Observations and cloud-resolving simulations suggest that a convective updraft structure drawing mass from a deep lower-tropospheric layer occurs over a wide range of conditions. This occurs for both mesoscale convective systems (MCSs) and less-organized convection, raising the question: Is there a simple, universal characteristic governing the deep inflow? Here we argue that nonlocal dynamics of the response to buoyancy are key. For precipitating deep-convective features including horizontal scales comparable to a substantial fraction of the troposphere depth, the response to buoyancy tends to yield deep inflow into the updraft mass flux. Precipitation features in this range of scales are found to dominate contributions to observed convective precipitation for both MCS and less-organized convection. The importance of such nonlocal dynamics implies thinking beyond parcel models with small-scale turbulence for representation of convection in climate models. Solutions here lend support to investment in parameterizations at a complexity between conventional and superparameterization.

14 15 Key Points: 16 (1) E3SMv1 captures spatial and temporal variability in the observed dust aerosol optical 17 depth, but underestimates long-range transport. 18 (2) The net direct radiative effect of dust simulated by E3SMv1 is-0.42 Wm-2 with a smaller 19 longwave warming than other recent studies. 20 (3) In addition to emission, dry removal of dust are highly sensitive to the increase of 21 horizontal or vertical model resolution. 22 23 24

Changes in atmospheric pressure continuously ventilate soils and snowpacks. This physical process, known as pressure pumping, is a major factor in the exchange fluxes of H2O, CO2 and other trace gases between the soil and atmosphere. Thus models of pressure pumping are relevant to many areas of critical importance. This study compares the three principal models used to describe pressure pumping. Beginning with the fundamental physical principles and whether the flow field is compressible or incompressible, these models are categorized as linear parabolic (one model – compressible) or nonlinear hyperbolic (two models – incompressible). Using observed soil surface pressure data, measured vertical profiles of soil permeability and standard linear analysis and numerical methods, this study shows that nonlinear models produce advective velocities that are one to two orders of magnitude greater than those associated with the linear model. Incorporating soil temperature and moisture dynamics made very little difference to the linear model, but a significant difference in the nonlinear models suggesting that advective velocities induced by pressure changes associated with soil heating and moisture dynamics may not always be small enough to ignore. All numerical results are sensitive to the frequency of the pressure forcing, which was band-pass filtered into low, mid and high frequencies with the greatest model differences at low frequencies. Partitioning the pressure forcing and model responses helped to establish that mid-frequency weather-related phenomena (empirically identified as inertia gravity waves and solitons) are important drivers of gas exchange between the soil and the atmosphere.

Subducted reliefs, such as seamounts and ridges, affect fluid processes in accretionary prisms of subduction zones. The Kyushu–Palau Ridge subducts along with the Philippine Sea Plate in Hyuganada, which is one of the regions that are best suited for studying the role of subducting topography. This study investigates the shear wave velocity structure using an array of ocean-bottom seismometers (OBSs) with a 2 km radius. Teleseismic Green’s functions and a surface wave dispersion curve are inverted to one-dimensional shear wave velocity structures using transdimensional inversion. The results indicate the presence of a low-velocity zone 3–4 km below the seafloor. The reduced shear wave velocities are consistent with a compressional velocity structure obtained in a previous seismic refraction survey. We conclude that the low velocities are representative of high pore fluid pressure. In addition, the resolved lithological boundaries exhibit a sharp offset that consistently appears across the OBS array, suggesting the presence of a blind fault beneath it. The predicted fault, which is located at the flank of the Kyushu–Palau Ridge and oriented roughly parallel to the ridge axis, is likely caused by the ridge subduction. The fracture caused by the ridge subduction may act as a fluid conduit, forming a fluid reservoir beneath the well-compacted sediment layers. The compilation of previous refraction surveys implies that the reservoir has a lateral extension of >100 km. Its spatial distribution roughly correlates with the ridge location, highlighting the significant role the ridge plays in the formation of the reservoir.

The retrival algorithms used for optical remote sensing satellite data to estimate Earth’s geophysical properties have specific requirements for spatial resolution, temporal revisit, spectral range and resolution, and instrument signal to noise ratio (SNR) performance to meet science objectives. Studies to estimate surface properties from hyperspectral data use a range of algorithms sensitive to various sources of spectroscopic uncertainty, which are in turn influenced by mission architecture choices. Retrieval algorithms vary across scientific fields and may be more or less sensitive to mission architecture choices that affect spectral, spatial, or temporal resolutions and spectrometer SNR. We used representative remote sensing algorithms across terrestrial and aquatic study domains to inform aspects of mission design that are most important for impacting accuracy in each scientific area. We simulated the propagation of uncertainties in the retrieval process including the effects of different instrument configuration choices. We found that retrieval accuracy and information content degrade consistently at >10 nm spectral resolution, >30 m spatial resolution, and >8 day revisit. In these studies, the noise reduction associated with lower spatial resolution improved accuracy vis à vis high spatial resolution measurements. The interplay between spatial resolution, temporal revisit and SNR can be quantitatively assessed for imaging spectroscopy missions and used to identify key components of algorithm performance and mission observing criteria.

We constrain Europa’s tenuous atmosphere on the subsolar hemisphere by combining two sets of observations: oxygen emissions at 1304 Å and 1356 Å from Hubble Space Telescope (HST) spectral images, and Galileo magnetic field measurements from its closest encounter, the E12 flyby. We describe Europa’s atmosphere with three neutral gas species: global molecular (O2) and atomic oxygen (O), and localized water (H2O) present as a near-equatorial plume and as a stable distribution concentrated around the subsolar point on the moon’s trailing hemisphere. Our combined modelling based on the ratio of OI 1356 Å to OI 1304 Å emissions from Roth (2021) and on magnetic field data allows us to derive constraints on the density and location of O2 and H2O in Europa’s atmosphere. We demonstrate that 50% of the O2 and H2O abundances from Roth (2021) are required to jointly explain both the HST and Galileo measurements. The column densities of 1.24*10^18 m^-2 and 1.47*10^19 m^-2 for O2 and H2O, respectively, derived by our analysis however still lie within the uncertainties of Roth (2021). Our results provide additional evidence for the existence of a stable H2O atmosphere at Europa.

Electric vehicle (EV) adoption promises potential air pollutant and greenhouse gas (GHG) reduction co-benefits. As such, China has aggressively incentivized EV adoption, however much remains unknown with regard to EVs’ mitigation potential, including optimal vehicle type prioritization, power generation contingencies, effects of Clean Air regulations, and the ability of EVs to reduce acute impacts of extreme air quality events. Here, we present a suite of scenarios with a chemistry-climate model that assess the potential co-benefits of EVs during an extreme winter air quality event. We find that regardless of power generation source, heavy-duty vehicle (HDV) electrification consistently improves air quality in terms of NO2 and fine particulate matter (PM2.5), potentially avoiding 562 deaths due to acute pollutant exposure during the infamous January 2013 pollution episode (~1% of total premature mortality). However, HDV electrification does not reduce GHG emissions without enhanced emission-free electricity generation. In contrast, due to differing emission profiles, light-duty vehicle (LDV) electrification in China consistently reduces GHG emissions (~2 Mt CO2), but results in fewer air quality and human health improvements (145 avoided deaths). The calculated economic impacts for human health endpoints and CO2 reductions for LDV electrification are nearly double those of HDV electrification in present-day (155M vs. 87M US$), but are within ~25% when enhanced emission-free generation is used to power them. Overall we find only a modest benefit for EVs to ameliorate severe wintertime pollution events, and that continued emission reductions in the power generation sector will have the greatest human health and economic benefits.

Groundwater flow in discontinuous permafrost is complex and often unpredictable. Frozen-soil obstructs flow causing groundwater to re-route through thawed zones comprised of hydraulicly conductive soils. Open taliks connect sub and suprapermafrost portions of aquifers creating mixing of groundwater from these two zones with different water qualities. In this study, spatial and temporal distributions of stable isotopes 2H and 18O measured in a floodplain aquifer were used to characterize groundwater flow in a discontinuous permafrost aquifer located in a river floodplain. Results show enrichment in 2H and 18O in shallow suprapermafrost groundwater through mixing of more enriched precipitation recharge water with more depleted river recharge water. Conversely, subpermafrost groundwater is depleted in 2H and 18O, similar to δ18O and δ2H concentrations in river water. Low concentrations of δ18O and δ2H measured at the water table identify areas of upward flowing subpermafrost groundwater through open taliks into the suprapermafrost portion of the aquifer. These open taliks are located along slough channels and randomly located throughout the large body of permafrost positioned in the floodplain. Well logs and the detectable decrease in δ18O and δ2H in areas where open talik exist show that the soils in open taliks are comprised of highly hydraulic conductive sands and gravels compared to frozen soils which are mainly silt. Results from this study show the process of permafrost degradation in floodplain aquifers consisting of rapid thawing in areas of highly permeable soil versus slow conductive heat transfer into low permeable silt layers.

Seismic hazard evaluation is important for urban construction, earthquake disaster prevention and mitigation. However, because of the long recurrence times of large earthquakes (hundreds to thousands of years), seismic hazard assessment based on relatively short-term (tens of years) observational seismic catalog is difficult. Synthetic seismic catalogs provide a useful way to obtain long-term seismic hazard. Based on Coulomb failure criterion, we apply a quasi-static physics-based earthquake simulator (Virtual Quake) in a tectonically complicated region with several major faults, namely the Anninghe, Zemuhe, Daliangshan and Xiaojiang faults, in the Southwestern China. Slip rates of those major faults are constrained by the GPS data, and frictions are constrained by the laboratory experiments. Considering the stress interactions among the fault system, a synthetic catalog over 20, 000 years is simulated. The simulated catalog shows consistence with the observed seismicity in spatial distribution of large earthquakes, b value and mean seismic rate. The synthetic catalog also shows that the mean intervals of M≥7.0 earthquakes for the Anninghe, Zemuhe, Daliangshan and Xiaojiang faults are 299a, 867a, 361a and 90a, respectively. Our results provide a helpful index to evaluate seismic hazard in such a complicated region.

Crystal lattice defects in quartz have long been exploited for age determination, yet also show potential for sediment provenance studies. Here we introduce a novel method for tracking aeolian dust provenance by utilising the natural accumulation of E1' and peroxy defect centres in quartz. Our approach is based on the previously observed premise that E1' and peroxy centres arise from Frenkel defect pairs, and that their concentration increases with age of the quartz-bearing source rock. We propose that these defect centres can be utilised as a characteristic feature of the source rock and consequently, for fingerprinting sediments derived from it. We successfully apply our new protocol to distinguish fine-grained quartz extracted from loess deposits from two regions in Central Asia which are known to derive from different source material of differing age. Our method offers strong potential for identifying variability in source, both spatially and through time down sedimentary sequences.

Motivated by the abundance of low clouds in the subtropics, where the easterly trade winds prevail, we study the role of shallow convection in the momentum budget of the trades. To this end, we use ICON-LEM hindcasts run over the North Atlantic for twelve days corresponding to the NARVAL1 (winter) and NARVAL2 (summer) flight campaigns. The simulation protocol consists of several nested domains, and we focus on the inner domains (≈100x100 km2) that have been run at resolutions of 150–600 m, which are subjected to a realistically varying flow that has developed in the outer domain. Combined, the resolved advection and the subgrid stresses decelerate the easterly flow from the surface up to about 2 km in winter and 1 km in summer, a result that is insensitive to horizontal resolution. The unresolved processes are strongest near surface and are well captured by traditional K-diffusion theory, but convective-scale motions that are not considered in K-diffusion theory contribute the most in the upper part of mixed layer and are strongest just below cloud base. The results point out that convection in the mixed-layer — the roots of trade-wind cumuli and subcloud layer circulations — play an important role in slowing down easterly flow below cloud base (but little in the cloud layer itself), which helps make the zonal wind jet more distinct. Most of the friction within the clouds and near the wind jet stems from smaller-scale turbulence stresses.

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.

A physical full-scale experimental set-up was designed and implemented in the wind tunnel to reproduce and capture the trajectories of falling water drops when approaching the collector of catching type precipitation gauges, reproducing rainfall measurements in windy conditions. The experiment allowed to collect, for the first time, a large dataset of high-resolution footages of the deviation of such trajectories, as induced by the bluff-body aerodynamics of the outer gauge shape. By processing the collected images, a consistent quantitative interpretation of each drop pattern was possible, based on a detailed Computational Fluid Dynamics simulation of the airflow updraft and acceleration features above the collector of the gauge. Numerical airflow simulations were extensively validated in the wind tunnel, using local flow measurements and Particle Image Velocimetry. Capturing the deviation of the drop trajectories in the wind tunnel allowed a clear visualisation of the physical reason for the wind-induced undercatch of precipitation gauges, since drops were individually observed to fall outside instead of inside of the collector, contrary to what would be expected by extrapolating their undisturbed trajectory. The adopted Lagrangian Particle Tracking model and the formulation used for the drag coefficient were suitable to closely reproduce the observed drop trajectories when affected by the airflow deformation due to the bluff-body aerodynamics of two investigated gauge geometries. The wind tunnel experiment provided the basis for the validation of the particle tracking model in terms of the difference between simulated and observed trajectories, after initial conditions were suitably set to represent the experimental setup.

Remotely sensed solar-induced fluorescence (SIF) has emerged as a novel and powerful approach for terrestrial vegetation monitoring. Continuous measurements of SIF in synergy with concurrent eddy covariance (EC) flux measurements can provide a new opportunity to advance terrestrial ecosystem science. Here we introduce a network of ground-based continuous SIF observations at flux tower sites across the mainland China referred to as ChinaSpec. The network consists of sixteen tower sites including 6 cropland sites, 4 grassland sites, 4 forest sites and 2 wetland sites. An automated SIF system was deployed at each of these sites to collect continuous high resolution spectra for high-frequency SIF retrievals in synergy with EC flux measurements. The goal of ChinaSpec is to provide long-term ground-based SIF measurements and promote the collaborations between optical remote sensing and EC flux observation communities in China. We present here the details of instrument specifications, data collection and processing procedures, data sharing and utilization protocols, and future plans. Furthermore, we show the examples how ground-based SIF observations can be used to track vegetation photosynthesis from diurnal to seasonal scales, and to assist in the validation of fluorescence models and satellite SIF products (e.g., from OCO-2 and TROPOMI) with the measurements from these sites since 2016. This network of SIF observations could improve our understanding of the controls on the biosphere-atmosphere carbon exchange and enable the improvement of carbon flux predictions. It will also help integrate ground-based SIF measurements with EC flux networks which will advance ecosystem and carbon cycle researches globally.

Hydraulically-forced crevassing is thought to reduce the stability of ice shelves and ice sheets, affecting structural integrity and providing pathways for surface meltwater to the bed. It can cause ice shelves to collapse and ice sheets to accelerate into the ocean. However, direct observations of the hydraulically-forced crevassing process remain elusive. Here we report a new, novel method and observations that use icequakes to directly observe crevassing and determine the role of hydrofracture. Crevasse icequake depths from seismic observations are compared to a theoretically derived maximum-dry-crevasse-depth. We observe icequakes below this depth, suggesting hydrofracture. Furthermore, icequake source mechanisms provide insight into the fracture process, with predominantly opening cracks observed, which have opening volumes of tens to hundreds of cubic meters. Our method and findings provide a framework for studying a critical process, key for the stability of ice shelves and ice sheets, and hence rates of future sea-level rise.

The one-dimensional (1D) lake model, a submodule in the Weather Research and Forecasting (WRF) system (WRF-lake) was evaluated in a large dimictic reservoir, Miyun Reservoir, in northern China. Another 1D lake model, Minlake, which has been successfully applied in this reservoir and many other lakes/reservoirs, was applied as a reference. Simulated results showed that Minlake was able to reproduce the whole temperature profile of Miyun Reservoir accurately. For WRF-lake, although we used carefully chosen parameterization (the same surface absorption fraction, light attenuation coefficient and initial temperature as with Minlake, as well as modified surface roughness lengths), the model still had imperfect surface temperature simulation and completely inaccurate simulation in the deep layers. Several numerical experiments were carried out to study the impact of three factors (thermal diffusivity, inflow-outflow and topography) on the two 1-D models’ performances, and we found: (1) Modifying the diffusion coefficient of WRF-lake can improve the simulation of deep layers but cannot influence the surface temperature. (2) Inflow-outflow and topography have a significant effect on the whole temperature profile. Overall, the WRF-lake model can be coupled with WRF when applied to reservoirs like Miyun, as it can reproduce surface water temperatures to some extent (Nash–Sutcliffe efficiency coefficient ＞ 0.9). However, for better model performance in reservoir physical processes description and more extensive application to other reservoirs with larger flow rates or larger storage capacity, optimizing the parameterization for thermal diffusivity, inflow-outflow and topography needs to be done in future work.

Previous lightning climatologies derived from Lightning Imaging Sensor (LIS) and Optical Transient Detector (OTD) total lightning measurements have quantified lightning frequency as a Flash Rate Density (FRD). This approach assumes that lightning flashes can be represented as points, and quantifies the frequency of lightning centered in each grid cell. However, lightning has a finite extent that can reach hundreds of kilometers. A new climatology based on Flash Extent Density (FED) is constructed for LIS (including ISS-LIS) and OTD that accounts for the horizontal dimension of lightning. The FED climatology documents the frequency that an observer can expect lightning to be visible overhead - regardless of where the flash began or ended. This new FED climatology confirms and elaborates on the previous global LIS / OTD FRD and Americas-only Geostationary Lightning Mapper (GLM) findings. Applying GLM reprocessing codes to LIS and OTD data reveals cases of megaflashes measured from Low Earth Orbit that were artificially split by the LIS / OTD clustering algorithms. The FED climatology maintains Lake Maracaibo as the global lightning hotspot with an average of 389 flashes / day, but designates Karabre in the Democratic Republic of the Congo as the global thunderstorm duty (percent of the total viewtime where lightning is observed) hotspot at 7.29%. Meanwhile, Kuala Lumpur is the national capital city with the most lightning, and its airport (KUL) is the top major airport affected by lightning. The FED seasonal cycle and month-to-month changes in the “center of lightning” for the three continental chimney regions are also discussed.

International transboundary aquifers provide important water supplies to over 150 countries. Long-term sustainability of these aquifers requires transboundary cooperation and yet only a select few (1%) transboundary aquifers are formally regulated by a treaty. To better understand the drivers and incentives that allow treaties to emerge, we develop a two-player game to model the social dilemma of transboundary aquifer cooperation. The game incorporates socio-economic and hydrogeological features of the system and highlights the importance of trust to evaluate the benefits and risks of any treaty. We validate the game through a case study of the Genevese aquifer, which is governed by the longest-running and most collaborative transboundary aquifer treaty on record. We then focus on the symmetric game between identical players to explore the role of groundwater connectivity, alternative water supply, water demand, and trust on the emergence of transboundary treaties. The solution space highlights how incentives for cooperation are greatest when the value of water is commensurate with the cost of groundwater abstraction. Cooperation requires high trust in situations characterized by water abundance or scarcity. The model further indicates how two different types of agreements are likely to emerge. Treaties that limit abstraction have greater potential when countries have access to an alternative water source, whereas treaties that restrict pumping near the border have greater potential in water-scarce regions with emerging concerns over groundwater depletion. In addition to helping explain the emergence of existing treaties, this framework offers potential to identify aquifers that may be amenable to cooperation.