The mechanics of olivine deformation play a key role in long-term planetary processes, including  the response of the lithosphere to tectonic loading or the response of the solid Earth to tidal forces,  and in short-term processes, such as post-seismic creep within the upper mantle. Previous studies  have emphasized the importance of grain-size effects in the deformation of olivine. Most of our  understanding of the role of grain boundaries in the deformation of olivine is inferred from comparison  of experiments on single crystals to experiments on polycrystalline samples, as there are no direct  studies of the mechanical properties of individual grain boundaries in olivine. In this study, we use  high-precision mechanical testing of synthetic forsterite bicrystals with well characterized interfaces  to directly observe and quantify the mechanical properties of olivine grain boundaries. We conduct  in-situ micropillar compression tests at high-temperature (700• C) on bicrystals containing low-angle (4• tilt about [100] on (014)) and high-angle (60• tilt about [100] on (011)) boundaries. During  the in-situ tests, we observe differences in deformation style between the pillars containing the  grain boundary and the pillars in the crystal interior. In the pillars containing the grain boundary,  the interface is oriented at ∼ 45• to the loading direction to promote shear. In-situ observations  and analysis of the mechanical data indicate that pillars containing the grain boundary consistently  support elastic loading to higher stresses than the pillars without a grain boundary. Moreover, the  pillars without the grain boundary sustain larger plastic strain. Post-deformation microstructural  characterization confirms that under the conditions of these deformation experiments, sliding did not occur along the grain boundary. These observations support the hypothesis that grain boundaries are stronger relative to the crystal interior at these conditions. 

Inflow anomalies at varying temporal scales, seasonally varying storage mandates, and multi-purpose allocation requirements contribute to reservoir operational decisions. The difficulty of capturing these constraints across many basins in a generalized framework has limited the accuracy of streamflow estimates in Land Surface Models for locations downstream of reservoirs. We develop a Piece Wise Linear Regression Tree to learn generalized daily operating policies from 76 reservoirs from four major basins across the coterminous US. Reservoir characteristics, such as residence time and maximum storage, and daily state variables, such as storage and inflow, are used to group similar observations across all reservoirs. Linear regression equations are then fit between daily state variables and release for each group. We recommend two models – Model 1 (M1) that performs the best when simulating untrained records but is complex, and Model 2 (M2) that is nearly as performant as M1 but more parsimonious. The simulated release median root mean squared error is 49.7% (53.2%) of mean daily release with a median Nash-Sutcliffe Efficiency of 0.62 (0.52) for M1 (M2). Long-term residence time is shown to be useful in grouping similar operating reservoirs. Release from low residence time reservoirs can be mostly described using inflow-based variables. Operations at higher residence time reservoirs are more related to previous release variables or storage variables, depending on the current inflow. The ability of the models presented to capture operational dynamics of many types of reservoirs indicates their potential to be used for untrained and limited data reservoirs.

The Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension (WACCM-X) is used to investigate the influence of stratosphere polar vortex variability on the mesosphere, thermosphere, and ionosphere during Northern Hemisphere winter. Based on 40 simulated Northern Hemisphere winters, the mesosphere and lower thermosphere (MLT) residual circulation is found to depend on whether the stratosphere polar vortex is strong or weak. In particular, during weak stratosphere polar vortex time periods, the MLT circulation anomalies are characterized by clockwise and anti-clockwise flow in the Northern and Southern Hemispheres, respectively. Opposite, though weaker, anomalies are found to occur during time periods when the stratosphere polar vortex is strong. The MLT circulation anomalies influence the composition of the lower thermosphere, leading to ±5% changes in the thermosphere column integrated atomic oxygen to molecular nitrogen ratio (O/N2). Large differences between strong and weak stratosphere polar vortex events are also found to occur in the semidiurnal migrating tide (SW2) in the MLT, which leads to ±15-20% differences in the SW2 component of the ionosphere total electron content (TEC) at low latitudes. The WACCM-X simulation results indicate that variability in the stratosphere polar vortex can explain ~30% and ~18% of the quiet time variability in thermosphere O/N2 and the SW2 component of TEC during Northern Hemisphere winter, respectively.

If lake ice is assumed to deform and fail as a linear viscoelastic material under the action of wind stress, then a simple ice concentration scaling law can be constructed suitable for one-dimensional lake models embedded within environmental prediction systems. Most 1-D lake models assume no ice mechanics at all, while others adapt the viscous-plastic rheology common in ice-ocean models for the purpose of estimating ice fraction. Elastic buckling is generally disregarded as a significant failure mechanism in ice under low stress conditions at geophysical scales. However, by adding viscosity to the constitutive equation, the conditions for viscoelastic buckling seem quite plausible over a wide range of lake size and ice thickness. An ice concentration scaling law based on this process is evaluated here in multiannual simulations over North America and found to produce superior ice phenology statistics compared with simulations based on plastic failure or no ice mechanics.

We present three events where high-resolution electric and magnetic field measurements from the Swarm satellite constellation coincided with excellent F-region ionospheric coverage from SuperDARN. Large-scale ionospheric convection patterns from SuperDARN, together with field-aligned-current patterns from AMPERE, provide information on quasi-static ionospheric dynamics traversed by Swarm. Because the Swarm observations and orbital path coincided with favorable SuperDARN/AMPERE observing conditions, it was possible to filter the Swarm electric field observations into a quasi-static component that agreed with the SuperDARN electric field. We contend that the residual electric field from Swarm is thus indicative of small- and mesoscale dynamics not captured by the convection and FAC patterns. We compare calculations of the Poynting flux between the different instruments and show that dynamics on small- to mesoscales can be highly variable within structures like field-aligned currents. In the events shown, small- and medium-scale Poynting fluxes occasionally dominate over that from large-scale processes.

Ensemble forecasting is a promising tool to aid in making informed decisions against risks of coastal storm surges. Although tropical cyclone (TC) ensemble forecasts are commonly used in operational numerical weather prediction systems, their potential for disaster prediction has not been maximized. Here we present a novel, efficient, and practical method to utilize a large ensemble forecast of 1000 members to analyze storm surge scenarios toward effective decision making such as evacuation planning and issuing surge warnings. We perform the simulation of TC Hagibis (2019) using the Japan Meteorological Agency’s (JMA) non-hydrostatic model. The simulated atmospheric predictions were utilized as inputs for a statistical surge model named the Storm Surge Hazard Potential Index (SSHPI) to estimate peak surge heights along the central coast of Japan. We show that Pareto optimized solutions from an ensemble storm surge forecast can describe potential worst (maximum) and optimum (minimum) storm surge scenarios while exemplifying a diversity of trade-off surge outcomes among different coastal places. For example, some of the Pareto optimized solutions that illustrate worst surge scenarios for inner bay locations are not necessarily accountable for bringing severe surge cases in open coasts. We further emphasize that an in-depth evaluation of Pareto optimal solutions can shed light on how meteorological variables such as track, intensity, and size of TCs influence the worst and optimum surge scenarios, which is not clearly quantified in current multi-scenario assessment methods such as those used by JMA/National Hurricane Center in the United States.

The monsoons in Pakistan have been exceptionally harsh in recent decades, resulting in extraordinary drought conditions and record flooding events. The changing frequency of extreme events is widely attributed to climate change. However, given this region's long history of floods and droughts, the role of natural climate variability cannot be rejected without a careful diagnosis. Here, we examine how oceanic and atmospheric variability has contributed to unusual precipitation distributions in West South Asia. Variations in sea surface temperatures in the tropical Pacific and northern Arabian Sea, and internal atmospheric variability related to the circumglobal teleconnection pattern and the subtropical westerly jet stream, explain more than 70% of monthly summer precipitation variability in the 21st century. Several of these forcings have co-occurred with record strength during episodes of extreme monsoons, which have exacerbated the overall effect. Climate change may have contributed to increased variability and the in-phase co-occurrences of the identified mechanisms, but further research is required to confirm any such connection.

The tool of phase-field modeling for the prediction of chemical as well as microstructural evolution during crystallization from a melt in a mineralogical system has been developed in this work. We provide a compact theoretical background and introduce new aspects such as the treatment of anisotropic surface energies that are essential for modeling mineralogical systems. These are then applied to two simple model systems - the binary olivine-melt and plagioclase-melt systems - to illustrate the application of the developed tools. In one case crystallization is modeled at a constant temperature and undercooling while in the other the process of crystallization is tracked for a constant cooling rate. These two examples serve to illustrate the capabilities of the modeling tool. The results are analyzed in terms of crystal size distributions (CSD) and with a view toward applications in diffusion chronometry; future possibilities are discussed. The modeling results demonstrate that growth at constant rates may be expected only for limited extents of crystallization, that breaks in slopes of CSD-plots should be common, and that the lifetime of a given crystal of a phase is different from the lifetime of this phase in a magmatic system. The last aspect imposes an inherent limit to timescales that may be accessed by diffusion chronometry. Most significantly, this tool provides a bridge between CSD analysis and diffusion chronometry - two common tools that are used to study timescales of magmatic processes.

Restoring and preventing losses of the world’s forests are promising natural pathways to mitigate climate change. In addition to regulating atmospheric carbon dioxide concentrations, forests modify surface and near-surface air temperatures through biophysical processes. In the eastern United States (EUS), widespread reforestation during the 20th century coincided with an anomalous lack of warming, raising the question of whether reforestation contributed to biophysical cooling and slowed local climate change. Using new cross-scale approaches and multiple independent sources of data, our analysis uncovered links between reforestation and the response of both surface and air temperature in the EUS. Ground- and satellite-based observations showed that EUS forests cool the land surface by 1-2 °C annually, with the strongest cooling effect during midday in the growing season, when cooling is 2 to 5 °C. Young forests aged 25-50 years have the strongest cooling effect on surface temperature, which extends to the near-surface air, with forests reducing midday air temperature by up to 1 °C. Our analyses of historical land cover and air temperature trends showed that the cooling benefits of reforestation extend across the landscape. Locations predominantly surrounded by reforestation were up to 1 °C cooler than neighboring locations that did not undergo land cover change, and areas dominated by regrowing forests were associated with cooling temperature trends in much of the EUS. Our work indicates that reforestation contributed to the historically slow pace of warming in the EUS, highlighting the potential for reforestation to provide local climate adaptation benefits in temperate regions worldwide.

Plasma bubbles are regions of depleted plasma within the upper thermosphere/ionosphere that form during post-sunset hours near the magnetic equator. These structures tend to align with local geomagnetic field lines, extend upwards hundreds of kilometers along geomagnetic longitudes, and thousands of kilometers along geomagnetic latitudes. These large scale plasma density gradients can attenuate lower frequency radio waves, while small scale structures along the walls can interfere with centimeter scale wavelengths via Fresnel and Bragg scattering. Large scale statistical analysis of this phenomenon can further understanding of their occurrence and subsequent behavior. The current study utilizes Global-Scale Observations of the Limb and Disk (GOLD) 135.6 nm nightglow data from October 5, 2018 to September 30, 2022. GOLD has a unique perspective from geostationary orbit, allowing a constant and consistent view of nightglow and structures over the Americas and Atlantic. A plasma bubble detection method is developed and used to generate a database of plasma bubble occurrences. Occurrences are used to calculate plasma bubble drift speeds and separations. Clear seasonality in plasma bubble occurrence rate is evident. Overall occurrences peak during December solstice months and minimize during June solstice for longitudes seen by GOLD. Within GOLD’s field of view, higher occurrences are seen to the west during December solstice and east during June solstice. Plasma bubble drift speeds and separations show consistent distributions regardless of magnetic region, geographic region, season, or local time. This suggests plasma bubbles behave consistently and regularly once formed, at least on spatial scales seen by GOLD.

Diatoms are among the most efficient marine organisms for primary production and carbon sequestration, absorbing at least 10 billion tonnes of carbon dioxide every year. Yet, the spatial distributions of these planktonic organisms remain puzzling and the underlying physical processes poorly known. Here we investigate what dynamical conditions are conductive to episodic diatom blooms in oligotrophic waters based on Lagrangian diagnosis and satellite-derived phytoplankton functional types and ocean currents. The Lagrangian coherence of the flow is diagnosed in space and time simultaneously to identify which structures favor diatom growth. Observations evidence that flow structures with a high degree of coherence (40 days or longer) in high turbulent kinetic energy and vorticity sustain high concentrations of diatoms in the sunlite layers. Our findings show that the integration of Eulerian kinematic variables into a Lagrangian frame allows revealing new dynamical aspects of geophysical turbulence and unveil transport properties having large biological impacts.

Radiation energy balance at the top of the atmosphere (TOA) is a critical boundary condition for the Earth climate. It is essential to validate it in the global climate models (GCM) on both global and regional scales. However, the comparison of overall radiation field is known to conceal compensating errors. Here we use a new set of radiative kernels to diagnose the radiation biases by different geophysical variables in the latest GCMs. We find although clouds remain a primary cause of radiation biases, the radiation biases caused by non-cloud variables are of comparable magnitudes. Many GCMs tend to have a cold bias in the air temperature and a moist bias in the tropospheric humidity, which lead to considerable biases in TOA radiation budget but are compensated by cloud biases. These findings signify the importance of validating the GCM-simulated radiation fields, with respect to both the overall and component radiation biases.

The current increase in temperature over Greenland and other glaciated regions allows for more surface melt, which poses the question of the impact of this extra amount of meltwater on ice dynamics. As subglacial hydrology models evolve they are now easier to apply to realistic scenarios to quantify the effect of an increase in melt on the dynamics of glaciers. However, a number of processes linking the surface melt to the water pressure at the base of glaciers are still overlooked in models due to a lack of knowledge or an excess of complexity. Here, we apply a subglacial hydrology model coupled to an ice dynamics model to a synthetic geometry to investigate the impact of moulins distribution on the dynamics of the glacier. Our results show that a sparser distribution of moulins leads to the faster development of the efficient drainage system and greatly slows down the glacier.

A document by Huan Liang. Click on the document to view its contents.

Capital works projects, particularly the modification of coastal rivers, are becoming increasingly significant to economic activities worldwide as a response to climate-driven changes and urbanization. The benefits of channel modification projects can be realized quickly, but the altered movement of sediments in the river channel can lead to unintended morphologic changes decades later. An example of this is the closure of the San Bernard River mouth, located on the central coast of Texas, which was clogged by sediments in the 1990s as a result of two major projects in the area: the diversion of the Brazos River channel (1929) and the construction of the Gulf Intracoastal Waterway (GIWW) (1940s). The objective of this study was to document the delayed geomorphic response to the projects using historical aerial imagery and provide a snapshot of flow pathways in the area using measurements collected in situ. Results showed that the GIWW was the main conduit for river flow as it bisects the San Bernard 2 km inland of its river mouth, reducing discharge in the terminal limb of the river. Due to reduced flow, the river mouth became clogged with wave-transported sediment supplied the Brazos River which had been diverted to within 6 km of the San Bernard. With no connection to the sea, altered sediment and flow pathways have led to numerous hazards and costly corrective dredging projects. To optimize the cost-effectiveness of channel modification projects their long-term impact must be considered as managers continue to adapt to ever-changing coastal zones.

The rapidly melting Totten Glacier of East Antarctica drains a basin containing ~3.5 m sea-level rise equivalent of ice, but the Totten Glacier dynamics and interaction with the Southern Ocean since the Last Glacial Maximum is not well understood. To better understand the response of the glacier to present and future climate changes, an accurate reconstruction of the retreat history of the Totten Glacier is needed. Hence, this study uses a multiproxy approach in analyzing beryllium isotopes, the first such record from this location, and grain size of a sediment core collected from the continental slope adjacent to Totten Glacier. The results, when evaluated together with nearby proxy records, reveal that the initial deglaciation of the Totten Glacier sector of the East Antarctic Ice Sheet began at ~18 ka BP. The rapid deglaciation from ~9 ka BP that followed is assumed to be caused by the intrusion of modified Circumpolar Deep Water to the grounding zone of the Totten Glacier. This intrusion may also be coupled with a weaker Antarctic Slope Current and southward shift of Antarctic easterlies. This result contributes to the body of knowledge regarding the dynamical response of marine-terminating glaciers to climate variability during the last deglaciation.

The Madden-Julian oscillation (MJO) has remarkable impacts on global weather and climate systems. Understanding its changes under a warming climate provides insights into how MJO-related phenomena may change accordingly. This study examines the future changes in MJO projected by 23 Coupled Model Intercomparison Project Phase 6 (CMIP6) models that produce a realistic MJO propagation in their historical runs. Results from the multi-model mean show a ~17% increase in MJO precipitation amplitude, a ~9% increase in propagation speed, a ~2-day decrease in MJO period, and a ~5° eastward extension. Analysis of the lower tropospheric moisture budget suggests the dominant role of an increased meridional advection of mean moisture caused by the steepening of mean moisture over the Indo-Pacific warm pool in a warming climate. This leads to a stronger positive moisture tendency to the east of MJO convection, and hence a more eastward MJO propagation with strengthened amplitude and faster speed.

The ‘signal-to-noise paradox’ for seasonal forecasts of the winter NAO is often described as an ‘underconfident’ forecast and measured using the ratio-of-predictable components metric (RPC). However, comparison of RPC with other measures of forecast confidence, such as spread-error ratios, can give conflicting impressions, challenging this informal description. We show, using a linear statistical model, that the ‘paradox’ is equivalent to a situation where the reliability diagram of any percentile forecast has a slope exceeding 1. The relationship with spread-error ratios is shown to be far less direct. We furthermore compute reliability diagrams of winter NAO forecasts using seasonal hindcasts from the European Centre for Medium-range Weather Forecasts and the UK Meteorological Office. While these broadly exhibit slopes exceeding 1, there is evidence of asymmetry between upper and lower terciles, indicating a potential violation of linearity/Gaussianity. The limitations and benefits of reliability diagrams as a diagnostic tool are discussed.