Feed aggregator

Science, Volume 385, Issue 6708, August 2024.

Science, Volume 385, Issue 6708, August 2024.

Science, Volume 385, Issue 6708, August 2024.

Science, Volume 385, Issue 6708, August 2024.

Science, Volume 385, Issue 6708, August 2024.

Abstract

Climate models indicate that a warmer environment will increase low-level moisture, potentially intensify extreme precipitation. However, its impact on different rainfall types remains unclear. Using satellite data, we examined changes in light (0-95th percentile, ≤5.28 mm hr−1) and heavy (95-100th percentile, >5.28 mm hr−1) precipitation in the tropics from 1998 to 2019. Our findings show a −9 ± 2% (23 ± 2%) change in heavy (light) rain intensity and a 13 ± 2% (−24 ± 1%) change in heavy (light) rain frequency. These changes link to warmer sea surface temperatures, increased atmospheric stability and water vapor, and weakened upward velocity. These insights shed light on how heavy and light precipitation patterns respond to changing climate, emphasizing the complexities within the hydrological cycle.

Abstract

Our current knowledge regarding the distribution patterns of ancient and recent recycled materials, as well as the origin of intraplate basalts in the eastern Asia Big Mantle Wedge (BMW), is limited. To address this, we conducted a detailed geochemical analysis of olivine melt inclusions (OLMI) in nephelinite samples. The normal OLMIs detected in our investigation exhibit geochemical features that closely resemble those of the hosting nephelinite, indicating a consistent association with a carbonated mantle source. Additionally, we identified a distinct group of anomalous OLMIs that displayed different geochemical characteristics from the hosting nephelinite but showed similarities to regional alkali basalts sourced from pyroxenite. The observed geochemical diversity in the nephelinite OLMIs suggests an interaction between deeply derived carbonated melts originating from the flattened Pacific slab in the mantle transition zone and pyroxenite in the lithospheric mantle. Carbonated fluid-fluxed melting is key to basalt formation in the BMW.

Abstract

Terminus change is a complex outcome of ice-ocean boundary processes and poses challenges for ice sheet models due to inadequate calving laws, creating uncertainty in sea level change projections. To address this, we quantify glacier termini sinuosity and convexity, testing the hypothesis that terminus morphology reflects dominant calving processes. Using 10 glaciers with diverse calving styles in Greenland over the period from 1985 to 2021, we establish a supervised classification of calving style by comparing morphology and literature-derived calving observations. Validation with four of these glaciers and flotation conditions and subglacial discharge routing observations confirms concave, smooth termini indicate buoyant flexure dominated-calving, while convex, sinuous termini suggest serac failure dominated-calving. We also identify a mixed style where both calving types may occur. We use these classes to label calving style from 1985 to 2021 for all 10 glaciers and explore how this changes over time as glaciers retreat.

Abstract

This study assesses the reliability and limitations of the Geostationary Lightning Mapper (GLM) in detecting continuing currents by comparing observations from ground-based high-speed cameras with GLM-16 data. Our findings show that the GLM's one-group detection efficiency (DE_1) is 53%, while the more stringent five-consecutive-group detection efficiency (DE_5) is 10%. Optical signals detected by the GLM predominantly occur during the early stages of continuing currents. Additionally, there is a notable disparity in detection efficiencies between positive and negative continuing currents, with positive continuing currents being detected more frequently. The application of the logistic regression model developed by Fairman and Bitzer (2022) further illustrates the limitations in continuing current identification. The study underscores the challenges of relying solely on satellite data to monitor and analyze continuing currents, emphasizing the need for advancements in detection technologies and methodologies to reliably detect continuing current at a large spatial scale.

Abstract

Omega bands are mesoscale auroral structures emerging as eastward moving quasi-periodic poleward protrusions well within the closed field line region of the auroral oval. Neither specific conditions of their appearance nor their causes are well understood. We perform a superposed epoch analysis of OMNI and SuperMAG measurements taken during 28 omega band events recorded by auroral all-sky imager observations from 2006 to 2013 to identify their solar wind drivers. We find local enhancements in the solar wind flow speed, magnetic field, pressure, and proton density at the time of the omega band observation. In the magnetosphere-ionosphere, we see enhancements in the ring current, partial ring current, and auroral electrojets. These features are consistent with geomagnetic activity caused by stream interaction regions (SIRs). 19 of our events overlap with SIRs from published event catalogs. Our findings suggest that omega bands are driven by compression regions commonly associated with SIR events.

Abstract

While weakening of the boreal polar vortex may be caused by autumnal Arctic sea ice loss, less is known about the interannual influence of Antarctic sea ice on stratosphere-troposphere coupling in the Southern Hemisphere. Identifying any relationship over the short satellite period is difficult due to sampling variability and anthropogenic modification of the austral polar vortex. To circumvent these issues, we use large ensembles of fixed boundary condition simulations from the Community Atmosphere Model (CAM) and Whole Atmosphere Community Climate Model (WACCM) to assess if and how interannual fluctuations in winter Antarctic sea ice influence spring planetary-scale waves and the coupled stratosphere-troposphere circulation. Low Antarctic sea ice conditions are found to modulate tropospheric stationary waves to project constructively onto the climatological stationary wave, enhancing upward planetary wave propagation into the austral polar stratosphere. In WACCM, the resulting vortex weakening coincides with development of negative Southern Annular Mode conditions during September–November.

Abstract

Studies have implicated the importance of longwave (LW) cloud-radiative forcing (CRF) in facilitating or accelerating the upscale development of tropical moist convection. While different cloud types are known to have distinct CRF, their individual roles in driving upscale development through radiative feedback is largely unexplored. Here we examine the hypothesis that CRF from stratiform regions has the greatest positive effect on upscale development of tropical convection. We do so through numerical model experiments using convection-permitting ensemble WRF (Weather Research and Forecasting) simulations of tropical cyclone formation. Using a new column-by-column cloud classification scheme, we identify the contributions of five cloud types (shallow, congestus, and deep convective; and stratiform and anvil clouds). We examine their relative impacts on longwave radiation moist static energy (MSE) variance feedback and test the removal of this forcing in additional mechanism-denial simulations. Our results indicate the importance stratiform and anvil regions in accelerating convective upscale development.

An urban module coupled with the Variable Infiltration Capacity model to improve hydrothermal simulations in urban systems
Yibing Wang, Xianhong Xie, Bowen Zhu, Arken Tursun, Fuxiao Jiang, Yao Liu, Dawei Peng, and Buyun Zheng
Geosci. Model Dev., 17, 5803–5819, https://doi.org/10.5194/gmd-17-5803-2024, 2024
Urban expansion intensifies challenges like urban heat and urban dry islands. To address this, we developed an urban module, VIC-urban, in the Variable Infiltration Capacity (VIC) model. Tested in Beijing, VIC-urban accurately simulated turbulent heat fluxes, runoff, and land surface temperature. We provide a reliable tool for large-scale simulations considering urban environment and a systematic urban modelling framework within VIC, offering crucial insights for urban planners and designers.

Wastewater matters: Incorporating wastewater reclamation into a process-based hydrological model (CWatM v1.08)
Dor Fridman, Mikhail Smilovic, Peter Burek, Sylvia Tramberend, and Taher Kahil
Geosci. Model Dev. Discuss., https//doi.org/10.5194/gmd-2024-143,2024
Preprint under review for GMD (discussion: open, 1 comment)
Global hydrological models are applied at high spatial resolutions to quantify water availability and evaluate water scarcity mitigation options. Yet they mostly oversee important local processes. This paper presents and demonstrates the inclusion of wastewater treatment and reclamation into a global hydrological model. As a result model performance is improved, and models are capable to utilize treated wastewater as an alternative water source.

Nature Geoscience, Published online: 02 August 2024; doi:10.1038/s41561-024-01485-3

Venusian highland terrains such as Ishtar Terra formed from melting beneath thinned lithosphere that created a stiff mantle root in a mechanism akin to craton formation on the early Earth, according to three-dimensional computational simulations.

SummarySeismic and tsunami hazard modelling and preparedness are challenged by uncertainties in the earthquake source process. Important parameters such as the recurrence interval of earthquakes of a given magnitude at a particular location, the probability of multi-fault rupture, earthquake clustering, rupture directivity and slip distribution are often poorly constrained. Physics-based earthquake simulators, such as RSQSim, offer a means of probing uncertainties in these parameters by generating long-term catalogues of earthquake ruptures on a system of known faults. The fault initial stress state in these simulations is typically prescribed as a single uniform value, which can promote characteristic earthquake behaviours and reduce variability in modelled events. Here, we test the role of spatial heterogeneity in the distribution of the initial stresses and frictional properties on earthquake cycle simulations. We focus on the Hikurangi-Kermadec subduction zone, which may produce Mw > 9.0 earthquakes and likely poses a major hazard and risk to Aotearoa New Zealand. We explore RSQSim simulations of Hikurangi-Kermadec subduction earthquake cycles in which we vary the rate and state coefficients (a and b). The results are compared with the magnitude-frequency distribution (MFD) of the instrumental earthquake catalogue and with empirical slip scaling laws from global earthquakes. Our results suggest stress heterogeneity produces more realistic and less characteristic synthetic catalogues, making them particularly well suited for hazard and risk assessment. We further find that the initial stress effects are dominated by the initial effective normal stresses, since the normal stresses evolve more slowly than the shear stresses. A heterogeneous stress model with a constant pore-fluid pressure ratio and a constant state coefficient (b) of 0.003 produces the best fit to MFDs and empirical scaling laws, while the model with variable frictional properties produces the best fit to earthquake depth distribution and empirical scaling laws. This model is our preferred initial stress state and frictional property settings for earthquake modelling of the Hikurangi-Kermadec subduction interface. Introducing heterogeneity of other parameters within RSQSim (e.g. friction coefficient, reference slip rate, characteristic distance, initial state variable, etc) could further improve the applicability of the synthetic earthquake catalogues to seismic hazard problems and form the focus of future research.

The hyperspectral camera for auroral imaging (HySCAI), which can provide a two-dimensional (2D) aurora image with full spectrum, was developed to study auroral physics. HySCAI consists of an all-sky lens, moni...

Abstract

This paper introduces a Triangle Network-Joint Slope (TN-JS) approach to characterize the spatial and temporal dynamics of Equatorial Plasma Bubbles (EPBs) during geomagnetic storms. To collaboratively determine the EPB drift directions from multiple stations, a Delaunay triangle network is constructed, utilizing the distribution of Ionospheric Piercing Points (IPPs). The Time Difference of Arrival (TDOA) is extracted through cross-correlating the Rate of Total Electron Content (ROT). The EPB drift direction can be approximately calculated by considering TDOA and IPP distances within each individual triangle of the network. This calculation is then refined through a joint statistical analysis. Using a reference station as the origin, the remaining stations within the network are projected along the estimated EPB drift direction. A spatial-temporal color map illustrating regional ionospheric anomaly ROT observations is constructed. The EPB drift velocity among multiple stations can be collectively estimated by fitting the slope of this map, facilitating outlier exclusion. Accounting for satellite dynamic effects and the diverse orbit characteristics of GPS and BDS, corresponding IPP scan velocity compensation is performed and analyzed for EPB dynamic estimation. Using the geomagnetic storm event that occurred on September 8 as a case study, the spatial-temporal kinetic properties of EPBs is characterized by analyzing Global Navigation Satellite System (GNSS) observations from 17 Hong Kong monitoring stations with the proposed TN-JS approach. The results indicate during this magnetic event, that EPBs exhibit a westward drift trend with velocities ranging from a few tens to hundreds of meters per second in GPS and BDS observations.

Abstract

Forecasting warm-sector rainfall (WR) remains a major challenge, primarily due to weak synoptic forcing. Through cloud-permitting numerical simulations, in addition to direct triggering mechanism from low-level jets, we identify the important role of gravity waves in a heavy WR event in South China via convective preconditioning. The preconditioning manifests as mid-level moistening and destabilization with wave-like variations. This process is driven by fast-propagating (∼24 m s−1) n = 2 waves, associated with lower-tropospheric ascents and upper-tropospheric descents. Waves are generated during the evolution of northern frontal rainfall (FR). As FR intensifies, surges in low-level diabatic cooling mainly resulting from microphysical processes, trigger n = 2 waves, which further precondition the environment along their path. In contrast, a sensitivity experiment involving stably developing FR fails to reproduce the preconditioning process by waves and the subsequent occurrence of WR. Overall, our study illuminates a new pathway through which FR significantly influences WR via gravity waves.

Abstract

River bedforms and their deposits—fluvial cross strata— respond to floods. However, it is unclear if all floods are equally represented in cross strata. Here, using a series of physical experiments in which bedforms were subjected to equivalent flood magnitudes over varying durations, we demonstrate the existence of a lower bound on flood durations that are represented in cross strata. We show that the scour depths and preserved set thickness are indistinguishable from baseflow conditions when the rising-limb duration of floods is shorter than the baseflow-equilibrated bedform turnover timescale—time required to displace the volume of a single bedform at baseflow conditions. In contrast, scour depth and preserved set thickness distributions deviate from baseflow conditions when flood rising-limb duration exceeds the baseflow-equilibrated bedform turnover timescale, causing preferential preservation of falling-limb bedform dynamics. Our work provides a previously unrecognized quantitative bound on flood durations that are represented in fluvial cross strata.