GRL

Follett et al. (2020a, https://doi.org/10.1029/2020gl089346) developed an analytical model to predict backwater rise by log jams, using the size and packing density of logs and the jam length, as well as river slope and bed roughness. We show that the model formulas can be rewritten using the Froude number instead of river slope and roughness, thus improving their applicability in engineering practice. The equation terms and results of Follett et al. (2020a, https://doi.org/10.1029/2020gl089346) are found to be similar to those of the empirically derived formula by Schalko et al. (2018, https://doi.org/10.1061/(asce)hy.1943-7900.0001501). However, some differences are identified, calling for further study. Most notably, these distinctions pertain to the effect of accumulation porosity, with additional minor differences in the exponent of the Froude number. Lastly, model implications for some broader applications are explored, showing a methodology to calculate the representative log size for log mixtures, and the expected effect of log orientation on backwater rise.

This study introduces a novel diagnostic method to assess tropical atmosphere-ocean coupling, using a two-dimensional plane defined by the 90-day high-pass-filtered sea surface temperature (SST) and column water vapor (CWV). The method was applied to reanalysis data and high-resolution coupled atmosphere-ocean simulation data. In the Indo–Pacific warm pool region, the phase relationship between SST and CWV remained consistent across both reanalysis and simulation data sets. However, differences in the temporal evolution of these variables were observed in the central Pacific region. The heat budget analysis results indicate that the differences between the two data sets in the central Pacific are related to variations in the effects of atmospheric disturbances on SST. This study demonstrates the potential of our novel diagnostic method for evaluating atmosphere–ocean coupling in climate models.

We present the first direct evidence of an in situ excitation of drift-compressional waves driven by drift resonance with ring current protons in the magnetosphere. Compressional Pc4–5 waves with frequencies of 4–12 mHz were observed by the Arase satellite near the magnetic equator at L ∼ 6 in the evening sector on 19 November 2018. Estimated azimuthal wave numbers (m) ranged from −100 to −130. The observed frequency was consistent with that calculated using the drift-compressional mode theory, whereas the plasma anisotropy was too small to excite the drift-mirror mode. We discovered that the energy source of the wave was a drift resonance instability, which was generated by the negative radial gradient in a proton phase space density at 20–25 keV. This proton distribution is attributed to a temporal variation of the electric field, which formed the observed multiple-nose structures of ring current protons.

Whistler mode waves in the plasmasphere and plumes drive significant losses of energetic electrons from the Earth's radiation belts into the upper atmosphere. In this study, we conducted a survey of amplitude-dependent whistler wave properties and analyzed their associated background plasma conditions and electron fluxes in the plasmasphere and plumes. Our findings indicate that extremely large amplitude (>400 pT) whistler waves (a) tend to occur at L > 4 over the midnight-dawn-noon sectors and have small wave normal angles; (b) are more likely to occur during active geomagnetic conditions associated with higher fluxes of anisotropic electrons at 10 s keV energies; and (c) tend to occur at higher latitudes up to 20° with increasing amplitude. These results suggest that extremely large amplitude whistler waves in the plasmasphere and plumes could be generated locally by injected electrons during substorms and further amplified when propagating to higher latitudes.

Transboundary air pollution is one of the critical environmental problems in Southeast Asia; nevertheless the interaction between transboundary haze and local planetary boundary layer (PBL) remains unclear due to a lack of sufficient observations and sophisticated simulations. This study applied LiDAR observations and model simulations to comprehensively evaluate the interaction between transboundary haze and local PBL during a recent transboundary haze episode in Singapore in October 2023. Results show that upper-level southeasterly wind, especially the nocturnal low-level jet, created favorable conditions for aerosol transport when fire hotspot numbers increased in Indonesia. The rapid diurnal increase in PBL height facilitated the entrainment of upper-level haze into the PBL, interacting with ground-level aerosols through turbulent mixing. Model simulations further show the significant contributions of fire emissions to the transboundary haze episode in maritime Southeast Asia. The impacts extended toward the southern region of Peninsular Malaysia, driven by the persistent prevailing southeasterly wind.

Aerosol particles play a critical role in the tropical tropopause layer (TTL) through cloud formation and heterogeneous chemistry, influencing the radiative and chemical balance of the stratosphere. However, aerosol measurements in the TTL are sparse, resulting in poor knowledge of aerosol abundance and distribution in this important region. Here, we present in situ aircraft measurements over the western tropical Pacific, revealing a persistent and altitude-dependent enhancement of aerosol mass in the TTL compared to the convectively influenced troposphere below. Notably, our data demonstrate a striking positive correlation between aerosol mass and ozone. Model simulations suggest that organic materials constitute a substantial fraction of the total aerosol mass within the TTL. We further derived an empirical parameterization of TTL aerosol mass as a function of ozone based on their linear relationship. This framework holds potential for estimating the TTL aerosol abundance but requires further validation and refinement through future measurements.

Stable water isotopes in inland Antarctic ice cores are powerful paleoclimate proxies; however, their relationship with dynamical atmospheric circulations remains controversial. Using a water isotope climate model (MIROC5-iso), we assessed the influence of the Last Glacial Maximum (LGM; ∼21,000 years ago) sea surface temperatures (SST) and sea ice (SIC) on Antarctic precipitation isotopes (δ18Op) through atmospheric circulation. The results revealed that the synoptic circulation mostly maintained southward moisture transport, reaching inland Antarctica. The steepened meridional SST gradient in the mid-latitudes increased δ18Op in inland Antarctica with the enhanced baroclinic instability and synoptic moisture transport. In contrast, expanded SIC distribution decreased δ18Op over Antarctica by enhanced preferential removal of heavy isotopes during vapor transport due to the increased transport distance and enhanced surface cooling. These findings propose to use Antarctic ice cores to describe the southern hemisphere atmospheric circulation, represented by the westerly jets, during the LGM and other past climates.

Boundary dynamics are crucial for the transport of energy, mass, and momentum in geospace. The recently discovered plasmapause surface wave (PSW) plays a key role in the inner magnetosphere dynamics. However, a comprehensive investigation of spatial variations of the PSW remains absent. In this study, we elucidate the spatial characteristics of a PSW through observations from multiple spacecrafts in the magnetosphere. Following the initiation of the PSW, quasi-periodic injections of energetic ions, rather than electrons, are suggested to serve as energy source of the PSW. Based on the distinct wave and particle signatures, we categorize the PSW into four regions: seed region, growth region, stabilization region and decay region, spanning from nightside to afternoon plasmapause. These findings advance our understanding of universal boundary dynamics and contribute to a deeper comprehension of the pivotal roles of surface waves in the energy couplings within the magnetosphere-plasmasphere-ionosphere system.

The fates of terrestrial organic carbon (OCterr) during fluvial transport from land to ocean are still not well constrained. This study systematically examines the evolution and dynamics of OCterr along the river-estuary-coastal ocean continuum in three fluvial systems discharging to the Chinese marginal seas. The 14C-depleted characteristics of bulk OC and molecular components of riverine suspended sediments and marine sediments suggest that the Chinese marginal seas are a significant sink of pre-aged OCterr. Our study reveals significant apparent aging of OCterr within estuaries, likely due to degradation of (younger) labile components, and apparent rejuvenation of OCterr in shelf systems, likely reflecting inputs of younger OCterr from proximal sources along the sediment dispersal pathway. The aging and rejuvenation of OCterr along the river-ocean continuum confounds the use of plant wax lipid 14C to constrain lateral transport times, and sheds light on more complex OCterr dynamics in marginal seas.

Thermal tides are atmospheric planetary-scale waves with periods that are harmonics of the solar day. In the Martian atmosphere thermal tides are known to be especially significant compared to any other known planet. Based on the data set of pressure timeseries produced by the InSight lander, which is unprecedented in terms of accuracy and temporal coverage, we investigate thermal tides on Mars and we find harmonics even beyond the number 24, which exceeds significantly the number of harmonics previously reported by other works. We explore comparatively the characteristics and seasonal evolution of tidal harmonics and find that even and odd harmonics exhibit some clearly differentiated trends that evolve seasonally and respond to dust events. High-order tidal harmonics with small amplitudes could transiently interfere constructively to produce meteorologically relevant patterns.

The Cambro-Ordovician interval marks a significant transition from extinction to bio-diversification in deep time. However, the relationship of bio-transition to volcanism, commonly characterized by mercury (Hg) systematics in sedimentary records, has not been examined. We present the first Cambro-Ordovician Hg systematics from the Scandinavian Alum Shale. Our results show pronounced Furongian Hg enrichments, coupled with positive Δ199Hg, Δ200Hg, and Δ201Hg values and negative Δ204Hg values that we ascribe to atmospheric Hg transport over long-distances, while Early Ordovician Hg anomalies, characterized by near-zero mass-independent isotope values, indicative of submarine source. Our findings are supported by two new proxies: molybdenum-Hg and vanadium-δ202Hg co-variations, demonstrating Hg systematics were strongly influenced by changes in source and depositional conditions. Constrained by a synchronous atmospheric-tectonic-oceanic model, we hypothesize Furongian subaerial volcanism contributed to global extinction and oceanic anoxia, whereas Early Ordovician submarine volcanism concurrent with ocean water upwelling promoted the nascent bio-diversification.

To advance our comprehension of the complex geological history and mantle dynamics in the North Atlantic region, we employ all available broadband seismic data recorded in Greenland to reveal an abnormal mantle transition zone (MTZ) structure. Central and eastern Greenland exhibits depressed 410 and 660 km discontinuities (d410 and d660, respectively) bordering the MTZ, indicative of a substantial thermal anomaly associated with an underlying plume, surpassing the 1,800°C threshold for post-garnet phase transitions at the d660. Variations in MTZ thickness across Greenland stem from differing temperature anomalies at the d410 and d660, possibly linked to a tilted plume within the MTZ. These findings corroborate geodynamic models, elucidating the interaction between post-garnet phase transitions and upwelling plumes. The results shed light on the origin of the enigmatic Icelandic hotspot track and its influence on the thermal and lithospheric structures beneath Greenland.

Unprecedented levels of seismicity have been seen in southern Sichuan, China, since the large-scale exploitation of shale gas. Fluid and pore pressure transported through hydrological channel are thought as pivotal elements in the induction of earthquakes. Our high-resolution tomography results reveal two inclined seismic anomalies featured by low V s and high V p /V s at different depth range. The deeper anomaly extends 15 km from NE to SE and connects the well g048 from 3 km depth to the vicinity of the Ms 4.7 Gongxian earthquake 5.4 km deep, which is hinted to be a hydrological channel inferred from the high fluid overpressure of 28 Mpa calculated from focal mechanism solution. The injection operation of multiple shale gas wells along the channel may potentially accumulate the pore pressure and cause the fault near the end of the channel to reach critical stress state through various mechanisms.

Plasmaspheric hiss, a whistler-mode emission confined in the high-density plasmasphere, is of great interest to the space community attributed to its important role in inner magnetospheric dynamics. Their frequency-time structures provide crucial evidence for understanding the wave origin. In this work, based on ∼7-year Van Allen Probes data, we statistically studied the frequency-drifting plasmaspheric hiss characterized by an increasing lower cutoff frequency over a timescale exceeding 1 hr. Frequency-drifting hiss waves predominantly occur at 3 < L < 6 from predawn to noon during geomagnetic active times. Observations and theoretical analyses suggest the frequency-drifting hiss could result from the local excitation inside the plasmasphere by energy-dispersive injected electrons. This unique feature of plasmaspheric hiss waves serves, to a certain extent, as an “identifier” for discerning the wave origins and as a “marker” facilitating the link between hiss waves across a broad spatial range.

Weather forecasts and climate projections of precipitation phase and type in winter storms are challenging due to the complicated underlying microphysical and dynamical processes. In the Canadian numerical weather prediction model, explicit freezing rain (FR) at the surface is often overestimated during the winter season for situations in which snow is observed. For a case study simulated using this model with the Predicted Particle Properties (P3) microphysics scheme, the secondary ice production (SIP) process has a major impact on the surface precipitation type. Parameterized SIP substantially reduces FR due to increased collection of supercooled drops with ice particles formed by rime splintering. Hindcast simulations of 40 winter cases show that these results are systematic, and the decreased frequency of FR leads to improved forecast skill relative to observations. Thus, accounting for SIP in the model is critical for accurately simulating precipitation types.

Present understanding of Greenland's subglacial geology is derived mostly from interpolation of geologic mapping of its ice-free margins and unconstrained by geophysical data. Here we refine the extent of its geologic provinces by synthesizing geophysical constraints on subglacial geology from seismic, gravity, magnetic and topographic data. North of 72°N, no province clearly extends across the whole island, leaving three distinct subglacial regions yet to be reconciled with margin geology. Geophysically coherent anomalies and apparent province boundaries are adjacent to the onset of faster ice flow at both Petermann Glacier and the Northeast Greenland Ice Stream. Separately, based on their subaerial expression, dozens of unusually long, straight and sub-parallel subglacial valleys cross Greenland's interior and are not yet resolved by current syntheses of its subglacial topography.

Sea surface temperature (SST) variability on decadal timescales has been associated with global and regional climate variability and impacts. The mechanisms that drive decadal SST variability, however, remain highly uncertain. Many previous studies have examined the role of atmospheric variability in driving decadal SST variations. Here we assess the strength of oceanic forcing in driving decadal SST variability in observations and state-of-the-art climate models by analyzing the relationship between surface heat flux and SST. We find a largely similar pattern of decadal oceanic forcing across all ocean basins, characterized by oceanic forcing about twice the strength of the atmospheric forcing in the mid- and high latitude regions, but comparable or weaker than the atmospheric forcing in the subtropics. The decadal oceanic forcing is hypothesized to be associated with the wind-driven oceanic circulation, which is common across all ocean basins.

El Niño/Southern Oscillation (ENSO) is the main climate mode that drives the interannual variability in climate and consequently vegetation greenness. While widespread green-up has been reported and examined in tropical America during El Niño, it remains unclear how vegetation in tropical Asia changes during the period. Here, we used four remote sensing-based leaf area index (LAI) products to investigate changes in vegetation greenness during the 2015/16 El Niño in tropical Asia. We found a strong green-up during the 2015/16 El Niño in tropical Asia, with its regional average LAI stronger than that of tropical America. The drivers for the green-up vary across the region, with radiation being the main driver for continental tropical Asia, and temperature and soil water anomalies in the west and east parts of maritime tropical Asia, respectively. These findings provide important insights into the response of tropical Asia's vegetation to extreme climate anomalies.

The secondary processes driven by the velocity shear driven Kelvin-Helmholtz Instability (KHI) in the magnetized plasmas have been shown to be important in producing plasma transport and heating from the shocked solar wind into the Earth's magnetosphere (MSP). The plasma transport into the MSP due to KHI has been shown to be strongest during northward interplanetary magnetic field (IMF) via KHI driven low- and mid-latitude reconnection process. In a recent article, Li et al. (2023), https://doi.org/10.1029/2023gl105539 show Magnetosphere Multi-Scale (MMS) spacecraft observations of multiple, Alfvénic reconnection jets during southward IMF at the dawn-side MSP flank. The quasi-periodic oscillations in plasma parameters and compressed, ion-scale current sheets were strongly indicative of the MMS crossing regions of MSP-like and magnetosheath-like plasma within Kelvin-Helmholtz waves. In this brief commentary, the importance of this new discovery for magnetospheric and solar wind dynamics is discussed.

This study combines 8 years of middle atmospheric wind data observed at 52°N latitude from two radars in different longitudinal sectors to investigate solar tides. The power spectral density of horizontal winds exhibits a −3 power law within the frequency range 2.0 < f < 7.0 cpd (equivalent to periods 3.6 − 12.0 hr). Particularly noteworthy are the 4.8- and 4-hr tides, exhibiting signal-to-noise ratios ranging between 13 and 16 dB, surpassing the 0.01 significance level. This challenges their previous oversight in literature, possibly due to inadequacies in prevailing noise models. Cross-spectra between longitudinal sectors emphasize the dominance of sun-synchronous components in the six lowest-frequency tides. Composite spectra indicate that tidal enhancements during SSWs resemble regular seasonal variations. Intriguingly, year-to-year spectral variations suggest that these enhancements are more influenced by seasonal dynamics than by SSW, contrasting with established literature. These findings underscore the need to reevaluate tidal harmonics and consider appropriate noise models in future studies.