Saturn’s F ring as seen by Cassini UVIS: Kinematics and statistics

We present a new orbital model of Saturn’s F ring core based on 93 occultations by the Cassini Ultraviolet Imaging Spectrograph (UVIS) and the Voyager radio and stellar occultations. We demonstrate that the core, despite its intrinsic variability, is well-described as an inclined, freely precessing ellipse. We find that post-fit residuals with a root-mean-square of 24 km are genuine, representing the well-known non-Keplerian features observed in the ring. Over the nearly 4 years of UVIS observations we find the residual variance to increase, coincident with the apse anti-alignment of Prometheus and F ring core in December 2009. This increase in dynamical F ring core temperature most likely reflects the ever-stronger perturbations by Prometheus. Our results are in good agreement with Earth-based and HST observations as well as Voyager imaging.Cassini UVIS stellar occultations resolve the F ring at unprecedented resolutions of a few meters and we identify the F ring core and inner and outer strands. We infer their normal optical depth and full width at half maximum (FWHM) and show that core and strands form distinct morphological groups. Typically, a strand is about ten times wider than the core (average FWHM is ～10 km) while having a ten times smaller optical depth. Unlike in pre-Cassini occultations the F ring core displays significant optical depth with in some cases >3. In many cases we find a narrow optically thick component (～ few km and τ > 0.5) embedded in the F ring core. Entertaining the possibility that this is the actual, “true” F ring core then UVIS results suggest that this “true” core is highly non-continuous. In addition, we report the detection of a previously unknown structure – dubbed the “secondary” as it visually resembles the F ring core. Its morphology is similar to that of the core in optical depth and FWHM and it displays individual opaque features. Despite its core-like appearance, we show that its kinematics is consistent with that of strands. We conclude that it is the most prominent strand seen to date. It represents a striking example of strand creation resulting in what could be called a morphological “small-scale” version of the F ring core. This extraordinary object should be one of the prime targets of future F ring studies.     

The analysis of using satellite soil moisture observations for flood detection,evaluating over the Thailand’s Great Flood of 2011

Natural Hazards - A flood monitoring and warning system provides critical information that can protect property and save lives. A basin-scale flood monitoring system requires an effective...     

The Flatness of U.S. States

Does perception match reality when people judge the flatness of large areas, such as U.S. states? The authors conducted a geomorphometric analysis of the contiguous United States, employing publicly available geographic software, Shuttle Radar Topography Mission (SRTM) elevation data, and a new algorithm for measuring flatness. Each 90‐meter cell was categorized as not flat, flat, flatter, or flattest, and each state was measured in terms of percentage flat, flatter, and flattest as well as absolute area in each category. Ultimately, forty‐eight states plus the District of Columbia were mapped and ranked according to these values. Keywords: flatness, U.S. states, slope, Kansas, Florida.     

Winners and Losers in Marine Conservation: Fishers' Displacement and Livelihood Benefits from Marine Reserves

Marine reserves can create both benefits and costs to fishers. This article explores the perceptions of fishers in Kenya and Seychelles about displacement, spillover, and overall impacts of local marine reserves on their livelihoods. We test whether these perceptions are different among fishers from different geographic and socioeconomic conditions. Sixty-six percent of fishers had been displaced from marine reserves or coastal development and 90% believed they had caught fishes that spilled over from marine reserves. Poorer fishers in Kenya were both displaced from, and also felt like they benefited from, marine reserves. This highlights how people's experiences with marine reserves, both positive and negative, are affected by a range of social considerations that may not be incorporated in typical evaluations of ecological and economic marine reserve success.     

Seismic performance of highway bridges with fusing bearing components for quasi‐isolation

Modern highway bridges in Illinois are often installed with economical elastomeric bearings that allow for thermal movement of the superstructure, and steel fixed bearings and transverse retainers that prevent excessive movement from service‐level loadings. In the event of an earthquake, the bearing system has the potential to provide a quasi‐isolated response where failure of sacrificial elements and sliding of the bearings can cause a period elongation and reduce or cap the force demands on the substructure. A computational model that has been calibrated for the expected nonlinear behaviors is used to carry out a parametric study to evaluate quasi‐isolated bridge behavior. The study investigates different superstructure types, substructure types, substructure heights, foundation types, and elastomeric bearing types. Overall, only a few bridge variants were noted to unseat for design‐level seismic input in the New Madrid Seismic Zone, indicating that most structures in Illinois would not experience severe damage during their typical design life. However, Type II bearing systems, which consist of an elastomeric bearing and a flat PTFE slider, would in some cases result in critical damage from unseating at moderate and high seismic input. The sequence of damage for many bridge cases indicates yielding of piers at low‐level seismic input. This is caused by the high strength of the fixed bearing element, which justifies further calibration of the quasi‐isolation design approach. Finally, the type of ground motion, pier height, and bearing type were noted to have significant influence on the global bridge response. Copyright © 2013 John Wiley & Sons, Ltd.     

Interpreting amenities,envisioning the future: common ground and conflict in North Carolina’s rural coastal communities

This paper contributes to ongoing discussions about the implications of rural change and amenity migration for members of diverse rural communities. We engage with recent amenity migration and political ecology literature that focuses on social constructions of nature and landscapes, and how these constructions affect the attitudes and opinions of community members. We use our case study of a mail-based survey in Down East, North Carolina to suggest that the ways in which people conceptualize the particular ‘natures’ and landscapes of a place matters in terms of shaping people’s attitudes with respect to ongoing processes of change. We find that people’s opinions about environment, culture, and land use are often superficially similar but that when conflicts arise or particular actions are considered, substantial differences in people’s underlying conceptual frameworks are revealed. In particular we find that despite widespread shared appreciation of the environment and culture Down East, differing interpretations of these key terms lead to potential misunderstandings and land use planning challenges.     

The role of aqueous alteration in the formation of martian soils

Martian equatorial dark regions are dominated by unweathered materials and it has often been assumed that they have not been significantly altered from their source lithology. The suite of minerals present is consistent with a basaltic composition and there has been no need to invoke additional processes to explain the origin of these compositions. We have begun to question this result based on detailed observations using a variety of datasets. Locally derived dark soils have a mineralogy distinct from that of adjacent rocky surfaces; most notably a lower olivine content. This pattern is common for many surfaces across the planet. Previous work using detailed measurements acquired within the Gusev Plains has shown that olivine dissolution via acidic weathering may explain chemical trends observed between rock rinds and interiors. Mineralogical trends obtained from rocks and soils within the Gusev Plains are more prominent than the elemental trends and support previous results that indicate that dissolution of olivine has occurred. However, clear differences are also present in elemental abundances that indicate a variety of inputs and processes are likely responsible for the formation of martian dark soils. Despite the potential complexity of source materials and processes, it appears that most martian dark regions have likely experienced aqueous alteration and chemical weathering appears to be closely linked to the mechanical breakdown of materials. Regardless of the responsible mechanism, there appears to be a general, though not perfect, correlation between elevated olivine abundance and high-thermal inertia surfaces on Mars.     

Waves in Cassini UVIS stellar occultations: 2. The C ring

We performed a complete wavelet analysis of Saturn’s C ring on 62 stellar occultation profiles. These profiles were obtained by Cassini’s Ultraviolet Imaging Spectrograph High Speed Photometer. We used a WWZ wavelet power transform to analyze them. With a co-adding process, we found evidence of 40 wavelike structures, 18 of which are reported here for the first time. Seventeen of these appear to be propagating waves (wavelength changing systematically with distance from Saturn). The longest new wavetrain in the C ring is a 52-km-long wave in a plateau at 86,397 km. We produced a complete map of resonances with external satellites and possible structures rotating with Saturn’s rotation period up to the eighth order, allowing us to associate a previously observed wave with the Atlas 2:1 inner Lindblad resonance (ILR) and newly detected waves with the Mimas 6:2 ILR and the Pandora 4:2 ILR. We derived surface mass densities and mass extinction coefficients, finding σ = 0.22(±0.03) g cm⁻² for the Atlas 2:1 ILR, σ = 1.31(±0.20) g cm⁻² for the Mimas 6:2 ILR, and σ = 1.42(±0.21) g cm⁻² for the Pandora 4:2 ILR. We determined a range of mass extinction coefficients (κ = τ/σ) for the waves associated with resonances with κ = 0.13 (±0.03) to 0.28(±0.06) cm² g⁻¹, where τ is the optical depth. These values are higher than the reported values for the A ring (0.01-0.02 cm² g⁻¹) and the Cassini Division (0.07-0.12 cm² g⁻¹ from Colwell et al. (Colwell, J.E., Cooney, J.H., Esposito, L.W., Srem?evi?, M. [2009]. Icarus 200, 574-580)). We also note that the mass extinction coefficient is probably not constant across the C ring (in contrast to the A ring and the Cassini Division): it is systematically higher in the plateaus than elsewhere, suggesting smaller particles in the plateaus. We present the results of our analysis of these waves in the C ring and estimate the mass of the C ring to be between3.7(±0.9) × 10¹⁶ kg and 7.9(±2.0) × 10¹⁶ kg (equivalent to an icy satellite of radius between 28.0(±2.3) km and 36.2(±3.0) km with a density of 400 kg m⁻³, close to that of Pan or Atlas). Using the ring viscosity derived from the wave damping length, we also estimate the vertical thickness of the C ring between 1.9(±0.4) m and 5.6(±1.4) m, comparable to the vertical thickness of the Cassini Division.     

Multi-spectral imaging of vegetation for detecting CO<Subscript>2</Subscript> leaking from underground

Practical geologic CO₂ sequestration will require long-term monitoring for detection of possible leakage back into the atmosphere. One potential monitoring method is multi-spectral imaging of vegetation reflectance to detect leakage through CO₂-induced plant stress. A multi-spectral imaging system was used to simultaneously record green, red, and near-infrared (NIR) images with a real-time reflectance calibration from a 3-m tall platform, viewing vegetation near shallow subsurface CO₂ releases during summers 2007 and 2008 at the Zero Emissions Research and Technology field site in Bozeman, Montana. Regression analysis of the band reflectances and the Normalized Difference Vegetation Index with time shows significant correlation with distance from the CO₂ well, indicating the viability of this method to monitor for CO₂ leakage. The 2007 data show rapid plant vigor degradation at high CO₂ levels next to the well and slight nourishment at lower, but above-background CO₂ concentrations. Results from the second year also show that the stress response of vegetation is strongly linked to the CO₂ sink–source relationship and vegetation density. The data also show short-term effects of rain and hail. The real-time calibrated imaging system successfully obtained data in an autonomous mode during all sky and daytime illumination conditions.     

Observations of Surface Energy Fluxes and Boundary-Layer Structure Over Heron Reef, Great Barrier Reef, Australia

Over warm, shallow coral reefs the surface radiation and energy fluxes differ from those of the open ocean and result in modification to the marine atmospheric boundary layer via the development of convective internal boundary layers. The complex interrelationships between the surface energy balance and boundary-layer characteristics influence local weather (wind, temperature, humidity) and hydrodynamics (water temperature and currents), as well as larger scale processes, including cloud field properties and precipitation. The nature of these inter-relationships has not been accurately described for coral reef environments. This study presents the first measurements of the surface energy balance, radiation budget and boundary layer thermodynamics made over a coral reef using an eddy-covariance system and radiosonde aerological profiling of the lower atmosphere. Results show that changes in surface properties and the associated energetics across the ocean-reef boundary resulted in modification to the marine atmospheric boundary layer during the Austral winter and summer. Internal convective boundary layers developed within the marine atmospheric boundary layer over the reef and were found to be deeper in the summer, yet more unstable during the winter when cold and drier flow from the mainland enhances heat and moisture fluxes to the atmosphere. A mixed layer was identified in the marine atmospheric boundary layer varying from 375 to 1,200 m above the surface, and was deeper during the summer, particularly under stable anticyclonic conditions. Significant cloud cover and at times rain resulted in the development of a stable stratified atmosphere over the reef. Our findings show that, for Heron Reef, a lagoonal platform reef, there was a horizontal discontinuity in surface energy fluxes across the ocean-reef boundary, which modified the marine atmospheric boundary layer.