Repeated Flaring from Loop–Loop Interaction

A series of solar flares was observed near the same location in NOAA active region 8996 on 18–20 May 2000. A detailed analysis of one of these flares is presented where the emitting structures in soft and hard X-rays, EUV, H, and radio at centimeter wavelengths are compared. Hard X-rays and radio emission were observed at two separate loop footpoints, while soft X-rays and EUV emission were observed mainly above the nearby positive polarity region. The flare was confined although the observed type III bursts at the time of the flare maximum indicate that some field lines were open to the corona. No flux emergence was evident but moving magnetic features were observed around the sunspot region and within the positive polarity (plage) region. We suggest that the flaring was due to loop–loop interactions over the positive polarity region, where accelerated electrons gained access to the two separate loop systems. The repeated radio flaring at the footpoint of one loop was visible because of the strong magnetic fields near the large sunspot region while at the footpoint of the other loop the electrons could precipitate and emit in hard X-rays. The simultaneous emission and fluctuations in radio and X-rays – in two different loop ends – further support the idea of a single acceleration site at the loop intersection.     

Observation and Research on the Twisting Characteristics of Flare Loop System

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Orbital Evolution of the Sun–Jupiter–Saturn–Uranus–Neptune Four-Planet System on Long-Time Scales

The four-planet problem is solved by constructing an averaged semi-analytical theory of secondorder motion by planetary masses. A discussion is given of the results obtained by numerical integration of the averaged equations of motion for the Sun–Jupiter–Saturn–Uranus–Neptune system over a time interval of 10 Gyr. The integration is based on high-order Runge–Kutta and Everhart methods. The motion of the planets is almost periodic in nature. The eccentricities and inclinations of the planetary orbits remain small. Short-period perturbations remain small over the entire interval of integration. Conclusions are drawn about the resonant properties of the motion. Estimates are given for the accuracy of the numerical integration.     

ION–Neutral Collisions Effect on MHD Surface Waves

The effect of ion–neutral collisions on the propagation of MHD waves and surface waves at a single magnetic interface is investigated. The dispersion equations for MHD waves in a partially ionized medium are derived. There are three damped propagating modes in a uniform unbounded medium: an Alfvén mode, and fast and slow modes. The damping of waves depends on both the collisional frequency and the ionization fraction. Wave damping increases as ionization fraction decreases. Surface waves are discussed in three cases: (a) the incompressible limit, (b) the low plasma, and (c) for parallel propagation. The incompressible limit leads to Alfvén surface waves in a partially ionized medium and the dispersion characteristics are similar to those obtained by Uberoi and Datta. In the low plasma of the Earth's auroral F region there are two damped propagating magnetoacoustic surface waves for =/3. There is only one damped surface mode for =/2, but no surface wave is able to propagate for =0°. For the case of parallel propagation (=0°) the results obtained in the absence of ion-neutral collisions are consistent with the results of Jain and Roberts. It is found that a three-mode structure of damped propagating waves occurs owing to ion–neutral collisions for a comparatively high ionization fraction. For the case of the solar photosphere, where the ionization fraction is low, two weakly damped surface waves are found, though the damping is almost negligible. The pattern of propagation is similar to that found in the case discussed by Jain and Roberts, but the wave speeds are lower due to ion–neutral collisions. The strong collisions tie the ion–neutral species together and reduce the damping.     

Reduced sulfur–carbon–water systems on Mars may yield shallow methane hydrate reservoirs

Methane clathrate hydrate reservoirs capped by overlying permafrost have been proposed as potential sources of atmospheric methane plumes on Mars. However, the surface flux of methane from hydrate dissociation is limited by the diffusion rate of methane through the overlying ice. Assuming hydrates underlay the entire plume footprint, the maximum diffusion path length is expected to be less than 15 m, depths too shallow to stabilize pure methane hydrates under Mars geothermal and lithostatic conditions at low to mid latitudes. Therefore, pure methane hydrates confined within permafrost could not produce methane surface fluxes of the magnitude observed near the equator. However, the addition of 10% H₂S, a secondary gas commonly associated with methane production on Earth, expands the hydrate stability field, with clathrates expected within 10 m of the surface at the equator and at depths less than 1 m at higher latitudes. This indicates that H₂S would also be expected to be released as well as methane if the plumes have a confined hydrate reservoir source.     

A note on algebraic potentials and Morales–Ramis theory

We present various properties of algebraic potentials, and then prove that some Morales–Ramis theorems readily apply for such potentials even if they are not in general meromorphic potentials. This allows in particular to precise some non-integrability proofs in Celestial Mechanics, where the mutual distances between the bodies appear in the potential, and thus making this analysis unavoidable.     

Spectral Flattening During Solar Radio Bursts At Cm–mm Wavelengths and the Dynamics of Energetic Electrons in a Flare Loop

Until recently, most of the information on particle acceleration processes in solar flares has been obtained from hard X-ray and cm-microwave observations. As a rule they provide information on electrons with energies below 300 keV. During recent years it became possible to measure the gamma-ray and millimeter radio emission with improved sensitivities. These spectral ranges carry information on much higher energy electrons. We studied the temporal and spectral behaviour of the radio burst emission at centimeter-millimeter wavelengths (8–50 GHz) by using the data from the patrol instruments of IAP (Bern University). We have analyzed more than 20 impulsive and long duration radio bursts (of 10 s to several 100 s duration).The main finding of the data analysis is the presence of spectral flattening throughout the bursts, which occurs always during the decay phase of flux peaks, at frequencies well above the spectral peak frequency and independently of burst duration. Furthermore, for some of the bursts, the flux maxima at higher frequencies are delayed. These findings can serve as evidence of the hardening of the electron spectrum at energies above some hundreds of keV during the decay phase of cm–mm flux peaks. As a most likely reason for such a hardening we consider Coulomb collisions of energetic electrons continuously injected and trapped in a flaring loop.     

Geodynamic observations on the quasar VLBI network in 2009–2011

The hardware and software upgrades to the Quasar VLBI network have allowed one to increase the measurement accuracy of the Earth orientation parameters (EOPs) and to improve the quality of geodynamic observations. At present, the observations are performed within two national programs: 24-h sessions on three radio telescopes of the network to determine all five EOPs (the Ru-E program) and 1-h sessions on the Zelenchukskaya-Badary and Svetloe-Badary baselines (the Ru-U program) for a prompt determination of the Universal Time. The results of processing the observations from January 2009 to November 2011 are presented. The rms deviations of the EOPs obtained in the Ru-E program from the IERS 08 C04 series are 1 mas for the coordinates of the Earth??s pole, 0.38 mas for the coordinates of the celestial pole, and 34 ??s for the Universal Time. The rms deviations of the Universal Time obtained in the Ru-U program are 53 ??s.     

Pulsations of intermediate–mass stars on the asymptotic giant branch

Evolutionary tracks from the zero age main sequence to the asymptotic giant branch were computed for stars with initial masses 2 M _⊙ ≤ M _ZAMS ≤ 5 M _⊙ and metallicity Z = 0.02. Some models of evolutionary sequences were used as initial conditions for equations of radiation hydrodynamics and turbulent convection describing radial stellar pulsations. The early asymptotic giant branch stars are shown to pulsate in the fundamental mode with periods 30 day ? Π ? 400day. The rate of period change gradually increases as the star evolves but is too small to be detected (Π?/Π < 10^?5 yr^?1). Pulsation properties of thermally pulsing AGB stars are investigated on time intervals comprising 17 thermal pulses for evolutionary sequences with initial masses M _ZAMS = 2 M _⊙ and 3 M _⊙ and 6 thermal pulses for M _ZAMS = 4 M _⊙ and 5 M _⊙. Stars with initial masses M _ZAMS ≤ 3 M _⊙ pulsate either in the fundamental mode or in the first overtone, whereas more massive red giants (M _ZAMS ≥ 4 M _⊙) pulsate in the fundamental mode with periods Π ? 10³ day. Most rapid pulsation period change with rate ?0.02 yr^?1 ? Π?/Π ? ?0.01 yr^?1 occurs during decrease of the surface luminosity after the maximum of the luminosity in the helium shell source. The rate of subsequent increase of the period is Π?/Π ? 5 × 10^?3 yr^?1.     

Formation Mechanism of Soft X-Ray Transient Trans-Equatorial Loop System

The Soft X-ray Telescope (SXT) onboard Yohkoh often observed large-scale coronal loops connecting two active regions situated in opposite hemispheres. These are the trans-equatorial loop systems (TLSs). The formation mechanism of TLSs is not yet known. We analyzed a TLS observed simultaneously with Yohkoh/SXT and a coronagraph (SOHO/LASCO-C1). SOHO/LASCO-C1 observed loop expansion and eruption at the west solar limb. Yohkoh/SXT observed a rising motion (chromospheric evaporation) of hot and dense plasmas from the active regions located at the footpoints of the loop. Important results of our analyses are that (1) the loop eruption and the rising motion of the plasmas were simultaneous, (2) the TLS had a cusp-like appearance, and (3) the highest temperature region of the TLS was located above the bright loop seen in soft X rays. These observational results (loop expansion, eruption, and chromospheric evaporation) suggest that this bright (high-density) TLS was created by the same mechanism by which a solar flare occurs, namely, magnetic reconnection. In this paper, we propose a formation mechanism of the TLS that forms between two independent active regions.     

Tidal effects on the LAGEOS–LARES satellites and the LARASE program

The effects of solid and ocean tides have been computed on the right ascension of the ascending node of the two LAGEOS and LARES satellites and on the argument of pericenter of LAGEOS II. Their effects—together with the possible mis-modeling related to systematic errors in the estimate of the tidal coefficients, especially in the case of ocean tides—are quite important to be well established for the key role of the LAGEOS satellites, as well as of the newly LARES, in space geodesy and geophysics as well as in fundamental physics measurements. In the case of the measurement of the Lense–Thirring effect, the mis-modeling of long-period tides may mimic a secular effect on the cited orbital elements, thus producing a degradation in the measurement of the relativistic precession. A suitable combination of the orbital elements of the three satellites can help in avoiding the effects of the long-period tides of degree \(\ell =2\) (as for the Lunar solid tides with periods of 18.6 and 9.3 years) and \(\ell =4\), but other long-period tides, as the ocean \(K_1\) tide, which has the same periodicities of the right ascension of the ascending node \(\varOmega \) of the satellites, may strongly influence the measurement, especially if it is performed over a relatively short time span. These results are particularly important in the case of LARES, since they are new and because of the role that the orbit of LARES, and especially of its ascending node right ascension, will have in a new measurement of the Lense–Thirring effect by the joint analysis of its orbit with that of the two LAGEOS.     

Excitation of Kinetic Alfvén Waves in a Flaring Loop

At the onset of a solar flare, initiated by magnetic reconnection high in the corona, reconnection outflow sets up warm proton beams (PBs), streaming down along just-reconnected field lines through steady underlying plasma. Incorporating this scenario, we study excitation of kinetic Alfvén waves (KAWs) by PBs, keeping the effects of a beam-induced electric field and thermal effects. Taking into account the high growth rate (105 s–1), short relaxation distance (106 cm), and energy flux partition between the waves and the beam after relaxation (PKAW/PPB1), we conclude that PB-driven KAW instability is an efficient energy conversion mechanism in flaring loops. The quasilinear spectral energy concentration at the largest wavenumbers indicates the possibility of nonlinear spectral modification. We suggest that the resulting turbulence of KAWs plays an important role in the flare plasma energization.     

The Temperature and Density Structure of an Hα Flaring Loop

We develop a simple method to deduce the temperature and density in the loop of a limb flare from the spectral observations of two lines, H and Caii 8542 Å. We first build a grid of homogeneous slab models with various temperature and density values and compute the emergent line intensities, and then find the relevant model that can match the observed intensities. This is an approximate method because there are several other factors which can influence the line intensities. We apply this method to the limb flare of 11 November 1998 and deduce the values of temperature and hydrogen number density at different spatial points in the flaring loop, as well as their temporal variations. The loop contains relatively high density and possibly the loop top is slightly hotter and more condensed than the legs of the loop at the flare maximum time. A favorable scenario to produce this result is that magnetic reconnection occurs above the loop, and the reconnection outflow may heat and condense the plasma near the loop top.     

Compressibility Effect on the Rayleigh–Taylor Instability with Sheared Magnetic Fields

Solar Physics - We analyze the evolution of Fe xii coronal plasma upflows from the edges of ten active regions (ARs) as they cross the solar disk using the Hinode Extreme Ultraviolet Imaging...     

Effect of Moon perturbation on the energy curves and equilibrium points in the Sun–Earth–Moon system

In this paper, we have considered that the Moon motion around the Earth is a source of a perturbation for the infinitesimal body motion in the Sun–Earth system. The perturbation effect is analyzed by using the Sun–Earth–Moon bi–circular model (BCM). We have determined the effect of this perturbation on the Lagrangian points and zero velocity curves. We have obtained the motion of infinitesimal body in the neighborhood of the equivalent equilibria of the triangular equilibrium points. Moreover, to know the nature of the trajectory, we have estimated the first order Lyapunov characteristic exponents of the trajectory emanating from the vicinity of the triangular equilibrium point in the proposed system. It is noticed that due to the generated perturbation by the Moon motion, the results are affected significantly, and the Jacobian constant is fluctuated periodically as the Moon is moving around the Earth. Finally, we emphasize that this model could be applicable to send either satellite or telescope for deep space exploration.     

A Note on Second Species Solutions Generated from p–q Resonant Orbits

The first image under the flow of the restricted three-body problem of the p—q resonant strips — that appear in the study of the p—q resonant orbits — do not have, in general, intersection with the strip. In this paper we show some particular situations in which the above intersections exist for some very simple p—q resonant orbits which, at the same time, are periodic second species solutions.This revised version was published online in October 2005 with corrections to the Cover Date.     

Dependence of Fanaroff–Riley break of radio galaxies on luminosity and redshift

We investigate the dependence of the Fanaroff–Riley (FR) 1/2 dichotomy of radio galaxies on their luminosities and redshifts. Because of a very strong redshift-luminosity correlation (Malmquist bias) in a flux-limited sample, any redshift-dependent effect could appear as a luminosity-related effect and vice versa. A question could then arise—do all the morphological differences seen in the two classes (FR 1 and 2 types) of sources, usually attributed to the differences in their luminosities, could as well be primarily a redshift-dependent effect? A sharp break in luminosity, seen among the two classes, could after all reflect a sharp redshift dependence due to a rather critical ambient density value at some cosmic epoch. A doubt on these lines does not seem to have been raised in past and things have never been examined with this particular aspect in mind. We want to ascertain the customary prevalent view in the literature that the systematic differences in the two broad morphology types of FR 1 and 2 radio galaxies are indeed due to the differences in their luminosities, and not due to a change in redshift. Here we investigate the dependence of FR 1/2 dichotomy of radio galaxies on luminosity and redshift by using the 3CR sample, where the FR 1/2 dichotomy was first seen, supplemented by data from an additional sample (MRC), that goes about a factor of 5 or more deeper in flux-density than the original 3CR sample. This lets us compare sources with similar luminosities but at different redshifts as well as examine sources at similar redshifts but with different luminosities, thereby allowing us a successful separation of the otherwise two intricately entangled effects. We find that the morphology type is not directly related to redshift and the break between the two types of morphologies seems to depend only upon the radio luminosity.     

Some comments on the east-west solar flare distribution during the 1976–1985 period

We present the results of an analysis of the east-west asymmetry in the solar flare distribution, observed during the years from 1976 to 1985. We conclude that flare events, all type of H flares, are not uniformly spread in heliolongitude over the solar disc when considering events with heliolongitudes greater than 60°, or even closer to central meridian for certain periods. This lack of homogeneity, however, does not have an influence on the definition of east-west asymmetries. Simple random distribution of flares over the solar disc can not account for the asymmetries found, but they can be explained in terms of the transit of active regions in front of the observer's position. Nonetheless, this is not the case for the distribution of flares equal or more intense than importance 1F observed during 1979.