock wave's collision with the magnetopause. In this case the waves S − and R − are weak. The fast rarefaction wave reflected from the magnetosphere is developed similar to the case for the collision of a perpendicular shock. The shock wave intensity is varied for Mach numbers from 2 to 10. Thus, in the limits of the first approximation, the validity of the one-dimensional consideration of the nonstationary interaction of travelling interplanetary shock waves with the bow shock-magnetosphere system is proved. The appearance of the fast rarefaction wave, R 4, decreasing the pressure on the magnetosphere of the Earth after the abrupt shock-like contraction, is proved. A possible geomagnetic effect during the global perturbation of the SSC or SI+ type is discussed.