GRL

The physical behavior of a falling raindrop is governed by delicate fluid dynamics and thermodynamics, and oscillates with time. Despite this time-variant nature, past observational and simulation studies have aimed to generalize parameterizations for describing rain microphysics bearing the assumption that raindrops fall at terminal speeds with an equilibrium shape. However, the applicability of this hypothesis in a realistic atmosphere that is inherently turbulent remains an open question. Here, we employ novel retrieval techniques to quantify the impact of turbulence on raindrop microphysics using long-term in situ observations with careful assessment of the wind effect. We find that raindrop microphysics increasingly deviate from the equilibrium state as the turbulence dissipation rate increases, and this effect is more pronounced for large raindrops. We present turbulence-invoked rain microphysical parameterizations which shed light on the complex interactions between turbulence dynamics and raindrop microphysics.

This study investigates the impact of vertical ionospheric drift during daytime on the evolution of predawn equatorial plasma bubbles by conducting model simulations using “Sami3 is Another Model of the Ionosphere.” The upward drift of the ionosphere transports bubbles to higher altitudes, where their lifetime is set by the atomic oxygen photoionization rate. While the bubbles generated at predawn persist into dayside, the bubbles generated shortly after sunset diminish before sunrise. Therefore, post-sunset bubbles do not contribute to daytime electron density irregularities. Bubbles maintain their field-aligned characteristics throughout the daytime regardless of the vertical ionospheric drift. This property allows bubbles to exist near the magnetic equator despite poleward plasma transport by the fountain process. The shift of irregularity concentration to higher latitudes over time in satellite observations is explained by the combined effect of transport of bubbles to higher altitudes and rapid refilling of depletions near the magnetic equator.

Observation-based quantification of ocean carbon dioxide (CO2) uptake relies on synthesis data sets such as the Surface Ocean CO2 ATlas (SOCAT). However, the data collection effort has dramatically declined and the number of annual data sets in SOCATv2023 decreased by ∼35% from 2017 to 2021. This decline has led to a 65% increase (from 0.15 to 0.25 Pg C yr−1) in the standard deviation of seven SOCAT-based air-sea CO2 flux estimates. Reducing the availability of the annual data to that in the year 2000 creates substantial bias (50%) in the long-term flux trend. The annual mean CO2 flux is insensitive to the seasonal skew of the SOCAT data and to the addition of the lower accuracy data set available in SOCAT. Our study highlights the need for sustained data collection and synthesis, to inform the Global Carbon Budget assessment, the UN-led climate negotiations, and measurement, reporting, and verification of ocean-based CO2 removal projects.

Herein, fast fracture initiation in glacier ice is modeled using a Material Point Method and a simplified constitutive law describing tensile strain softening. Relying on a simple configuration where ice flows over a vertical step, crevasse patterns emerge and are consistent with previous observations reported in the literature. The model’s few parameters allows identification of a single dimensionless number controlling fracture spacing and depth. This scaling law delineates two regimes. In the first one, ice thickness does not play a role and only ice tensile strength controls the spacing, giving rise to numerous surface crevasses, as observed in crevasse fields. In this regime, scaling can recover classical values for ice tensile strength from macroscopic field observations. The second regime, governed by ice bending, produces large-scale, deep fractures resembling serac falls or calving events.

Oblique convergence across the northern Qilian Shan is accommodated by sub-parallel strike-slip and thrust faults that ruptured simultaneously in the Mw 8 Gulang earthquake in 1927. We investigate the kinematics of fault loading in the northern Qilian Shan and provide insights into the conditions necessary for generating multi-fault earthquakes. We perform Bayesian inversions for the geometry and creep rate on the fault network. We infer that all of the thrust faults are locked north of the Qilian-Haiyuan strike-slip fault and are accumulating elastic strain. Multi-fault earthquakes may occurr in this fault system because the faults are simultaneously loaded by the same source of deformation and are linked together by locked fault segments. The interseismic velocity field alone can not contain the location or activity of individual faults visible in the geomorphology, therefore the short-term geodetic measurements may not reliably indicate the long-term behavior of the fault system.

Slope instability due to tectonic, hydrological and anthropogenic activities cause severe landslides in Himalaya. Joshimath, a densely populated Himalayan town witnessed a catastrophic landslide event during December 2022 and January 2023 causing damages to ∼700 buildings. We use Interferometric synthetic aperture radar, Global Positioning System and rainfall measurements to probe the kinematics of the Joshimath landslide. We separate the seasonal and episodic deformation components using singular spectrum analysis. While the low amplitude annual landslide motions are modulated by seasonal precipitation, acceleration phases are triggered by extreme rain events. Our analysis revealed episodes of cascading motions triggered by extreme rain events resulting an overall increase in landslide velocity from −22 mm/yr during 2004–2010 to −325 mm/yr during 2022–2023. We estimate the landslide depth (∼30 m) and hydraulic diffusivity (∼3 × 10−5 m2/s) using a 1-D pore-water pressure diffusion model. Our study reveals the importance of systematic monitoring of ground deformation and weather parameters for landslide hazard mitigation.

At marine-terminating glaciers, both buoyant plumes and local currents energize turbulent exchanges that control ice melt. Because of challenges in making centimeter-scale measurements at glaciers, these dynamics at near-vertical ice-ocean boundaries are poorly constrained. Here we present the first observations from instruments robotically bolted to an underwater ice face, and use these to elucidate the interplay between buoyancy and externally forced currents in meltwater plumes. Our observations captured two limiting cases of the flow. When external currents are weak, meltwater buoyancy energizes the turbulence and dominates the near-boundary stress. When external currents strengthen, the plume diffuses far from the boundary and the associated turbulence decreases. As a result, even relatively weak buoyant melt plumes are as effective as moderate shear flows in delivering heat to the ice. These are the first in-situ observations to demonstrate how buoyant melt plumes energize near-boundary turbulence, and why their dynamics are critical in predicting ice melt.

FeO is an important component in both mantle silicates and core iron alloys. Understanding its melting behavior and physical properties is crucial for exploring the chemistry and physics of our planet. Here we report the melting curve of FeO up to 186 GPa from laser-heating experiments in a diamond-anvil cell coupled with synchrotron X-ray diffraction (XRD) techniques. In-situ observations of both temperature plateau and changes in XRD patterns were used as primary melting criteria. The ex-situ examination of a recovered sample shows consistent melting temperatures of FeO with in-situ determinations. Our melting curve of FeO agrees with existing low-pressure data within uncertainties and is much lower than earlier experimental results above 100 GPa including those extrapolated by Lindemann's law. Our results indicate that FeO-rich materials could be present as melts coexisting with surrounding solids in the lowermost mantle, providing plausible explanations to the seismically observed ultra-low velocity zones.

Australia is one of the regions strongly affected by the El Niño-Southern Oscillation (ENSO). The recent 2020–2023 La Niña event was marked by record-breaking rainfall and flooding across eastern Australia. The continuous wet conditions during the triple La Niña motivated us to explore the impacts of single-year and multi-year ENSO events on Australian rainfall using observational data sets. We find that, while there is no difference in the rainfall impacts during single or double El Niño events, Australian rainfall tends to increase in the third year of triple La Niña events compared to the first and second years. The enhanced rainfall impact during the third La Niña year occurs despite no strengthening of La Niña in the tropical Pacific, suggesting that other processes such as local rainfall-soil moisture feedback may play a role in prolonging the effects of multi-year La Niña events in Australia.

Observations of marine stratus clouds in clean air off the Californian coast reveal a functional relationship between the number of cloud condensation nuclei (CCN) and supersaturation. Satellite-derived liquid droplet density estimates the number density of CCN. Combining the estimated supersaturation using Köhler theory, global maps of supersaturation and the critical activation size of CCN are estimated. Here, we show that high supersaturation >0.5% persists over the oceans with a critical CCN size of 25–30 nm, which is smaller than the conventional wisdom of 60 nm. Independent support for such high supersaturation in the marine cloud is obtained from CCN measurements provided by the “Atmospheric Tomography Mission.” Higher supersaturation implies smaller activation size for CCN making cloud formation more sensitive to changes in aerosol nucleation.

Urban aquatic ecosystems in plains are often subject to extensive anthropogenic pollutant inputs and have prolonged times for pollutant degradation, potentially leading to diverse carbon emission patterns. This study explored carbon emission patterns and underlying mechanisms in Ge Lake and its tributaries, located in an urban area within a plain in China. The results revealed that carbon emissions from rivers were significantly higher than those from the downstream lake. Spatial interpolation analysis further revealed that CO2-eq emissions from a 1-km2 river area can be equivalent to those from an area as large as 86-km2 of the downstream lake. Rivers are the gateway for the entry of organic compounds, often carrying substances that are readily biodegradable. As the river water moves slowly, these compounds accumulate and undergo degradation in rivers before they reach downstream lakes. The findings may benefit the estimates of carbon emissions in these regions with greater precision.

Machine learning (ML) has been used to study the predictability of laboratory earthquakes. However, the question remains whether or not this approach can be applied in a tectonic setting where one may have to rely on sparse earthquake catalogs, and where important timescales vary by orders of magnitude. Here, we apply ML to a synthetic seismicity catalog, generated by continuum models of a rate-and-state fault with frictional heterogeneities, which contains foreshocks, mainshocks, and aftershocks that nucleate in a similar manner. We develop a network representation of the seismicity catalog to calculate input features and find that the trained ML model can predict the time-to-mainshock with great accuracy, from the scale of decades to minutes. Our results offer clues as to why ML can predict laboratory earthquakes and how the developed approach could be applied to more complex problems where multiple timescales are at play.

The South China Sea (SCS) is a semi-enclosed marginal sea linked to the broader oceans via various geographically constrained channels. Beneath the main thermocline depth, Luzon Strait is the only conduit for water-mass exchanges. Observations indicate a substantial seasonal variability in the inflow transport of deep water from the Pacific Ocean. This study aims to identify and examine key drivers for such seasonal changes. It is found that seasonal variability of the deep-water transport into the SCS is primarily driven by surface wind stress. An imbalance in wind-driven exchanges of surface water between the SCS and external seas demands compensational transports in subsurface layers so that the net volume transport into the SCS is conserved, resulting in seasonal variations in deep-water overflow. Changes in Karimata Strait exert a particularly influential impact on deep-water inflow, likely due to its unique position as the sole connecting channel across the Equator.

In August 2021, Askja caldera switched to reinflation following ∼40 years of continuous deflation that was first measured some 20 years after its last eruption in 1961. Various lines of evidence, including from geodetic modeling, suggest that both the deflation and reinflation events are related to a shallow magma body. To better understand the subsurface plumbing system, we derive P-wave velocity (Vp), S-wave velocity (Vs), and Vp/Vs models of the mid-upper crust by leveraging a new local earthquake traveltime data set. A cylindrical low-velocity zone, ∼3 km wide and extending to ∼8 km below sea level (bsl), was imaged beneath the caldera. Within it, two distinct lower velocity and higher Vp/Vs anomalies are illuminated, one centered at ∼0.5 km and the other at ∼6 km bsl. The shallower anomaly lies directly beneath the zone of uplift and is likely associated with the current reinflation event.

The Himalayas and Tibetan Plateau (the HTP), referred to as “the third pole” with an excessive warming rate, exerts strong impacts on the global environment. As one of warming contributors, atmospheric brown carbon (BrC) remains limited scientific understanding in the HTP due to a scarcity of observations. In this study, we present a study of the light-absorbing properties of methanol-soluble brown carbon (MeS-BrC) and water-soluble brown carbon (WS-BrC) during 2018–2021. Highly spatiotemporal variations of BrC light absorptions were observed. In the HTP marginal area, elevated BrC absorption coefficients at 365 nm (b abs,365) and levoglucosan concentrations were obtained, and MeS-BrC exhibits approximately 1.3–1.8 times higher absorption compared to WS-BrC. We determined that BrC light absorptions was largely attributed to biomass burning (29%–35%). BrC can act as a potent warming agent in the HTP marginal area, with high direct solar absorption (25%–47% relative to black carbon).

We identify and analyze a large shortening structure (surface expression of a thrust fault) in western Arabia Terra, Mars, exhibiting recent, repeated, and long-lasting tectonic activity. Where the fault system deforms Marsabit crater rim, four landslides with differing degradation states extend onto the crater floor. We propose these were triggered by episodic re-activation of the thrust system. Using a morphological map and crater size frequency statistics we show that the fault system experienced at least four landslide-inducing events during the Middle to Late Amazonian. We note that 1.4 km total displacement on the fault plane must have required many events to accumulate if motion was by brittle failure rather than continuous creep. The current understanding of tectonic activity and stress-sources since 3.6 Ga, cannot account for these repeated and large Amazonian marsquakes—suggesting revaluation of sources of stress to account for a more active and complex Amazonian tectonic history.

The micro Advanced Stellar Compass is an attitude reference for the MAG investigation onboard Juno. The μASC camera head unit images the star field with a CCD that is also sensitive to particles with enough energy to pass through the camera shielding: >15 MeV electrons and >80 MeV protons. This provides the capability to monitor fluxes of high-energy particles in Jupiter’s magnetosphere. A survey of energetic electron fluxes sampled during the first 47 Juno orbits reveals instances of variations observed when Juno is traversing the M-shell of the Galilean moons. Juno's traversal of the Europa M-shell often results in distinctly particle signatures. We present the μASC observations of increased electron flux during the crossing of Europa’s plasma wake, and depletion of energetic electron flux on the upstream side. The upstream/downstream differences indicate that the wake environment of Europa drives strong pitch angle scattering on relativistic electrons.

Seismic tomography has shown that the shear wave velocities (Vs) under continents, especially under cratons, are extremely fast at 100–200 km depth, which is difficult to explain by low temperatures or high Mg#. Alternatively, delaminated eclogitic lower continental crust has been proposed to account for these fast seismic anomalies. However, the thermoelastic properties of jadeite which constitutes up to 60–80 mol% of clinopyroxene in the potentially delaminated lower continental crust are not well constrained. In this study, we measured the single-crystal elasticity of jadeite by Brillouin spectroscopy under simultaneous high pressure and temperature conditions for the first time. We found that the temperature dependence of Vs of jadeite is extremely small if not negligible. The seismic velocities of the potentially delaminated lower continental crusts were subsequently modeled and found to match the widely observed fast seismic anomalies under cratons between 100 and 200 km depth.

The dust direct radiative effect (DRE) depends strongly on the dust particle size distribution (PSD) and complex refractive index (CRI). Although recent studies constrained the dust PSD in the models, its CRI uncertainties are still large. As a result, whether dust warms or cools the climate system remains unclear. Here, we estimate the dust DRE by employing the regionally-dependent dust CRI based on global measurements. We find that new dust CRI significantly enhances the scattering of dust in the shortwave while reduces its absorption in the longwave, which is opposite to that caused by increasing the coarse and giant dust fraction via constraining the PSD. Constraining both PSD and CRI ultimately leads to a net dust DRE of −0.68 W m−2, a cooling stronger than current model estimates.

Knowledge regarding the abundance and distribution of solar wind (SW)-sourced water (OH/H2O) on the Moon in the shallow subsurface remains limited. Here, we report the NanoSIMS measurements of H abundances and D/H ratios on soil grains from three deepest sections of the Chang'E-5 drill core sampled at depths of 0.45–0.8 m. High water contents of 0.13–1.3 wt.% are present on approximately half of the grain surfaces (topmost ∼100 nm), comparable to the values of Chang'E-5 scooped soils. The extremely low δD values (as low as −995‰) and negative correlations between δD and water contents indicate that SW implantation is an important source of water beneath the lunar surface. The results are indicative of homogeneous distribution of SW-derived water in the vertical direction, providing compelling evidence for the well-mixed nature of the lunar regolith. Moreover, the findings demonstrate that the shallow subsurface regolith of the Moon contains a considerable amount of water.