A predator–prey model for moon-triggered clumping in Saturn’s rings

UVIS occultation data show clumping in Saturn’s F ring and at the B ring outer edge, indicating aggregation and disaggregation at these locations that are perturbed by Prometheus and by Mimas. The inferred timescales range from hours to months. Occultation profiles of the edge show wide variability, indicating perturbations by local mass aggregations. Structure near the B ring edge is seen in power spectral analysis at scales 200–2000 m. Similar structure is also seen at the strongest density waves, with significance increasing with resonance strength. For the B ring outer edge, the strongest structure is seen at longitudes 90° and 270° relative to Mimas. This indicates a direct relation between the moon and the ring clumping. We propose that the collective behavior of the ring particles resembles a predator–prey system: the mean aggregate size is the prey, which feeds the velocity dispersion; conversely, increasing dispersion breaks up the aggregates. Moons may trigger clumping by streamline crowding, which reduces the relative velocity, leading to more aggregation and more clumping. Disaggregation may follow from disruptive collisions or tidal shedding as the clumps stir the relative velocity. For realistic values of the parameters this yields a limit cycle behavior, as for the ecology of foxes and hares or the “boom-bust” economic cycle. Solving for the long-term behavior of this forced system gives a periodic response at the perturbing frequency, with a phase lag roughly consistent with the UVIS occultation measurements. We conclude that the agitation by the moons in the F ring and at the B ring outer edge drives aggregation and disaggregation in the forcing frame. This agitation of the ring material may also allow fortuitous formation of solid objects from the temporary clumps, via stochastic processes like compaction, adhesion, sintering or reorganization that drives the denser parts of the aggregate to the center or ejects the lighter elements. Any of these more persistent objects would then orbit at the Kepler rate. We would also expect the formation of clumps and some more permanent objects at the other perturbed regions in the rings… including satellite resonances, shepherded ring edges, and near embedded objects like Pan and Daphnis (where the aggregation/disaggregation cycles are forced similar to Prometheus forcing of the F ring).     

Classification of F ring features observed in Cassini UVIS occultations

The Cassini Ultraviolet Imaging Spectrograph (UVIS) has detected 27 statistically significant features in 101 occultations by Saturn’s F ring since July 2004. This work nearly doubles the number of features reported by Esposito et al. (Esposito, L.W. et al. [2008]. Icarus 194, 278–289). As the number of statistically significant features has grown, it has become useful to classify them for the purposes of cataloging. We define three classes: Moonlet, Icicle, and Core, which visually classify the shapes of features seen to date in the occultation profiles of Saturn’s F ring. Two features fall into the Moonlet class. Each is opaque in its occultation, which makes them candidates for solid objects. A majority of features are classified as Icicles, which partially block stellar signal for 22 m to just over 3.7 km along the radial expanse of the occultation. The density enhancements responsible for such signal attenuations are likely due to transient clumping of material, evidence that aggregations of material are ubiquitous in the F ring. Finally, the variety of core region shapes displays how even the general shape of the F ring is ever-changing. The core region of the F ring (typically ～10 km wide) usually has a smooth U-shape to it, but the core region takes the shape of Ws and Vs in some occultation profiles. Our lengthy observing campaign reveals that Icicles are likely transient clumps, moonlets are possible solid objects, and cores show the variety of F ring morphology. We suggest that icicles may evolve into moonlets, which are an order of magnitude less abundant.     

Factors that contributed to recent eutrophication of two Slovenian mountain lakes

Increased eutrophication was recently observed in the 5th (5J) and 6th (6J) Triglav Lakes, two remote Slovenian mountain lakes. Sediment phosphorus (P) pools were analysed and potential external P sources affecting the lakes (atmospheric deposition, terrestrial export and nearby hut) evaluated, to assess the effects of internal and external changes on the lakes. A sequential extraction procedure was used to quantify five P fractions from the sediments: adsorbed (NH₄Cl–P), redox-sensitive (BD–P), aluminium- (NaOH–P) and calcium- (HCl–P) bound, and refractory organic (Res–P) P. Total phosphorus (TP) contents in surface sediment of 5J and 6J were 1430 and 641 µg P g^?1 dry weight sediment (dw), respectively. TP varied with depth in 5J sediments, but displayed no discernible pattern, whereas it decreased steadily downcore in 6J. Contents of all P forms were distinctly higher in 5J than 6J, but their rank order and relative abundances were similar in the two lakes. Res–P was the most abundant P fraction, followed by HCl–P. Together, the two P forms accounted for nearly 80 and 90% of TP in 5J and 6J sediments, respectively. BD–P and NaOH–P were less abundant, with each fraction accounting for 3 to 9% of TP, whereas NH₄Cl–P was least abundant. Atmospheric deposition and terrestrial export were substantial sources of P for the lakes. Delivery of the former was estimated to be at least 7.5 mg P m^?2 yr^?1 and the latter around 20 mg P m^?2 yr^?1. We concluded that P was not retained in the catchment effectively, likely because of only slightly acidic soil pH (5.9), relatively low aluminium content and high organic matter content (53%) in soils, resulting in higher vulnerability of the studied lakes to eutrophication. The mountain hut could also be a significant source of P for the lakes. Each year, it could potentially contribute ~12 kg of soluble P to the environment, but the true impact of the hut on lake trophic status remains unclear.     

Morphometric and geological conditions for sediment accumulation in the Udava River,Outer Carpathians,Slovakia

The accumulation of sediment in river channels is a phenomenon that is not only influenced by the channel morphology, but also by the physical and geographical characteristics and the endogenous and exogenous processes taking place in the catchment. This paper presents an analysis of the impact the changes in lithological conditions have on the morphological and morphometric parameters of the Udava River channel and their relation to the channel accumulation forms representative of the river’s longitudinal profile as well as of its planform. Results document when accumulation forms occur and what is their spatial distribution within the longitudinal and cross-sectional river profiles. More resistant structures created sections with a lower degree of sedimentation, while in depression segments the degree of sedimentation was higher. With the increase in longitudinal slope, the impact of channel width on the average channel bar size increased. Also a difference in the accumulation was observed between the left and right bank which could be possibly explained by the impact of Coriolis force.     

Numerical Study of Winter Diurnal Convection Over the City of Krasnoyarsk: Effects of Non-freezing River,Undulating Fog and Steam Devils

We performed a numerical simulation of penetrative convection of an inversion-topped weakly stratified atmospheric boundary layer over urban terrain with a strong localized source of heat and moisture. With some simplifications, the case mimics the real environment of the Krasnoyarsk region in Russia where the non-freezing river Yenisei acts as a thermal and humidity source during winter, generating an undulating fog pattern along the river accompanied with scattered ‘steam devils’. An idealized full diurnal cycle was simulated using an unsteady Reynolds-averaged Navier–Stokes (RANS) three-equation algebraic flux model and the novel buoyancy-accounting functions for treating the ground boundary conditions. The results show a significant effect of the river on the net temperature and moisture distribution. The localized heat and moisture source leads to strong horizontal convection and marked non-uniformity of humidity concentration in the air. An interplay of several distinct large-scale vortex systems leads to a wavy pattern of moisture plumes over the river. The simulations deal with rare natural phenomena and show the capability of the RANS turbulence closure to capture the main features of flow and scalar fields on an affordable, relatively coarse, computational grid.     

Flares in Sigmoidal Coronal Structures – a Case Study

We analyze radio observations, magnetograms and extrapolated field line maps, Hα filtergrams, and X-ray observations of two flare events (6 February 1992 in AR 7042 and 25 October 1994 in AR 7792) and study properties, evolution and energy release signatures of sigmoidal loop systems. During both events, the loop configuration seen in soft X-ray (SXR) images changes from a preflare sigmoidal shape to a relaxed post-flare loop system. The underlying magnetic field system consists of a quadrupolar configuration formed by a sheared arcade core and a remote field concentration. We demonstrate two possibilities: a sigmoidal SXR pattern can be due to a single continuous flux tube (the 1992 event). Alternatively, it can be due to a set of independent loops appearing like a sigmoid (the 1994 event). In both cases, the preflare and post-flare loops can be well reproduced by a linear force-free field and potential field, respectively, computed using preflare magnetograms. We find that thermal and non-thermal flare energy release indicators of both events become remarkably similar after applying spatial and temporal scale transformations. Using the spatial scaling between both events we estimated that the non-thermal energy release in the second event liberated about 1.7 times more energy per unit volume. A two-and-a-half times faster evolution indicates that the rate of the energy release per unit volume is more than four times higher in this event. A coronal type II burst reveals ignition and propagation of a coronal shock wave. In contrast, the first event, which was larger and released about a 10 times more energy during the non-thermal phase, was associated with a CME, but no type II burst was recorded. During both events, in addition to the two-ribbon flare process an interaction was observed between the flaring arcade and an emerging magnetic flux region of opposite polarity next to the dominant leading sunspot. The arcade flare seems to stimulate the reconnection process in an `emerging flux-type' configuration, which significantly contributes to the energy release. This regime is characterized by the quasiperiodic injection of electron beams into the surrounding extended field line systems. The repeated beam injections excite pulsating broadband radio emission in the decimetric-metric wavelength range. Each radio pulse is due to a new electron beam injection. The pulsation period (seconds) reflects the spatial scale of the emerging flux-type field configuration. Since broadband decimetric-metric radio pulsations are a frequent radio flare phenomenon, we speculate that opposite-polarity small-scale flux intrusions located in the vicinity of strong field regions may be an essential component of the energy release process in dynamic flares.     

Estimation of Mining Tremor Occurrence by Using Neural Networks

—Changes of the primary strain-stress state (caused by interaction between natural conditions and mining activity) can result, under special circumstances, to the origin of seismic induced events. The question of induced seismic activity prediction was treated as a problem of time series extrapolation of maximum cumulative amplitudes and numbers of seismic events recorded per day. The treatment was carried out by means of Multilayered Perceptron Neural Networks (MLP NN). The application to mining tremor prediction has been tested and methodological conditions have been obtained. It was proved that the prediction of the number of mining tremors per day is more precise than the prediction of future energy (maximum amplitudes). Further advance, based on the processing of seismo-acoustic activity series, is introduced.     

Refraction Effect in Geothermal Heat Flow Due to a 3-D Prism in a Two-Layered Earth

A mathematical model of the disturbance of the stationary geothermal field due to a three-dimensional perturbing body embedded near the surface of a two layered earth. The theoretical analysis is based on the generalized theory of the double-layer potential, similar to the boundary integral method likely to direct current geoelectricity problems. Special attention is paid to cases in which a pan of the body's surface is tangential to the planar boundaries of the substratum or of the surface of the earth The numerical calculations are performed for a three-dimensional prism using methods similar to the boundary element method (BEM). Numerous graphs are shown for the disturbance of the temperature field and of the heat flow on the surface of the earth and along vertical profiles (boreholes).     

Plastic litter in sediments from the Croatian marine protected area of the natural park of Telaščica bay (Adriatic Sea)

This paper reports baseline levels of litter (macro, meso and microplastics) in sediments collected from different areas of the Croatian MPA of the Natural Park of Tela??ica bay (Adriatic Sea, GSA n. 17). The distribution of total abundance according to size, for all analysed locations evidences that microplastics are the dominant fraction concerning item's numbers. In all analysed samples no macroplastics were found, while microplastics are 88.71% and mesoplastics are 11.29% of the total.