Large ensembles of model simulations require considerable resources, and thus defining an appropriate ensemble size for a particular application is an important experimental design criterion. Utilizing the recently developed CLIVAR ENSO Metrics Package (Planton et al., 2021), we estimate the ensemble size (N) needed to assess a model’s ability to capture observed ENSO behavior. Using the larger ensembles available from CMIP6 and the CLIVAR Large Ensemble Project, we find that larger ensembles are needed to robustly capture baseline ENSO characteristics (N > 65) and physical processes (N > 50) than the background climatology (N ≥ 12) and remote ENSO teleconnections (N ≥ 6). While these results vary somewhat across metrics and models, our study highlights that ensembles are required to robustly evaluate simulated historical ENSO behavior, and provide initial guidance for designing model ensembles to reliably evaluate and compare ENSO simulations.

Submarine volcano monitoring is vital for assessing volcanic hazards but challenging in remote and inaccessible environments. In the vicinity of Kita-Ioto Island, south of Japan, unusual M~5 non-double-couple volcanic earthquakes exhibited quasi-regular repetition near a submarine caldera. Following the 2008 earthquake, a distant ocean bottom pressure sensor recorded a distinct tsunami signal. In this study, we aim to find a source model of the tsunami-generating earthquake and quantify the pre-seismic magma overpressure within the caldera’s magma reservoir. Based on the earthquake’s atypical focal mechanism and efficient tsunami generation, we hypothesize that submarine trapdoor faulting occurred due to highly pressurized magma. To investigate this hypothesis, we establish a mechanical earthquake model that links pre-seismic magma overpressure to the size of the resulting trapdoor faulting, by considering stress interaction between a ring-fault system and a reservoir of the caldera. The model reproduces the observed tsunami waveform data. Our estimates indicate trapdoor faulting with large fault slip occurred in the critically stressed submarine caldera accommodating pre-seismic magma overpressure of ~10 MPa. The model infers that the earthquake partially reduced magma overpressure by 10–20%, indicating that the magmatic system maintained high stress levels even after the earthquake. Due to limited data, uncertainties persist, and alternative source geometries of trapdoor faulting could lead to estimate variations. These results suggest that magmatic systems beneath calderas are influenced much by intra-caldera fault systems. Monitoring and investigation of volcanic tsunamis and earthquakes help to obtain quantitative insights into submarine volcanism hidden under the ocean.

Until the Mw 6.8 Elazığ earthquake ruptured the central portion of the East Anatolian Fault (EAF) on January 24, 2020, the region had only experienced moderate magnitude (Mw 6.2) earthquakes over the last century. Here, we use geodetic data to constrain a model of subsurface fault slip. We adopt an unregularized Bayesian sampling approach relying solely on physically justifiable prior information and account for uncertainties in both the assumed elastic structure and fault geometry. The rupture of the Elazığ earthquake was bilateral, with two primary disconnected regions of slip. This rupture pattern may be controlled by structural complexity. Both the Elazığ and 2010 Mw 6.1 Kovancılar events ruptured portions of the central EAF that are believed to be coupled during interseismic periods, and the Palu segment is the last portion of the EAF showing a large deficit of fault slip which has not yet ruptured in the last 145 years.

We utilize twelve-year ambient seismic noise (ASN) recordings to measure near-surface seismic velocity variations (dv/v) within the YNP flooding watersheds. We have observed that the annual peaks of dv/v variations have two to three months lead-time in comparison to anomalous water discharges. Our analysis indicates that the annual cycle of dv/v is highly correlated with the effective precipitation, which takes into account the snowpack loading and melting water infiltration processes. The annual peaks of dv/v are likely caused by abnormal melt water, which exceed the water storage capacity of the land. Furthermore, the best-fit poroelastic model provides further evidence that precipitation factors primarily influence the variations of the seismic field. Our analysis successfully explains the indicative changes in dv/v prior to the 2014 and 2022 YNP floods. This study demonstrates the potential of using seismic observables to monitor and assess the risk of devastating floods in the YNP.  

Direct-runoff and baseflow are the two primary components of total streamflow and their accurate estimation is indispensable for a variety of hydrologic applications. While direct runoff is the quick response stemming from surface and shallow subsurface flow paths, and is often associated with floods, baseflow represents the groundwater contribution to streams and is crucial for environmental flow regulations, groundwater recharge, and water supply, among others. L’vovich (1979) proposed a two-step water balance where precipitation is divided into direct runoff and catchment wetting followed by the disaggregation of the latter into baseflow and evapotranspiration. Although arguably a better approach than the traditional Budyko framework, the physical controls of direct runoff and baseflow are still not fully understood. Here, we investigate the role of the aridity index (ratio between mean annual potential evapotranspiration and precipitation) in controlling the long-term (mean-annual) fluxes of direct runoff and baseflow. We present an analytical solution beginning with similar assumptions as proposed by Budyko (1974), leading to two complementary expressions for the two fluxes. The aridity index explained 83% and 91% of variability in direct runoff and baseflow from 499 catchments within the continental US, and our formulations were able to reproduce the patterns of water balance proposed by L’vovich (1979) at the mean annual timescale. Our approach allows for the prediction of baseflow and direct runoff at ungauged basins and can be used to further understand how climate and landscape controls the terrestrial water balance at mean annual timescales.

Sorghum is an important cereal crop grown across the globe for its grain and biomass value. It can also efficiently use resources such as nitrogen, and multiple varieties that are nitrogen-use and light-capture efficient are constantly being developed. This study focuses on using the spectral signature of sorghum varieties to predict flowering days, which could be used as a proxy for plants’ growth/productivity and development trends, thus helping breeders make quick decisions about what varieties to move to the next stage. Multiple sorghum varieties from the sorghum association panel were planted in a replicate-design field experiment with the variable supply of nitrogen. The flowering days were monitored and recorded. The hyperspectral reflectance data were collected and used to build a sorghum flowering days predictive model. Although regression models such as partial least square have been used to predict plants’ phenotypes, the non-parametric ensemble machine learning model turned out to perform better on flowering days with an accurate model up to 5 days.

The Zagros orogen in the Iranian Plateau is a natural laboratory in which to investigate the tectonic evolution of the transition from oceanic subduction to continental collision. However, where slab detachment occurred and how slab detachment affects shallower continental subduction remain poorly understood. The formation mechanism of the post-collision magmatism is also unclear. Here, we construct a high-resolution Pn-wave attenuation model for the uppermost mantle beneath the Iranian Plateau and surrounding areas using a newly compiled dataset. Weak Pn attenuation delineates the Arabian Plate front near the Moho discontinuity, extending further toward the subduction direction in the northwestern and southeastern parts, possibly due to the up-bending and underplating of the Arabian lithosphere after the loss of slab pull. The correlations among the surface Miocene-Quaternary volcanism and strong Pn attenuation in the uppermost mantle suggest that asthenospheric materials escaped from slab windows and further feed the post-collision volcanoes.

Elastic properties of rocks in subduction zones are indicators of stress states and play important roles in earthquake nucleation. We measured elastic properties of core samples taken from Susaki area in the Shimanto accretionary complex, SW Japan, which experienced the depth condition of the seismogenic zone. We found that the samples have higher P- and S-wave velocities of 5.4-5.8 km/s and lower porosities of 1-2.5 % than other sedimentary rocks in the Shimanto accretionary complex. This may be caused by tight contacts among grains due to pressure solution processes according to microstructural observations. Comparison with seismological observations in the present Nankai Trough indicated that the samples correspond to the hanging wall rocks of the megasplay fault where now a high velocity body is resolved. We further considered velocity-porosity relation using both the samples in this study and the drilled samples from the Nankai Trough, and proposed a model explaining from low to high porosities that is applicable to shallow to deep depths toward the seismogenic zone. The obtained elastic properties provided a critical nucleation length for an earthquake along the plate boundary fault of ~0.5 m. Material and structural heterogeneities below this length scale have the potential to modulate earthquake nucleation processes and future studies on this length scale will be necessary to bridge between laboratories and natural conditions.

Following the 15 January 2022 Hunga Tonga-Hunga Ha’apai eruption, several trace gases measured by the Aura Microwave Limb Sounder displayed anomalous stratospheric values. Trajectories and radiance simulations confirm that the H2O, SO2, and HCl enhancements were injected by the eruption. In comparison with those from previous eruptions, the SO2 and HCl injections were unexceptional, although they reached higher altitudes. In contrast, the H2O injection was unprecedented in both magnitude (far exceeding any previous values in the 17-year MLS record) and altitude (penetrating into the mesosphere). We estimate the mass of H2O injected into the stratosphere to be 146+-5 Tg - ~10% of the stratospheric burden. It may take several years for the H2O plume to dissipate. This eruption could impact climate not through surface cooling due to sulfate aerosols, but rather through surface warming due to the radiative forcing from the excess stratospheric H2O.

Inter-annual to decadal variability in the strength of the land and ocean carbon sinks impede accurate predictions of year-to-year atmospheric carbon dioxide (CO2) growth rate. Such information is crucial to verify the effectiveness of fossil fuel emissions reduction measures. Using a multi-model framework comprising prediction systems based on Earth system models, we find a predictive skill for the global ocean carbon sink of up to 6 years. Longer regional predictability horizons and robust spatial patterns are found across single models. On land, a predictive skill of up to 2 years is primarily maintained in the tropics and extra-tropics enabled by the initialization of the physical climate variables towards observations. We further show that anomalies of atmospheric CO2 growth rate inferred from natural variations of the land and ocean carbon sinks are predictable at lead time of 2 years and the skill is limited by the land carbon sink predictability horizon.

Multi-plume convection schemes based on discretized size densities can be easily made scale-aware by size filtering the parametrized plumes to fit the model resolution. Combined with their capability to smoothly transition from shallow to deep convection while being both numerically robust and computationally viable, these bin macrophysics models are well suited to the needs of high resolution NWP and regional climate modeling. One such approach is the ED(MF)n scheme which has previously been evaluated in a single column model against maritime cumulus LES. In this presentation we will confront the ED(MF)n scheme with long-term Doppler lidar observations of shallow cumulus days from the ARM-SGP site in Oklahoma. To do so the ED(MF)n scheme is implemented and tested in a non-hydrostatic model on a microgrid of 8x8 or 16x16 gridpoints. By using a ~10 km resolution this system behaves as a collection of weakly interacting single column models. We will compare the modeled relationship of vertical velocity to plume size against the relationship found in both the Doppler lidar observations and the LASSO LES run routinely at the ARM-SGP site. Next we examine which effect the assumed cloud-size distribution and entrainment as a function of plume size have on the resulting vertical transport.

Quantifying variability in the lowermost stratosphere (LMS) is important because of feedbacks among changing temperature, dynamics and species like ozone. We used reprocessed Southern Hemisphere Additional Ozonesondes data from 1998-2018 in a Multiple Linear Regression (MLR) model to analyze variability and trends in free tropospheric (FT) and LMS ozoneacross five well-distributed tropical regions. The MLR also computed trends in a proxy for convection as determined from laminae in each ozonesonde-radiosonde pair. Only the equatorial Americas exhibits statistically significant annual trends in FT or LMS ozone. At the other sites, ozonetrends occur in isolated layers during months when convection has changed, February-April or July-November. Our results imply that large FT ozone increases reported for populated tropical areas may be caused by growing pollution overlying smaller changes caused by perturbed dynamics. They also provide regional data for evaluating LMS ozonetrends based on zonal averages of often sparse satellite measurements

The Underground Gas Storage (UGS) project of Castor, Spain, was strategically conceived to guarantee the Spanish gas demand during 50 days. Yet, the project did not enter into operation because it was cancelled as a result of a sequence of felt earthquakes induced after cushion gas injection. The project cancellation implied an investment compensation to the operating company that may cost up to 4.73 billion euros to Spanish citizens. The sequence contained the three largest earthquakes (M4.08, M4.01 and M3.97) ever induced by any of the more than 640 UGS facilities around the world. The largest earthquakes were induced some 20 days after stopping injection, which lasted for 15 days. The focal depth of these earthquakes was between 4 to 10 km, far deeper than the 1.7 km injection depth. To understand the causes of this induced seismicity, we have performed coupled two-phase flow and geomechanical numerical simulations and we have employed Okada’s solution to analyze the shear slip stress transfer. We analyzed four seismicity-inducing mechanisms (pore pressure build-up, stress transfer, destabilizing buoyancy, and recovery of pressure drops that ensure transient stability in regions that are mechanically destabilized after a microseism). We found that the onset of seismicity was induced by gas injection, which reactivated the critically stressed Amposta fault through pore pressure buildup and buoyancy. The Amposta fault, a mature fault bounding the storage formation, crept, accumulating aseismic slip. Destabilization of the fault continued even after the stop of injection because of the permanent effect of buoyancy caused by the low density of the injected gas. The progressive accumulation of slip perturbed the stress around the rupture area of the Amposta fault and eventually reactivated a critically stressed unmapped fault located in the crystalline basement. Once this deep fault was reactivated, the sequence of earthquakes was induced by shear slip stress transfer, with transient slip-driven pore pressure changes likely controlling the delay between earthquakes. We contend that an analysis of fault stability prior to gas injection would have identified the high risk of inducing seismicity at Castor.

The seismic structure of the Earth’s lowermost mantle is characterized by two large low shear provinces (LLSVPs) beneath the Pacific and Africa. Surrounding the LLSVPs are regions with generally higher-than-average seismic velocities which are likely caused by ancient subducted slabs. However, seismic observations have also revealed relatively low-velocity structures in the subducting regions outside of the LLSVPs in the lowermost mantle. The question is what cause these low velocity structures? Here, three-dimensional, high-resolution geodynamic models are performed to study the thermal structure and dynamics of the Earth’s lowermost mantle outside of the LLSVPs. Widespread hot thermal anomalies, or thermal ridges as named here, are found in the relatively cold, downwelling regions of the lowermost mantle in our models, with linear, ridge-like morphology, elongated in the lateral mantle flow directions. A systematic parameter-space exploration shows that thermal ridges only form when there are gaps and thermal heterogeneities in the cold downwellings, and their formation is promoted by an increase of the core-mantle boundary (CMB) heat flux and Rayleigh number and by a reduction of the lowermost mantle viscosity. The low seismic velocity anomalies outside of the LLSVPs above the CMB may be related to the formation of thermal ridges in the lowermost mantle.

Attempts to determine physical property across thrust faults at subduction zones through drilling, logging and core sampling have been limited and restricted to exhumed accretionary prisms or shallow parts of active wedges. However, characterizing porosity evolution across the sedimentary section entering subduction zones and accreted sediments is crucial to understand deformation history at accretionary margins through determination of sediment trajectories, quantification of transported volumes of sediments and fluids with related mechanical responses and understanding deformation processes in and around fault zones. International Ocean Discovery Program Expeditions 372 and 375 drilled, logged and cored the entering basin (Site U1520) and active Pāpaku thrust (Site U1518) few kilometers landward of the northern Hikurangi margin deformation front where tsunami earthquakes and recurrent slow slip events occur. Here, we examine physical properties evolution across the Pāpaku thrust at Site U1518 including geophysical logging data, pore size distribution obtained by combining Nuclear Magnetic Resonance and Mercury Injection Capillary Pressure, and interstitial porosity that is representative of sediment compaction state, and compare with that of Site U1520. Interstitial porosity is determined by correcting total connected porosity from clay-bound water content based on cation exchange capacity. We evidence strong variations of physical properties across the thrust fault, with lower porosity, higher P-wave velocity and resistivity in the hanging-wall than in the footwall. We suggest that the porosity pattern at the Pāpaku thrust evidences differences in maximum burial depth with an overcompacted hanging-wall that has been uplifted, thrusted and concomitantly eroded above a nearly normally consolidated younger footwall.

Soil organic carbon (SOC) stocks represent a large component of the global carbon cycle that is sensitive to warming. Modeling and empirical studies often assume that temperature responses of microbial physiological functions and extracellular enzymatic reactions are predictive of ecosystem-scale SOC decomposition responses to warming. However, temperature-dependent soil trophic interactions such as predation of microbial decomposers by other organisms have not yet been incorporated into quantitative SOC models. Here, we incorporated a microbial predator into a tri-trophic population ecology model and a global-scale predictive SOC model to determine how predation would affect soil community population dynamics and temperature sensitivity of SOC stocks. Predators increased SOC stocks and their dependence on substrate input rates. Top-down controls of predators on microbial biomass caused SOC warming responses to diverge from microbial temperature responses, with warming-induced SOC losses reduced or reversed when predators were more temperature-sensitive. Our results suggest that higher trophic levels can reduce the sensitivity of SOC to warming, and that differences in temperature sensitivity across trophic levels may be a key determinant of SOC warming responses.

In a recent study, Sosa-Gutierrez et al. (2022, https://doi.org/10.1029/2021GL097484) evaluated the potential impacts of tropical cyclones (TCs) on the Atlantic pelagic Sargassum using satellite-based Sargassum maps, 86 hurricane tracks during 2011 – 2020, and statistical analysis. The results showed an average drop of 40% in Sargassum coverage under TC trajectories, attributed to Sargassum sinking. However, there appear two issues: 1) the Sargassum maps contain large uncertainties due to methodology used in developing the maps. The impacts of these uncertainties on change detection are largely unknown, especially along the TC trajectories where cloud cover prevails; 2) there is a lack of a “control” experiment in the logic to infer causality. Based on these observations and arguments, while it is possible that TCs may have significant impacts, either positively or negatively, on pelagic Sargassum, a revisit appears necessary to use improved Sargassum maps and better experimental design before drawing conclusions.

Precipitation projections in transient climate change scenarios have been extensively studied over multiple climate model generations. Although these simulations have also been used to make projections at specific Global Warming Levels (GWLs), dedicated simulations are more appropriate to study changes in a stabilising climate. Here, we analyse precipitation projections in six multi-century experiments with fixed atmospheric concentrations of greenhouse gases, conducted with the UK Earth System Model (UKESM) and which span a range of GWLs between 1.5 and 5°C of warming. Regions are identified where the sign of precipitation trends in high-emission transient projections is reversed in the stabilisation experiments. For example, stabilisation reverses a summertime precipitation decline across Europe. This precipitation recovery occurs concurrently with changes in the pattern of Atlantic sea surface temperature trends due to a slow recovery of the Atlantic Meridional Overturning Circulation in the stabilisation experiments, along with changes in humidity and atmospheric circulation.