Local maximum in the microwave spectrum of solar active regions as a factor in predicting powerful flares

We discuss the results of a study of microwave radiation from three flare-active regions??NOAA 10300, 10930, and 11158??with powerful eruptive events (X-class flares and coronal mass ejections) recorded on July 15, 2002; December 13, 2006; and February 15, 2011, when the regions were in the central part of the disk. There exists evidence of a ??-configuration in the structure of the photospheric magnetic field formed one or two days prior to the eruptive process as a result of the emergence of a new magnetic flux and shifting movements of the sunspots and accompanied by changes in the spectral characteristics of the microwave radiation of the active regions (ARs), which suggests the development of a peculiar radio source. The analysis of these regions continues a series of studies of eruptive events carried out at RATAN-600 in the 1980s?C1990s and gives a reason to conclude that early detections of peculiar sources in the microwave radiation of ARs, which are essentially areas of high energy release in the solar atmosphere, can be used as a factor in predicting powerful eruptive (geoeffective) processes on the Sun.     

Microwave radiation of solar active regions before X flares according to the RATAN-600 observations in 2011

The evolution of the microwave radiation from four active regions, where strong X-ray flares (X-class, GOES) occurred in 2011, has been studied. Daily multiwavelength RATAN-600 radio observations of the Sun in the 1.6–8.0 cm range have been used. It has been indicated that the radiosource above the photospheric magnetic field neutral line (above the region with the maximal convergence of the fields opposite in sign) becomes predominant in the structure of the active region microwave radiation one to two days before a powerful flare as in the eruptive events previously studied with RATAN-600. The appearance of such a radiosource possibly reflects the current sheet formation in the corona above the active region. The energy necessary for a flare is stored in the magnetic field of active region, which can be considered as a factor for predicting a powerful flare.     

Studies of the solar corona based on solar eclipse observations at IZMIRAN

From 1945 to 2009, fellows of IZMIRAN participated in 24 expeditions devoted to observations of solar eclipses. The following characteristics of the solar corona were mainly studied: the emission structure, intensity, and polarization; the line and continuous spectra; etc. This paper reviews the most important results, which promoted the development of the present-day concepts of the solar corona structure and physical properties.     

Physical conditions in the low corona and chromosphere of solar active regions according to spectral radar measurements

The physical conditions in the low corona and chromosphere of solar active regions are studied. A diagnostics technique based on multiwave observations in the centimeter range, photospheric magnetic field extrapolation, and radioemission calculations has been applied. The calculated spatial and spectral structure of the radioemission has been compared with RATAN-600 spectral-polarization observations with a high spatial resolution. The effect of the plasma physical parameters on the emission structure character in a complex magnetic field topology in active regions is analyzed. Modeling of the spectral singularities at a quasi-periodic propagation of the radioemission is presented.     

Relation between the active region magnetic field and solar flares

A weak active region (NOAA 11158) appeared on the solar disk near the eastern limb. This region increased rapidly and, having reached the magnetic flux higher than 10²² Mx, produced an X-class flare. Only weak field variations at individual points were observed during the flare. An analysis of data with a resolution of 45 s did not indicate any characteristic features in the photospheric field dynamics during the flare. When the flux became higher than 3 × 10²² Mx, active region NOAA 10720 produced six X-class flares. The field remained quiet during these flares. An increase in the magnetic flux above ～10²² Mx is a necessary, but not sufficient, condition for the appearance of powerful flares. Simple active regions do not produce flares. A flare originates only when the field distribution in an active region is complex and lines of polarity inversion have a complex shape. Singular lines of the magnetic field can exist only above such active regions. The current sheets, in the magnetic field of which the solar flare energy is accumulated, originate in the vicinity of these lines.     

Disturbances in the topside ionosphere during solar flares

The results of studying the ionospheric response to solar flares, obtained from the data of the GPS signal observations and incoherent scatter radars and as a result of the model calculations, are presented. It is shown that, according to the GPS data, a flare can cause a decrease in the electron content at altitudes of the topside ionosphere (h > 300 km). Similar effects of formation of a negative disturbance in the ionospheric F region were also observed during the solar flares of May 21 and 23, 1967, with the Arecibo incoherent scatter radar. The mechanism by which negative disturbances appear in the topside ionosphere during solar flares has been studied in this work based on the theoretical model of the ionosphere-plasmasphere coupling. It has been indicated that the formation of the electron density negative disturbance in the topside ionosphere is caused by an intense removal of O⁺ ions into the overlying plasmasphere under the action of an abrupt increase in the ion production rate and thermal expansion of the ionospheric plasma.     

Magnetic topologies in the solar corona due to four discrete photospheric flux regions

Many dynamic phenomena in the solar corona are driven by the complex and ever-changing magnetic field. It is helpful, in trying to model these phenomena, to understand the structure of the magnetic field, i.e. the magnetic topology. We study here the topological structure of the coronal magnetic field arising from four discrete photospheric flux patches, for which we find that seven distinct, topologically stable states are possible; the changes between these are caused by six types of bifurcation. Two bifurcation diagrams are produced, showing how the changes occur as the relative positions and strengths of the flux patches are varied. A method for extending the analysis to higher numbers of sources is discussed.     

Interplanetary scintillation observations of interaction regions in the solar wind

Co-rotating interaction regions (CIRs) between fast and slow streams of plasma are a prominent feature of the solar wind. Measurements of interplanetary scintillation (IPS) using the three widely separated antennas of the EISCAT facility have been used to detect the compression regions at the leading edges of interaction regions and to determine the location and velocity of the structure. Observations show that interaction regions have developed as close to the Sun as 25–30 solar radii, a result supported by theoretical modelling which shows that the conditions needed for CIRs to develop exist inside 30 solar radii.     

On the existence of the east-west asymmetry in the optical observations of the solar corona

The east-west asymmetry has been analyzed using the 1946–2000 corona observation data for the green line at the Kislovodsk station. A positive east-west asymmetry has been revealed throughout the entire observation period except for three years, 1994–1996. Time variations of the east-west asymmetry for certain periods coincide with those for flares. Seasonal variations of the east-west asymmetry revealed earlier by other authors are not confirmed. If seasonal variations of the east-west asymmetry in the corona exist, their amplitudes are smaller than or comparable to the instrumental errors, errors caused by atmospheric variations during the observation period and to differences between the corona-intensity measuring systems used at different observatories.     

The solar corona during the eclipse of August 1, 2008

A new telescope has been created to investigate the solar corona during eclipses. One lens simultaneously forms three corona images occurring as coronal radiation passes through three polarizers with transmission directions rotated 0°, 60°, and 120° relative to the selected direction; in addition, one image is formed without the polarizer. The telescope was used for solar corona observation during the eclipse of August 1, 2008. We obtained the distributions of polarization brightness, K corona brightness, degree of K corona polarization, and total degree of polarization as well as polarization directions depending on the latitude and radius in the sky plane. Radial distributions of the electron density depending on latitude were calculated. The coronal plasma temperature was determined for different corona structures under the assumption of hydrostatic equilibrium.     

Tracing magnetic helicity from the solar corona to the interplanetary space

On October 14, 1995, a C1.6 long duration event (LDE) started in active region (AR) NOAA 7912 at approximately 5:00 UT and lasted for about 15 h. On October 18, 1995, the Solar Wind Experiment and the Magnetic Field Instrument (MFI) on board the Wind spacecraft registered a magnetic cloud (MC) at 1 AU, which was followed by a strong geomagnetic storm. We identify the solar source of this phenomenon as AR 7912. We use magnetograms obtained by the Imaging Vector Magnetograph at Mees Solar Observatory, as boundary conditions to the linear force-free model of the coronal field, and, we determine the model in which the field lines best fit the loops observed by the Soft X-ray Telescope on board Yohkoh. The computations are done before and after the ejection accompanying the LDE. We deduce the loss of magnetic helicity from AR 7912. We also estimate the magnetic helicity of the MC from in situ observations and force-free models. We find the same sign of magnetic helicity in the MC and in its solar source. Furthermore, the helicity values turn out to be quite similar considering the large errors that could be present. Our results are a first step towards a quantitative confirmation of the link between solar and interplanetary phenomena through the study of magnetic helicity.     

星载电场数据处理方法研究

给出一种新的非线性、非平稳信号的处理方法——HHT方法,并把该方法首次应用于星载电场数据处理中.以2004年9月15日菲律宾6.0级地震前两天(13日)DEMETER卫星经过震中区域上空所记录到的数据为例,对ULF频段的电场数据进行了处理,得到了相应的HHT时频图谱.另外,还利用DEMETER卫星中心网站提供的SWAN软件计算得到了相应的小波变换时频图谱,通过比较发现,虽然两种方法对异常信号出现的位置时刻的描述有相同的能力,但HHT方法在异常信号的细节描述上更为清晰,从而为今后进一步的研究工作奠定了基础.     

On the determination of satellite coordinates from doppler observations

The basic task of satellite geodesy is the construction of a unified 3 or 4 dimensional world-wide geodetic network. In this frame the station position, the parameters of the Earth's gravity field, and the orbital elements of the observed satellite would be known.The satellite observations by Doppler method are independent of weather and daylight conditions; they can be done fully automatically and no accumulation of errors occurs. For these reasons, the satellite observations by Doppler methods are getting more and more weight.A simple method is given for the determination of the satellite's position using Doppler shifts observed at several stations of known coordinates.     

Lidar observations of the stratospheric aerosol during 1993 above McMurdo Station,Antarctica

Scattering ratios of stratospheric aerosol obtained by lidar at McMurdo Station, Antarctica (78°S, 167°E), during February–December 1993, have been analysed in relation to the stratospheric polar vortex. Seasonal changes in their properties are used to infer dynamic processes occurring in the Antarctic stratosphere during the year. Descent rates are calculated and compared to values obtained with different studies. Our analysis suggests that the apparent springtime cleansing of the Antarctic stratosphere is the result of subsidence of air masses inside the vortex and of sedimentation of larger particles. Below 20 km of height, an enhancement of the aerosol descent rates during July was associated with high occurrence of Polar Stratospheric Cloud events above McMurdo Station in that period. A synoptic approach using potential vorticity values at 425 K above the station has been employed to figure out the behaviour of the aerosol across the vortex boundary during its early formation.     

Parameters of the normal gravity field deduced from satellite observations

Summary The parameters of the normal gravity field were deduced from the harmonic coefficients[3, 4] upto n=6 and compared with the parameters used hitherto. The symbols used are the same as in papers[5, 6, 8] with which this paper connects up.     

Radio observations during the decay period of the sovjetic satellite 58-delta two

Summary During the decay period of Sputnik III between March 14, and April 6, 1960 it was found by measurements of its revolution period that the braking varies considerably from one day to the next one.

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Zusammenfassung Während der Untergangs-Periode des Sputnik III zwischen dem 14. März und dem 6. April 1960 wurde durch Messungen seiner Umlaufzeit festgestellt, dass der Abbremsungsvorgang von Tag zu Tag beträchtlich variiert.

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Work done on contrat with US Airforce, No. AF 61(052)-165.