In this paper, THz channel propagation characterization and modeling for a desktop environment is presented. Path loss and PDPs measured on the motherboard in both free-space and desktop resemble metal cavity are compared. To characterize the large scale fading of the channel, mean path loss model as a function of antenna height is proposed by treating the motherboard desktop environment as a partially dielectric filled resonant cavity. Good match between the measured and modeled path loss proves the model validity. For the shadowing across the frequency, Gamma-mixture model is applied to characterize the oscillations of in-cavity measured path loss. Results show that with proper choice of the number of mixed Gamma distributions $k$, the goodness of fit between the model and the probability density function (PDF) of path loss oscillations can reach more than 97\%. Multipath components are characterized by cluster-based channel modeling. Modifications were made on the conventional S-V model to accurately characterize the channel by rewriting the cluster power decay with step-wise functions and each sub-function is expressed exponentially in dB, and the ray power decay with power law approach. A good agreement can be observed between the model and the measurements.

The carbonate chemistry of Arctic Ocean seafloor and its vulnerability to ocean acidification remains poorly explored. This limits our ability to quantify how biogeochemical processes and bottom water conditions shape sedimentary carbonate chemistry, and to predict how climate change may affect such biogeochemical processes at the Arctic Ocean seafloor. Here, we employ an integrated model assessment that explicitly resolves benthic pH and carbonate chemistry along a S—N transect in the Barents Sea. We identify the main drivers of observed carbonate dynamics and estimate benthic fluxes of dissolved inorganic carbon and alkalinity to the Arctic Ocean. We explore how bottom water conditions and in-situ organic matter degradation shape these processes and show that organic matter transformation strongly impacts pH and carbonate saturation (Ω) variations. Aerobic organic matter degradation drives a negative pH shift (pH < 7.6) in the upper 2—5 cm, producing Ω < 1. This causes shallow carbonate dissolution, buffering porewater pH to around 8.0. Organic matter degradation via metal oxide (Mn/Fe) reduction pathways further increases pH and carbonate saturation state. At the northern stations, where Ω > 5 at around 10–25 cm, model simulations result in authigenic carbonate precipitation. Furthermore, benthic fluxes of dissolved inorganic carbon (12.5—59.5 µmol cm−2 yr−1) and alkalinity (11.3—63.2 µmol cm−2 yr−1) are 2—3-fold greater in the northern sites due to greater carbonate dissolution. Our assessment is of significant relevance to predict how changes in the Arctic Ocean may shift carbon burial and pH buffering into the next century.

Convective turbulence driven by gravitational instability is a fundamental mixing mechanism in geophysical flows, but in situ estimation of its characteristics is obscured by the background flows and the relatively slow temporal scales. We present characteristics of the full Reynolds tensor from a convective surface boundary layer of an ice-covered lake. The results were obtained by using an original method of measuring the full set of turbulent stresses by a combined use of two ADCPs. The strong horizontal shear stress was revealed as a characteristic feature of free convection differing from the “conventional” turbulent boundary flows. The ratio of normal stresses along vertical and horizontal axes remained below 1/4, suggesting strongly anisotropic character of turbulence. The vertical r.m.s. velocity fluctuations obeyed the buoyancy flux scaling with the coefficient of 1/3, which is at lower boundary of the previously reported values.

Using borehole strainmeters, we detected a 13-day long slow slip event on the Longitudinal Valley Fault, Taiwan. It is located between 8 to 15 km depth and has an equivalent moment magnitude of 5.5. The slow event has likely been promoted by the significant Coulomb stress changes (∼ + 1 MPa) imparted by a combination of coseismic and postseismic slip of the M w 6.8 Chengkung earthquake. Besides, insignificant coseismic slip is observed in the slow event region, suggesting that the latter could have acted as a barrier during the Chengkung earthquake. We also found a spatiotemporal correlation between the slow event and a cluster of repeating microearthquakes, suggesting aseismic slip as a possible driven mechanism of repeating ruptures. These results highlight the complex interplay between seismic and aseismic processes along the fault.

We use GPS observations to investigate the magnitude and spatial distribution of vertical coseismic and postseismic deformation of the Australian continent and compare these with elastic and viscoelastic model outputs. We observe and model surface deformation in Australia caused by six recent large far-field events: 2004 Mw 8.1 Macquarie Ridge, 2004 Mw 9.3 Sumatra-Anderman, 2005 Mw 8.6 in northern Sumatra, the 2007 series of Mw 8.5 and 7.9 in southern Sumatra, two events in 2012 of Mw 8.6 and 8.2 in northern Sumatra, and the 2009 Mw 7.8 south of New Zealand. Observed vertical coseismic deformation reaches 3 mm, with the magnitude varying spatially and by earthquake in broad agreement with modelling of coseismic deformation. Postseismic deformation is observed in all three coordinate components at Australian GPS sites nearest to these earthquakes, with deformations reaching several mm/yr in the vertical over multiple years. In particular, the Sumatran sequence produces observed subsidence in north-western Australia of up to 4 mm/yr over 2004.9-2010.0 where predictions based on one-dimensional viscoelastic Earth models replicate the subsidence but underpredict the vertical rate by a factor of two. Across all earthquakes, the models often fit one or two coordinate components of the observations, but rarely all three. Unmodeled lateral rheological structure likely contributes to this given the difference between the oceanic location of the earthquakes and the Australian continental setting of the GPS sites. The magnitude and spatial extent of these coseismic and postseismic deformations warrant their consideration in future updates of the geodetic terrestrial reference frame.

Flux transfer events (FTEs), as flux ropes (FRs), are considered key agents for solar wind energy to enter the terrestrial magnetosphere. Recent observations identify entangled flux tubes that collide and pull against each other. Reconnection occurs to disentangle and produce a new pair of flux ropes with different connectivity. In this paper, we examine how such an entanglement process evolve in time by comparing 17 entanglements observed by the Magnetospheric Multiscale (MMS) mission. The By-dominated interplanetary magnetic field (IMF) distribution of the entangled tubes agrees with previous findings. We have identified three evolutionary stages characterized by the magnetic field and pressure enhancement. Our study confirms the flux rope nature of these events and explains how a disparate pair of ropes is formed from two entangled flux tubes, each initially connected to a different hemisphere of the magnetosphere.

High energy electrons observed in the magnetosheath must be accelerated by some mech- anism that is as yet undetermined. We present observations of high-energy electrons trapped in diamagnetic cavities as measured by Magnetospheric Multiscale from 2015-2018. The observations support the notion of local acceleration in the reconnection quasi-potential as many of events show particles with pitch angles that are increasingly closer to 90 de- grees with increasing energy. It is suggested that these particles can end up in the loss cone and be transported to the magnetosheath. We also characterize each diamagnetic cavity as formed due to low- or high-latitude reconnection based on prevailing solar wind conditions. The character of the ions in the diamagnetic cavity is only briefly mentioned as their properties warrant another stand-alone investigation.

Rooting depth is an ecosystem trait that determines the extent of soil development and carbon cycling. Recent hypotheses propose that human-induced changes to Earth’s biogeochemical cycles propagate deeply due to rooting depth changes from agricultural and climate-induced land cover changes. Yet, the lack of a global-scale quantification of rooting depth responses to human activity limits knowledge of hydrosphere-atmosphere-lithosphere feedbacks in the Anthropocene. Here we use land cover datasets to demonstrate that global rooting depths have become shallower in the Anthropocene, and are likely to become yet shallower this century. Specifically, globally averaged depths above which 99% of root biomass occurs (D99) are 8.7%, or 16 cm, shallower relative to those for potential vegetation. This net shallowing results from agricultural expansion truncating D99 by 82 cm, and woody encroachment linked to anthropogenic climate change extending D99 by 65 cm. Projected land cover scenarios in 2100 suggest further D99 shallowing of 63 to 72 cm, exceeding that experienced to date and suggesting that the pace of root shallowing will quicken in the coming century. Losses of Earth’s deepest roots—soil-forming agents—suggest unanticipated changes in fluxes of water, solutes, and carbon. Our work constrains rooting depth distributions for global models, allowing the land modeling community to explore cascading effects of rooting depth changes on water, carbon, and energy dynamics, and can guide design of field-based efforts to quantify deep anthropogenic influences. Understanding human influence on biota’s reach into Earth’s subsurface will improve predictions of interactive functioning of the biosphere, lithosphere, and hydrosphere.

Probing the flow permeability of porous media with elastic waves is a formidable challenge, also because the wave-induced oscillatory motion renders the permeability frequency dependent. Existing theoretical models for such a dynamic permeability assume that the frequency dependence is primarily controlled by a single characteristic length scale of the pore space. However, the fact that in most natural porous media there exists a distinct range of pore sizes is ignored. To overcome this limitation, we develop a dynamic permeability model that explicitly incorporates the pore size distribution. We show that the pore size distribution has a first-order effect on the dynamic permeability. Since the pore size distribution is measurable from techniques such as nuclear magnetic resonance, the results indicate the possibility to jointly use remote-sensing technologies for improved geomaterial characterization and optimized permeability manipulation of manufactured porous media.

Erosion, transport, and deposition of a river-bed has attracted attentions from various disciplines. To understand those issues, bed shear stress should be evaluated first. However, calculating bed shear stress with existing formulas have certain limitations because uniform and/or gradually-varied flow was assumed in their studies, which is hardly found in an actual river. Therefore, direct applying them into three-dimensional complex flow field, such as flow around a bridge obstruction or a large-rock, is questionable. Thus, laboratory experiment was conducted in a flume and the results were used to suggest a method of bed shear stress estimation in the complex flow field. To generate the complex flow field, three different width of obstruction was constructed and installed in one side of the flume. Water depth, velocities, and turbulence intensities were measured, and the measurements were used as input variables of four different widely used existing shear stress formulas for their evaluation. Then, the effects of local turbulence on the shear stress were discussed in terms of Reynolds stress and turbulent kinetic energy (TKE) measured under a wide range of flow variables. Based on the findings, bed shear stress can be estimated with an empirical correction factor for the local turbulence around the obstruction where elevated region of bed shear stress is found, and the experimental result shows that the correction factor is function of the value of flow contraction ratio. The results are expected to be a useful outcome to understand the mechanism of geomorphological change under rapidly-varied non-uniform flow.

We present new and previously unreported in-situ observations of Hertz frequency multi-harmonic mode field line resonances detected by the Electric Field and Waves (EFW) instrument on-board the NASA Van Allen Probes during low-L perigee passes. Spectral analysis of the spin plane electric field data reveals the waves in numerous perigee passes, in sequential passes of Probes A and B, and with harmonic frequency structures from ~0.5 to 3.5 Hz which vary with L-shell, altitude, and from day to day. Comparing the observations to wave models using plasma mass density values along the field line given by empirical power laws and from the International Reference Ionosphere model (IRI), we conclude the waves are standing Alfvén field line resonances, and that only odd-mode harmonics are excited. The model eigenfrequencies are strongly controlled by the density close to the apex of the field line, suggesting a new diagnostic for equatorial ionospheric density dynamics.

Various indices have been defined to characterize the phase and amplitude of the Madden-Julian oscillation (MJO). One widely used index is the Outgoing Longwave Radiation (OLR) based MJO index (OMI), which is calculated using the spatial pattern of 30-96-day eastward-filtered OLR. The EOFs used to calculate the OMI in observations are prone to degeneracy and exhibit oscillations on the order of 10-20 days, despite initial filtering of the OLR. We propose a simple modification to the OMI that involves aligning the EOFs between neighboring days while retaining the spatial pattern described by the EOFs. This rotation method is implemented as a postprocessing step of the current OMI calculation and cleanly removes the spurious oscillations and degeneracy issues seen in the standard method. A similar rotation procedure can be implemented in calculations of other MJO indices.

We introduce a minimal stochastic lattice model for the column relative humidity ($R$) in the tropics, which incorporates convective moistening, lateral mixing and subsidence drying. The probability of convection occurring in a location increases with $R$, based on TRMM observations, providing a positive feedback that could lead to aggregation. We show that the simple model reproduces many aspects of full-physics cloud resolving model experiments. Depending on model parameter settings and domain size and resolution choices, it can produce both random or aggregated equilibrium states. Clustering occurs more readily with larger domains and coarser resolutions, in agreement with full physics models. Using dimensional arguments and fits from empirical data, we derive a dimensionless parameter we call the aggregation number, $N_{ag}$, that predicts whether a specific model and experiment setup will result in an aggregated or random state. The parameter includes the moistening feedback strength, the diffusion, the subsidence timescale, the domain size and spatial resolution. Using large ensembles of experiments, we show that the transition between random and aggregated states occurs at a critical value of $N_{ag}$. We argue that $N_{ag}$ could help to understand the differences in aggregation states between full physics, cloud resolving models.

We use a Landscape Evolution Model (FastScape S2S) to explore the impact of inherited topography in the foreland domain of a rising mountain range on its stratigraphic architecture and sediment accumulation history, inspired by the northern Pyrenean foreland. We simulate an uplifting half mountain range, its foreland basin and forebulge, and beyond, an open marine domain. We ran models with 4 different initial reliefs in the foreland domain: an initially flat foreland domain at sea-level, an elevated flat continental foreland (+300 m), a pre-existing 1 km-deep and 100 km-wide bathymetry at the location of the future foreland basin associated with a forebulge domain either at sea-level or elevated at +300m. All models show a prograding mega-sequence associated with building of mountain topography and development of the flexural foreland basin and forebulge, coalescence of alluvial fans at the foot of the range, progressive continentalization of the foreland domain, and burial of the forebulge. An initially elevated foreland domain ultimately produces a thinner foreland basin while an initially deep foreland basin produces a thicker one. After 10-13 Myr, the initial relief of foreland domain is smoothed out and the landscape does not exhibit a record of pre-existing relief. In contrast, the stratigraphic architecture of the foreland basin allows to trace inherited relief with deep marine sediments in the initially deep foreland basin, marine sediments onlapping and then burying the forebulge initially at sea-level, and continental sediments onlapping and burying the initially elevated foreland domain. We compare these interpretations to the Pyrenean retro-foreland.

The significant impact of soil structure on soil hydraulic properties and then on the associated water and solute transport is well recognized. However, existing soil hydraulic models that account for the effect of soil structure are often at the cost of overparameterization, hindering further application on large scales. In this study, we developed a new model that considers the effect of soil structure in hydraulic conductivity prediction when introducing no new free parameters. Testing with 152 soil samples that include different soil types shows that the new model considerably improves the prediction of conductivity, with an average root-mean-square-value (RMSE) of 0.65 cm d−1. When applying the new model in fitting observations, the model showed excellent performance, with an RMSE of only 0.30 cm d−1 remaining. This new soil hydraulic model provides a simple and practical way to incorporate the influence of soil structure in water and solute transport simulations.

In this paper, we introduce a testbed for evaluating and comparing climate modeling systems at cloud resolving scales using hindcasts of the June 2012 North American derecho. The testbed is applied to two models: the regionally-refined Simple Cloud-Resolving E3SM Atmosphere Model (SCREAM) at horizontal resolutions ranging from 6.5 to 1.625 km and the Weather Research and Forecasting (WRF) model with 4 km grid spacing. We find the simulation results to be highly sensitive to the initial conditions, initialization time, and model configurations, with initial conditions from the Rapid Refresh (RAP) producing the best simulation. Significant improvement is identified in the SCREAM simulations as horizontal grid spacing is refined. While a propagation delay of approximately 2 hours is found in both models, SCREAM at 1.625 km simulates the observed bow echo structure of the derecho well and predicts strong surface gusts that exceed 30 m/s. In comparison, WRF hardly produces surface wind over 25 m/s, and the derecho wind gust in WRF is 42-46% lower than in SCREAM. Moreover, WRF has a lower bias in simulating cold clouds but overestimates the precipitation intensity. Both models well reproduce the observed outgoing longwave radiation spatial patterns (Pearson correlation > 0.88) while they simulate larger areas of composite radar reflectivity > 40 dBZ by up to 4 times and underestimate the precipitating area by ~ 70\% in WRF and 47\% in SCREAM compared to observations.

Megathrust earthquakes with a wide along-dip rupture extent show clearly depth-dependent variations in rupture characteristics such as rupture velocity, frequency contents of seismic radiation and slip distribution. Some recent studies propose that heterogeneous upper-plate rigidity determines this phenomenon, though along-dip variations in fault friction have long been thought to play a dominant role. In this study, we use dynamic rupture modeling to explore and compare roles of these two factors in depth-dependent rupture characteristics of megathrust earthquakes along a shallow-dipping subduction plane that is governed by the rate- and state- dependent friction. We find that an updip transition from velocity-weakening behavior downdip to velocity-strengthening behavior near the trench suppresses rupture propagation toward the trench and a thicker transition zone results in a more confined slip at depth. The updip transition in velocity-dependent frictional property also dominates high-frequency depletion in seismic radiation at shallow depth. With an addition of a conditionally stable zone at shallow depth, rupture velocity significantly decreases, resulting in longer rupture duration as the thickness of the conditionally stable zone increases. The low-velocity layers in the upper plate at shallow depth lead to a more compliant prism and thus significantly higher total slip near the trench. Although they place some limits to rupture velocity at shallow depth, they enhance high-frequency radiation and thus do not contribute to high-frequency depletion observed in recent megathrust earthquakes. We conclude that fault friction plays more important roles than upper-plate rigidity in determining depth-dependent rupture characteristics of megathrust earthquakes.

Extratropical cyclones are major contributors to consequential weather in the mid-latitudes and tend to develop in regions of enhanced cyclogenesis and progress along climatological storm tracks. Numerous studies have noted the influence that terrestrial snow cover exerts on atmospheric baroclinicity which is critical to the formation and trajectories of such cyclones. Fewer studies have examined the explicit role which continental snow cover extent has in determining cyclones intensities, trajectories, and precipitation characteristics. While several examinations of climate model projections have generally shown a poleward shift in storm tracks by the late 21st century, none have determined the degree to which the coincident poleward shift in snow extent is responsible. A method of imposing 10th , 50th , and 90th percentile values of snow retreat between the late 20th and 21st centuries as projected by 14 Coupled Model Intercomparison Project Phase Five (CMIP5) models is used to alter 20 historical cold season cyclones which tracked over or adjacent to the North American Great Plains. Simulations by the Advanced Research version of the Weather Research and Forecast Model (WRF-ARW) are initialized at 0 to 4 days prior to cyclogenesis. Cyclone trajectories and their central sea level pressure did not change substantially, but followed consistent spatial trends. Near-surface wind speed generally increased, as did precipitation with preferred phase change from solid to liquid state. Cyclone-associated precipitation often shifted poleward as snow was removed. Variable responses were dependent on the month in which cyclones occurred, with stronger responses in the midwinter than the shoulder months.