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Experimental Astronomy - At peak, long-duration gamma-ray bursts are the most luminous sources of electromagnetic radiation known. Since their progenitors are massive stars, they provide a tracer...     

Atmospheric processes responsible for generation of the 2008 Boothbay meteotsunami

We investigated the atmospheric processes and physics that were active during a tsunami-like event hitting Boothbay Harbor area (Maine, USA) on 28 October 2008. The data collected by tide gauges, ground and sounding stations and meteo–ocean buoys in the area were analyzed, together with satellite and radar images. The atmospheric processes were reproduced by the weather research and forecasting model, verified by in situ and remote sensing data. A cold front moved over the area at the time of the event, with embedded convective clouds detected by satellite and radar data and the internal gravity waves (IGWs) detected by radar and reproduced by the model at the rear of the frontal precipitation band. According to the model, the IGWs that passed over Boothbay Harbor generated strong ground air-pressure oscillations reaching 2.5 hPa/3 min. The IGWs were ducted towards the coast without significant dissipation, propagating in a stable near-surface layer capped by an instability at approximately 3.5 km height and satisfying all conditions for their maintenance over larger areas. The intensity, speed and direction of the IGWs were favourable for generation of a meteotsunami wave along the Gulf of Maine shelf. Operational observation systems were not capable of sufficiently capturing the ground disturbance due to a too coarse sampling rate, while the numerical model was found to be a useful tool in eventual future detection and warning systems.     

Constraints on superdense preon stars andtheir formation scenarios

We address in this work the general features of a possible compact stars composed by elementary fermions beyond the quark level. The locus of these hypothetic objects in the mass-radius plane is constructed for the maximum mass (minimum radius) of the sequence of models in terms of a compositeness scale only, and in fact this approach applies for any composite model postulating fermions at or beyond the preon level. We point out a constraint on the preon mass arising from the applicability of the General Relativity structure equations, leading to the questioning of the hypothesis of light preons if the preon scale is high, provided classical compact objects are enforced. Some remarks on the existence of superdense stars of astrophysical and primordial origin are made and discussed.      

Fast Radio Bursts as Crustal Dynamical Events Induced by Magnetic Field Evolution in Young Magnetars

We revisit in this work a model for repeating Fast Radio Bursts based of the release of energy provoked by the magnetic field dynamics affecting a magnetar's cr...     

Pion condensates in the Vela pulsar and the energetics of its glitch events

Pion condensates can help to explain a variety of physical properties owned by pulsars if they are present in their interiors. It has been noted that they offer, for example, an attractive alternative to understand glitches by improving former core-quake models. We discuss this scenario and show in this work some constraints on the properties of this type of matter arise from X-ray observations of the Vela pulsar performed by theEinstein Observatory. Further information on this subject will be soon obtained from improved facilities and we expect them to give further constraints to the viability of those models.     

Droughts in the desert: Medieval Warm Period associated with coarse sediment layers in the Gulf of Aqaba-Eilat,Red Sea

Prolonged droughts can cause environmental stress, even in ecosystems that are already adapted to dry conditions. In these areas life greatly depends on rare, sporadic rainfall events that can produce flash floods. Today, urban expansion, population growth and development are occurring worldwide, including along hyperarid coastlines, an ecological zone on the extreme of habitability. In such places, the absence of the already limited precipitation can lead to long-lasting damage, and recognizing drought conditions in the past is useful for planning. Recognizing droughts, however, is challenging because they are not known as depositional events, and therefore may be under-recognized in the sedimentological record. Floods in these hyperarid deserts carry eroded sediments and deposit them in either terrestrial or marine terminal basins. In the hyperarid (ca 30 mm rain per year) desert surrounding the northern Gulf of Aqaba-Eilat some flash floods reach the sea and deposit alluvial sediments (mostly silt and clay) on the shelf. Following a recent 17 year drought period (1995 to 2012) a coarser surface layer was recognized offshore the outlet of an ephemeral river, despite the lack of incoming flood material. This coarsened layer resulted from a prolonged period wherein mixing and winnowing of fine particles at the surface was not interrupted by recurrent flash floods. In the bottom of two sediment cores collected from the same shelf, a similarly coarsened layer was observed. The terminal level of this deep coarse layer was dated to ca 660 yr bp , corresponding with the end of the Medieval Warm Period (ca 1350 ad ). These findings suggest that the medieval anomaly resulted in a prolonged drought period in this already arid region. These results present a new interpretation of grain-size distribution records that provides a means to reconstruct drought histories in hyperarid regions globally.     

Recent rheologic processes on dark polar dunes of Mars: Driven by interfacial water?

In springtime on HiRISE images of the Southern polar terrain of Mars flow-like or rheologic features were observed. Their dark color is interpreted as partly defrosted surface where the temperature is too high for CO₂ but low enough for H₂O ice to be present there. These branching streaks grow in size and can move by an average velocity of up to about 1 m/day and could terminate in pond-like accumulation features. The phenomenon may be the result of interfacial water driven rheologic processes. Liquid interfacial water can in the presence of water ice exist well below the melting point of bulk water, by melting in course of interfacial attractive pressure by intermolecular forces (van der Waals forces e.g.), curvature of water film surfaces, and e.g. by macroscopic weight, acting upon ice. This melting phenomenon can be described in terms of “premelting of ice”. It is a challenging consequence, that liquid interfacial water unavoidably must in form of nanometric layers be present in water ice containing soil in the subsurface of Mars. It is the aim of this paper to study possible rheologic consequences in relation to observations, which seem to happen at sites of dark polar dunes on Mars at present. The model in this work assumes that interfacial water accumulates at the bottom of a translucent water-ice layer above a dark and insolated ground. This is warmed up towards the melting point of water. The evolving layer of liquid interfacial water between the covering ice sheet and the heated ground is assumed to drive downward directed flow-like features on slopes, and it can, at least partially, infiltrate (seep) into a porous ground. There, in at least temporarily cooler subsurface layers, the infiltrated liquid water refreezes and forms ice. The related stress built-up is shown to be sufficient to cause destructive erosive processes. The above-mentioned processes may cause change in the structure and thickness of the covering ice and/or may cause the movement of dune grains. All these processes may explain the observed springtime growing and downward extension of the slope streaks analyzed here.     

The Bag Tephra, a widespread tephrochronological marker in Middle Europe: chemical and mineralogical investigations

 The Bag Tephra is a widespread tephra layer interbedded in Quaternary loess deposits along the Danubian valley of Hungary and Slovakia. Its age is poorly defined between 788 and 380 ka B.P. The glass and mineral composition – micropumice clasts of phono-tephrite and blocky shards of tephri-phonolite associated with two kinds of clinopyroxene, fassaitic diopside, and salite – is very distinctive. This tephra could be used as a chronological marker, as soon as its age is refined. The probable origin is the middle Italian volcanic area. Received: 3 November 1998 / Accepted: 18 January 1999     

Numerical simulation of severe convective phenomena over Croatian and Hungarian territory

Squall lines and supercells cause severe weather and huge damages in the territory of Croatia and Hungary. These long living events can be recognised by radar very well, but the problem of early warning, especially successful numerical forecast of these phenomena, has not yet been solved in this region. Two case studies are presented here in which dynamical modelling approach gives promising results: a squall line preceding a cold front and a single supercell generated because of a prefrontal instability. The numerical simulation is performed using the PSU/NCAR meso-scale model MM5, with horizontal resolution of 3 km. Lateral boundary conditions are taken from the ECMWF model. The moist processes are resolved by Reisner mixed-phase explicit moisture scheme and for the radiation scheme a rapid radiative transfer model is applied. The analysis nudging technique is applied for the first two hours of the model run. The results of the simulation are very promising. The MM5 model reconstructed the appearance of the convective phenomena and showed the development of thunderstorm into the supercell phase. The model results give very detailed insight into wind changes showing the rotation of supercells, clearly distinguish warm core of the cell and give rather good precipitation estimate. The successful simulation of convective phenomena by a high-resolution MM5 model showed that even smaller scale conditions are contained in synoptic scale patterns, represented in this case by the ECMWF model.