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Abstract

Modeling atmospheric black carbon (BC) aerosol optical properties remains largely uncertain due to their complex mixing states, nonsphericity, and heterogeneity of coating distribution. Although there exist numerical models with realistic BC morphologies, these models are mostly limited to particle-scale studies and have not been coupled to large-scale atmospheric or climate models. In this study, a multidimensional parameterization scheme is developed by an accurate numerical algorithm for BC optical property calculation in global climate models, by incorporating their mixing state and nonspherical structure as well as heterogeneous coating distribution. The scheme was coupled and tested with the Community Atmosphere Model version 6 (CAM6) by a weighted averaging algorithm for individual particles and integration for particle ensembles. The simulation results indicate that BC morphology has a limited influence on the aerosol absorption cross section (C abs), and the differences in C abs between irregularly coated fractal aggregates and ideal core-shell spherical (CS) counterparts are ∼3% on average. However, the relative positions between the BC core and coating parts may introduce C abs variations of up to 69% as compared with the CS results. The BC mixing state introduce ∼20% relative variations in the global average aerosol absorption optical depth, which is comparable to that of heterogeneity of coating distribution and three times greater than that of particle nonsphericity. Furthermore, the normalized mean biases of modeled single scattering coalbedo (1−SSA, i.e., the ratio of absorption to extinction) compared to those observed in BC-rich regions are reduced by 20%∼80% when applying our new parameterization in CAM6.

Abstract

The Bay of Bengal summer monsoon (BOBSM) is the most prominent branch of the Asian summer monsoon system, which exhibits complex interannual variability. While previous studies have focused on the onset conditions of the BOBSM, less attention has been paid to the retreat of the BOBSM. In this study, we propose an index to measure BOBSM retreat, based on the mean zonal wind field at 850 hPa during the summer-to-winter monsoon transitions. By analyzing the climatic characteristics and interannual variability of the BOBSM retreat using this index, we find that BOBSM retreat exhibits significant interannual variability, which is closely related to the occurrence of Indian Ocean Dipole (IOD) events. Statistically, when a positive IOD event takes place in the boreal autumn season, the retreat of the summer monsoon occurs earlier correspondingly. Conversely, the retreat is delayed when a negative IOD event occurs.

Abstract

The source of dust in the global atmosphere is an important factor to better understand the role of dust aerosols in the climate system. However, it is a difficult task to attribute the airborne dust over the remote land and ocean regions to their origins since dust from various sources are mixed during long-range transport. Recently, a multi-model experiment, namely the AeroCom-III Dust Source Attribution (DUSA), has been conducted to estimate the relative contribution of dust in various locations from different sources with tagged simulations from seven participating global models. The BASE run and a series of runs with nine tagged regions were made to estimate the contribution of dust emitted in East- and West-Africa, Middle East, Central- and East-Asia, North America, the Southern Hemisphere, and the prominent dust hot spots of the Bodélé and Taklimakan Deserts. The models generally agree in large scale mean dust distributions, however models show large diversity in dust source attribution. The inter-model differences are significant with the global model dust diversity in 30%–50%, but the differences in regional and seasonal scales are even larger. The multi-model analysis estimates that North Africa contributes 60% of global atmospheric dust loading, followed by Middle East and Central Asia sources (24%). Southern hemispheric sources account for 10% of global dust loading, however it contributes more than 70% of dust over the Southern Hemisphere. The study provides quantitative estimates of the impact of dust emitted from different source regions on the globe and various receptor regions including remote land, ocean, and the polar regions synthesized from the seven models.

Abstract

City size is a primary determinant of the urban heat island (UHI) intensity, with its effects further nuanced by the urban form. But how to factor in the urban form into the UHI assessment remains unresolved. We propose an every-pair-interaction model that meaningfully incorporates urban size and fractal dimension to characterize the UHI intensity. Regression on the summertime surface UHI intensity of 5,000 European cities shows that the model outperforms the simple linear combination of logarithmic size and fractal dimension. Subject to the interplay between the range of the every-pair interaction and the urban fractal shape, the model also represents a generalization as it includes power-law, logarithmic, and saturating size dependence of UHI—all three possibilities have been reported empirically in the literature. Our theoretical framework indicates that the surface UHI intensity saturates with urban size, opening up new research perspectives around UHI intensity.

Abstract

An obvious long-term drying trend in recent early springs (February–March–April) is observed over southeastern China (SEC). Here, we attribute this drying to the weakened subtropical westerlies and deflected by the Tibetan Plateau (TP). Climatologically, the low-level southwesterlies at the southeastern margin of the TP, a branch of the upstream subtropical westerly jet deflected by the TP terrain, bring water vapor to SEC and the southerlies move upward over SEC mainly through isentropic gliding mechanism, inducing persistent precipitation in early spring. However, the subtropical westerlies weakened significantly in recent decades due potentially to the decreased Eurasian snow cover. Consequently, an easterly trend appears along the southern margin of the TP with anomalous northeasterlies over SEC. These northeasterlies suppress both moisture supply and upward motions over SEC, and reduce regional early spring precipitation. Our results highlight the interaction between the TP terrain and the weakened subtropical westerlies that leads to the drying SEC.

Abstract

Based on observations from the Magnetospheric Multiscale mission, this study presents an analysis of a short large-amplitude magnetic structures (SLAMS) event with simultaneous occurrence of low- and high-frequency magnetosonic whistler waves. It was found that low-frequency magnetosonic whistler waves around the lower-hybrid frequency emerge in the presence of solar wind ions and local low-energy ions in the trailing region of SLAMS. Additionally, counter-propagating whistler waves (the high-frequency branch of the magnetosonic whistler wave) are observed within SLAMS, coinciding with a perpendicular temperature anisotropy in the electron population. Instability analyses demonstrate that these low-frequency waves are induced by the two-stream instability associated with the cross-field relative velocity between low-energy ions and electrons, while whistler waves are locally generated by the whistler anisotropy instability. Our results shed light on the impact of SLAMS on particle and wave dynamics in the terrestrial foreshock.

Abstract

Post-collisional potassic-ultrapotassic rocks can provide key clues to the change of the recycled material type and/or tectonic transition in subduction-related zones. Despite continental materials widely recognized in their sources, it remains unclear whether such continental materials were contributed by former oceanic subduction or recent continental subduction. Here we address this issue by systematically investigating previously reported and our new chemical and Sr–Nd–Pb isotopic compositions of the post-collisional K-rich rocks in Southeast Tibet. Kink-like compositional variations provide solid evidence for a primary control of fractional crystallization on the evolution of these K-rich magmas. Their primary melts are demonstrated to have been produced by partial melting of phlogopite-bearing peridotites in subcontinental lithospheric mantle (SCLM). The trace element and Sr–Nd–Pb isotopic signatures argue against involvement of the deeply subducted Indian continent but suggest a great contribution from sediments in oceanic slabs. A thinned (∼70–100 km) and hot (∼55–70 mW/m2) lithosphere is also unraveled beneath Southeast Tibet during the potassic-ultrapotassic magmatism. Together with geophysical data, here we suggest a two-stage geodynamic model for post-collisional potassic-ultrapotassic magmatism in Southeast Tibet: (a) Before the Indian-Asia continental collision, phlogopite/K-richterite-bearing SCLM sources were formed through oceanic subduction-related metasomatism; (b) After the Indian-Asia continental collision, asthenosphere upwelling induced by post-collisional tectonic extension or deep subduction of the Indian continental slab caused lithospheric thinning, partial melting of pre-existing phlogopite/K-richterite-rich SCLM and thus K-rich magmatism. This study provides new insights into the role of oceanic subduction and continental collision in post-collisional potassic-ultrapotassic magmatism.

Abstract

Recent numerical simulation studies suggest the existence of a seismic type that is distinct from regular earthquakes—the slow self-arresting rupture (SSAR). Unlike regular earthquakes that propagate dynamically following the initiation, The SSARs automatically arrest within the nucleation zone without interference. Additionally, numerical simulations indicate that SSARs exhibit a significantly lower energy release compared to regular earthquakes, while also exhibiting a relatively long source duration. Given these distinctive properties, comprehending the source processes of SSARs assumes great strategic importance. However, our current understanding of SSARs, particularly regarding their response to different frictional conditions and their correlation with natural phenomena, remains limited in scope. To further explore the intricacies of SSARs, we employ a three-dimensional fully dynamic source model to simulate SSARs under various slip-weakening frictional conditions. The findings indicate that SSARs occur in frictional environments characterized by large normalized critical slip distances, with the seismic source process being primarily influenced by this parameter. Apart from displaying significantly smaller average slip and stress drop, which are two to three orders of magnitude lower than those of regular earthquakes of comparable magnitude, SSARs also showcase a decrease in duration, seismic moment, slip rate, and stress drop as the normalized critical slip distance increases. The moment-duration scaling law of SSARs exhibits a linear pattern. Moreover, the observation of slow earthquakes offers further implications for the presence of SSARs, indicating their potential association with a wider range of intricate seismic phenomena.

Abstract

Antigorite occurs at seismogenic depth along plate boundary shear zones, particularly in subduction and oceanic transform settings, and has been suggested to control a low-strength bulk rheology. To constrain dominant deformation mechanisms, we perform hydrothermal ring-shear experiments on antigorite and antigorite-quartz mixtures at temperatures between 20 and 500°C at 150 MPa effective normal stress. Pure antigorite is strain hardening, with frictional coefficient (μ) > 0.5, and developed cataclastic microstructures. In contrast, antigorite-quartz mixtures (10% quartz) are strain weakening with μ decreasing with temperature from 0.36 at 200°C to 0.22 at 500°C. Antigorite-quartz mixtures developed foliation similar to natural serpentinite shear zones. Although antigorite-quartz reactions may form mechanically weak talc, we only find small, localized amounts of talc in our deformed samples, and room temperature friction is higher than expected for talc. Instead, we propose that the observed weakening at temperatures ≥200°C primarily results from silica dissolution leading to a lowered pore-fluid pH that increases antigorite solubility and dissolution rate and thus the rate of dissolution-precipitation creep. We suggest that under our experimental conditions, efficient dissolution-precipitation creep coupled to grain boundary sliding results in a mechanically weak frictional-viscous rheology. Antigorite with this rheology is much weaker than antigorite deforming frictionally, and strength is sensitive to effective normal stress and strain rate. The activation of dissolution-precipitation in antigorite may allow steady or transient creep at low driving stress where antigorite solubility and dissolution rate are high relative to strain rate, for example, in faults juxtaposing serpentinite with quartz-bearing rocks.

Abstract

Before exploiting a geothermal resource in a volcanic setting such as the Asal rift, it is necessary to acquire a better knowledge of the subsoil, with the objective of locating the geothermal reservoir and evaluating the resource characteristic (permeability, temperature, etc.). For this type of resource, geophysical exploration methods are essential (such as gravimetry, magnetotellurics, etc.). However, a particular data type does not necessarily have the resolution and sensitivity. Furthermore, individual inversions of these geophysical data face the ambiguity of the non-uniqueness of the inverse solution. In this paper, we present a new linear approach of gravity data using the constraint of a MT resistivity model. We coupled the resistivity and density using inversion cross-gradients and the linear correlations. The approach was tested and validated on synthetic data and applied to gravity and MT data in the Asal Rift. Multiple inversions with different levels of coupling provided a series of density models. We applied the principal component analysis (PCA) technique to assess these models. We were able to define two dominant processes acting differently on the density and resistivity distribution at depth, namely the geothermal activity of the rift and the structural control of active tectonics.

Abstract

We numerically solve the acoustic radiative transfer equation for seismic S-waves via Monte Carlo simulation. By assuming a von Kármán-type random medium with anisotropic scattering, we are able to simulate a realistic medium and determine its attenuation properties. In this study, we present an improved method, called QEST, to determine the frequency-dependent intrinsic and scattering attenuation by nonlinear envelope inversion for a 1-D multilayer model. Additionally, the spectral source energy of earthquakes and the energy site amplification of stations are determined. The code was applied to real data from the northern and southern Leipzig-Regensburg fault zone (LRZ), Germany, as well as fluid-induced earthquakes at the Insheim geothermal reservoir, Germany. The attenuation was analyzed in several frequency bands between 4.2 and 33.9 Hz and between 6.0 and 67.9 Hz, respectively. The inversion results reveal that the crystalline crustal subsurface along the LRZ shows little to no depth dependence, but there are differences in attenuation between the north and south. At Insheim, the near-surface sedimentary basin exhibits significantly greater absorption and scattering than the crystalline basement. The inversion also shows that isotropic scattering can be an oversimplification and thus underestimate attenuation.

Abstract

In this study, a wideband circularly polarized (CP) H-plane horn antenna based on Gap Waveguide (GW) technology in K-band is presented. The proposed antenna consists of two unconnected metal planes. To produce broadband CP radiation, two main methods are utilized. First, two antipodal tapered plates (ATPs) are added in front of the horn. The ATPs are carefully designed for dissimilar polarization orientations. By this technique, the orthogonal electric fields can be prepared. Then, by embedding three metal square pins near the center of the aperture in both inner plates, the impedance bandwidth (BW) and BW of CP radiation of the proposed horn is entirely improved. Its BW for target |S11| < −10 dB is 18–28 GHz. Also, the peak gain fluctuates between 11.5 and 13 dB. This antenna can provide a 3 dB polarization axial-ratio BW of about 28.5% (20–26 GHz). Total radiation efficiency is higher than 94%. To verify the design, the proposed structure is manufactured and tested. The proposed horn antenna result has an appropriate agreement between measurement and simulation. Its miniaturized dimensions, easy and cheap fabrication, and broadband CP capability make it a proper volunteer for broadband communication systems.

Modelling chemical advection during magma ascent
Hugo Dominguez, Nicolas Riel, and Pierre Lanari
Geosci. Model Dev., 17, 6105–6122, https://doi.org/10.5194/gmd-17-6105-2024, 2024
Predicting the behaviour of magmatic systems is important for understanding Earth's matter and heat transport. Numerical modelling is a technique that can predict complex systems at different scales of space and time by solving equations using various techniques. This study tests four algorithms to find the best way to transport the melt composition. The "weighted essentially non-oscillatory" algorithm emerges as the best choice, minimising errors and preserving system mass well.

Towards a real-time modeling of global ocean waves by the fully GPU-accelerated spectral wave model WAM6-GPU v1.0
Ye Yuan, Fujiang Yu, Zhi Chen, Xueding Li, Fang Hou, Yuanyong Gao, Zhiyi Gao, and Renbo Pang
Geosci. Model Dev., 17, 6123–6136, https://doi.org/10.5194/gmd-17-6123-2024, 2024
Accurate and timely forecasting of ocean waves is of great importance to the safety of marine transportation and offshore engineering. In this study, GPU-accelerated computing is introduced in WAve Modeling Cycle 6 (WAM6). With this effort, global high-resolution wave simulations can now run on GPUs up to tens of times faster than the currently available models can on a CPU node with results that are just as accurate.

How hard do avalanche practitioners tap during snow stability tests?
Håvard B. Toft, Samuel V. Verplanck, and Markus Landrø
Nat. Hazards Earth Syst. Sci., 24, 2757–2772, https://doi.org/10.5194/nhess-24-2757-2024, 2024
This study investigates inconsistencies in impact force as part of extended column tests (ECTs). We measured force-time curves from 286 practitioners in Scandinavia, Central Europe, and North America. The results show a large variability in peak forces and loading rates across wrist, elbow, and shoulder taps, challenging the ECT's reliability. 

Reconstruction of ancient drought in Northwest China and societal responses: A case study of 1759
Zhixin Hao, Meirun Jiang, Haonan Yang, Danyang Xiong, and Jingyun Zheng
Nat. Hazards Earth Syst. Sci. Discuss., https//doi.org/10.5194/nhess-2024-111,2024
Preprint under review for NHESS (discussion: open, 0 comments)
At ancient time, social system could successfully responded most extreme climate events, such as droughts. To explore society’s adaptability to extreme climate events, we chosen the 1759 drought as a typical case study, then reconstructed the meteorological distribution of drought spatially and temporally, analyzed the impacts of the drought on society, and summarized the adaptive measures employed at the time.

Abstract

Large bursts of non-volcanic tremor (“major” tremor episodes) correlated with geodetic deformation recur regularly in the Cascadia subduction zone and are often called episodic tremor and slip (ETS). Minor episodes of tremor between ETS are ubiquitous but have been understudied. This paper assesses time-invariant characteristics of tremor episodes of all sizes within northern Cascadia. We derive a catalog of tremor episodes ranging in size from 10 to >13,000 tremor events using the results of 17 years of tremor monitoring. Minor episodes represent ∼96% of all 896 tremor episodes and their occurrence varies on 10-km scales. Using estimates for the depth of the forearc Moho and subducting slab, we observe an association between the location of the forearc mantle corner (FMC) and tremor occurrence that leads to along-dip modality. Bimodality, present in southern Washington and Vancouver Island, represents the segmentation of major and minor episodes up-dip and down-dip of the FMC, respectively. Unimodality, present in Puget Sound, results when the FMC is located near the down-dip edge of the ETS zone and no segmentation occurs. We also use our extensive tremor episode catalog alongside three-dimensional regional tomographic velocity models to reassess the relationship between tremor activity and low Vp/Vs signatures in the forearc. We do not find a correlation between tremor episode recurrence intervals and Vp/Vs, contrary to some previous work, suggesting that controls on silica precipitation in the forearc crust are not dominant controls of tremor episode recurrence, or that the association is not widely observable.

Abstract

After days of intense solar activity, active region AR3664 launched seven CMEs toward Earth producing an extreme G5 geomagnetic storm commencing at 17:05 UT on 10 May 2024. The storm impacted power grids, disrupted precision navigational systems used by farming equipment, and generated aurora seen around the globe. The storm produced remarkable effects on composition, temperature, and dynamics in the Earth's thermosphere that were observed by NASA's Global-scale Observations of the Limb and Disk (GOLD) mission and are reported here for the first time. We use synoptic disk images of ΣO/N2 and neutral temperature (at ∼160 km) measured by GOLD to directly link dynamics resulting from the storm with dramatic changes in thermospheric composition and temperature. We observe a heretofore unseen spatial morphology simultaneously in ΣO/N2, neutral temperature, and total electron content. Equator-to-pole temperature differences reach 400 K with high latitude peak neutral temperatures near 160 km exceeding 1400 K.

Abstract

Colorado River streamflow has decreased 19% since 2000. Spring (March-April-May) weather strongly influences Upper Colorado River streamflow because it controls not only water input but also when snow melts and how much energy is available for evaporation when soils are wettest. Since 2000, spring precipitation decreased by 14% on average across 26 unregulated headwater basins, but this decrease did not fully account for the reduced streamflow. In drier springs, increases in energy from reduced cloud cover, and lowered surface albedo from earlier snow disappearance, coincided with potential evapotranspiration (PET) increases of up to 10%. Combining spring precipitation decreases with PET increases accounted for 67% of the variance in post-2000 streamflow deficits. Streamflow deficits were most substantial in lower elevation basins (<2,950 m), where snowmelt occurred earliest, and precipitation declines were largest. Refining seasonal spring precipitation forecasts is imperative for future water availability predictions in this snow-dominated water resource region.

Abstract

We show that the winter Beaufort High (BH) index defined by sea level pressure (SLP) has a robust negative trend under the scenarios SSP5-8.5 and SSP2-4.5, with a reduction by about 5 hPa and 2 hPa, respectively, by the end of the 21st century. The negative trends in the BH SLP are associated with the changes in the background SLP over the Arctic basin. However, the vorticity of the winter BH tends to intensify under SSP5-8.5, but shows no robust increase under SSP2-4.5. The intensification is associated with the enhanced ridge over the Western Arctic. Therefore, it is necessary to take into account the dynamic aspects of the BH, such as vorticity. Based on this assessment, under the most likely emissions scenario, the winter BH is likely to weaken through the 21st century, in terms of SLP, but shows no robust changes in term of vorticity.