Stability of prominences exposing helical-like patterns

The internal structure of prominences appearing as twisted tubes was studied. The sample embraced 15 stable and 13 eruptive prominences, exposing patterns which possibly reflect a helical configuration. The equivalent pitch angles () of twisted fine structure features were measured. In some cases the evolution of the internal structure was followed and 49 independent measurements of the parameter were performed in total. The results are presented in the plane relating the parameter and the normalized prominence height. The eruptive prominences occupy the region characterized by > 50° and h > 0.8d, where h and d are the prominence height and the footpoint half-separation, respectively. All prominences characterized by h < 0.6d or by < 35° were stable. Such a result is in good agreement with an order of magnitude treatment of the forces acting in a curved magnetic tube, anchored at both ends in the photosphere.     

Spotless flares and the associated radio continuum emission

We studied 24 spotless flares of Ha importance 1 which occurred during the 21st cycle of solar activity. The spotless flares could be grouped in three categories according to their location and time history of the associated active region. Our association of the flares with radio events was based on relative timing and on the flare importances. Weak microwave gradual rise and fall events were frequently recorded during the occurrence of the spotless flares. A few flares from our sample could be associated with impulsive and complex microwave bursts. Only in one case an association of a spotless flare with a significant metric type II/IV event seems to be justified.Proceedings of the Second CESRA Workshop on Particle Acceleration and Trapping in Solar Flares, held at Aubigny-sur-Nère (France), 23–26 June, 1986.     

The observation of intrinsically different emergences for large and small active regions

The analysis of high-resolution H and white-light observations on the emergence of 73 active regions shows an intrinsically different behaviour for both the large and small ones. The small active regions (magnetic flux as 5 × 10²¹ Mx) display circular structures of supergranular size with pores only at the borders, whereas the large active regions show elongated structures with pores which develop at the center and later migrate towards the extremes. These observations are used to suggest two different models for the emergence of these two kinds of active regions: the small ones are produced by the superficial convective concentration of loosely packed dux and the large ones are the result of tightly wound flux ropes.     

Definition of the large-scale extinction — A new solution of the central void phenomenon

The Estonian School results (Jõeveeret al., 1977) concerning the galaxy cell structure were partly interpreted in the spirit of Zwicky's idea on intergalactic dust, although it remained a speculation. The same view was proposed also by Rudnicki to explain the evident deficit of galaxies in the central region (Central Void) of the Jagellonian field. (Ziba (1974) tried to explain the effect of the central void in terms of an interstellar obscuration.) This explanation of the central void (CV) in terms of a possible intergalactic dust was opened up again inNuovo Cimento, 1984 and 1985; and its merits considered by Rudnickiet al. inComments on Astrophysics, 1989. Now we present a new solution of the problem of the CV mystery.     

A simple population synthesis model for the continuum of the Seyfert type-2 galaxy Mk 348

The spectral energy distribution of the Seyfert type-2 galaxy Mk 348 is analyzed based on IUE observations and published data. It is found that most of the optical and near-IR flux comes from the underlying galaxy bulge population. The rest of the emission can be fitted by a power law of the formF _v v ^– with =0.6. In order to explain the X-ray emission this power law requires either a change of slope or a cutoff before 2 keV. The possibility that the emission originates in a young star cluster is discussed and a simple population synthesis model for the continuum of the galaxy is presented.     

Certain cosmological models and a new principle of equivalence

In this paper we prove an equivalence of velocity and Bellert's dilatation of metric. It is the kind of principle such as the equality of gravitational and inertial masses, noted by Newton, or equivalence of acceleration and space curvature, proved by Einstein. Our equivalence can be a foundation of a new theory, as it was in the two mentioned cases.The result is presented in two ways. One of these is a comparison of cosmological theories; and a dependence between the most important cosmological models is obtained. In this paper one of the results from the previous paper of the author (Rydzyska, 1989) is corrected.     

Flood hazards at ford stream crossings on ephemeral channels (south‐east coast of Spain)

Most road‐stream crossings over ephemeral channels are vulnerable to extreme hydrologic events. Ford stream crossings (FSCs) are usually dangerous for the road traffic during periods of high flow, in particular under flash flood conditions. The present paper analyzes the flood hazards on the Mediterranean coast in the Region of Murcia (south‐east Spain), affecting this type of road‐stream crossing over dry channels, according to hydraulic variables and bedload transport rates estimated for discharges at bankfull and flood‐prone stages. Under such conditions, the safety of people and vehicles was obtained using numerical models, developed by previous researchers; in particular, water levels and flow velocities across ford reaches were compared with different trend curves between water depths and corresponding critical velocities for children and adults, and for various prototype vehicles. Specifically, two approaches to assess this type of hazards were proposed: a specific Hydraulic Hazard Index and an algorithm for estimating the flood hazard from criteria of bed stability and bedload transport capacity (Flood Hazard at Fords, FHF). In addition, different exposure levels were established, using a Flood Vulnerability Index, based on the FHF, the road category, and the annual average daily traffic. The FHF model gave the best results with regard to the magnitude of the damage observed in recent flash floods for flow stages similar to those simulated. According to the danger thresholds established for this index, half‐bankfull flows represent here a high risk: 27.3% of FSCs for mini‐cars and 18.2% for large cars. At bankfull, the FHF exhibits very high values for mini‐cars (77.3% of FSCs) and for large passenger vehicles (50% of FSCs), while at the floodprone stage, extreme FHF values are reached for all kinds of vehicles at most of the ford crossings.     

Lithological control of land subsidence induced by groundwater withdrawal in new urban AREAS (Granada Basin,SE Spain). Multiband DInSAR monitoring

Ground subsidence in the southeastern border of the Granada Basin (SE Spain) has been studied using remote sensing techniques. Over the last decades, the region has experienced a huge urban expansion, which has caused a substantial increase in water supply requirements. Water needs are exclusively met by groundwater by means of numerous pumping wells, which exploit a confined detrital aquifer of alluvial fan deposits with a heterogeneous facies distribution. A general piezometric level decline (up to 50 m) has been recorded in the aquifer during the past 30 years that has induced the generation of a subsiding area with oval shape oriented WNW‐ESE just where the new urban areas and pumping wells are located. Subsidence has been monitored by exploiting synthetic aperture radar (SAR) images from ENVISAT (2003–2009) and Cosmo‐SkyMed (2011–2014). A new approach, which combines A‐DInSAR and small‐area persistent scatterer interferometry (PSI) analysis, has been applied obtaining a good accuracy regarding temporal and spatial dimension of the subsidence. ENVISAT data (2003–2009) reveal subsidence rates up to 10–15 mm/year, and Cosmo‐SkyMed (2011–2014) values slightly lower; up to 10 mm/year. Temporal variations in the subsidence velocity are in accordance with the rainfall pattern and piezometric fluctuations in the aquifer. The sector with highest rates of subsidence does not correspond to the area with more intense groundwater exploitation but to the area with greater presence of clays in the confining layer of the aquifer. There is a clear lithological control in the spatial distribution of the ground subsidence. This work integrates detailed geological and hydrogeological data with differential SAR interferometry monitoring with the aim to better understand subsidence processes in detrital aquifers with small‐scale heterogeneity. Copyright © 2016 John Wiley & Sons, Ltd.