GRL

The evolution of the magma ocean that occupied the early Earth is influenced by the buoyancy of crystals in silicate liquid. At lower mantle pressures, silicate crystals are denser than the iso-chemical liquid, but heavy elements like iron can cause crystals to float if they partition into the liquid phase. Crystal flotation allows for a basal magma ocean, which might explain geochemical anomalies in mantle-derived magmas, seismic anomalies in the lower mantle, and the source of the Earth's early magnetic field. To examine whether a basal magma ocean is gravitationally stable, we investigate the degree of iron partitioning between (Mg,Fe)SiO3 liquid and bridgmanite. By utilizing ab initio molecular dynamics simulations coupled with thermodynamic integration, we find that iron partitions into the liquid, and increasingly so with increasing pressure. Bridgmanite crystals are found to be buoyant at lower mantle conditions, stabilizing the basal magma ocean.

Climate change represents a profound threat to the diversity and stability of global climate zones. However, the complex interplay between climate change and elevation in shaping climate heterogeneity is not yet fully understood. Here, we combine Shannon's diversity index (SHDI) with the Köppen-Geiger climate classification to explore the altitudinal distributions of global climate heterogeneity; and their responses to climate change. The study reveals a distinctive pattern: SHDI, a proxy for climate heterogeneity tends to slow down or decline at lower elevations with increasing temperatures, while at higher elevations, it continues to rise due to continuing cold conditions. Examination of climate simulations, both with and without anthropogenic forcing, confirms that observed changes in climate heterogeneity are primarily attributable to anthropogenic climate change within these high-elevation regions. This study underscores the importance of high-elevation regions as not only custodians of diverse climate types but also potential refuges for species fleeing warmer climates.

We examine tropical rainfall from the Geophysical Fluid Dynamics Laboratory's Atmosphere Model version 4 (GFDL AM4) at three horizontal resolutions of 100 km, 50 km, and 25 km. The model produces more intense rainfall at finer resolutions, but a large discrepancy still exists between the simulated and the observed frequency distribution. We use a theoretical precipitation scaling diagnostic to examine the frequency distribution of the simulated rainfall. The scaling accurately produces the frequency distribution at moderate-to-high intensity (≥10 mm day−1). Intense tropical rainfall at finer resolutions is produced primarily from the increased contribution of resolved precipitation and enhanced updrafts. The model becomes more sensitive to the grid-scale updrafts than local thermodynamics at high rain rates as the contribution from the resolved precipitation increases.

Bright basal reflections from the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) have been proposed to be consistent with permittivities characteristic of a wet material beneath the south polar layered deposits (SPLD). The characterization of a recently formed impact crater highlight the existence of a several meters thick ice-poor layer associated to a unit blanketing a large portion of the SPLD. We revise the radar propagation model used to invert the basal permittivity by including a surficial thin layer. We find that the inverted basal permittivity is highly sensitive to the properties of such a layer, with solutions ranging from common dry rocks to an unambiguously wet base. We advocate toward a better characterization of the surficial cover to assess the wet or dry nature for the base, and possibly reconcile most of the literature on the topic.

The present study considers tropical cyclogenesis as a multi-stage process in which pre-cursor disturbances develop first and a fraction of them further strengthen to become a tropical cyclone (TC). Using this framework, we analyze the impact of Madden-Julian oscillation (MJO)- associated anomalous large-scale environmental conditions on the triggering of tropical convective clusters (TCCs)—a type of pre-cursor disturbance—and the TCC-to-TC transition in the western Pacific. We find that, within the MJO's lifecycle, the modulation of the TCC frequency by the MJO drives TC genesis frequency anomalies earlier than the TCC-to-TC transition rate. Also, the fluctuation of TCC occurrence frequency is most strongly associated with the MJO's large-scale ascent and relative humidity anomalies, while that of the transition of TCCs to a TC is mainly associated with the MJO's vorticity anomalies. Our results suggest the distinct roles of large-scale environmental variables in different stages of tropical cyclogenesis.

The mesoscale dynamics of a record-breaking Atmospheric River (AR) that impacted the Middle East in mid-April 2023 and caused property damage and loss of life are investigated using model, reanalysis and observational data. The high-resolution (2.5 km) simulations revealed the presence of AR rapids, narrow and long convective structures embedded within the AR that generated heavy precipitation (>4 mm hr−1) as they moved at high speeds (>30 m s−1) from northeastern Africa into western Iran. Gravity waves triggered by the complex terrain in Saudi Arabia further intensified their effects. Given the rising frequency of ARs in this region, AR rapids may be even more impactful in a warming climate, and need to be accounted for in reanalysis and numerical models.

Observations show that equatorial ionospheric vertical drifts during solar minimum differ from the climatology between late afternoon and midnight. By analyzing WACCM-X simulations, which reproduce this solar cycle dependence, we show that the interplay of the dominant migrating tides, their propagating and in situ forced components, and their solar cycle dependence impact the F-region wind dynamo. In particular, the amplitude and phase of the propagating migrating semidiurnal tide (SW2) in the F-region plays a key role. Under solar minimum conditions, the SW2 tide propagate to and beyond the F-region in the winter hemisphere, and consequently its zonal wind amplitude in the F-region is much stronger than that under solar maximum conditions. Furthermore, its phase shift leads to a strong eastward wind perturbation near local midnight. This in turn drives a F-region dynamo with an equatorial upward drift between 18 and 1 hr local times.

This work evaluates glacial dust as a source of sediment, and associated iron (Fe), to the Fe-limited Gulf of Alaska (GoA). A reanalysis of GoA sediment data, using rare earth elements and thorium as provenance tracers, suggests a flux to the ocean surface of Copper River (AK) glacial dust, and associated Fe, that is comparable to the flux of dust from Asia, at least 1,000 km from the narrow mountain valley glacial dust source area. This work suggests dust from Asia may not be the largest source of Fe to the GoA. Dust models fail to accurately simulate this glacial dust transport because their coarse resolution underestimates wind speeds, and the dust flux. This work suggests that glacial dust fluxes may have been important in the geologic past (e.g., the last glacial maximum) from locations where there was more extensive coverage by glaciers than at present.

Measuring the temperature changes of the deep ocean will be critical to understanding how the earth system will respond to climate change. In this work, we present a method for measuring the depth-averaged, deep ocean temperature at local (∼3 km) spatial scales using passive estimates of acoustic propagation. These passive acoustic estimates of deep ocean temperature can be used with existing and future passive acoustic monitoring infrastructure to provide complimentary observations of the ocean to in situ measurements, and could be particularly useful in areas of poor ocean observation coverage. Using 8 years of ambient sound data, we demonstrate that the passive estimates agree with global ocean models and measurements by ARGO floats. The rms difference between the HYCOM ocean model is shown to be 0.13°C, and the rms difference between ARGO measurements is shown to be 0.086°C.

In the past two decades, the central portion of Campi Flegrei caldera has experienced ground uplift up to 15 mm/month, with an increase of rate, magnitude and extent of the seismicity. In this work, we perform multi-scale precise earthquake relocation of the 2014–2024 seismicity, mapping in detail activated fault zones. We relate the geometry, extent, and depth of these zones with up-to-date structural reconstructions of the caldera. The current seismicity is mainly driven by ground-uplift-induced stress concentration on pre-existing, weaker fault zones, some of which identified for the first time. These structures are not only related to the inner caldera and dome resurgence but also to volcano-tectonic events of the last 10 ka. The extent of imaged fault segments suggests they can accommodate ruptures up to a moment magnitude 5.1, significantly increasing seismic hazard in the area.

Land monsoon rainfall has a distinct annual cycle. Under global warming, whether the phase and amplitude of this annual cycle would be changed is still unclear. Here, a global investigation is conducted using 34 CMIP6 and 34 CMIP5 models under a high emission scenario. Seasonal delays would occur in the Southern Hemisphere (SH) American (3.43 days), Northern Hemisphere (NH) African (5.98 days) and SH African (3.76 days) monsoon regions, while no robust signal is found in other monsoon regions. Except NH American monsoon, amplitude is enhanced in all the monsoon regions. Compared to amplitude, the phase changes dominate the future changes of precipitation in the SH American, NH African and SH African monsoon regions. In these phase-dominated regions, atmospheric energetic framework is proved to be reliable at regional scale and the enhanced effective atmospheric heat capacity is found to be the dominant factor.

Rapid intensification (RI) of tropical cyclones (TCs) not only plays a crucial role in the development of major TCs but also poses great challenges to operational forecasting. Previous studies predominantly focused on RI over 24-hr periods, overlooking the potential for extended durations with intermittent moments. Here, we investigate the actual duration of RI and show that, when considering the interruption and intermittent moments, the longest RI can persist for up to 90 hr. Declines and resurgences in maximum potential intensity (MPI) and tropical cyclone heat potential (TCHP) are associated with the interruption of RI process. Given that the error in TC track prediction is much lower compared with that in intensity prediction, such a local minimum in MPI and TCHP could be better forecasted and potentially assist the prediction of RI, ultimately reducing TC-related hazards.

The dynamics shaping the El Niño-Southern Oscillation's (ENSO) response to present and future climate change remain unclear, partly due to limited paleo-ENSO records spanning past abrupt climate events. Here, we measure Mg/Ca ratios on individual foraminifera to reconstruct east Pacific subsurface temperature variability, a proxy for ENSO variability, across the last 25,000 years, including the millennial-scale events of the last deglaciation. Combining these data with proxy system model output reveals divergent ENSO responses to Northern Hemisphere stadials: enhanced variability during Heinrich Stadial 1 (H1) and reduced variability during the Younger Dryas (YD), relative to the Holocene. H1 ENSO likely intensified through meltwater-induced changes to ocean/atmospheric circulation, a response observed in models, but the lack of a similar response during the YD challenges model simulations. We suggest the tropical Pacific mean state during H1 primed ENSO for larger fluctuations under meltwater forcing, whereas the YD mean state likely buffered against it.

We investigate the role of ocean heat transport (OHT) in driving the decadal variability of the Arctic climate by analyzing the pre-industrial control simulation of a high-resolution climate model. While the OHT variability at 65°N is greater in the Atlantic, we find that the decadal variability of Arctic-wide surface temperature and sea ice area is much better correlated with Bering Strait OHT than Atlantic OHT. In particular, decadal Bering Strait OHT variability causes significant changes in local sea ice cover and air-sea heat fluxes, which are amplified by shortwave feedbacks. These heat flux anomalies are regionally balanced by longwave radiation at the top of the atmosphere, without compensation by atmospheric heat transport (Bjerknes compensation). The sensitivity of the Arctic to changes in OHT may thus rely on an accurate representation of the heat transport through the Bering Strait, which is difficult to resolve in coarse-resolution ocean models.

Understanding how changing seasonal precipitation will affect ecosystems and water resources can benefit from understanding how precipitation from different seasons contributes to runoff versus evapotranspiration (ET). We use stable-isotope data from 23 National Ecological Observatory Network watersheds to quantify the fractions of winter and summer precipitation that supply ET, and the fractions of ET supplied by summer versus winter precipitation. Across 20 watersheds, 34%–101% of summer precipitation supplied ET, with 8%–105% of ET supplied by summer precipitation; these end-member-splitting solutions were poorly constrained in the other three watersheds. These precipitation partitioning fractions were significantly correlated with many topographic, climatic, and vegetation metrics. This first empirical study of seasonal precipitation partitioning fractions across diverse ecoregions demonstrates that they can be well-constrained in many locations using existing public data sets, and that partitioning-fraction variations are largely explained by climate variations.

This study investigates boreal spring events of Pacific Meridional Mode (PMM) from 1950 to 2022, revealing that cold PMM is more effective in triggering subsequent La Niña compared to warm PMM's induction of following El Niño. This asymmetry stems from the varying origins and sub-efficacies of PMM groups. The cold PMM is primarily initiated by pre-existing La Niña, while the warm PMM is comparably activated by pre-existing El Niño and internal atmospheric dynamics. PMMs initiated by pre-existing El Niño or La Niña play a crucial role in determining the efficacies of PMMs in triggering subsequent El Niño-Southern Oscillation (ENSO). The strong discharge of pre-existing El Niño hampers warm PMM's induction of subsequent El Niño, whereas weak recharge from pre-existing La Niña enhances the efficacy of cold PMM in inducing subsequent La Niña. Comprehending not only the PMM phase but also its origin is crucial for ENSO research and prediction.

We report in situ observation of magnetic reconnection between magnetic flux rope (MFR) and magnetic hole (MH) in the magnetosheath by the Magnetospheric Multiscale mission. The MFR was rooted in the magnetopause and could be generated by magnetopause reconnection therein. A thin current sheet was generated due to the interaction between MFR and MH. The sub-Alfvénic ion bulk flow and the Hall field were detected inside this thin current sheet, indicating an ongoing reconnection. An elongated electron diffusion region characterized by non-frozen-in electrons, magnetic-to-particle energy conversion, and crescent-shaped electron distribution was detected in the reconnection exhaust. The observation provides a mechanism for the dissipation of MFRs and thus opens a new perspective on the evolution of MFRs at the magnetopause. Our work also reveals one potential fate of the MHs in the magnetosheath which could reconnect with the MFRs and further merge into the magnetopause.

Martian CO2 ice clouds are intriguing features, representing a rare occurrence of atmospheric condensation of a major component. These clouds play a crucial role due to their radiative properties, interactions with surface, and coupling with microphysical cycles of aerosols. Observations have been limited, prompting modeling studies to understand their formation and dynamics. Here, we present the first high-resolution 3D simulations of CO2 ice clouds using a Large-Eddy Simulation (LES) model incorporating CO2 microphysics. We investigate cloud formation in idealized temperature perturbations in the polar night. A reference simulation with a −2K perturbation demonstrates that the formed CO2 ice cloud possesses a convective potential, leading to its ascent in the troposphere. We determine the timescales and orders of magnitude of various phenomena involved in the lifecycle of a CO2 ice cloud. Sensitivity tests show that convection can be inhibited or intensified by the thermodynamic and microphysical conditions of the simulated environment.

We report a citizen science-motivated study on the cause of an unusually bright red aurora as witnessed from Hokkaido, Japan during a magnetic storm on 1 December 2023. The auroral brightness of 5 kR is unusual for the Dst index peak of only −107 nT. In spite of the moderate storm amplitude, the extremely high solar wind density of >50/cc and dynamic pressure of >25 nPa caused the aurora oval extension to 53 magnetic latitudes (L = 2.8). We discuss that the drift loss of the ring current particles across the small-size magnetopause is important, and Hokkaido was at the right position to see the direct effect of the large particle injection of the storm-time substorm.

The operation of hydropower plants leads to sudden changes in river stage and to a flow regime known as hydropeaking. Hydropeaking alters the morphology of the riverbed and water quality, and ultimately poses a risk to riverine ecosystems. While many indicators are available to quantitatively assess this problem in rivers, the impact of hydropeaking on aquifers is largely unknown and lacks of quantitative indicators. We analyze with wavelet techniques the spatial and temporal dynamics of surface water-groundwater interaction in an aquifer impacted by two differently regulated rivers. We propose four indicators to study the aquifer stress produced by hydropeaking and classify the observed groundwater head time series into weakly, moderately and highly impacted. This study opens the possibility for a quantitative assessment of the impact of hydropeaking on the groundwater ecosystem.