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Abstract

We utilize train tremors as P-wave seismic sources to investigate velocity-strain sensitivity near the San Jacinto Fault Zone. A dense nodal array deployed at the Piñon Flat Observatory is used to detect and identify repeating train energy emitted from a railway in the Coachella valley. We construct P-wave correlation functions across the fault zone and estimate the spatially averaged dt/t versus strain sensitivity to be 6.25 × 104. Through numerical simulations, we explore how the sensitivity decays exponentially with depth. The optimal solution reveals a subsurface sensitivity of 1.2 × 105 and a depth decay rate of 0.05 km−1. This sensitivity aligns with previous findings but is toward the higher end, likely due to the fractured fault-zone rocks. The depth decay rate, previously unreported, is notably smaller than assumed in empirical models. This raises the necessity of further investigations of this parameter, which is crucial to study stress and velocity variations at seismogenic depth.

Abstract

The Eastern Himalayan Syntaxis (EHS) serves as a natural laboratory for the study of intense continental collision and lateral extrusion tectonics. By aiming at the intricate tectonic dynamics south and southeast of the EHS, we integrate seismic data from new broadband stations in central Myanmar with permanent stations in southeastern Tibet to establish a high-resolution 3-D shear wave velocity model through ambient noise surface wave tomography. Our imaging results reveal distinct differences in crustal seismic velocity structures between the West Burma Block, Chuan-Dian Block, and the Shan Plateau, highlighting the extent of oblique subduction and restricted crustal extrusion. Notably, two north-south oriented low-velocity zones in the mid-to-lower crust of southeastern Tibet are mainly confined within the Chuan-Dian Block and terminate near the Red River Fault, with limited extension into the Shan Plateau.

Abstract

Sea ice formation over open water exerts critical control on polar atmosphere-ocean-ice interactions, but is only crudely represented in sea ice models. In this study, a collection depth parameterization of new ice for flux polynya models is modified by including the sea ice concentration and ice growth rate as additional factors. We evaluated it in a climate model BCC-CSM2-MR and found that it improves simulation of Antarctic sea ice concentration and thickness in most of Indian and Atlantic sectors. Disagreement between the observed Antarctic sea ice expansion during 1981–2014 and the modeled decline still exists but is mitigated when the modified scheme is implemented. Further analysis indicates that these improvements are associated with the overcoming of premature closure of open water, which enhances the response of ocean to surface wind intensification during 1981–2014, and consequently slowdowns the sea surface temperature increase and the resulting Antarctic sea ice reduction.

Shallow-landslide stability evaluation in loess areas according to the Revised Infinite Slope Model: a case study of the 7.25 Tianshui sliding-flow landslide events of 2013 in the southwest of the Loess Plateau, China
Jianqi Zhuang, Jianbing Peng, Chenhui Du, Yi Zhu, and Jiaxu Kong
Nat. Hazards Earth Syst. Sci., 24, 2615–2631, https://doi.org/10.5194/nhess-24-2615-2024, 2024
The Revised Infinite Slope Model (RISM) is proposed using the equal differential unit method and correcting the deficiency of the safety factor increasing with the slope increasing when the slope is larger than 40°, as calculated using the Taylor slope infinite model. The intensity–duration (I–D) prediction curve of the rainfall-induced shallow loess landslides with different slopes was constructed and can be used in forecasting regional shallow loess landslides.

Abstract

Overshooting convection can significantly impact the chemical and radiative properties of the upper troposphere and lower stratosphere through the transport of various chemical species. These impacts include enhancements of water vapor and ozone-depleting halocarbons, which both have important consequences for climate change. Therefore, accurate prediction of the Earth's climate system requires convective overshooting to be included. To better understand how convective transport is represented in current state-of-the-art models, approximately 75,000 individual updrafts in the central and eastern United States are analyzed from High-Resolution Rapid Refresh (HRRR) simulations and NEXRAD radar observations during May and July 2021. Distributions of echo top potential temperatures and heights, as well as diurnal cycles of overshooting frequency, are compared to observations. These distributions show mean, median, and maximum echo tops 2–3 km lower than observations, both in absolute and tropopause-relative space, with evidence of updrafts losing momentum too rapidly above the tropopause. Diurnal cycles show accurate times of maximum and minimum overshooting, but significant errors at model initialization and evidence that some simulated overshoots continue too late into the overnight hours. Despite these deficiencies, distributions of simulated levels of maximum detrainment show decent agreement with observations. All results, including the severe underprediction of echo top heights, persist at shorter forecast lead times. This indicates a need to improve representation of overshooting storms in weather and climate models, even those that are convection-permitting, or introduce a transport parameterization.

Abstract

The climate characteristics of remote rainfall events in Taiwan from September to February over 41 years (1980–2020) are studied. These events are induced by the interaction between the northeasterly flow and the typhoon's outer circulation. Our findings reveal that rainfall in northeastern Taiwan becomes more prominent when tropical cyclones move to the remote rainfall-prone area, located in the north Philippine area to the northern South China Sea, and when the background northeasterly wind speed exceeds 7 m s−1. Under these criteria, the confluence of the typhoon's outer circulation and the northeasterly flow creates a convergence area that enhances rainfall in northeastern Taiwan, increasing the occurrence of moderate to extreme rainfall (ER) events. This leads to an average enhancement in rainfall amount of 80–220 mm per day. Additionally, when typhoons are in the remote rainfall-prone area, there is a greater than 20% chance for events with maximum rainfall over 200 mm day−1 to occur, particularly in the region of 20°–22°N, 116°−124°E, and north to Luzon Island. In this area, the occurrence rate can exceed more than a 45% chance. The highest risk of ER events occurs between 20°–22°N and 118°−120°E, with a probability of over 90%. Notably, the convergence area for the Taiwan cases does not necessarily coincide with the baroclinic forcing as that associated with remote rainfall events observed in Japan, Korea, and North America.

No abstract is available for this article.

Abstract

A holistic review is given of the Southern Ocean dynamic system, in the context of the crucial role it plays in the global climate and the profound changes it is experiencing. The review focuses on connections between different components of the Southern Ocean dynamic system, drawing together contemporary perspectives from different research communities, with the objective of closing loops in our understanding of the complex network of feedbacks in the overall system. The review is targeted at researchers in Southern Ocean physical science with the ambition of broadening their knowledge beyond their specific field, and aims at facilitating better-informed interdisciplinary collaborations. For the purposes of this review, the Southern Ocean dynamic system is divided into four main components: large-scale circulation; cryosphere; turbulence; and gravity waves. Overviews are given of the key dynamical phenomena for each component, before describing the linkages between the components. The reviews are complemented by an overview of observed Southern Ocean trends and future climate projections. Priority research areas are identified to close remaining loops in our understanding of the Southern Ocean system.

Abstract

Electron cyclotron harmonic (ECH) waves are electrostatic emissions with frequencies between the harmonics of the electron gyrofrequencies. Their frequency properties provide clues for understanding their generation and are keys to evaluating their scattering efficiency. Based on Magnetospheric Multiscale satellite observations, we explored the statistical frequency properties of first-harmonic band ECH waves in the outer magnetosphere. The frequencies at the peak power of ECH waves are found to be day-night and dawn-dusk asymmetries, with higher values in the regions from dawn to post-noon, and these asymmetries are more evident during weaker geomagnetic activity. Furthermore, the frequencies at the peak power of ECH waves decrease gradually with increasing |MLAT| and are positively correlated with their amplitudes at each magnetic local time or |MLAT|. Information on the frequency properties of ECH waves presented in this study can be crucial for future modeling of their contributions to magnetospheric electron dynamics.

Abstract

Detached subauroral proton arcs are commonly observed during the recovery phase of geomagnetic storms, and have been extensively investigated. However, there is limited study on their occurrence during the main phase of storms. This study investigated nightside detached auroras (NDAs) observed by the far-ultraviolet imager onboard the Defense Meteorological Satellite Program spacecraft. The NDAs occurred in the nightside sector, separated from the equatorward boundary of the auroral oval, and were observed during the main and recovery phases of the geomagnetic storm on 02 October 2013. The occurrence of the NDAs appears to correlate with the expanding auroral oval toward lower latitudes, and is independent of the polarity change in the interplanetary magnetic field Bz component. Particle measurements indicate that the NDAs were generated by energetic protons, primarily above 10 keV, originating from the ring current. These precipitating proton fluxes, predominantly anisotropic, were observed to be detached from the isotropic boundary within the auroral oval. Analysis of Pc1 data obtained by ground stations suggests that electromagnetic ion cyclotron waves account for the generation of the NDAs. The limited latitudinal distribution of the NDAs indicates the wave activity in the magnetospheric source region within a narrow L-shell region. The observations presented in this study would contribute to our understanding of the coupling processes between the magnetosphere and ionosphere within the subauroral region.

Abstract

This study focuses on the poorly known effect of polar cap patches (PCPs) on the ion-neutral coupling in the F-region. The PCPs were identified by total electron content measurements from the Global Navigation Satellite System (GNSS) and the ionospheric parameters from the Defense Meteorological Satellite Program spacecraft. The EISCAT incoherent scatter radars on Svalbard and at Tromsø, Norway observed that PCPs entered the nightside auroral oval from the polar cap and became plasma blobs. The ionospheric convection further transported the plasma blobs to the duskside. Simultaneously, long-lasting strong upper thermospheric winds were detected in the duskside auroral oval by a Fabry-Perot Interferometer (FPI) at Tromsø and in the polar cap by the Gravity Recovery and Climate Experiment satellite. Using EISCAT ion velocities and plasma parameters as well as FPI winds, the ion drag acting on neutrals and the time constant for the ion drag could be estimated. Due to the arrival of PCPs/blobs and the accompanied increase in the F-region electron densities, the ion drag is enhanced between about 220 and 500 km altitudes. At the F peak altitudes near 300 km, the median ion drag acceleration affecting neutrals more than doubled and the associated median e-folding time decreased from 4.4 to 2 hr. The strong neutral wind was found to be driven primarily by the ion drag force due to large-scale ionospheric convection. Our results provide a new insight into ionosphere-thermosphere coupling in the presence of PCPs/blobs.

Abstract

Grasping the physical interactions when two tropical cyclones (TCs) (TC) are in proximity is essential for boosting the accuracy of TC forecasts. This study dissects an uncommon scenario wherein the merging with Tropical Depression 13 W significantly hastened the rapid weakening of Super Typhoon Hinnamnor (2022), utilizing comparative experiments with and without 13 W in simulation's initial field. The findings reveal strong correlations between the merger, amplified environmental vertical wind shear (VWS), and Hinnamnor's consecutive weakening, unfolding in two stages— “top-down” (Stage 1) and “bottom-up” weakening (Stage 2) stage. In Stage 1, 13 W led to downdrafts from upper level, hindering the eyewall updrafts and weakening the warm core. In Stage 2, 13 W merged into Hinnamnor's outer rainband, introduced low-entropy air into the boundary layer and also vied with the eyewall for energy. This research emphasizes that even minor, less-intense vortices can have profound impacts on the rapid intensity change in TCs.

No abstract is available for this article.

Abstract

Vegetation optical depth (VOD) satellite microwave retrievals provide significant insights into vegetation water content and responses to hydroclimatic changes. While VOD variations are commonly linked to dry biomass and live fuel moisture content (LFMC), the impact of canopy temperature (T c ) remains overlooked in large-scale studies. Here, we investigated the impact of T c on L-band (1.4 GHz) and X-band (10.7 GHz) VOD at diurnal and seasonal timescales. Synthetic benchmark VOD was created using realistic fields of T c , LFMC, and biomass in an electromagnetic model. Perturbation experiments revealed that T c strongly affects diurnal VOD variations at both L-band and X-band. Seasonally, while biomass emerges as the largest contributor to VOD variations in 70% (at X-band) and 90% (at L-band) of our study region, T c and LFMC still play substantial roles. The findings stress the importance of refining retrieval algorithms to distinguish T c , LFMC, and biomass effects for future VOD applications in ecohydrology.

Abstract

In recent decades, an increase in rainfall has been observed on the northwestern edge of the Indian summer monsoon (ISM; NWEISM). However, no studies have focused on model performances over NWEISM, which calls for an urgent evaluation of models. Here, we utilize historical simulations from 24 CMIP6 models to demonstrate that current models tend to underestimate the observed increasing rainfall over NWEISM, with only ∼30% of the observed intensity. The models broadly capture the spring Middle East land warming, which is the main driver of increased rainfall over NWEISM. Unfortunately, most models fail to reproduce the associated significant decrease in sea level pressure over the surrounding landmasses. This deficiency results in an ineffective trigger of cross-equatorial southwesterly winds, impeding the accurate simulation of the poleward shift of the summer low-level jet (LLJ). Consequently, it leads to a weaker link from the Middle East warming to rainfall enhancement over NWEISM.

Abstract

Juno conducted two close Io flybys on 30 December 2023 and 03 February 2024, both at a minimum altitude of 1,500 km. Filamentary structures in the electric and magnetic field spectra indicate Juno crossed the Alfvén wing, the magnetic structure connecting Io to Jupiter's polar ionosphere. We show that the first pass took Juno diametrically through the northern Alfvén wing, while the second pass had Juno graze the southern Alfvén wing boundary, enabling extended measurements of the transition region between Io's vicinity and the Jovian magnetosphere. Of note, evidence of local electron beams is inferred from whistler-mode emissions. We demonstrate that their energies are sub-keV, are sourced from Io's ionosphere or local torus, and are part of a distributed current system connecting Io to Jupiter. Finally, upper hybrid resonances indicate electron densities are significantly elevated in Io's polar region (∼28,000 cm−3) compared to the local Io torus (∼2,000 cm−3).

No abstract is available for this article.

Abstract

This study uses Mars Atmosphere and Volatile EvolutioN observations of electron density and magnetic field for a period of four Martian years (MYs 33–36) (∼8 Earth years) to investigate the effects of Martian crustal magnetic fields on the distribution and variability of Mars' ionosphere. The results show a clear enhancement in electron density in the southern hemisphere in the region where the strong crustal magnetic fields are present with the longitudes between 120° and 240° (i.e., the central longitude), which is in agreement with previous studies. On the contrary, the corresponding northern hemisphere region in the central longitudes shows an exactly opposite behavior that the electron density is lower compared to the surrounding longitude regions. These effects are found to be primarily dayside phenomena. As opposed to dayside, the nightside electron density in the central longitudes are slightly reduced at altitudes below 200 km, compared to longitudes on its western and eastern sides. Above 200 km, the nightside effects are not very clear. Significant hemispheric asymmetry is observed in the longitude regions of enhanced crustal magnetic fields compared to other longitude regions during the daytime. This dayside south-north asymmetry in the central longitude region is observed to be a constant feature across all seasons. However, on the nightside, the south-north asymmetry remains more or less similar across all longitude regions, during all seasons implying a weakened control of the crustal fields over the nightside ionosphere. Even then, the southern hemisphere retains a stronger nightside ionosphere during all seasons except summer.

Abstract

The interplay between compaction-driven fluid flow and plastic yielding within porous media is investigated through numerical modeling. We establish a framework for understanding the dynamics of fluid flow in deforming porous materials that corresponds to the equations describing solitary porosity wave propagation. A concise derivation of the coupled fluid flow and poro-viscoelastoplastic matrix behavior is presented, revealing a connection to Biot's equations of poroelasticity and Gassmann's theory in the elastic limit. Our findings demonstrate that fluid overpressure resulting from channelized fluid flow initiates the formation of new shear zones. Through three-dimensional simulations, we observe that the newly formed shear zones exhibit a parabolic shape. Furthermore, plasticity exerts a significant influence on both the velocity of fluid flow and the shape of fluid channels. Importantly, our study highlights the potential of spontaneous channeling of porous fluids to trigger seismic events by activating both new and pre-existing faults.

Evaluation of optimized flux chamber design for measurement of ammonia emission after field application of slurry with full-scale farm machinery
Johanna Pedersen, Sasha D. Hafner, Andreas Pacholski, Valthor I. Karlsson, Li Rong, Rodrigo Labouriau, and Jesper N. Kamp
Atmos. Meas. Tech., 17, 4493–4505, https://doi.org/10.5194/amt-17-4493-2024, 2024
Field-applied animal slurry is a significant source of NH3 emission. A new system of dynamic flux chambers for NH3 measurements was developed and validated using three field trials in order to assess the variability after application with a trailing hose at different scales: manual (handheld) application,  a 3 m slurry boom, and a 30 m slurry boom. The system facilitates NH3 emission measurement with replication after both manual and farm-scale slurry application with relatively high precision.