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.
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.
Abstract
Shear strain localization refers to the phenomenon of accumulation of material deformation in narrow slip zones. Many materials exhibit strain localization under different spatial and temporal scales, particularly rocks, metals, soils, and concrete. In the Earth's crust, irreversible deformation can occur in brittle as well as in ductile regimes. Modeling of shear zones is essential in the geodynamic framework. Numerical modeling of strain localization remains challenging due to the non-linearity and multi-scale nature of the problem. We develop a numerical approach based on graphical processing units (GPU) to resolve the strain localization in two and three dimensions of a (visco)-hypoelastic-perfectly plastic medium. Our approach allows modeling both the compressible and incompressible visco-elasto-plastic flows. In contrast to symmetric shear bands frequently observed in the literature, we demonstrate that using sufficiently small strain or strain rate increments, a non-symmetric strain localization pattern is resolved in two- and three-dimensions, highlighting the importance of high spatial and temporal resolution. We show that elasto-plastic and visco-plastic models yield similar strain localization patterns for material properties relevant to applications in geodynamics. We achieve fast computations using three-dimensional high-resolution models involving more than 1.3 billion degrees of freedom. We propose a new physics-based approach explaining spontaneous stress drops in a deforming medium.
Abstract
The long-standing “energy crisis” at the giant planets refers to the anomalous heating of planetary thermospheres compared to the available energy from solar irradiance. The coupling between planetary magnetospheres and their upper atmospheres is thought to address these crises, though the sources and pathways of energy transport have not been fully explored at each system. In particular, the total available energy from the upstream solar wind at each planet has not been comprehensively quantified. Here we apply recently developed models of energy conversion by magnetic reconnection and the Kelvin-Helmholtz instability to each of the Giant Planets, providing estimates of the average external energy inputs for each system between 1985 and 2020. We find that external energy associated with solar-wind-magnetospheric coupling significantly exceeds that from solar extreme ultraviolet photons. While internal energy sources are known to dominate at Jupiter and Saturn, external sources may be significant at Uranus and Neptune.
Time-resolved measurements of the densities of individual frozen hydrometeors and fresh snowfall
Dhiraj K. Singh, Eric R. Pardyjak, and Timothy J. Garrett
Atmos. Meas. Tech., 17, 4581–4598, https://doi.org/10.5194/amt-17-4581-2024, 2024
Accurate measurements of the properties of snowflakes are challenging to make. We present a new technique for the real-time measurement of the density of freshly fallen individual snowflakes. A new thermal-imaging instrument, the Differential Emissivity Imaging Disdrometer (DEID), is shown to be capable of providing accurate estimates of individual snowflake and bulk snow hydrometeor density. The method exploits the rate of heat transfer during the melting of a snowflake on a hotplate.
Synergy of active and passive airborne observations for heating rates calculation during the AEROCLO-SA field campaign in Namibia
Mégane Ventura, Fabien Waquet, Isabelle Chiapello, Gérard Brogniez, Frédéric Parol, Frédérique Auriol, Rodrigue Loisil, Cyril Delegove, Luc Blarel, Oleg Dubovik, Marc Mallet, Cyrille Flamant, and Paola Formenti
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2024-121,2024
Preprint under review for AMT (discussion: open, 0 comments)
Biomass burning aerosols (BBA) from Central Africa, are transported above stratocumulus clouds. The absorption of solar energy by aerosols induce warming, altering the clouds dynamics. We developed an approach that combines polarimeter and lidar to quantify it. This methodology is assessed during the AEROCLO-SA campaign. To validate it, we used flux measurements acquired during aircraft loop descents. Major perspective is the generalization of this method to the global level.
Vertical Retrieval of AOD using SEVIRI data, Case Study: European Continent
Maryam Pashayi, Mehran Satari, and Mehdi Momeni Shahraki
Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2024-105,2024
Preprint under review for AMT (discussion: open, 0 comments)
Our study estimates the SEVIRI AOD profile across Europe with 3 km spatial and 15-minute temporal resolution. Using machine learning models trained on 2017–2019 SEVIRI data and validated with 2020 CALIOP data, we found that RF performs best at higher altitudes, with wind speed and direction playing a crucial role in improving accuracy. Validation with EARLINET data confirms strong agreement with XGB.
Surprise floods: the role of our imagination in preparing for disasters
Joy Ommer, Jessica Neumann, Milan Kalas, Sophie Blackburn, and Hannah L. Cloke
Nat. Hazards Earth Syst. Sci., 24, 2633–2646, https://doi.org/10.5194/nhess-24-2633-2024, 2024
What’s the worst that could happen? Recent floods are often claimed to be beyond our imagination. Imagination is the picturing of a situation in our mind and the emotions that we connect with this situation. But why is this important for disasters? This survey found that when we cannot imagine a devastating flood, we are not preparing in advance. Severe-weather forecasts and warnings need to advance in order to trigger our imagination of what might happen and enable us to start preparing.
Abstract
Climate feedbacks over the historical period (here defined as 1850–2014) have been investigated in large ensembles of historical and single forcing experiments (hist-ghg, hist-aer, and hist-nat), with 47 members for each experiment. Across the historical ensemble with all forcings, a range in estimated Effective Climate Sensitivity (EffCS) between approximately 3–6 K is found, a considerable spread stemming solely from initial condition uncertainty. The spread in EffCS is associated with varying Sea Surface Temperature (SST) patterns seen across the ensemble due to their influence on different feedback processes. For example, the level of polar amplification is strongly correlated with the amount of sea ice melt per degree of global warming. This mechanism is related to the large spread in shortwave clear-sky feedbacks and is the main contributor to the different forcing efficacies seen across the different forcing agents, although in HadGEM3-GC3.1-LL these differences in forcing efficacy are shown to be small. The spread in other feedbacks is also investigated, with the level of tropical SST warming strongly correlated with the longwave clear-sky feedbacks, and the local surface-air-temperatures well correlated with the spread in cloud radiative effect feedbacks. The metrics used to understand the spread in feedbacks can also help to explain the disparity between feedbacks seen in the historical experiment simulations and modeled estimate of the feedbacks seen in the real world derived from an atmosphere-only experiment prescribed with observed SSTs (termed amip-piForcing).
Abstract
Zonal extensions of the Western Pacific subtropical high (WPSH) strongly modulate extreme rainfall activity and tropical cyclone (TC) landfall over the Western North Pacific (WNP) region. These zonal extensions are primarily forced on seasonal timescales by inter-basin zonal sea surface temperature (SST) gradients. However, despite the presence of large-scale zonal SST gradients, the WPSH response to SSTs varies from year to year. In this study, we force the atmosphere-only NCAR Community Earth System Model version 2 simulations with two real-world SST patterns, both featuring the large-scale zonal SST gradient characteristic of decaying El Niño-developing La Niña summers. For each of these patterns, we performed four experimental sets that tested the relative contributions of the tropical Indian Ocean, Pacific, and Atlantic basin SSTs to simulated westward extensions over the WNP during June–August. Our results indicate that the subtle differences between the two SST anomaly patterns belie two different mechanisms forcing the WPSH's westward extensions. In one SST anomaly pattern, extratropical North Pacific SST forcing suppresses the tropical Pacific zonal SST gradient forcing, resulting in tropical Atlantic and Indian Ocean SSTs being the dominant driver. The second SST anomaly pattern drives a similar westward extension as the first pattern, but the underlying SST gradient driving the WPSH points to intra-basin forcing mechanisms originating in the Pacific. The results of this study have implications for understanding and predicting the impact of the WPSH's zonal variability on tropical cyclones and extreme rainfall over the WNP.
Abstract
In this study, a variable-resolution version of the Community Earth System Model (VR-CESM) with mesh refinement (∼0.125°) over East Asia is used to simulate the regional climate in this region. For the evaluation of model performance and sensitivity to model resolution, the simulated near-surface temperature and precipitation are compared with observations and simulation results from a globally quasi-uniform (∼1°) CESM (UN-CESM). Results show that VR-CESM better simulates the spatial patterns and seasonal variations of mean temperature and precipitation than UN-CESM over China. For extreme events, VR-CESM improves the simulation of the occurrence frequency of wintertime daily minimum temperature and heavy precipitation. In regions with complex terrains, VR-CESM better resolves the topographic forcing and captures the observed fine-scale spatial patterns of temperature and precipitation, although precipitation is still overestimated. For East Asian summer monsoon precipitation, both UN-CESM and VR-CESM tend to overestimate (underestimate) the precipitation over northern (southern) China, which is associated with too strong meridional water vapor transport in the models and biases in the large-scale circulation in the middle and upper troposphere. Different from previous studies with different physics parameterizations and refined domains, as the model resolution increases, simulated monsoon precipitation evolution is not obviously improved, and convective precipitation intensity decreases over eastern China. Despite this, our results indicate that VR-CESM simulates regional climate, topographical forcing, and large-scale circulations over East Asia reasonably well, and thus it can be applied for the future climate projection in the region.
Abstract
In rivers worldwide, multiple scales of dunes coexist. It is unknown how the larger, primary dunes interact with secondary bedforms that are superimposed. We test the hypothesis that streamwise variability in the sediment flux inferred from the downstream migration of secondary bedforms explains migration of the host dune, based on bathymetric data from a lowland, sand-bedded river. Results indicate that transport estimated from secondary bedform migration increases along the host dune stoss, eroding the stoss slope. When the superimposed bedforms disintegrate at the primary lee slopes, results indicate that all sediment transport associated to secondary bedform migration is arrested in the lee of the host dune, explaining migration of the host dune. When secondary dunes persist however, only part of the sediments transport linked to secondary dunes contributes to the migration of the host dune. This study gives novel insight into the fundamental mechanisms controlling the kinematics of compound dunes.
