Some features of the interplanetary disturbances in the post-solar maximum year period

Features of strong interplanetary disturbances (including 14 shock waves) are considered by the solar wind plasma measurements onboard the PROGNOZ-8 satellite. Examination of large-scale structure of the plasma fluxes enabled us to discover extreme values of proton temperature (～10⁶K) and density (～10²cm^?3) in some cases.The energy transferred by the interplanetary shock waves (10³¹–10³² erg) and their deceleration are estimated. Determination of the plasma parameter jumps for protons and α-particles at the shock front made it possible to estimate the potential barrier (40–400V) depending on magnetosonic Mach number.     

Normalized electron production rate profiles as a result of penetration of high-energy solar particles into the lower ionosphere

We compute the height profile of the electron production rate q resulting from high energy solar particle flux with spectrum D(E)=KE^?n. Cut-offs energies of 10, 20, 30 and 40 MeV and power indices n from 1 to 6 are used. The profiles are normalized for K = 1 particle/(cm².s.sr.MeV) such that they might be helpful when quantitatively investigating corpuscular effects of proton flares in the height interval 35 to 100 km.     

Venus EUV measurements of hydrogen and helium from Venera 11 and Venera 12

Lyman α and 58.4 nm HeI radiations resonantly scattered were observed with EUV spectrophotometers flown on Venera 11 and Venera 12. The altitude distribution of hydrogen was derived by limb observations from 250 km (exobase level) to 50,000 km. In the inner exosphere (up to ? 2,000 km of altitude) the distribution can be described by a classical exospheric distribution with T_C = 275 ± 25 K and n = 4_?2⁺³ × 10⁴ atom. cm^?3 at 250 km. The integrated number density from 250 to 110 km (the level of CO₂ absorption) is 2.1 × 10¹² atom. cm^?2, a factor of 3 to 6 lower than that predicted by aeronomical models. This number density decreases from the morning side to the afternoon side, or alternately from equatorial to polar regions. Above 2,000 km a “hot” hydrogen population dominates, which can be simulated by T = 10³K and n = 10³ atom. cm^?3 at the exobase level.The optical thickness of helium above 141 km (the level of CO₂ absorption for 58.4 nm radiation) was determined to be τ_o = 3, corresponding to a density at 150 km of 1.6 × 10⁶ cm^?3. This is about 3 times less than what was obtained with the Bus Neutral Mass Spectrometer of Pioneer Venus, and about twice less than ONMS measurements, but is in agreement with earlier EUV measurement by Mariner 10 (2 ± 1 × 10⁶ cm^?3).     

Positron annihilaton radiation from the nuclei of Seyfert galaxies

Recent gamma-ray observations of two Seyfert Galaxies are interpreted in terms of electron-positron pair annihilation radiation. A simplified scenario is envisaged in which a massive black hole is accreting material from an optically thin disk characterized by a hot (T > 10⁹ °K) e^± plasma. At these very high temperatures the 511 keV line emission loses its characteristic features to become both broadened and blue shifted. Observational X and gamma-ray data are used to investigate the possibility that the “bump” in the spectral emission at photon energies E ～ 1 MeV observed in Seyfert galaxies may be due to this annihilation feature. In particular the self consistency of the parameters estimated from the gamma-ray data is explored. Furthermore we investigate the possibility that this annihilation feature may be mirrored in the cosmic diffuse background and, under this assumption, we calculate the maximum temperature of the annihilation region and the average annihilation rate for Seyfert galaxies.     

Multiple wavelength observations of flaring active regions

We present observations of flaring active regions with the Very Large Array (V.L.A. at 6 cm and 20 cm wavelengths) and the Westerbork Synthesis Radio Telescope (W.S.R.T. at 6 cm wavelength). These are compared with photospheric magnetograms (Meudon) and with Hα and offband Hα photographs (Big Bear and Ottawa River Solar Observatories). The 6 cm radiation of these active regions marks the legs of dipolar loops which have their footpoints in lower-lying sunspots. The intense, million degree radiation at 6 cm lies above sunspot umbrae in coronal regions where the longitudinal magnetic field strength H_? = 600 Gauss and the height above the sunspot umbrae h = 3.5±0.5 × 10⁹ cm. Circularly polarized horseshoe structures at 6 cm ring the sunspot umbrae. The high degree of circular polarization (?_c = 95%) of the horseshoes is attributed to gyroresonant emission above sunspot^? penumbrae. The 20 cm radiation of these active regions exhibits looplike coronal structures which extend across regions of opposite magnetic polarity in the underlying photosphere. The 20 cm loops are the radio wavelength counterparts of the X-ray coronal loops. We infer semilengths L = 5 × 10⁹ cm, maximum electron temperatures T_e(max) = 3 × 10⁶ K, emission measures ∫N_e²d$\text{l}$ = 10²⁸ cm^?5, and electron densities N_e = 10⁹ cm^?3 (or pressures p = 1 dyn cm^?2) for the 20 cm bremsstrahlung. A total of eight solar bursts were observed at 6 cm or 20 cm wavelength with second-of-arc angular resolution. The regions of burst energy were all resolved with angular sizes between 5″ and 30″, brightness temperatures between 2 × 10⁷ K and 2 × 10⁸ K, and degrees of circular polarization between 10% and 90%. The impulsive phase of the radio bursts are located near the magnetic neutral lines of the active regions, and between the flaring Hα kernels which mark the footpoints of magnetic loops. In one case there was preburst heating in the coronal loop in which a burst occurred. Snapshot maps at 10 s intervals reveal interesting burst evolution including rapid changes of circular polarization and an impulsive burst which was physically separated from both the preburst radio emission and the gradual decay phase of the burst.     

Energy input in solar flares and coronal explosions

A coronal explosion is a density wave observed in X-ray images of solar flares. The wave occurs at the end of the impulsive phase, which is the time at which the flare's thermal energy content has reached its maximum value. It starts in a small area from where it spreads out, mainly into one hemisphere, with velocities that tend to rapidly decrease with time, and which are between ～ 10³ and a few tens of km s^?1. We interpret them as magneto-hydrodynamic waves that (mainly) move downward from the low corona into denser regions.     

Recent infrared observations of comets with UKIRT and IRAS

A preliminary analysis of infrared observations of comets P/Crommelin and P/Tempel 1 is presented. Comet P/Crommelin was observed from UKIRT over the range 1–20 micron, using standard filters. From the shape of the thermal emission spectrum, the temperature of the dust grains is estimated (T = 314 ± ₃₃⁴⁴K) and also the dust production rate (1.3 × 10⁵gs^?1). Comet P/Tempel 1 was observed with the Infrared Astronomical Satellite (IRAS). The emission is found to be considerably extended and there is also evidence for temperature variation of the dust grains as indicated by the 12 to 25 micron flux ratio.     

He-like Ar xvii triplet observed by RESIK

We present the observations of He-like Ar triplet lines obtained by RESIK spectrometer aboard CORONAS-F. Interpretation of intensity ratios between triplet lines of lower Z elements is known to provide useful diagnostics of plasma conditions within the emitting source. Here, we investigate whether triplet line ratios are useful for interpretation of higher Z element spectra. A high sensitivity, low background and precise absolute calibration of RESIK allow to consider in addition also the continuum contribution. This provides a way to determine the Ar absolute abundance from the observed triplet component ratios. The method is presented and the results are shown for two selected flares. Derived values of Ar absolute abundance for these flares are found to be similar: 2.6 × 10⁻⁶ and 2.9 × 10⁻⁶. They fall in the range between presently accepted Ar photospheric and coronal abundances.     

Post-flare thermal waves in the solar corona

While imaging giant post-flare arches in the solar corona, the Hard X-Ray Spectrometer aboard the SMM detected thermal disturbances propagating through the corona after two-ribbon flares. The speed of propagation is close to, or below, 10 km s^?1, and no obvious time-variation of the speed is indicated in the HXIS data. For subsequent two-ribbon flares in the same active region, these thermal disturbances (waves) exhibit highly homologous properties; thus the waves appear to propagate through preexisting arches formed after earlier flares. Temperatures of > 20 × 10⁶ K have been detected in these moving phenomena. We suggest that we see here in X-rays upper products of the consecutive reconnections which create the post-flare loops below. Temperature maps in fine field of view of HXIS offer now a new possibility to detect postflare arches in the corona built during two-ribbon flares.     

On soft electron beams in solar active and flare region

On the basis of the experimental data obtained from the high resolution X-ray spectra for solar flares and active regions the Suprathermal electron model (SEM) was proposed. This model suggests the existance of the multitemperature structure of the solar plasma emitting Fe and Ca X-rays and the presence of additional electrons with low energies E ? 10 keV and small densities ～ 1–5% relative to the thermal component.     

Solar magnetic feature detection and tracking for space weather monitoring

We present an automated system for detecting, tracking, and cataloging emerging active regions throughout their evolution and decay using SOHO Michelson Doppler Interferometer (MDI) magnetograms. The SolarMonitor Active Region Tracking (SMART) algorithm relies on consecutive image differencing to remove both quiet-Sun and transient magnetic features, and region-growing techniques to group flux concentrations into classifiable features. We determine magnetic properties such as region size, total flux, flux imbalance, flux emergence rate, Schrijver’s R-value, R^∗ (a modified version of R), and Falconer’s measurement of non-potentiality. A persistence algorithm is used to associate developed active regions with emerging flux regions in previous measurements, and to track regions beyond the limb through multiple solar rotations. We find that the total number and area of magnetic regions on disk vary with the sunspot cycle. While sunspot numbers are a proxy to the solar magnetic field, SMART offers a direct diagnostic of the surface magnetic field and its variation over timescale of hours to years. SMART will form the basis of the active region extraction and tracking algorithm for the Heliophysics Integrated Observatory (HELIO).     

Ionosphere-plasmasphere electron fluxes at middle latitudes obtained from whistlers

985 whistlers observed between 1970 and 1975 in Hungary have been processed for equatorial plasmaspheric electron density and tube electron content above 1000 km (N_T). The hourly median value of N_T exhibits a diurnal variation with an amplitude of 1×10¹³ electrons/cm²-tube. 75 per cent of the electron flux values obtained from the time variation of N_T are lower than 6×10⁸ el cm^?2s^?1, while in some cases the fluxes reach a value as high as 3×10⁹ el cm^?2s^?1. Between 17 and 04 LT the dominant flux direction is toward the ionosphere. The data also indicate that the day to day filling of the plasmasphere after magnetic disturbances continues through several days without exhibiting saturation, with higher filling rates for lower values of average K_p.     

Actors of the main activity in large complex centres during the 23 solar cycle maximum

During the maximum of Solar Cycle 23, large active regions had a long life, spanning several solar rotations, and produced large numbers of X-class flares and CMEs, some of them associated to magnetic clouds (MCs). This is the case for the Halloween active regions in 2003. The most geoeffective MC of the cycle (Dst = −457) had its source during the disk passage of one of these active regions (NOAA 10501) on 18 November 2003. Such an activity was presumably due to continuous emerging magnetic flux that was observed during this passage. Moreover, the region exhibited a complex topology with multiple domains of different magnetic helicities. The complexity was observed to reach such unprecedented levels that a detailed multi-wavelength analysis is necessary to precisely identify the solar sources of CMEs and MCs. Magnetic clouds are identified using in situ measurements and interplanetary scintillation (IPS) data. Results from these two different sets of data are also compared.     

Spherical accretion of massive black holes: A model for galactic nuclei

The possibility of explaining the continuous emission of active galactic nuclei in the frame of a model of spherical accretion onto a massive black hole is discussed. Cool inhomogeneities (T 10⁴°K) within the accretion flow could be responsible for the broad line emission if half of the accreting matter is in the dense phase. A crucial test of this hypothesis is the expected correlation between the ratio of the luminosity in lines to the total luminosity and the hardness of the continuous spectrum.     

Motion of the HXR sources in solar flares: Yohkoh images and statistics

Using the Yohkoh Hard X-Ray Telescope (HXT) data, we have examined motions of the hard X-ray (HXR) sources during 72 solar flares occurred from 1991 September to 2001 December. In these flares, we have found 198 intense sources that are presumably the chromospheric footpoints (FPs) of flare loops. The average velocity V and the velocity dispersion σ were determined by a linear regression for these sources. For 80% of them, the ratio of V to 3σ is larger than 1, strongly suggesting that the regular motions of the HXR sources dominate their chaotic motions.For 43 of 72 flares, coalignment of the HXT images with the photospheric magnetograms allows us to consider the HXR sources located on the both sides of the photospheric neutral line (NL) as the FP sources, and to distinguish between three main types of the FP motions. The type I is the motions of the HXR sources preferentially away from and nearly perpendicular to the NL. Less than 5% of the flares show this pattern of motion. In the type II, the sources move mainly along the NL in anti-parallel directions. Such motions have been found in 26% of flares. The type III involves a similar pattern of motions as the type II but all the HXR sources move in the same direction along the NL. Flares of this type constitute 30% of the flares. About 19% of flares can be described as a combination of these basic types. The remaining 20% of flares seem to be more complicated or less regular in the motion scale under consideration. An interpretation of results is suggested.     

Particle acceleration and gamma rays in solar flares: Recent observations and new modeling

Experiments on SMM, GAMMA, Yohkoh, GRANAT, Compton GRO, INTEGRAL, RHESSI and CORONAS-F satellites over the past three decades have provided copious data for fundamental research relating to particle acceleration, transport and energetics of flares and to the ambient abundance of the solar corona, chromosphere and photosphere. We summarize main results of solar gamma-astronomy (including some results of several joint Russian–Chinese projects) and try to appraise critically a real contribution of those results into modern understanding of solar flares, particle acceleration at the Sun and some properties of the solar atmosphere. Recent findings based on the RHESSI, INTEGRAL and CORONAS-F measurements (source locations, spectrum peculiarities, ³He abundance etc.) are especially discussed. Some unusual features of extreme solar events (e.g., 28 October 2003 and 20 January 2005) have been found in gamma-ray production and generation of relativistic particles (solar cosmic rays, or SCR). A number of different plausible assumptions are considered concerning the details of underlying physical processes during large flares: (1) existence of a steeper distribution of surrounding medium density as compared to a standard astrophysical model (HSRA) for the solar atmosphere; (2) enhanced content of the ³He isotope; (3) formation of magnetic trap with specific properties; (4) prevailing non-uniform (e.g., fan-like) velocity (angular) distributions of secondary neutrons, etc. It is emphasized that real progress in this field may be achieved only by combination of gamma-ray data in different energy ranges with multi-wave and energetic particle observations during the same event. We especially note several promising lines for the further studies: (1) resonant acceleration of the ³He ions in the corona; (2) timing of the flare evolution by gamma-ray fluxes in energy range above 90 MeV; (3) separation of gamma-ray fluxes from different sources at/near the Sun (e.g., different acceleration sources/episodes during the same flare, contribution of energetic particles accelerated by the CME-driven shocks etc.); (4) asymmetric magnetic geometry and new magnetic topology models of the near-limb flares; (5) modeling of self-consistent time scenario of the event.     

Evolution of the chromospheric and coronal activity of intermediate mass stars

Recent ultraviolet and X-ray observations pertaining to the outer atmospheric structure of intermediate mass (4–6 M₀) stars and the evolution of their structure are presented. A distance-limited (d ≤ 200 pc) IUE ultraviolet survey of early K bright giants shows that C IV emission commonly is present. These stars are almost evenly split between stars showing hybrid-chromospheric and coronal outer atmospheric structures. EXOSAT observations have been obtained for three hybrid stars, of which only α TrA, the nearest, is detected. The temperature of the emitting plasma is likely to be ∼10⁶K. Observations of six K II stars made with the Einstein satellite show no detections. The general conclusion from the available X-ray data is that early K bright giants are not strong X-ray sources.     

The homologous flare sites and the general solar activity

The homologous flares observed in the same region of a spotgroup testify the existence and the duration of a permanent instability. However, they also attest that the general magnetic configuration is not destroyed by these flares and that it changes $\text{slowly}$ up to the death of the site.The study of every flaring sites where more than ten flares occur has been performed in Meudon for the 1974–1980 period.One hundred and sixty-six sites have been analysed from the rotation where the A.R. is observed up to five rotations ahead. The basis of the study are the “Synoptic Maps”. A relation is found between the presence of crossing of “filament-phantom” corridors and the location of the homologous flare sites.¹     

A global weighted mean temperature model based on empirical orthogonal function analysis

A global empirical orthogonal function (EOF) model of the tropospheric weighted mean temperature called GEOFM_Tm was developed using high-precision Global Geodetic Observing System (GGOS) Atmosphere T_m data during the years 2008–2014. Due to the quick convergence of EOF decomposition, it is possible to use the first four EOF series, which consists base functions U_k and associated coefficients P_k, to represent 99.99% of the overall variance of the original data sets and its spatial-temporal variations. Results show that U₁ displays a prominent latitude distribution profile with positive peaks located at low latitude region. U₂ manifests an asymmetric pattern that positive values occurred over 30° in the Northern Hemisphere, and negative values were observed at other regions. U₃ and U₄ displayed significant anomalies in Tibet and North America, respectively. Annual variation is the major component of the first and second associated coefficients P₁ and P₂, whereas P₃ and P₄ mainly reflects both annual and semi-annual variation components. Furthermore, the performance of constructed GEOFM_Tm was validated by comparison with GTm_III and GTm_N with different kinds of data including GGOS Atmosphere T_m data in 2015 and radiosonde data from Integrated Global Radiosonde Archive (IGRA) in 2014. Generally speaking, GEOFM_Tm can achieve the same accuracy and reliability as GTm_III and GTm_N models in a global scale, even has improved in the Antarctic and Greenland regions. The MAE and RMS of GEOFM_Tm tend to be 2.49?K and 3.14?K with respect to GGOS T_m data, respectively; and 3.38?K and 4.23?K with respect to IGRA sounding data, respectively. In addition, those three models have higher precision at low latitude than middle and high latitude regions. The magnitude of T_m remains at the range of 220–300?K, presented a high correlation with geographic latitude. In the Northern Hemisphere, there was a significant enhancement at high latitude region reaching 270?K during summer. GEOFM_Tm is capable to represent the spatiotemporal variations of T_m, with the high accuracy and reliability in a global scale, therefore, will be of great significance to the real-time GNSS water vapor inversion and climate studies.     

Consecutive homologous flares and their relation to sunspot motions

The large sunspot group in Hale region 17098 was in the decaying phase of its development when a new flux emerged in its middle part on 3 September 1980. This region displayed chromospheric activity all that day. By the next day the spot of highest velocity (0.37 km s^?1) formed a delta-configuration with one of the spots of following polarity of the old group. The centre of the observed flares was not in the vicinity of this spot moving parallel to the magnetic zero-line, it was in the western part of the group, where two spots were moving nearly perpendicularly to the magnetic zero-line (v=0.09 km s^?1), and deformed the border of a gulf of opposite polarity. With the changing configuration the form of the observed flares also changed.