Soil moisture (SM) representation varies among Earth System Models (ESMs) like those in the 6th Coupled Model Intercomparison Project (CMIP6). While surface SM (averaged over the top 10 cm) is similarly defined across models, the layered SM differs due to varying definitions of the soil profile in models. This inconsistency complicates ESM-based analyses involving vertical SM profiles. Here, we compare the vertically integrated layered SM (mrsol) with surface SM (mrsos) across different CMIP6 models. Our findings reveal that for some models, the integrated mrsol matches mrsos globally; for others, it matches only in certain grid cells; and for a few, it never matches. We showcase these discrepancies and discuss several potential causes, including inconsistent variable mapping, interpolation errors, and model-specific issues such as frozen soil handling and incorrect depth definitions. These discrepancies impact ESM-based SM studies, highlighting the need for careful consideration when using mrsol or mrsos from model simulations.

Vertical mode and rotary-with-depth statistics are compiled from a global dataset of full-depth lowered ADCP baroclinic velocity profiles. Mode-1 standing waves make up half (~0.5) profiles at the equator, increasing to ~0.9 at 60-70ºS and in boundary currents and the Antarctic Circumpolar Current. However, this implies that higher modes dominate in almost half of the profiles. Rotary clockwise-and counterclockwise-with-depth profiles each make up ~0.2 of the profiles at mid and low latitudes, mostly in modes 2 and higher. The mode-1 zero-crossing or node is often offset relative to WKB-stretched mid-depth. Surface and bottom anomalies are present in ~0.9 of the profiles, particularly those with higher energy, with bottom anomalies slightly more common over rougher topography. Low modes are responsible for redistributng and homogenizing the internal-wave field from localized sources but the practice of fitting coarsely-resolved profile data to mode-1 standing-wave structure is not valid everywhere, particularly near the equator.

Slow slip events (SSEs) are transient slow fault slips primarily occurring at plate boundaries and are sometimes linked to large earthquakes and earthquake swarms. In the Middle America subduction zone, SSEs have been observed primarily in Guerrero and Oaxaca, Mexico, and the Nicoya Peninsula, Costa Rica. The relationship between megathrust earthquakes and SSEs has been actively investigated in this subduction zone. However, much still remains unclear on the relationship between moderate earthquakes and SSEs. Clarifying this relationship is important for comprehending the mechanisms governing seismicity in this subduction zone. Here, we employed the spatiotemporal epidemic-type aftershock-sequence model to detect swarms of M 4.3 or larger earthquakes in the ANSS catalog from 2001 to 2024. We identified 59 earthquake swarm sequences and delineated three earthquake swarm concentration areas: in the vicinity of the Guerrero seismic gap, off the coast of Chiapas, Mexico, and around the Burica Peninsula at the Costa Rica–Panama border. To explore the potential link between earthquake swarms and SSEs, a comparative analysis was conducted between the earthquake swarms and previously documented SSEs. Additionally, global navigation satellite system data was analyzed to identify transient displacements potentially caused by previously unreported SSEs. The findings reveal that the 2002 and 2007 Guerrero and 2014 Nicoya Peninsula SSEs were accompanied or followed by earthquake swarms. Furthermore, transient crustal movements, possibly attributable to SSEs, coincided with earthquake swarms in Costa Rica, Panama, and Chiapas. The study offers new insights into the connection between seismicity and SSEs in the Middle America subduction zone.

Normal fault slip is regularly quantified for instantaneous seismic events and across geological timescales in rate-and-state friction frameworks. However, recent studies have shown that normal faults may undergo transient aseismic slip exceeding time-averaged rates, outside of steady state conditions. This highlights the need for further detailed observation of both coseismic and aseismic deformation on normal faults to better constrain how structures accommodate and release strain across all seismic stages. Here, we exploit open-source, InSAR-derived vertical ground motion data from the European Ground Motion Service (EGMS) to evaluate sub-mm scale deformation across active faults in the Larissa Basin, where two Mw > 6 earthquakes occurred in 2021, and the North Gulf of Evia, Central Greece. We resolve the spatial and temporal evolution of uplift and subsidence fields of the Larissa earthquake sequence, finding elevated coseismic uplift to subsidence ratios of 1:6-9. EGMS time series across the Costal Fault System of the North Gulf of Evia imply normal fault slip at above-creep throw rates of 2-3 mm/yr with limited associated seismicity. The nearby seismogenic Atalanti Fault shows no differential ground motion across its plane and is in an apparent locked state. Observed variable slip behaviours imply that long-term, geologically derived throw rates may combine transient periods of elevated aseismic slip, coseismic slip, and steady state motion. We consider these findings in the context of seismic hazard while assessing the applicability of EGMS data in tectonic studies to bridge an important gap in resolving fault motion across all spatial and temporal scales.

Tracking individual clouds in geostationary satellite observations and numerical simulations allows to quantify cloud lifetime and development. These higher-dimensional parameters are used in a novel approach to assess the fidelity of cloud-resolving models. Clouds are tracked in two months of satellite observations and accompanying model simulations of trade-wind cumulus clouds during the EUREC$^4$A campaign. Two ICON-LEM simulations with different spatial resolution give time series of cloud cover that reasonably resemble the GOES-16 observations, despite large differences in the number of clouds. Analysis of the tracked clouds yields similar distributions of cloud size, development, and lifetime in line with the expected values for different dynamic regimes from energy cascade theory. However, we find that the model underestimates the occurrence frequency of larger, longer-lived clouds. This effect is enhanced for finer model resolutions and might be related to the transfer of energy from larger-scale processes into the domain of the large-eddy simulation.

This study uses the Versatile Electron Radiation Belt (VERB) code to model Saturn’s radiation belt environment, investigating electron acceleration, loss, and transport mechanisms. The simulations consider various physical processes, including convection particularly also driven by a Volland-Stern (VS) electric field, radial diffusion, collisional energy loss, and local wave-particle diffusion driven by chorus and hiss waves. Starting from initial conditions derived from Cassini observations, our simulations successfully reproduce the characteristic ”zebra stripes” pattern in spectrograms of Saturn’s radiation belts. Our results suggest that radial diffusion and neutral-particle interactions have negligible effects on zebra stripe formation. However, the presence of a persistent VS electric field results in significant electron acceleration above the Corotation Drift Resonance (CDR) energies in the MeV energy range, producing flux levels exceeding typical observations. Additional local wave-particle diffusion further enhances electron acceleration in this energy range. When the VS electric field pulse is treated as transient instead of constant to imitate dynamic conditions, the overestimation of MeV electron flux is reduced but remains elevated. Despite these differences, the simulations underscore the critical role of the VS electric field and local diffusion in controlling electron acceleration and transport. Our results highlight the necessity of understanding the interplay between global electric fields and localized diffusion processes in shaping electron dynamics within Saturn’s radiation belts.

• We spatially attribute the variability of global CO 2 fluxes using estimates from SINDBAD, a simple process-based model with data fusion • SINDBAD simulates CO 2 fluxes reasonably at regional and global scales, compared to TRENDY models and OCO-2 MIP • The contributions of tropical humid regions to the interannual variability of global net land CO 2 uptake are large, but uncertain.

A document by Savannah Lynn. Click on the document to view its contents.

Internal tides (ITs) are sub-surface gravity waves that generate significant sea surface height (SSH) signals detectable with satellite altimetry. The Surface Water Ocean Topography (SWOT) mission is capturing ocean surface data at an unprecedented spatial resolution of 2 km. Accurately identifying these IT signals is crucial for effectively monitoring other non-tidal oceanic signals. We use data-assimilative forecast system based on the HYbrid Coordinate Ocean Model (HYCOM) to identify both coherent and incoherent ITs and compared its performance with the state-of-the-art IT correction model (High Resolution Empirical Tide, HRET8.1). HYCOM demonstrated a 9% greater variance removal for coherent IT compared to HRET8.1 and eliminated an additional 14.6% of incoherent IT. Specifically, at the M2 frequency, HYCOM removed 40-60% of coherent IT variance and 10-20% of incoherent IT variance. Ocean forecast models like HYCOM enhance our understanding of IT dynamics and serve as alternative tools for IT mapping and altimetry correction.

Interhemispheric coupling (IHC) is the positive correlation between temperatures in the polar winter stratosphere and polar summer upper mesosphere and lower thermosphere. Over the past two decades, several mechanisms have been proposed to explain the IHC. However, a consensus on the mechanism has yet to be fully reached, particularly regarding the role of gravity waves (GWs). We conduct hindcast simulations for seven boreal winters using a GW-permitting general circulation model encompassing the whole neutral atmosphere. The model is initialized through spectral nudging to state-of-the-art reanalysis data of identical vertical coverage. Treating the 7-year averages of the model outputs as a climatology, the IHC is investigated as a sequential evolution of anomalies relative to it. The results showed that consequential interplay of GWs and quasi-two-day waves in the summer mesosphere is the key driver of the IHC, as is consistent with Yasui et al. (2021) except for the final step toward the summer pole facilitated by primary GWs in the Antarctic. These waves are filtered by an anomalously weak westward jet due to a temperature gradient caused by quasi-two-day wave forcing. The mechanism is mostly applicable to both types of IHC events: those associated with sudden stratospheric warming and those with vortex intensification. Meanwhile, comparisons across the seven boreal winters indicate vulnerabilities in specific processes underlying the mechanism. In the reanalysis, it is suggested that GW parameterizations underestimate the GW forcing anomalies, but analysis increments reduce this discrepancy.

Understanding the impacts of high-resolution ocean model provides valuable insights for future research. However, the outcomes of sea surface state changes in both the tropics and mid-latitudes remain unclear, and initialized seasonal forecasts have not been studied extensively. This study investigates the impact of ocean model resolution with the first long-term hindcast experiment of an eddy-resolving (0.1°) ocean model used for global seasonal forecasting. We show that using the high-resolution ocean model significantly changes boreal winter jet streams in the atmosphere, based on the comparison of 30-year hindcasts with ocean resolutions ranging from 1° to 0.1° for the Japan Meteorological Agency/Meteorological Research Institute Coupled Prediction System version 3. In boreal winters, the cold sea surface bias in the equatorial Pacific is significantly reduced, leading to an equatorward shift in the intertropical convergence zone and enhanced convective activity in the western equatorial Pacific. The subtropical jet shifts southward due to the intertropical convergence zone shift and the weakening of equatorward propagation of mid-latitude atmospheric eddies. The enhanced convective activity in the tropics has a remote influence in the mid-latitudes, significantly reducing the upward eddy propagation of zonal wavenumber 1. Sea surface warm-up in the mid-latitudes partially cancels the reduction impact by enhancing the zonal wavenumber 2. Overall, the polar night jet accelerates due to the reduced supply of eddy forcing.

We present a statistical study of large magnetic field vector residuals between Swarm observations and the 13th generation International Geomagnetic Reference Field (IGRF-13) model under quiet to weakly disturbed geomagnetic conditions. Since the vast majority of data are taken during relatively quiet geomagnetic conditions, statistics of these large residuals are important for estimating potential errors for satellite operation when using IGRF-13 as reference, as well as for magnetosphere-ionosphere-thermosphere (MIT) studies. Residuals with magnitude of vector differences between Swarm observations and IGRF-13 estimations larger than 300 nT under Dst >-50 nT are studied from 2014 to 2020. All large residuals appear in the high-latitude auroral zone region peaking around 70° (-70°) magnetic latitude (MLAT) in the northern hemisphere (southern hemisphere) but there is also a secondary occurrence peak just below 80° (-80°) MLAT. However, the two hemispheres show clear asymmetries in the magnetic longitude (MLON) distribution where both hemispheres show high concentration of large residuals around the geographic poles. Since the two geographic poles are located at different geomagnetic locations and polar satellite’s orbits give rise to highly biased number of observations around the geographic poles, it results in high occurrence of large residuals around the geographic poles but a decrease in occurrence rate with respect to the total number of measurements. Identifying the interhemispheric asymmetries resulting from the asymmetry of the geographic poles with respect to the magnetic poles under relatively quiet geomagnetic conditions is helpful for a better understanding of interhemispheric asymmetry for the MIT system.

The high-latitude ionospheric electric field plays a key role in ionospheric plasma dynamics and energetics. Various ground- and satellite-based observations have been utilized to develop empirical models of the convection electric field. Empirical modeling typically relies on statistical regression techniques in which predefined (and inherently biased) functions are fitted to measurements. In many convection models, it remains common practice to combine data from the Northern and Southern Hemispheres or to disregard differences between the March and September equinoxes. Such approaches make it challenging to identify important input variables and limit their ability to account for equinoctial and hemispheric asymmetries. These asymmetries, which are not fully understood, require further analysis and improved representation in models. In this work, we use nearly ten years of electric field data from the Swarm satellites’ Thermal Ion Imagers (TIIs) together with artificial neural networks (ANNs) to develop a model of high-latitude ionospheric electric potential. The Swarm ‘TII-ANN’ electric potential model explicitly incorporates the day of the year, universal time, solar and geomagnetic activity, 3-D interplanetary magnetic field, and 3-D solar wind velocity. Importantly, it also accounts for equinoctial and hemispheric variations. We describe the new model, validate its performance by comparing corresponding ion drifts to independent measurements from the DMSP satellite, and study the hemispheric and equinoctial asymmetries of high-latitude electric potential. Our results show that the cross-polar cap potential is larger in the Southern Hemisphere than in the Northern Hemisphere during the March equinox, with equinoctial asymmetry being particularly prominent in the south.

A document by Fucent Hsuan Wei Hsu. Click on the document to view its contents.

On seasonal time scales, atmospheric angular momentum, mainly constituted by wind but also pressure effects, is known as the most important driver of Earth rotation variations reflected in those of the length of day. However, in connection with long-term climatic changes, we additionally anticipate secular trends resulting from shifts or changes in the intensity of atmospheric circulation. We investigate potential atmospheric transitions and their consequences for length of day using historical and 21st century simulations of a CMIP6 multi-model ensemble. The future projections used rely on five scenarios of differing greenhouse gas emission strengths and societal development. In each scenario, the resulting mean in the atmospheric angular momentum ensemble trajectory aligns with that of the projected surface temperature. The two pathways characterized by sustainability do not indicate significant centennial trends in atmospheric angular momentum and the respective length of day excitation. The scenarios with medium, high, and very high emission intensity project gradual increases in atmospheric angular momentum, dominated by strengthening subtropical westerly jet streams. For the most intense scenario, this would correspond to an atmosphere-induced slowdown of the Earth's rotation, with a 0.43 ms cy-1 increase in length of day, which amounts to about one-fifth of the slowdown due to the effect of tidal friction. In contrast, we identify no clear trend regarding the long-term change in the amplitude of the annual oscillation. Our results emphasize that climate change can affect Earth's rotation rate or, equivalently, the length of day through secular variations in atmospheric angular momentum.

A document by Vincenzo Saponaro. Click on the document to view its contents.

Recent advances in machine learning (ML)-based earthquake detection and location techniques combined with dense seismic networks have dramatically increased the quantity of low-magnitude earthquakes that can be detected and accurately located. We analyze the seismicity of the Northern Apennines (Italy) using data from the Alto Tiberina Near Fault Observatory (TABOO-NFO), an ideal site for applying modern detection techniques due to the presence of a dense seismic network, intense microseismic activity involving a complex fault system and deep fluid circulation. We use a ML-based workflow tailored to the TABOO area from 2010 to 2023 to construct an earthquake catalog with 420k events relocated with double difference. We leverage available data in the TABOO-NFO by using manually picked waveforms to train a new regional version of PhaseNet, a DL-phase picker designed for high accuracy P and S wave phase identification. The catalog provides new insights into geological and structural features in the area. We evaluate its quality by comparing the distribution of the hypocenters with the known active faults of the seismogenic region at TABOO. Our catalog illuminates structures and fault geometries with great detail, allowing detailed characterization of the spatiotemporal evolution of both the microseismicity occurring along the ATF and the shallow sequences. The focal mechanisms we obtain show more complex fault kinematics for deeper events compared minor, shallower fault segments. We illuminate a correlation between earthquake source properties and host rock lithology that includes the spatial pattern of the seismicity and the frequency-magnitude behavior.

NASA’s Psyche mission will arrive at the metal-rich asteroid (16) Psyche in 2029. The mission will test if (16) Psyche is a remnant of a melted, differentiated planetesimal that formed a molten iron metallic core. Previous studies have suggested that a molten metallic core fluid could erupt volcanically, explaining the high metal content of (16) Psyche’s surface. Here we describe an origin story for (16) Psyche using thermal and compositional evolution modeling that outlines when ferrovolcanism could occur. We highlight how Psyche’s magnetometer could detect remanent magnetization associated with such ferrovolcanic eruptions.