Chromospheric and Coronal Radio Sources from Observations of the Partial Solar Eclipse of March 20, 2015, at the Mountain Astronomical Station of the Central Astronomical Observatory

This paper presents the results of processing the data on the partial solar eclipse that occurred on March 20, 2015, and was observed with the RT-3 (λ = 4.9 cm) and RT-2 (λ = 3.2 cm) radio telescopes of the Kislovodsk Mountain Astronomical Station, Central Astronomical Observatory, Russian Academy of Sciences (MAS CAO RAS). They were compared with observations in the optical and X-ray ranges. The local radio sources at the limb and on the disc of the Sun were identified: an eruptive and a quiet prominence; filaments; a coronal hole; facular plages; and a sunspot group. The curves of the center-to-limb variations in the radio brightness of the undisturbed regions of the Sun were plotted for λ = 4.9 and λ = 3.2 cm. The solar radio maps were presented. The altitude of the radiating layer in the chromosphere above the sunspot and the facular sources for λ = 4.9 cm λ = 3.2 cm was compared.     

Vla and Spacecraft Observations of Solar Activity

We describe the world's largest synthesis radio telescope, the Very Large Array (VLA), and how it can be used to complement observations with the Solar and Heliospheric Observatory (SOHO) and the Yohkoh solar spacecraft. The VLA provides images with high spatial and temporal resolution, often across the visible solar disk. The VLA also detects nonthermal radiation that is not observed with SOHO and Yohkoh, and provides estimates for the coronal magnetic field strengths that are not directly measured by these spacecraft. The VLA data can be combined with SOHO CDS, SOHO EIT, or Yohkoh SXT observations to provide new insights to the compact, variable sources, called blinkers and bright points, in the solar transition region or low corona. A new 400 cm VLA system provides images of nonthermal burst activity associated with Coronal Mass Ejections (CMEs), and may detect thermal emission from CMEs, that can be compared with SOHO's LASCO and EIT instruments to obtain new information about the origin and evolution of CMEs.     

Studying local sources in the radio range based on the partial solar eclipse of January 4, 2011, at the Mountain Astronomical Station, Central Astronomical Observatory, Russian Academy of Sciences

Data are presented on a partial solar eclipse, which occurred on January 4, 2011, and was observed with RT-3 (?? = 4.9 cm) and RT-2 (?? = 3.2 cm) radio telescopes at the Mountain Astronomical Station, Central Astronomical Observatory, Russian Academy of Sciences (MAS CAO RAS). The radioemission flux in two channels was registered using digital methods with a time resolution of 0.5 s. Comparisons were performed with observations in the optical, UV, and X-ray ranges. The following local sources of increased radioemission on the solar disk have been identified: sunspot groups 1 (NOAA 1142) and 126 (NOAA 1141), unipolar sunspot 127 (NOAA 1140), facula areas, and polar and midlatitude coronal holes. It has been indicated that the brightness of a unipolar sunspot (for ?? = 4.9 cm, I _rel = 29.5; for ?? = 3.2 cm, I _rel = 10.1) and two sunspot groups (for ?? = 4.9 cm, I _rel = 10.1 and 14.2; for ?? = 3.2 cm, I _rel = 5.1 and 6.2) is maximal. The radioemission flux of all found coronal holes is decreased, and the decrease is more contrasting in the 4.9-cm range as compared to such a decrease in the 3.2-cm range. Radio maps of the Sun and changes in the radioemission flux of undisturbed solar regions from the center to the limb for ?? = 4.9 and 3.2 cm have been constructed based on the eclipse data.     

Studying the solar corona above active regions from microwave observations during solar flares recorded by CORONAS-F satellite

In 2001–2003, 45 flares of hard X ray (HXR) and gamma ray radiation, identified with a particular active region (AR) that produced each event, were recorded during the experiments onboard the Russian Solar Observatory CORONAS-F using the SONG (solar neutrons and gamma ray quanta) instrument. The solar corona structure and dynamics above these ARs is studied on the basis of the microwave observations with two Russian radio telescopes RATAN-600 and Siberian Solar Radio Telescope (SSRT). The results are illustrated using the active region NOAA 9601 and flare of September 5, 2001 (～ 1430 UT) as an example. The flare is interesting because the energy of its gamma radiation exceeded 1 MeV, while its power was only M6.0 in soft X rays. Such a combination of the event characteristics is not too frequent, which indicates that the spectrum of the studied event was rather hard. The type of the source of microwave radiation above NOAA 9601 has been determined. Some properties of this-type sources of a diagnostic value for detecting ARs capable of producing HXR and gamma radiation are indicated.     

Manifestation of the Identity of Brightness Temperatures of the Polar Coronal Hole and Low-Latitude Coronal Holes in the Centimeter Wave Range

This paper is devoted to an analysis of brightness temperatures of the polar and low-latitude coronal holes on the Sun in the cm-wave range during periods of minimum solar activity. Data from observations of the polar coronal hole received by the RATAN-600 radio telescope during the solar eclipse of March 29, 2006, and low-latitude observations of coronal holes and quiet Sun received earlier with the RATAN-600 and BPR radio telescopes in the period of minimum solar activity have been used in the paper. The obtained good agreement between the brightness temperatures of cm-wave emission of the polar coronal hole above the North Pole of the Sun and of the low-latitude coronal holes against the background of the quiet Sun reveals the identity of the temperature properties of large coronal holes, irrespective of the mode of their arrangement and location on the Sun during the periods of minimum solar activity.     

Possibilities for the application of adaptive optics at solar telescopes

Possibilities for the application of adaptive optics at solar telescopes are studied. A modified correlation tracker to measure the image motion at the first focus of the Big Solar Vacuum Telescope (BSVT) at the Baikal Astrophysical Observatory of the Institute for Solar-Terrestrial Physics, the Siberian Branch of the Russian Academy of Sciences, has been investigated experimentally.     

Ring-shaped cyclotron radiation source on the example of the NOAA 11140 active region according to high angular resolution observations

Using observations with a high angular resolution of ??1??, we reveal a cyclotron radiation source with a ring-shaped structure of the image. The source is located in the solar corona above the main spot of the NOAA 11140 active region. Observations were carried out during the solar eclipse of January 4, 2011, using two RT-32 radio telescopes that operated at wavelengths of 3.5, 6.2, and 13 cm and registered Stokes parameters I and V. The features of the structure are interpreted within the known theory of the cyclotron radio radiation of hot coronal plasma (2?C4 MK) in the presence of the strong magnetic field of the sunspot (??3 kG).     

冕洞阻碍太阳高能粒子事件形成的典型事例分析

通过对比两次快速晕状日冕物质抛射(CME)事件,分析相应的日面和行星际的观测资料,发现源区距离冕洞较远的CME引起了极强的太阳高能粒子(Solar Energetic Particle,SEP)事件,而源区非常靠近冕洞的CME则没有引起大的SEP事件.该结果表明,冕洞可能对CME形成SEP事件有阻碍作用.继而分析1997～2003年所有爆发在冕洞边缘的快速晕状CME,发现源区离冕洞距离小于02Rs(太阳半径)的CME均没有引起大的SEP事件.从而进一步证实了冕洞可能对邻近CME形成大SEP事件有影响,它阻碍SEP事件的形成.最后讨论了冕洞阻碍CME形成大SEP事件的可能原因.     

Method for the determination of the height of a solar filament

A comparison of the actual filament height above the solar photosphere with the limiting height calculated by magnetic data provides information about the filament stability margin and its readiness for eruption. A method is proposed for the determination of the height of solar filaments by a comparison of the position of the upper edge of the filament (spine) with the position of the polarity-inversion line of the potential magnetic field calculated for different heights. The line closest to the filament spine corresponds to its height. Observations of the Solar Terrestrial Relations Observatory (STEREO) spacecraft were used to verify the proposed method when they were at an angular distance of ~90° from the Earth and provided a side view of the filaments near the central meridian in observations from the Earth and near-Earth orbits. The proposed method can be useful in the estimation of the possible geoeffectiveness of filaments on the solar disk.     

利用F10.7和Mg II构建太阳极紫外辐射长时间序列

利用SOHO/SEM在1996-2008年的太阳EUV观测数据,比较和评估F10.7和Mg II作为EUV代理参数的代表性,不能支持Viereck等关于Mg II是比F10.7更好的代理参数的结论.通过比较对两种参数的多种回归计算结果,确立双因子极大似然估计方法构建EUV计算模式,通过模型计算结果与SEM观测数据比较,表明该模型能够很好地重建EUV数据系列.利用该模式,构建了1978年11月以来的太阳极紫外辐射数据序列.     

An Upper Limit to Ground Deformation in the Island of Tenerife, Canary Islands, for the Period 1997–2006

Continuous monitoring of ground deformation in the volcanic island of Tenerife, Canary Islands, is based on GPS networks, since there are as yet no tiltmeter stations installed on the island. However, there is a world-class astronomical observatory on the island, the El Teide Observatory, where four tiltmeters, two aligned in the North-South and the other two in the East-West, are monitoring the movements of the solar telescope THEMIS. THEMIS (Heliographic Telescope for the Study of Solar Magnetism and Instabilites) is among the three largest solar telescopes in the world. Since THEMIS is located a few kilometers from the main volcanic structures of the island, in particular the El Teide-Pico Viejo stratovolcano, and the precision of the inclinometers is comparable to those used in geophysical studies, we carried out the analysis of the tilt measurements for the period 1997–2006. The tiltmeters at THEMIS are placed in the seventh floor of a tower, hence their sensitivity to geological processes is reduced compared to geophysical installations. However, THEMIS measurements are the only terrestrial data available in Tenerife for such a long period of observations, which include the sustained increase in seismic activity that started in 2001. In this sense, a significant change was found in the East-West tilt of approximately 35 μ-radians between the years 2000 and 2002. Some theoretical models were calculated and it was concluded that such tilt variation could not be due to dike intrusions, nor a volcanic reactivation below the El Teide-Pico Viejo volcano. The most likely explanation comes from dislocations produced by a secondary fault associated to a major submarine fault off the eastern coast of Tenerife. In any case, taking into account the nearly permanent data recording at THEMIS, they could be considered as a complement for any ground deformation monitoring system in the island.     

First combined observations in the German–Argentinean solar observatory: correlations in quiet and eruptive phenomena at the limb

This is a first report of combined observations form the solar instruments at the recently inaugurated German–Argentinean Solar-Observatory at El Leoncito, San Juan, Argentina. The Hα telescope (HASTA) and the mirror coronagraph (MICA) daily image the solar disk and the inner solar corona respectively with high temporal and spatial resolution. The excellent weather conditions for solar studies of the Observatory, and its south equatorial location allow a complementary summer-condition data with respect to the majority of the other observatories, mainly located in the northern hemisphere. In this paper, we present four events in order to study possible correlations between observations taken by both telescopes. Since each instrument records data in quite different temperature regimes, correlation between both set of data appears when the phenomena span a broad range of temperatures. This is explicitly shown for two of the four set of data presented here. On the other hand, the four cases are good examples of the contributions the two instruments can provide to the better understanding of the mechanisms at work in the inner solar atmosphere.     

Seasonal and nighttime behaviors of emissions of hydroxyl and the atmospheric system of molecular oxygen of the midlatitude mesopause

Based on observations of mesopause emissions, namely, emissions of hydroxyl (band (6-2)) and molecular oxygen (band (0-1) of the atmospheric system), their systematic nighttime and seasonal variations are determined at Zvenigorod Observatory in 2000–2008. It is shown that the intensity of hydroxyl emission decreases during the entire night or first half-night, probably due to the influence of the chemical sink of atomic oxygen on the nighttime behavior of hydroxyl emission. The nighttime behavior of the intensity of molecular oxygen emission is explained by the action of atmospheric tides. The seasonal behavior of emissions is characterized by two minima, in April–May and December; it is caused by the annual behavior of the atomic oxygen content, temperature, and atmospheric density in the emitting layer. Based on the emission data, we determined the seasonal variations of atomic oxygen at heights of ∼87 km (maximum of hydroxyl emission) and ∼95 km (maximum of molecular oxygen emission).     

Using GPS–GLONASS–GALILEO data and IRI modeling for ionospheric calibration of radio telescopes and radio interferometers

VHF and HF radio signals are widely used to observe the Sun and pulsars. Nowadays, large low-frequency radio astronomical arrays (LOFAR, 30–240 MHz; MIRA, 80–300 MHz) are being constructed to record radiation of pulsars at the maximum distance. registration of the solar radio emission intensity at fixed frequencies and in the spectral VHF band is very important along with other methods of monitoring of coronal mass ejections. Interpreting radio astronomical data is known to be necessary to take into account possible distortions of these signals in the Earth ionosphere. However, in contrast to modern navigation systems (Global Position System (GPS), GLObal NAvigation Satellite System (GLONASS), GALILEO), in which a very accurate reconstruction of ionosphere parameters is a built-in function, in present-day radio astronomy a retrieve of ionosphere transfer characteristics has not been appropriately worked out. This collides with increasing requirements to accuracy of the analysis of a radio emission amplitude profile and to the angular and polarizing resolution of radio telescopes of new generation (LOFAR, SKA, etc.). We have developed a method and software to calculate the ionosphere rotation measure (RM) and dispersion measure (DM). We used the ionosphere model IRI-2001, magnetic field model IGRF-10, and the ionosphere total electron content values obtained from GPS measurements. The obtained values of DM and RM were recalculated into characteristics of the phase delay, Faraday amplitude modulation, and polarization changes. We calculated ones for different levels of geomagnetic activity as well as different angular positions of radio sources. Our main idea is to use a signal of navigation satellites (GPS, GLONASS, GALILEO) as a testing signal from a “reference” source located at minimal angle distance from a source studied. Our project allows development of methods and systems of ADAPTIVE RADIO ASTRONOMY, adaptive to the non-uniform and non-stationary ionosphere, by analogy with known systems of adaptive optics intended to adapt optical telescopes to varying conditions of the optically non-uniform and non-stationary troposphere.     

Dynamics of the large-scale open solar magnetic field and its specific features in the zone of the main active longitudes in 2006–2012

The dynamics of the absolute global values (Φ) of the large-scale open solar magnetic field (LOSMF) fluxes at an interval of one solar rotation in 2006–2012 has been studied based on the Wilcox Solar Observatory data and using the ISOPAK original package for modeling the solar magnetic field. The reference points and the duration of the final quasi-biennial interval in cycle 23 (January 2006–May 2007; 17 months) and the phases of the cycle 24 minimum (May 2007–November 2009; 30 months), growth (November 2009–May 2012; 30 months), and the beginning of the maximum (May 2012–January 2013) have been determined. It has been indicated that the absolute values (Φ) decreased sharply at the beginning of the minimum, growth, and the maximum phases to ～(2, 1.25, 0.75) × 10²² Mx, respectively. During the entire minimum phase, LOSMF corotated super-quasi-rigidly westward in the direction of solar rotation; at the beginning of the growth phase, this field started corotating mostly eastward. The LOSMF polarity reversal in the current cycle 24 started in May–June 2012 (CR 2123–2124), when fields of southern polarity rushed from the Sun’s southern hemisphere toward the north. The statement that the solar cycle is a continuous series of quasi-biennial LOSMF intervals is confirmed. In particular, the minimum and growth phases are characterized by opposite LOSMF rotation directions, i.e., super-quasi-rigid corotation (twisting) and detwisting, with identical duration at least in cycle 24.     

Radio-heliographic diagnostics of the potential flare productivity of active regions

As deduced from the data with high spatial resolution obtained at the radio heliographs of the Siberian Solar Radio Telescope (SSRT, 5.7 GHz) and the Nobeyama radio heliograph (NoRH, 17 GHz), radio brightness centers in the distribution of the Stokes parameter I are shifted relative to the distribution of the parameter V 1–2 days before an intense flare. It has been shown that this phenomenon can be related to the behavior of quasi-stationary sources over the inversion line of the radial component of the magnetic field (neutral-line associated sources (NLSs)). These sources have a brightness temperature up to 106 K and a circular polarization up to 90%. The origination of NLSs is associated with the outflow of a new magnetic flux into the atmosphere of an active region that is a classical factor of the flare activity. Therefore, an NLS is a precursor of power solar flares and can be used as a forecast factor. Owing to the high resolution of the SSRT, the deviation of the observed polarization distribution of microwave radiation of the active region from the normal one within the solar disk zone containing the active region can be used as a precursor of the preflare state of the active region. As a result, the single-frequency Tanaka-Enome criterion is modified. The use of the data from two radio heliographs (SSRT and NoRH) allows us to propose a two-frequency criterion of normal longitudinal zones that is more efficient for short-term forecasting of solar flares. Preflare features associated with the displacement of brightness centers in I and V, which is manifested as the transformation of NLSs into spot sources, are fine attributes added to forecast according to the two-frequency criterion. This is illustrated by an example of active region 10930, which produced power proton flares on December 6 and 13, 2006.     

Powerful solar radio bursts as a global and free tool for testing satellite broadband radio systems,including GPS–GLONASS–GALILEO

We investigated failures in the global positioning system (GPS) performance produced by solar radio bursts with unprecedented radio flux density during the X6.5 and X3.4 solar flares on 6 and 13 December 2006, respectively. The effect of these events on GPS was compared to that of the X17.2 solar flare of 28 October 2003. Significant experimental evidence was found that high-precision GPS positioning on the Earth's entire sunlit side was partially disrupted for more than 10–15 min on 6 and 13 December 2006. The high level of phase slips and count omissions resulted from the wideband solar radio noise emission. Our results provide serious grounds for revising the role of space weather factors in the functioning of modern satellite systems and for considering these factors more carefully in practice. Similar failures in the operation of satellite navigation systems (GPS, GLONASS, and GALILEO) can be fatal for operating safety systems as a whole and lead to great financial losses. Another important conclusion of our investigation concerns the continuous calibrated monitoring of the level of the solar radio emission flux. This monitoring involved a large number of solar radio spectrographs and allowed us to estimate the solar radio noise level in the range of the GPS–GLONASS–GALILEO frequencies.     

Coronal Holes as Tracers of the Sun’s Global Magnetic Field in Cycles 21–23 of Solar Activity

The dependences of the number and parameters of non-polar coronal holes (CHs) on characteristics of the Sun’s global magnetic field (GMF) are investigated in cycles 21–23 of solar activity (1976–2012) based on data from the CH catalog of the Mountain Astronomical Station of the Main (Pulkovo) Astronomical Observatory of the Russian Academy of Sciences. The influence of variations in the GMF structural arrangement on the CH number and parameters is considered. It is shown that the more stable and steadystate the GMF topology is in the cycle, the higher are the GMF values. The majority of CHs form over periods of stable GMF structure. With a growth in the rate of structural GMF changes, the CH number and the values of all CH parameters decrease. The correlation between the area, extension in latitude and longitude, and magnetic flux of CHs and the intensity of both the calculated coronal field and the observed large-scale photospheric magnetic field is higher in cycles with larger magnetic-field values and with a more stable GMF structure. Non-polar CHs are divided into three groups depending on the GMF value and a rate of the structural GMF rearrangement.     

Two-stage acceleration of solar cosmic rays

On the basis of data from the Radio Solar Telescope Network (RSTN), as well as the Geostationary Operational Environmental Satellite (GOES) and the WIND spacecraft, for the period from 1989 to 2006 covering 107 flare events, we investigated the relationship between the intensity of solar cosmic rays and parameters of continuum radio bursts (25?C15400 MHz), as well as type II radio bursts in the meter and decahectometer wavelength ranges. Proton fluxes with energies E _p > 1?100 MeV were calculated with regard to a reduced heliolongitude. The maximum correlation between solar cosmic rays and solar parameters of microwave bursts was 0.80. Its value was no more than 0.40 for the drift rate of type II bursts and 0.70 for the compression rate of coronal shock waves. Based on linear regression equations, we estimated the contribution of coronal shock waves to the acceleration of protons. We found that major acceleration processes occur in the area of burst energy release and complimentary processes occur at the fronts of coronal shock waves. The contribution of the latter to the acceleration process increases significantly with proton energy.     

Sunspot groups with high flare activity: Specific features of magnetic configuration,morphology, and dynamics

Specific features of the magnetic configuration, morphological structure, dynamics, and evolution of sunspot groups of the current (24th) cycle of solar activity with high flare activity are considered. The gradients of longitudinal magnetic fields at places of δ-configuration are calculated. The main finding is a time delay of 24–30 h between the time when the magnetic field gradient reaches a critical level of 0.1 G/km and the time when the first of powerful flares occurs in the active region. The study is based on data from the SDO and GOES-15 spacecrafts and ground-based solar telescopes (TST-2 at the Crimean Astrophysical Observatory of the Russian Academy of Sciences and the 150-foot telescope at the Mount Wilson Observatory).