Improving the Representation of Aggregation in a Two-moment Microphysical Scheme with Statistics of Multi-frequency Doppler Radar Observations

The simulation of aggregation of ice particles is critical for precipitation prediction, but still a major challenge. Its simulation requires assumptions about numerous parameters, many of which are either not well known or difficult to represent accurately in bulk microphysics schemes. However, knowing the sensitivity of aggregation to various simplified assumptions can help to identify critical parameters. By comparison with suitable observations, these critical parameters can even be constrained. We investigate the sensitivity of the model variables, and the modeled multi-frequency and Doppler radar observables to different parameters in a two-moment microphysics scheme. Therefore, we revise hydrometeor parameters by using a recently published dataset of particle properties, modify the formulations of the aggregation process (which allows using an area-based differential sedimentation kernel) and update other ice microphysical parameters in the scheme such as the sticking efficiency Estick and the shape of the size distribution. Overall, particle properties, definition of the aggregation kernel, and size distribution width prove to be most important, while Estick and the cloud ice habit have less influence. Finally, we run multi-week simulations with the most promising parameter combinations. The statistical comparison between real and synthetic observables shows a reduction in the velocity and snow particle size. With this study, we show a possible way to revise processes in microphysical schemes by using statistics of detailed cloud radar observations.

The bivergent growth of the Cenozoic Qilian Shan, northeastern Tibetan Plateau: Insights from numerical models

<p>The Qilian Shan orogenic belt, located in the northeastern margin of the Tibetan Plateau, undergoes intensive Cenozoic structural deformation with large lateral growth since the Miocene. The Cenozoic growth of the Qilian Shan is possibly resulted by the passive subduction of the North China Craton due to the far-field effect of the continuous Indo-Asian collision. Thus, the Qilian Shan can be seen as a syntectonic crustal-scale accretionary wedge above a middle intra-crustal weak layer. To date, the detailed Cenozoic crustal deformation manner of the Qilian Shan and its adjacent two basins remains unclear, especially for the southward propagation towards the Qaidam Basin. Whereas, the spatio-temporal characteristics of deformation distribution between the Qilian Shan and the adjacent two basins are critical to fulfill the lateral growth of the Tibetan Plateau. Hence, we conducted a series of high-resolution 2-D numerical models to investigate factors that influence crustal strain distribution. The first series models are thick-skinned models with single décollement, while Series II are two-décollement layer model, regarding the interaction between thick- and thin-skinned tectonics beneath the two adjacent basins. After 150 km of total convergence, model results suggest that the single décollement layer model is not sufficient in depicting the present-day crustal deformation pattern, while strain localization pattern from two-décollement layer model meets well with the geological and geophysical observations. The Hexi Corridor Basin may be involved with deep-crustal thrusting while the dominant deformation is still thin-skinned tectonics. Series III adds the filling-up sedimentation based on the conditions of Series II. We reveal that the differential sedimentation types between the Qaidam Basin and the Hexi Corridor Basin greatly depress fault propagation towards the Qaidam Basin. Note that, how deformation transfers into the Qaidam Basin remains controversial. To date, the above models still need to evolve. However, in summary, our study highlights the crustal deformation of the two margins of northeastern Tibetan Plateau is controlled by the décollements and differential sedimentation styles.</p>

Investigating the Relative Contributions of Charge Deposition and Turbulence in Organizing Charge within a Thunderstorm

Large-eddy-resolving simulations using the Collaborative Model for Multiscale Atmospheric Simulation (COMMAS), which contains microphysical charging and branched-lightning parameterizations, produce much more complex net charge structures than conventionally visualized from previous observations, simulations, and conceptual diagrams. Many processes contribute to the hydrometeor charge budget within a thunderstorm, including advection, hydrometeor differential sedimentation, subgrid turbulent mixing and diffusion, ion drift, microphysical separation, and the attachment of ion charge deposited by the lightning channel. The lightning deposition, sedimentation, and noninductive charging tendencies contribute the most overall charge at relatively large scales, while the advection tendency, from resolved turbulence, provides the most “texture” at small scales to the net charge density near the updraft region of the storm. The scale separation increases for stronger storm simulations. In aggregate, lightning deposition and sedimentation resemble the smoother distribution of the electric potential, while evidence suggests individual flashes could be responding to the fine texture in the net charge. The clear scale separation between the advection and other net charge tendencies suggest the charge advection is most capable of providing net charge texture; however, a clear-cut causality is not obtained from this study.

Secondary nucleation of monomers on fibril surface dominatesα-synuclein aggregation and provides autocatalytic amyloid amplification

Parkinson's disease (PD) is characterized by proteinaceous aggregates named Lewy Bodies and Lewy Neurites containingα-synuclein fibrils. The underlying aggregation mechanism of this protein is dominated by a secondary process at mildly acidic pH, as in endosomes and other organelles. This effect manifests as a strong acceleration of the aggregation in the presence of seeds and a weak dependence of the aggregation rate on monomer concentration. The molecular mechanism underlying this process could be nucleation of monomers on fibril surfaces or fibril fragmentation. Here, we aim to distinguish between these mechanisms. The nature of the secondary processes was investigated using differential sedimentation analysis, trap and seed experiments, quartz crystal microbalance experiments and super-resolution microscopy. The results identify secondary nucleation of monomers on the fibril surface as the dominant secondary process leading to rapid generation of new aggregates, while no significant contribution from fragmentation was found. The newly generated oligomeric species quickly elongate to further serve as templates for secondary nucleation and this may have important implications in the spreading of PD.

Biostratigraphy of the Campanian-Maastrichtian, Mid-Maastrichtian, and Cretaceous-tertiary boundaries in the Raton Basin: Implications for models of early Laramide tectonism and for the origin of the enigmatic Disturbed Zone

The Campanian-Maastrichtian stage boundary is placed within the upper part of the Pierre Shale about 100 m below the base of the Trinidad Sandstone at Berwind Canyon, Colorado. Correlation of ammonite biostratigraphy with palynostratigraphy places this boundary near the top of the Vermejo Formation in the southwestern part of the Raton Basin, northeastern New Mexico. The informal mid-Maastrichtian boundary should be placed at the level of the Trinidad Sandstone at Berwind Canyon, although it should be placed at the level of the Vermejo-Raton unconformity in northeastern New Mexico based upon palynostratigraphy. High-resolution megafloral biostratigraphy of the K-T boundary is also discussed. Chronostratigraphic and paleoenvironmental indicator species reveal differential sedimentation rates across the basin. The magnitude of the Vermejo-Raton unconformity varies primarily in a north-south direction across the Raton Basin and was greatest in northeastern New Mexico and least in south-central Colorado, which may affect interpretations of the early Laramide history of the Raton Basin. The results of this study preclude correlation of the basal part of the Vermejo Formation with the Disturbed Zone of southwestern South Dakota.

Salt-marsh evolution at Northwick and Aust warths, Severn Estuary, UK: a case of constrained autocyclicity.

Historic maps, remote imagery and field surveys reveal that a terraced sequence of four salt marshes has arisen on a decadal-centennial time-scale over a frontage of about 4 km at Northwick and Aust warths exposed to westerly to northerly winds on the east bank of the Severn Estuary, UK. Except for the youngest marsh, at present very immature, each marsh built up through differential sedimentation from a mudflat until the outer zone reached a critical steepness; at that point wave-attack caused erosion that led to the rapid landward retreat of a bold, laterally extensive, marsh-edge cliff. This observed behaviour is consistent with previous models of autocyclic marshes, but evidence suggests that the extrinsic factor of medium-scale changes in wind-wave climate constrained the particular timing of marsh responses.

The evolution of the Lansarine–Baouala salt canopy in the North African Cretaceous passive margin in Tunisia

Detailed geological mapping, dating, and gravimetric and seismic data are used to interpret the Lansarine–Baouala salt structure (North Tunisia) as a salt canopy emplaced during the Cretaceous Period. The extensional tectonic regime related to the Cretaceous continental margin offered at least two factors that encouraged buried Triassic salt to extrude onto the sea floor and flow downslope: (i) extension induced normal faults that provided routes to the surface, and led to the formation of sub-marine slopes along which salt could flow; (ii) this structural setting led to differential sedimentation and consequently differential loading as a mechanism for salt movement. The present 40-km-long Lansarine–Baouala salt structure with its unique mass of allochthonous Triassic salt at surface was fed from at least four stems. The salt structure is recognized as one of the few examples worldwide of a subaerial salt canopy due to the coalescence of submarine sheets of Triassic salt extruded in Cretaceous times.

Observations and modelling of microphysical variability, aggregation and sedimentation in tropical anvil cirrus outflow regions

Aircraft measurements of the microphysics of a tropical convective anvil (at temperatures ~−60 °C) forming above the Hector storm, over the Tiwi Islands, Northern Australia, have been conducted with a view to determining ice crystal aggregation efficiencies from in situ measurements. The observed microphysics have been compared to an explicit bin-microphysical model of the anvil region, which includes crystal growth by vapour diffusion and aggregation and the process of differential sedimentation. It has been found in flights made using straight and level runs perpendicular to the storm that the number of ice crystals initially decreased with distance from the storm as aggregation took place resulting in larger crystals, followed by their loss from the cloud layer due to sedimentation. The net result was that the mass (i.e. Ice Water Content) in the anvil Ci cloud decreased, but also that the average particle size (weighted by number) remained relatively constant along the length of the anvil outflow. Comparisons with the explicit microphysics model showed that the changes in the shapes of the ice crystal spectra as a function of distance from the storm could be explained by the model if the aggregation efficiency was set to values of Eagg~0.5 and higher. This result is supported by recent literature on aggregation efficiencies for complex ice particles and suggests that either the mechanism of particle interlocking is important to the aggregation process, or that other effects are occuring, such as enhancement of ice-aggregation by high electric fields that arise as a consequence of charge separation within the storm. It is noteworthy that this value of the ice crystal aggregation efficiency is much larger than values used in cloud resolving models at these temperatures, which typically use E~0.0016. These results are important to understanding how cold clouds evolve in time and for the treatment of the evolution of tropical Ci in numerical models.

The Optimum Dispersion of Carbon Nanotubes for Epoxy Nanocomposites: Evolution of the Particle Size Distribution by Ultrasonic Treatment

The ultrasonic dispersion of multiwalled carbon nanotube (MWCNT) suspensions was assessed by studying the differential sedimentation of the particles in an acid anhydride often employed as a curing agent for epoxy resins. The particle size distributions were characterized by the means of a disc centrifuge, and the effect of dispersion time, power density, and total energy input, for both bath and circulation probe ultrasonic dispersing equipment was investigated. The mass of freely suspended MWCNTs relative to agglomerated MWCNTs was estimated as a measure of the quality of the dispersions, and the results showed that this ratio followed a power law scaling with the energy dissipated in the sonication treatment. If the sonication power level was too high, sonochemical degradation of the curing agent could occur. The mean agglomerate MWCNT size distribution was estimated, and the fragmentation of the agglomerates was modeled by means of fragmentation theory. Indications of both rupture and erosion fragmentation processes for the MWCNT agglomerates were observed.