Resonant interactions of modes in coronal magnetic flux tubes

Nonlinear resonant interactions of different kinds of fast magnetosonic (FMS) waves trapped in the inhomogeneity of a low- plasma density, stretched along a magnetic field (as, for example, in coronal loops) are investigated. A set of equations describing the amplitudes of interactive modes is derived for an arbitrary density profile. The quantitative characteristics of such interactions are found. The decay instability of the wave with highest frequency is possible in the system. If amplitudes of interactive modes have close values, the long-period temporal and spatial oscillations are in the system.For a quantitative illustration, the parabolic approximation of the transverse density profile has been chosen. Dispersion relations of FMS waves trapped in a low- plasma slab with a parabolic transverse density profile are found. The transverse structure of the waves in this case can be expressed through Hermitian polynomials. The interaction of kink and sausage waves is investigated. The sausage wave, with a sufficiently large amplitude, may be unstable with respect to the decay into two kink waves, in particular. The spatial scale of a standing wave structure and the time spectrum of radiation are formed due to the nonlinear interactions of loop modes which contain information about the parameters of the plasma slab.     

Comprehensive studies of solar activity on the CORONAS-F satellite

The first results of comprehensive CORONAS-F observations of solar activity are presented. The CORONAS-F instrumentation and principal scientific objectives are briefly described and examples of the first results of data reduction are given.     

Erratum: Comprehensive studies of solar activity on the CORONAS-F satellite [<Emphasis Type="Italic">Astronomy letters</Emphasis> 28, 401–410 (2002)]

The first results of comprehensive CORONAS-F observations of solar activity are presented. The CORONAS-F instrumentation and principal scientific objectives are briefly described and examples of the first results of data reduction are given. This article was republished due to two color figures (nos. 4 and 5) missed in the original translation. Our apologies to the authors and the readers of the journal. The online version of the original article can be found at     

The fine structure of intensive small-scale electric and magnetic fields in the high-latitude ionosphere as observed by Intercosmos-Bulgaria 1300 satellite

The data on intensive small-scale electric fields and related transverse magnetic disturbances observed from Intercosmos-Bulgaria 1300 satellite at altitudes of 800–900 km in the auroral ionosphere are presented here. The typical time scale of the phenomena is of the order of 1 s, the amplitudes reach 250 mV m⁻¹ in electric field and up to 300 nT in magnetic field. A detailed correlation between the variations of electric and magnetic fields in such structures is shown. Some peculiarities are presented which show that the observed electric jumps are transient electromagnetic disturbances rather than steady electrostatic structures.     

Solar Flux and Spectrum Measurements in the EUV Spectral Region on Board Coronas-I Satellite

There are presented data on solar emission variations in the extreme ultraviolet range?inebreak (λ < 130 nm) which were obtained on board the CORONAS-I satellite during the solar activity minimum epoch in 1994. Based on the thermoluminescent technique, the measurements were performed using the SUFR (Solar Ultraviolet Radiometer) equipment for recording the solar emission flux at λ < 130 nm. The technique provides absolute measurements. The intensity of the Heii 30.4 nm line emission was also measured on board the CORONAS by means of the Vacuum Ultraviolet Solar Spectrometer (VUSS), which uses gas-photoelectron energy and intensity analysis to register the spectrum. The characteristics of both devices are given, as well as calibration methods and the main results. The observation period may be characterized by a very low activity level. The solar flux in the region λ < 130 nm was 7.5–8 erg cm^-2 s^-1, the Lα line intensity was～ (3.3 –3.7) × 10¹¹ photon cm^-2 s^-1 and the Heii (30.4 nm) line intensity was (6–7.5) × 10⁹ photon cm^-2 s^-1. Intensive solar flares were not registered during the period of observation. During the flare of B4.5 X-ray class (30 June 1994, 01:08 UT), an increase of flux of ～ 15% was registered in the range λ < 130 nm.     

On the Envelope Soliton – Like Fine Structure in Solar Radio Emission

Several quasi-periodic, milliseconds fine structures in the metric wave band occurring during the evolution of solar type IV bursts have been observed by Yunnan Radio Telescope, Trieste Radio Telescope and IZMIRAN dynamic spectrometer. The envelope of these quasi-period modulational fine structures have a soliton pattern, so it is called an envelope soliton-like fine structure. A modulational instability model of electromagnetic wave has been adopted here. It is found that the longitudinal modulational instability can occur only in the solar coronal region of low magnetic field and high temperature, as well as high density plasma, which will give rise to the envelope soliton-like fine structures in the solar metric and decimetric radio emission. The propagation effects of envelope soliton-like fine structure from corona to the observer on the Earth have been briefly considered. This revised version was published online in July 2006 with corrections to the Cover Date.     

On stereoimages of some structures in the solar atmosphere

Three-dimensional structures in the solar chromosphere and corona are considered. It is demonstrated that two photoheliograms separated by ～1 day can be used (using computer-graphics methods) to construct a stereo image of the Sun. The algorithm for this is presented and carried out for H_α images of the total disk. A bulge in the equatorial region resulting from the differential rotation of the Sun can be seen in the stereo image. Structures called Whitney pleats in catastrophe theory are observed in the solar corona. Such structures are encountered in prominences. The well-known helmets (or streamers) are pleats of heliospheric plasma sheets. Isophotes for such a sheet and the degree of polarization of the radiation in the pleat are calculated and compared with observational data.     

Resik: A Bent Crystal X-ray Spectrometer for Studies of Solar Coronal Plasma Composition

We describe the RESIK (REntgenovsky Spektrometr s Izognutymi Kristalami) instrument, consisting of two double-channel X-ray spectrometers, designed to observe solar active region and flare plasmas. RESIK is one of the instruments making up the scientific payload of the Russian CORONAS-F solar mission. The uncollimated spectrometer uses two silicon and two quartz bent crystals observing flare, active region and coronal spectra in four wavelength bands with a resolving power (/ ) of 1000. The wavelength coverage, 3.3–6.1 Å, includes emission lines of Si, S, Cl, Ar, and K and in the third diffraction order, the wavelength range includes He-like Fe lines (1.85 Å) and Ni lines (1.55 Å) with dielectronic satellites, emitted during intense, hot flares. The instrument is believed to be the best calibrated space-borne crystal spectrometer flown to date. The spectrometer dynamically adjusts the data gathering intervals from 1 s to 5 minutes, depending on the level of solar X-ray emission at the time of observation. The principal aims of RESIK are the measurements of relative and absolute element abundances in the emitting plasma and the temperature distribution of plasma (differential emission measure) over the temperature interval 3 and 50 MK. This paper summarizes the scientific objectives of RESIK and describes the design, characteristics, and performance of the instrument.     

Waves in cosmic magnetic structures taking into account the anisotropic plasma pressure

This paper provides an analysis of magneto-sonic eigenwaves travelling in magnetic plasma structures based on the Chew-Goldberger-Low approximation, for which the plasma kinetic pressure is different along and across the magnetic field. The anisotropy does not lead to the emergence of new modes. The dependence of phase velocities of the waves, trapped by a single magnetic surface, on the pressure anisotropy is investigated. For a magnetic slab with field-free surroundings, the dispersion relations for the eigenwaves are obtained. The pressure anisotropy may change dispersion relations of such modes significantly. In particular, backward waves are possible in the case of strong anisotropy. The dependences of the thresholds for the mirror and hose instabilities on the system parameters are obtained. In particular, hose and mirror instabilities of such waves are absent for some wave number regions. The results are used to obtain the eigenwave characteristics in coronal loops and chromospheric flux tubes.