Fluctuations in the interplanetary plasma

Spacecraft based observations of fluctuations in the interplanetary magnetic field and solar wind speed yield dominant spatial scales of the order 10⁶ km, and negligible structure below about 500 km. Earth based observations of the angular broadening and scintillation of cosmic radio sources have been interpreted in terms of electron density scales of order a few hundred km. It is suggested that for scales below a few hundred km, there exists an enhanced level of small scale density fluctuations not accompanied by comparable magnetic variations. This proposal is shown to be consistent with radio observations, the contribution of the much larger electron density irregularities being quite negligible. A physical mechanism that might account for the small scale fluctuations is described.     

Power spectrum of small-scale irregularities in the solar wind

Day to day observations of interplanetary scintillation on ten strongly scintillating radio sources over a period of twelve months show that the power spectrum of the small scale irregularities flattens considerably at temporal frequencies ν < 0·5 Hz. This flattening defines a scale which increases uniformly between 0·1 and 1·0 a.u. from the Sun. The implication of this result will be discussed.     

Scintillations of cosmic radio sources in the decametre waveband

The effect of fluctuations of the interplanetary plasma and the ionosphere upon the scintillation spectra of radio sources at decametre waves is considered with due regard for the finite antenna aperture, fluctuation anisotropy, and the direction of their drift in space. It has been shown that scintillation due to interplanetary plasma (IPP), can be reliably separated from the ionospheric scintillation background at decametre wavelengths.For elongations between 90° to 150°, the IPP scintillation power spectrum observed in the 12.6–25 MHz waveband is of a power law form with the index 3.1±0.6, which is in close agreement with the values known for smaller elongations. The solar wind velocity projection orthogonal to the line of sight is estimated for elongations about 110° and has been found to be 300±80 km s^–1. As in the case of smaller elongations, the velocity dispersion is significant.At night, wideband spectra of ionospheric scintillations are observed in the decametre band, with the breaking point at approximately 0.01 Hz in the 12 m band, and narrow-band spectra whose cut-off frequency is below 0.01 Hz. The power spectrum of ionospheric scintillations is of a power-law form with the index 3.4±0.5. In some cases steeper spectra are observed.     

The velocity of pulsars and interstellar irregularities in the scintillation pattern

The scintillation theory is developed for application to the interstellar medium taking into account both the movement of the pulsars and the movement of the interstellar irregularities.It is shown that the velocity of the drifting pattern differs essentially from that for the pulsars. This difference is due to the medium extent effect and to the motion of the irregularities. The pulsar velocityv ₀ and the parameters of the motion of the irregularities ( , ) can be derived from the obtained formulae, using the known parameters of the cross-correlation function of scintillations (V _ef, ₁,S).In contrast with the interplanetary scintillation, the asymmetry of the form of the cross-correlation function of the interstellar scintillations is caused not only by the motion of the interstellar irregularities, but also by the movement of the source itself.     

Equatorial scintillation

Equatorial scintillations have been observed at Legon, Ghana for nearly 20 yr. The occurrence characteristics of the scintillations are reviewed, and the physical characteristics of the electron density irregularities summarized. A much more comprehensive summary of the seasonal variation of scintillation is given, and it is found to be remarkably similar to the variations in thermospheric temperature. Evidence for the suppression of scintillation during magnetic disturbances is given. Curves for the daily variation of the Faraday rotation angle φ are presented and their unusual post-sunset behaviour noted. It is suggested that this can be explained in terms of a theory presented by Rishbeth, in which the F region ionization moves with nearly the full velocity of the neutral atmospheric wind at night, after the E region conductivity has fallen to a relatively low value. This can account for the observed drift velocity of the irregularities. The rapid increase in the post-sunset horizontal velocity of the ionization together with the observed vertical rise, can account for the variations of φ. It is further suggested that the large gradients in the density and drift velocity of the ionization resulting from the mechanism suggested by Rishbeth give rise to the production of the observed F region irregularities in electron density which cause equatorial scintillation.     

Monitoring of interplanetary and ionospheric scintillation of an ensemble of radio sources

The results of a series of 24-hour observations of radio-source interplanetary and ionospheric scintillation performed on April 4–10, 2006, at the Pushchino Radio Astronomy Observatory are presented. The observations were carried out with the Large Phased Array radio telescope of the Lebedev Institute of Physics, Russian Academy of Sciences, at a frequency of 110 MHz. The scintillating fluxes of all radio sources that fall within a field of sky between declinations +28° and +31° were automatically recorded applying eight beams of the reception pattern operating simultaneously. All of the sources with flux densities of 0.2 Jy or higher were detected. The structure functions of the flux fluctuations were measured for time shifts 1 and 10 s, which characterize the interplanetary (1 s) and ionospheric (10 s) scintillation, respectively. The mean scintillation index m _IPP (on a characteristic time scale of 1 s) of an ensemble of radio sources located within a sky band 4° wide in declination and 1 h wide in right ascension was measured as the parameter that characterizes the interplanetary plasma. Diurnal variations of the interplanetary scintillation index were determined. The maximum m _IPP value at daytime equals 0.3, and the minimum value at nighttime equals 0.10. Weak interday variations of the mean daytime and nighttime scintillation indices were detected. The ionospheric scintillation indices m _Ion are small compared to m _IPP at daytime, but m _Ion ? m _IPP at nighttime. On the whole, both the interplanetary plasma and ionosphere were quiet during the observations.     

On the model of the solar wind-interstellar medium interaction with two shock waves

The model of the solar wind interaction with interstellar medium suggested by Baranovet al. (1970) is developed. In this model (TSM) the presence of two shock waves is assumed, through which the solar wind and interstellar gas pass, the latter moving relative to the Sun at supersonic speed (20 km s^–1).The distance between shocks was considered earlier (Baranovet al., 1970; Baranov and Krasnobaev, 1971) to be small compared with their distance from the Sun, due to the hypersonic character of the flow. The structure of the subsonic flow portion may not be taken into account.In the present paper the distribution of the gas parameters in the region between shocks is calculated which, in particular, allows us to estimate the possibility of its experimental detection, observing radio-scintillation on interstellar irregularities (Baranovet al., 1975).The possible influence on the model of galactic hydrogen neutral atoms penetrating into interplanetary medium is estimated.     

Stratospheric Measurements of Magnetospheric Electron Precipitation and Interplanetary Medium Conditions in Solar Activity Cycles 22–24

High-energy electrons precipitate into the atmosphere under the influence of disturbances of the interplanetary medium on the magnetosphere. Electrons captured from interplanetary space interact in the magnetosphere with waves, resulting in both acceleration and electron energy loss. Some high-energy electrons precipitate into the atmosphere where they generate bremsstrahlung X-rays, which can penetrate deep into the atmosphere to heights of the order of 20 km. The current 11-year cycle is characterized by weak solar activity and a small number of precipitations. The paper discusses the correlation between the parameters of the interplanetary medium and the magnetosphere with the number of precipitations recorded from 1987 to the present during regular measurements of ionizing radiation in the atmosphere in the Murmansk region.     

Note on solar plasma irregularities and plasma instabilities

Observations of interplanetary scintillation of radio sources are used to estimate the size of plasma irregularities down to a distance of about 6 R from the Sun. This is compared with the values of the ion gyro-radius estimated for a range of distance from 1 AU to about 6 R from the Sun. The results of the calculations are discussed in the context of the hypothesis of plasma instability which is invoked to interpret the observations of the scattering of radio waves in the solar corona and of interplanetary scintillations.     

Synoptic Maps of Solar Wind: Comparison of IPS Data and the NOAA/SEC Version of the Wang and Sheeley Model

Since the 1970s, the Solar-Terrestrial Environment Laboratory, Japan, has been publishing synoptic maps of solar wind velocity prepared using the technique of interplanetary scintillation. These maps, known as V-maps, are useful to study the global distribution of solar wind in the heliosphere. As the Earth-orbiting satellites are unable to probe regions outside the ecliptic, it is important to exploit the scope of interplanetary scintillation to study the solar wind properties at these regions and their relation with coronal features. It has been shown by Wang and Sheeley that there exists an inverse correlation between rate of magnetic flux expansion and the solar wind velocity. The NOAA/Space Environment Center daily updated version of the Wang and Sheeley model has been used to produce synoptic maps of solar wind velocity and magnetic field polarity for individual Carrington rotations. The predictions of the model at 1 AU have been found to be in good agreement with the observed values of the same. The present work is a comparison of the synoptic maps on the source surface using the interplanetary scintillation measurements from Japan and the NOAA/SEC version of the Wang and Sheeley model. The two results agree near the equatorial regions and the slow solar wind locations are consistent most of the times. However, at higher latitudes within ±60°, the wind velocities differ considerably. In the Wang and Sheeley model the highest speed obtained is 600 km s^–1 whereas in the IPS results velocities as high as 800 km s^–1 have been detected. The paper discusses the possible causes for this discrepancy and suggestion to improve the agreement between the two results.     

Study of equatorial plasma bubbles using all sky imager and scintillation technique from Kolhapur station: a case study

The nightglow observations of OI 630.0 nm emission carried out from low latitude station Kolhapur using All Sky Imager (ASI) with \(140^{\circ}\) field of view (FOV) for the month of April 2011 are used. The images were processed to study the field aligned irregularities often called as equatorial plasma bubbles (EPBs). The present study focuses on the occurrence of scintillation during the traversal of EPBs over ionospheric pierce point (IPP). Here we dealt with the depletion level (depth) of the EPB structures and its effect on VHF signals. We compared VHF scintillation data with airglow intensities at Ionospheric pierce point (IPP) from the same location and found that the largely depleted EPBs make stronger scintillation. From previous literature, it is believed that the small scale structures are present near the steeper walls of EPBs which often degrades the communication, the analysis presented in this paper confirms this belief.     

Spatial distribution of large-scale solar magnetic fields and their relation to the interplanetary magnetic field

The spatial organization of the observed photospheric magnetic field, as well as its relation to the polarity of the interplanetary field, have been studied using high resolution magnetograms from Kitt Peak National Observatory. Systematic patterns in the large scale field have been found to be due to contributions from both concentrated flux and more diffuse flux. It is not necessary to assume, as has often been done in previous studies, that there is a weak background solar magnetic field causing the large-scale patterns in the photosphere, although the existence of such a field cannot be excluded. The largest scale structures in the photosphere correspond to the expected pattern at the base of a warped heliomagnetic equator.The polarity of the photospheric field, determined on various spatial scales, correlates with the polarity of the interplanetary field, with the most significant correlation due to mid-latitude fields. However, because the interplanetary field is likely to be rooted in concentrated photospheric regions, rather than across an entire polarity region, both the strength and polarity of the field are important in determining the interplanetary field. Thus studies of the interplanetary field which are based on either instrumental or numerical averaging of fields in the solar photosphere are subject to serious inherent limitations.Analyses based on several spatial scales in the photosphere suggest that new flux in the interplanetary medium is often due to relatively small photospheric features which appear in the photosphere up to one month before they are manifest at the Earth. The evolution of the over-all photospheric pattern may be due to individual sub-patterns which have slightly different rotation properties and which alternate in their relative dominance of the interplanetary medium.     

Multiwavelength Study on Solar and Interplanetary Origins of the Strongest Geomagnetic Storm of Solar Cycle 23

We study the solar sources of an intense geomagnetic storm of solar cycle 23 that occurred on 20 November 2003, based on ground- and space-based multiwavelength observations. The coronal mass ejections (CMEs) responsible for the above geomagnetic storm originated from the super-active region NOAA 10501. We investigate the H?? observations of the flare events made with a 15 cm solar tower telescope at ARIES, Nainital, India. The propagation characteristics of the CMEs have been derived from the three-dimensional images of the solar wind (i.e., density and speed) obtained from the interplanetary scintillation data, supplemented with other ground- and space-based measurements. The TRACE, SXI and H?? observations revealed two successive ejections (of speeds ???350 and ???100 km?s^?1), originating from the same filament channel, which were associated with two high speed CMEs (???1223 and ???1660 km?s^?1, respectively). These two ejections generated propagating fast shock waves (i.e., fast-drifting type II radio bursts) in the corona. The interaction of these CMEs along the Sun?CEarth line has led to the severity of the storm. According to our investigation, the interplanetary medium consisted of two merging magnetic clouds (MCs) that preserved their identity during their propagation. These magnetic clouds made the interplanetary magnetic field (IMF) southward for a long time, which reconnected with the geomagnetic field, resulting the super-storm (Dst _peak=?472 nT) on the Earth.     

SCR Distribution Function in the Radial IMF Approximation

The transport of cosmic rays in the interplanetary medium is considered in terms of the kinetic equation describing the energetic particle scattering by magnetic irregularities and their focusing by the regular interplanetary magnetic field. The analytical expression for solar cosmic ray distribution function in the approximation of radial regular magnetic field is obtained and the evolution of energetic particle angular distribution is analyzed. The obtained results can be used for the analysis of ground-level enhancements of cosmic ray intensity.     

Differences between solar wind plasmoids and ideal magnetohydrodynamic filaments

Plasma irregularities present in the solar wind are plasmoids, i.e. plasma-magnetic field entities. These actual plasmoids differ from ideal magnetohydrodynamic (MHD) filaments. Indeed, (1) their “skin” is not infinitely thin but has a physical thickness which is determined by the gyromotion of the thermal ions and electrons, (2) they are of finite extent and their magnetic flux is interconnected with the interplanetary magnetic flux, (3) when they penetrate into the magnetosphere their magnetic field lines become rooted in the ionosphere (i.e. in a medium with finite transverse conductivity), (4) the external Lorentz force acting on their boundary surface depends on the orientation of their magnetic moment with respect to the external magnetic field, (5) when their mechanical equilibrium is disturbed, hydromagnetic oscillations can be generated. It is also suggested that the front side of all solar wind plasmoids which have penetrated into the magnetosphere is the inner edge of the magnetospheric boundary layer while the magnetopause is considered to be the surface where the magnetospheric plasma ceases to have a trapped pitch angle distribution.     

The Coefficient of Asymmetry of Radio-Source Interplanetary Scintillation

It is proposed to use the coefficient of asymmetry of the distribution function of fluctuations of a scintillating source flux density as a parameter that characterizes interplanetary turbulent plasma. It is demonstrated that this parameter can be measured with a differential method and that its informative capacity is equivalent to that of the source scintillation index. A series of test observations of scintillations was performed with the Large Phased Array antenna of the Lebedev Institute of Physics, Russian Academy of Sciences, simultaneously with measurements of the source scintillation indices and coefficients of asymmetry. Comparative analysis of the measured quantities showed that the coefficient of asymmetry within a numerical coefficient equals the source scintillation index, normalized to the flux density of the scintillating component. The coefficient of asymmetry makes it possible to restore scintillation indices when the radio sources are weak and it is difficult to measure their mean flux densities, and, hence, it enlarges the number of observable scintillating sources and makes the exploration of interplanetary plasma by means of the mapping of scintillation indices more efficient.__________Translated from Astronomicheskii Vestnik, Vol. 39, No. 4, 2005, pp. 375–380.Original Russian Text Copyright © 2005 by Shishov, Tyul’bashev, Artyukh, Subaev, Chashei, Chernikov.     

Decametric sounding of near Earth plasma: correlation and fractal analysis of scintillation data

Solar wind observations by means of bi-static decametric radar SURA-WIND allow studying a fine structure of solar wind plasma irregularities with resolution up to 40 km. Spectral analysis and Hurst exponents method were applied to analyze the scintillation of radio signal transmitted through turbulent layers of Ionosphere and Solar wind plasma. This revised version was published online in July 2006 with corrections to the Cover Date.     

Some aspects of electric field mapping in the auroral ionosphere

The mapping of the spectra of electrostatic field below 300 km altitude is theoretically calculated for a horizontally stratified auroral ionosphere. Perpendicular electric fields of large scale size are the same for different altitudes of the ionosphere. However, electric fields of small scale size vary with altitude and decrease drastically when the scale size is smaller than a certain value which depends on altitude. These results are similar to those observed by satellites above 300 km altitude. In the case of a homogeneous anisotropic ionosphere, analytical results are obtained for the penetration of electric field into the ionosphere as a function of wavenumber. The “smoothing” of the electric field when penetrating a horizontally stratified ionosphere is demonstrated. The smallest possible scale of parallel electric field structure within the ionosphere is found. Also presented is a method of finding the smallest horizontal length with which the electric field can penetrate the ionosphere with little distortion. For an average conductivity model, this length is found to be about 1 km. Finally, the mapping of packets of electric field to the ground is constructed.