Hurst scaling with crossover of a drought indicator: a case study in Belem and Manaus,Brazil

Natural Hazards - Some Amazonia regions are vulnerable to natural disasters. Hurst analysis of hydrological events can provide more information than classical statistical methods. The objectives of...     

Inter-hemispheric asymmetry in polar mesosphere summer echoes and temperature at 69° latitude

An inter-hemispheric asymmetry is found in the characteristics of polar mesosphere summer echoes (PMSE) and upper mesosphere temperatures at conjugate latitudes (～69°) above Antarctica and the Arctic. The second complete mesosphere–stratosphere–troposphere (MST) radar summer observation season at Davis (68.6°S) revealed that PMSE occur less frequently, with lower strength and on average 1 km higher compared with their northern counterparts at Andenes (69.3°N). We consider the thermodynamic state of the mesosphere for conjoining hemispheric summers based on satellite and ground-based radar measurements, and show the mesopause region near ～80–87 km of the Southern Hemisphere (SH) to be up to 7.5 K warmer than its Northern Hemisphere (NH) counterpart. We show that this is consistent with our observation of asymmetries in the characteristics of PMSE and demonstrate how the mesosphere meridional wind field influences the existence and strength of the echoes in both hemispheres.     

Statistical properties of the Transantarctic Mountains (TAM) micrometeorite collection

Micrometeorites have been recovered from traps located at the summit of nunataks in the Transantarctic Mountains (TAM), Antarctica. They constitute the TAM micrometeorite collection. Micrometeorites accumulated by direct infall for hundreds of thousands of years. This long collection duration is confirmed by the wide range of weathering by dissolution of olivine in the stony micrometeorites from the TAM collection. A statistical study of the size distribution and frequency by type of this collection, and comparison with other Antarctic micrometeorite collections (the South Pole Water Well collection and the Walcott Névé collection), suggest that the TAM collection is essentially unbiased. Thanks to the very long exposure of the traps, large diameter (>1000 μm) micrometeorites are present in sufficiently large numbers to allow a statistically meaningful estimate of their size distribution in this size range for the first time. We found that the slope of the size distribution remains constant in the 100–1600 μm size range. Therefore, the size distribution of micrometeorites in this size range is controlled by a single process.     

Seeing through porous media: An experimental study for unveiling interstitial flows

We describe a novel inexpensive method, utilizing particle image velocimetry (PIV) and refractive index‐matching (RIM) for visualizing and quantifying the flow field within bio‐amended porous media. To date, this technique has been limited to idealized particles, whose refractive index does not match that of fresh water and thus requires specialized and often toxic or hazardous fluids. Here, we use irregularly shaped grains made of hydrogel as the solid matrix and water as the fluid. The advantage of using water is that it provides, for the first time, the opportunity to study both hydraulic and biological processes, which typically occur in soils and streambeds. By using RIM coupled with PIV (RIM‐PIV), we measured the interstitial flow field within a cell packed with granular material consisting of hydrogel grains in a size range of 1–8 mm, both in the presence and in the absence of Sinorhizobium meliloti bacteria (strain Rm8530). We also performed experiments with fluorescent tracer (fluorescein) and fluorescent microbes (Shewanella GPF MR‐1) to test the capability of visualizing solute transport and microbial movements. Results showed that the RIM‐PIV can measure the flow field for both biofilm‐free and biofilm‐covered hydrogel grains. The fluorescent tracer injection showed the ability to visualize both physical (concave surfaces and eddies) and biological (biofilms) transient storage zones, whereas the fluorescent microbe treatment showed the ability to track microbial movements within fluids. We conclude that the proposed methodology is a promising tool to visualize and quantify biofilm attachment, growth, and detachment in a system closer to natural conditions than a 2D flow cell experiment.     

Wave transformation across a macrotidal shore platform under low to moderate energy conditions

We investigate how waves are transformed across a shore platform as this is a central question in rock coast geomorphology. We present results from deployment of three pressure transducers over four days, across a sloping, wide (~200 m) cliff‐backed shore platform in a macrotidal setting, in South Wales, United Kingdom. Cross‐shore variations in wave heights were evident under the predominantly low to moderate (significant wave height < 1.4 m) energy conditions measured. At the outer transducer 50 m from the seaward edge of the platform (163 m from the cliff) high tide water depths were 8+ m meaning that waves crossed the shore platform without breaking. At the mid‐platform position water depth was 5 m. Water depth at the inner transducer (6 m from the cliff platform junction) at high tide was 1.4 m. This shallow water depth forced wave breaking, thereby limiting wave heights on the inner platform. Maximum wave height at the middle and inner transducers were 2.41 and 2.39 m, respectively, and significant wave height 1.35 m and 1.34 m, respectively. Inner platform high tide wave heights were generally larger where energy was up to 335% greater than near the seaward edge where waves were smaller. Infragravity energy was less than 13% of the total energy spectra with energy in the swell, wind and capillary frequencies accounting for 87% of the total energy. Wave transformation is thus spatially variable and is strongly modulated by platform elevation and the tidal range. While shore platforms in microtidal environments have been shown to be highly dissipative, in this macro‐tidal setting up to 90% of the offshore wave energy reached the landward cliff at high tide, so that the shore platform cliff is much more reflective. Copyright © 2017 John Wiley & Sons, Ltd.     

Ionospheric potential as a proxy index for global temperature

Since the global circuit is maintained by currents from thunderstorms and electrified clouds, which are controlled by temperature, we are investigating the use of ionospheric potential (V_I) as a measure of the variation of global temperature. We report positive correlation between V_I and global temperature obtained from three different data sets. V_I is also positively correlated with an inferred global lightning/deep cloud index which is positively correlated with global temperature. Thus, there is a consistent picture of warmer temperatures leading to more deep convection and higher V_I. Since a series of single V_I soundings at any appropriate location may provide a globally representative measure of temperature variation in real time, it is suggested that routine monitoring of this parameter could provide considerable cost and operational advantages compared to current methodology involving observations at thousands of ground stations and satellite radiation measurements.     

The Impact of the Herbicide Diuron on Photosynthesis in Three Species of Tropical Seagrass

The impact and recovery from exposure to the herbicide diuron [DCMU; 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea] was assessed for three tropical seagrasses, maintained in outdoor aquaria over a 10-day period. Photosynthetic stress was detected using chlorophyll a fluorescence, measured with a Diving-PAM (pulse amplitude modulated fluorometer). Exposure to 10 and 100 μg l⁻¹ diuron resulted in a decline in effective quantum yield (ΔF/F_m^′) within 2 h of herbicide exposure in Cymodocea serrulata, Halophila ovalis and Zostera capricorni. Effective quantum yield also declined over the first 24 h of exposure in H. ovalis at even lower diuron concentrations (0.1 and 1.0 μg l⁻¹). Effective quantum yield in H. ovalis and Z. capricorni was significantly depressed at all diuron concentrations (0.1–100 μg l⁻¹) after 5 days exposure, whereas effective quantum yield in C. serrulata was only significantly lower in plants exposed to highest diuron concentrations (10 and 100 μg l⁻¹). Effective quantum yield depression was present 5 days after plants exposed to 10 and 100 μg l⁻¹ diuron were returned to fresh seawater. These results indicate that exposure to herbicide concentrations present in nearshore Queensland sediments present a potential risk to seagrass functioning.     

Turbidite-reservoir architecture in complex foredeep-margin and wedge-top depocenters,Tertiary Molasse foreland basin system,Austria

We employ an integrated subsurface dataset, including >400 m of drill cores and three-dimensional (3D) seismic-reflection data from >530 km² of the Tertiary Molasse foreland basin system in Austria, to characterize turbidite-system architecture across structurally complex foredeep-margin and wedge-top depocenters and to interpret the influence of tectonic deformation and submarine topography on hydrocarbon-reservoir quality and distribution. Turbidite-system architecture and depositional processes were correlated with associated topographic features in order to identify zones of preferential sediment gravity-flow convergence or divergence. Zones of flow convergence facilitate flow acceleration and accumulative flow behavior, whereas zones of flow divergence facilitate deceleration and depletion. Zones of preferential flow convergence include narrow (<2 km) and steep (<20°) foredeep-margin slope channels along thrust front-segmenting tear faults, and steep, unchannelized piggyback-basin and foredeep margins (local gradients as great as 40° across piggyback-basin margins). The foredeep-margin gradient is exaggerated principally by tectonic deformation that post-dates turbidite-system development, based on a paucity of growth strata. Piggyback-basin-margin gradients are exaggerated as a result of deformation synchronous with and following turbidite-system development, judging from the presence of growth strata. Slope-channel topography facilitated the development of relatively coarse-grained, amalgamated turbidite reservoirs, whereas unchannelized basin-margin topography facilitated deposition of fine-grained, chaotic non-reservoirs. Zones of preferential flow divergence are flat (<1°), unconfined (i.e., large in comparison to sediment gravity flows) piggyback-basin floors, which facilitated the development of relatively coarse-grained, non-amalgamated, upward fining turbidite reservoirs, stratigraphically partitioned by fine-grained mass transport-complex deposits. The results of this study elucidate the influence of foredeep-margin and wedge-top tectonic deformation and topography on turbidite-system and associated reservoir character and distribution across the Molasse foreland basin system in Austria, and can be applied to oil and gas exploration in analogous, structurally complex settings.     

High-Resolution Simulations of the Impacts of Asteroids into the Venusian Atmosphere II: 3D Models

We compare high-resolution 2D and 3D numerical hydrocode simulations of asteroids striking the atmosphere of Venus. Our focus is on aerobraking and its effect on the size of impact craters. We consider impacts both by spheres and by the real asteroid 4769 Castalia, a severely nonspherical body in a Venus-crossing orbit. We compute mass and momentum fluxes as functions of altitude as global measures of the asteroid's progress. We find that, on average, the 2D and 3D simulations are in broad agreement over how quickly an asteroid slows down, but that the scatter about the average is much larger for the 2D models than for the 3D models. The 2D models appear to be rather strongly susceptible to the “butterfly effect,” in which tiny changes in initial conditions (e.g., 0.05% change in the impact velocity) produce quite different chaotic evolutions. By contrast, the global properties of the 3D models appear more reproducible despite seemingly large differences in initial conditions. We argue that this difference between 2D and 3D models has its root in the greater geometrical constraints present in any 2D model, and in particular in the global conservation of enstrophy in 2D that forces energy to pool in large-scale structures. It is the interaction of these artificial large-scale structures that causes slightly different 2D models to diverge so greatly. These constraints do not apply in 3D and large scale structures are not observed to form. A one-parameter modified pancake model reproduces the expected crater diameters of the 3D Castalias reasonably well.