It is unclear why two-phase fluid flows in porous media develop a series of fluid displacement patterns. This study treats a two-phase flow system as an open thermodynamical system with a two-phase displacement process that follows the principle of the minimum operating power (MOPR). When different constraints are imposed on the system, the pore-scale interfacial dynamic response to this principle varies significantly, and a series of self-regulation mechanisms exist. These new findings not only explain the physical origins of the diverse fluid displacement patterns and interface reconstruction events but also provide new insights into the interface invasion protocol.
Raindrop Size Distributions (RSDs) samples from 17 flight missions though 6 hurricanes collected by Precipitation Imaging Probe (PIP) during National Oceanic and Atmospheric Administration’s hurricane field program in 2020 are used to study gamma fits of the RSDs in hurricanes. The method of moment (MM) is adopted for solving for the three parameters in gamma distribution. The results show that the usage of lower (higher) moments produces large biases for integral rain variables (IRV) of higher (lower) moments. These biases can be alleviated by extracting the best fits from five groups that use increasing higher orders of moments for MM. An intercept (N0)— slope (λ) relation identified from the fitted gamma distributions captures 92% of the variance of the data, where the majority of remaining 8% can be further captured by including the impact of liquid water content (LWC), as shown in the results from a random forest regression model.
Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) is a space-borne instrument dedicated to monitoring high-energy transients, thereinto Terrestrial Gamma-ray Flashes (TGFs) and Terrestrial Electron Beams (TEBs). We propose a TGF/TEB search algorithm, with which 147 bright TGFs and 4 TEBs are identified during an effective observation time of $\sim$ 9 months. We show that, with gamma-ray and charged particle detectors, GECAM can effectively identify and distinguish TGFs and TEBs, and measure their temporal and spectral properties in detail. Moreover, we find an interesting TEB consisting of two pulses with a separation of $\sim$ 150 ms, which is expected to originate from a lightning process near the geomagnetic footprint. We also find that the GECAM TGF’s lightning-association ratio is $\sim$ 80\% in the east Asia region using the GLD360 lightning network, which is significantly higher than previous observations.
Accurate predictions of fluid flow, mass transport, and reaction rates critically impact the efficiency and reliability of subsurface exploration and sustainable use of subsurface resources. Quantitative dynamical sensing and imaging can play a pivotal role in the ability to make such predictions. Geophysical thermoacoustic technology has the potential to provide the aforementioned capabilities since it builds upon the principle that electromagnetic and mechanical wave fields can be coupled through a thermodynamic process. In this letter, we present laboratory experiments featuring the efficacy of thermoacustic imaging in the monitoring of preferential flow of water in porous media. Our laboratory experimental equipment can be readily packaged in a form factor that fits in a borehole, and the use of multiple acoustic transducers—which can be combined with volumetric coding techniques—has the potential to provide quasi-real-time imaging (0.5 Hertz video rate) of regions in close proximity (a few meters) of an open field well.
Floods are often disastrous due to underestimation of the magnitude of rare events. When the occurrence of floods follows a heavy-tailed distribution the chance of extreme events is sizable. However, identifying heavy-tailed flood behavior is challenging because of limited data records and the lack of physical support for currently used indices. We address these issues by deriving a new index of heavy-tailed flood behavior from a physically-based description of streamflow dynamics. The proposed index, which is embodied by the hydrograph recession exponent, enables inferring heavy-tailed flood behavior from daily flow records. We test the index in a large set of case studies across Germany. Results show its ability to identify cases with either heavy- or nonheavy-tailed flood behavior, and to evaluate the tail heaviness. Remarkably, the results are robust also for decreasing the lengths of data records. The new index thus allows for assessing flood hazards from commonly available data.
In the absence of consistent meteorological data on Mars, the morphology of dunes can be employed to study its atmosphere. Specifically, barchan dunes, which form under approximately unimodal winds, are reliable proxies for the dominant wind direction. Here, we characterize near-surface winds on Mars from the morphology of >106 barchans mapped globally on the planet by a convolutional neural network. Barchan migration is predominantly aligned with the global circulation: northerly at mid-latitudes and cyclonic near the north pole, with the addition of an anti-cyclonic north-polar component that likely originates from winds emerging from the ice cap. Locally, migration directions deviate from regional trends in areas with high topographic roughness. Notably, obstacles <100 km such as impact craters are efficient at deflecting surface winds. Our database, which provides insights into planetary-scale aeolian processes on modern-day Mars, can be used to constrain global circulation models to assist with predictions for future missions.
The strength of CO2 fertilisation is a major uncertainty across terrestrial biosphere models (TBMs) and is suggested to be overestimated without a representation of nitrogen (N) limitation. Here, we compare TBM projections with and without coupled C and N cycling over alternative future scenarios (the Shared Socioeconomic Pathways) to examine how representing N cycling influences CO2 fertilisation as well as the effects of a comprehensive group of physical and socioeconomic global change drivers. Because elevated N deposition and N mineralisation (driven by elevated temperature) have stimulated terrestrial C sequestration over the historical period, a TBM without N cycling must exaggerate the strength of CO2 fertilisation to compensate for these unrepresented N processes and to reproduce the historical terrestrial C sink. As a result, it cannot reliably project the future terrestrial C sink, overestimating CO2 fertilisation as CO2 increases faster than N deposition and temperature in future scenarios.
Denitrification is a key process in the global nitrogen (N) cycle, causing both nitrous oxide (N2O) and dinitrogen (N2) emissions. However, estimates of seasonal denitrification losses (N2O+N2) are scarce, reflecting methodological difficulties in measuring soil-borne N2 emissions against the high atmospheric N2 background and challenges regarding their spatio-temporal upscaling. This study investigated N2O+N2 losses in response to N fertiliser rates (0, 100, 150, 200 and 250 kg N ha-1) on two intensively managed tropical sugarcane farms in Australia, by combining automated N2O monitoring, in-situ N2 and N2O measurements using the 15N gas flux method and fertiliser 15N recoveries at harvest. Dynamic changes in the N2O/(N2O+N2) ratio (< 0.01 to 0.768) were explained by fitting generalised additive mixed models (GAMMs) with soil factors to upscale high temporal-resolution N2O data to daily N2 emissions over the season. Cumulative N2O+N2 losses ranged from 12 to 87 kg N ha-1, increasing non-linearly with increasing N fertiliser rates. Emissions of N2O+N2 accounted for 31–78% of fertiliser 15N losses and were dominated by environmentally benign N2 emissions. The contribution of denitrification to N fertiliser loss decreased with increasing N rates, suggesting increasing significance of other N loss pathways including leaching and runoff at higher N rates. This study delivers a blueprint approach to extrapolate denitrification measurements at both temporal and spatial scales, which can be applied in fertilised agroecosystems. Robust estimates of denitrification losses determined using this method will help to improve cropping system modelling approaches, advancing our understanding of the N cycle across scales.
Information from total electron content (TEC) from Global Navigation Satellite Systems (GNSS) could be assessed to know the impact of weather events to help in developing prediction and warning systems. The majority of studies focus on the occurrence of only one event neglecting situations where these weather events happen almost simultaneously or consecutively. This current study tends to fill the gap by analyzing ionosphere response following the simultaneous and/or consecutive occurrence of geomagnetic storm and lightning events at various intensities in southern China coastal region. The results showed that the magnitude of the frequency lightning-related events using continuous wavelet transform (CWT) was 0.3-0.4 while that of geomagnetic storm was 0.15-0.3. However, the various levels of intensity could not be distinguished. Being able to differentiate the weather events by the magnitude values following the ionosphere response is good for prediction and modeling purposes as the use of TEC in some studies does not provide this clear distinction.
The Arctic is marked by deep intrusions of warm, moist air, alternating with outbreaks of cold air down to lower latitudes. The typical vertical structure of clouds and precipitation during these two synoptic weather extremes is examined at a coastal site at 69°N in Norway. The Norwegian Sea is a corridor for warm-air intrusions (WAIs) and frequently witnesses cold-air outbreaks (CAOs). This study uses data from profiling radar, lidar, and microwave radiometer, radiosondes and other probes that were collected during the Cold air Outbreaks in the Marine Boundary Layer Experiment (COMBLE) between 1 December 2019 and 31 May 2020. Marine CAOs are defined in terms of thermal instability relative to the sea surface temperature, and warm-air intrusions in terms of stratification of moist static energy between the surface and 850 hPa. Cloud structures in CAOs are convective, driven by strong surface heat fluxes over a long fetch of open water, with cloud tops between 2-4 km. The mostly open-cellular convection may contain substantial ice and produce intermittent moderate precipitation at the observational site, notwithstanding the low precipitable water vapor. In contrast, WAIs are marked by high values of precipitable water vapor and integrated vapor transport. WAI clouds are stratiform, with cloud tops often exceeding 6 km, sometimes layered, and generally producing persistent precipitation that can be heavier than in CAOs.
Over the continental slope off Oregon at the US West Coast, at 44.6N, vertical stratification is found to be anomalously weak in July-August of 2014 and 2015 both in a regional ocean circulation model and Conductivity-Temperature-Depth (CTD) profile observations. To understand the responsible mechanism, we focus on the layer between the isopycnal surfaces $\sigma_\theta=26.5$ and 26.25 kg/m3 that is found between depths 100-300 m and represents material properties characteristic of the slope poleward undercurrent and shelf-slope exchange. This layer thickness, about 50 m on average, can be twice as large during the above-mentioned periods. In the 2009-2018 model analysis, this anomaly is revealed over the continental slope only in summers 2014 and 2015 and only off the Oregon and Washington coasts (40-47N). The stratification anomaly is explained as the effect of advection of the seasonal alongslope potential vorticity (PV) gradient by an anomalously strong poleward slope current. In the annual cycle, the zone of strong alongslope PV gradient is found between 40-47N, supported by the local upwelling that results in the injection of the large PV in the bottom boundary layer over the shelf followed by its offshore transport in the slope region. The positive alongslope current anomaly propagates to Oregon with coastally trapped waves as part of the El Niño oceanic response and can be up to 0.1 m/s. Advection by this anomalous poleward current results in transporting the seasonal PV gradient earlier in the season than on average.
The observed retreat and anticipated further decline in Arctic sea ice hold strong climate, environmental, and societal implications. In predicting climate evolution, ensembles of coupled climate models have demonstrated appreciable accuracy in simulating sea ice area and volume trends throughout the historical period. However, individual climate models still show significant differences in simulating the sea ice thickness distribution. To better understand individual model performance in sea ice simulation, nine climate models previously identified to provide plausible sea ice decline and global temperature change were evaluated in comparison with Arctic satellite and reanalysis derived sea ice thickness data, sea ice extent records, and atmospheric reanalysis data of surface wind and air temperature. Assessment found that the simulated spatial distribution of historical sea ice thickness varies greatly between models and that several key limitations persist among models. Primarily, most models do not capture the thickest regimes of multi-year ice present in the Wandel and Lincoln Seas; those that do, often possess erroneous positive bias in other regions such as the Laptev Sea or along the Eurasian Arctic Shelf. From analysis, no model could be identified as performing best overall in simulating historic sea ice, as model bias varies regionally and seasonally. Nonetheless, the bias maps and statistical measures derived from this analysis should enhance understanding of the limitations of each climate model. This research is motivated in-part to inform future usage of coupled climate model projection for regional modeling efforts and enhance climate change preparedness and resilience in the Arctic.
High-resolution simulations by the Regional Ocean Modeling System (ROMS) were used to investigate the dispersal of the San Francisco Bay (SFB) plume over the northern-central California continental shelf during the period of 2011 to 2012. The modeled bulk dynamics of surface currents and state variables showed many similarities to corresponding observations. After entering the Pacific Ocean through the Golden Gate, the SFB plume is dispersed across the shelf via three pathways: (i) along the southern coast towards Monterey Bay, (ii) along the northern coast towards Point Arena, and (iii) an offshore pathway restricted within the shelf break. On the two-year mean timescale, the along-shore zone of impact of the northward-dispersed plume is about 1.5 times longer than that of the southern branch. Due to the opposite surface Ekman transports induced by the northerly or southerly winds, the southern plume branch occupies a broader cross-shore extent, roughly twice as wide as the northern branch which extends roughly two times deeper due to coastal downwelling. Besides these mean characteristics, the SFB plume dispersal also shows considerable temporal variability in response to various forcings, with wind and surface-current forcing most strongly related to the dispersing direction. Applying constituent-oriented age theory, we determine that it can be as long as 50 days since the SFB plume was last in contact with SFB before being flushed away from the Gulf of the Farallones. This study sheds light on the transport and fate of SFB plume and its impact zone with implications for California’s marine ecosystems.
Basin-scale quasi-geostrophic gyres are common features of large lakes subject to Coriolis force. Cyclonic gyres are often characterized by dome-shaped thermoclines that form due to pelagic upwelling which takes place in their center. At present, dynamics of pelagic upwelling in the Surface Mixed Layer (SML) of oceans and lakes are poorly documented. A unique combination of high-resolution 3D numerical modeling, satellite imagery and field observations allowed confirming for the first time in a lake, the existence of intense pelagic upwelling in the center of cyclonic gyres under strong shallow (summer) and weak deep (winter) stratified conditions/thermocline. Field observations in Lake Geneva revealed that surprisingly intense upwelling from the thermocline to the SML and even to the lake surface occurred as chimney-like structures of cold water within the SML, as confirmed by Advanced Very High-Resolution Radiometer data. Results of a calibrated 3D numerical model suggest that the classical Ekman pumping mechanism cannot explain such pelagic upwelling. Analysis of the contribution of various terms in the vertically-averaged momentum equation showed that the nonlinear (advective) term dominates, resulting in heterogeneous divergent flows within cyclonic gyres. The combination of nonlinear heterogeneous divergent flow and 3D ageostrophic strain caused by gyre distortion is responsible for the chimney-like upwelling in the SML. The potential impact of such pelagic upwelling on long-term observations at a measurement station in the center of Lake Geneva suggests that caution should be exercised when relying on limited (in space and/or time) profile measurements for monitoring and quantifying processes in large lakes.
Using imaging spectroscopy (hyperspectral imaging), we sought to assess the effects of image pixel resolution, size of mapping windows composed of pixels, and number of spectral species assigned to pixels on the capacity to map plant beta diversity using the biodivMapR algorithm, in support of the planned NASA Surface Biology and Geology (SBG) satellite remote sensing mission. BiodivMapR classifies pixels as spectral species, then calculates beta diversity as dissimilarity of spectral species among mapping windows each composed of multiple pixels. We used NEON airborne 1 m resolution hyperspectral images collected at three sites representing native longleaf pine ecosystems in the southeastern U.S. and aggregated pixels to sizes ranging from 1-90 m for comparative analyses. Plant community composition was groundtruthed. Results show that the capacity to detect plant beta diversity decreases with fewer pixels per mapping window, such that pixel resolution limits the size of mapping windows effective for representing beta diversity. Mapping window size in turn limits the spatial resolution of beta diversity maps composed of mapping windows. Assigning too few pixels per window, as well as assigning too many spectral species per image, results in overestimation of dissimilarity among locations that have plant species in common. This overestimation undermines the capacity to contrast mapping window dissimilarity within versus among community types and reduces the information content of beta diversity maps. These results demonstrate the advantage of maximizing spatial resolution of hyperspectral imaging instruments on the anticipated NASA SBG satellite mission and similar remote sensing projects.
We exploit nonlinear elastodynamic properties of fractured rock to probe the micro-scale mechanics of fractures and understand the relation between fluid transport and fracture aperture and area, stiffness proxy, under dynamic stressing. Experiments are conducted on rough, tensile-fractured Westerly granite specimen subject to triaxial stresses. Fracture permeability is measured from steady-state fluid flow with deionized water. Pore pressure oscillations are applied at amplitudes ranging from 0.2 to 1~MPa at 1~Hz frequency. During dynamic stressing we transmit acoustic signals through the fracture using an array of piezoelectric transducers (PZTs) to monitor the evolution of fracture interface properties. We examine the influence of fracture aperture and contact area by conducting measurements at effective normal stresses of 10, 12.5, 15, 17.5, and 20~MPa. Additionally, the evolution of contact area with stress is characterized using pressure sensitive film. These experiments are conducted separately with the same fracture and they map contact area at stresses from 9 to 21~MPa. The resulting ‘true’ area of contact measurements made for the entire fracture surface and within the calculated PZT sensor footprints, numerical modeling of Fresnel zone. We compare the elastodynamic response of the the fracture using the stress-induced changes ultrasonic wave velocities for a range of transmitter-receiver pairs to image spatial variations in contact properties, which is informed by fracture contact area measurements. These measurements of the nonlinear elasticity are related to the fluid-flow, permeability, in response to dynamic stressing and similar comparisons are made for the slow-dynamics, recovery, of the fracture interface following the stress perturbations.
Earthquakes are frequently accompanied by electromagnetic (EM) anomalies. These anomalies are thought to be caused by earthquakes but the generation mechanism is still unclear. The piezoelectric effect has been proposed as a possible mechanism but the EM responses to earthquakes due to such an effect has not been well understood. In this article, we study the EM signals generated by an earthquake source due to the piezoelectric effect. We develop a semi-analytical method to solve the seismic and EM fields in a 3D layered model and conduct numerical simulations to investigate the characteristics of the EM fields. The results show that the earthquake can generate two kinds of EM signals. One is the early-EM signal which arrives earlier than the seismic wave. The other is the co-seismic EM signal accompanying the seismic wave. For an earthquake the co-seismic electric field can reach ~10 μV/m and the magnetic field can reach ~10-4 nT. We also study the sensitivity of the co-seismic EM fields to the rock conductivity. The results show that the co-seismic EM fields are mainly affected by the conductivity of the shallow layer, and they are also affected by the conductivity of the deep layer when the top layer is thin.
Soil erosion is impacted by climate and land use changes which need to be quantified to assess future risks and to design efficient soil conservation measures. The Coupled Model Intercomparison Project Phase 5 (CMIP5) simulations have provided the basis for most such assessments and yet are being gradually superseded by more recent simulations from Phase 6 (CMIP6). The High-Resolution Model Intercomparison Project (HighResMIP) experiment in CMIP6 adds value over the downscaled CMIP5 simulations by improving process representation in the global climate system. Our study investigates and compares high-resolution model simulations from CMIP6 against CMIP5. Model evaluation for the reference period (1986–2005) indicates that the CMIP6 model outperforms the regional climate models (RCM) from CMIP5 for better circulation simulations, but both overestimate soil erosion in China. The average projected soil erosion increases by 27.85 from CMIP5 and 20.03 t·hm-2·a-1 from the CMIP6 model with remarkable geographical heterogeneity. Soil erosion is projected to decrease in black soil regions, purple soil regions, and karst regions from CMIP6 results, which is opposite to the increasing trend found in those regions from CMIP5. Land use and climatic changes contributed 51.68% and -5.92% respectively from CMIP5 simulations while 35.74% and -13.77% from CMIP6 to the increased soil erosion rate. The negative contribution of land use change is gradually intensified with the CMIP6 model representing finer-scale processes of converting land-use type into cropland, pasture, and urban land. Overall, the CMIP6 projections provide a less severe soil erosion situation while addressing the need to pursue soil conservation more.