In angled river plumes, the river flow is oriented obliquely to the coast, resulting in a lateral expansion into the sea rather than a radial one. However, the frontal structure and dynamics in these systems are not straightforward, especially under the influence of coastal currents. Here, we present detailed observations of an angled river plume and its fronts in the Macao waters. During the ebb tide, the river plume transitions from subcritical to supercritical due to the acceleration caused by lateral contraction. Despite these changes, the plume front remains nearly stationary, forming a steady gravity current that meets the critical conditions in a coordinate system normal to the front. Furthermore, the adjustment of the cross-flow changes the Froude angle, leading the frontal shape to a parabolic planform. Beneath the surface front, internal bores have observed, predominantly driving frontogenesis processes via vertical straining rather than horizontal advection. These findings offer novel understanding of stationary surface fronts, which may trap the river-borne materials and pose significant challenges to coastal environments and ecosystems.

A document by Samba Siva Sai Prasad Thota. Click on the document to view its contents.

The equatorial cold tongue region has not warmed up in response to historical radiative forcing in the real world, contrary to the strong warming often simulated by climate models. Here we demonstrate that climate models fail to represent one or both of the key processes driving observed sea surface temperature (SST) pattern formation: a realistic surface wind stress pattern shaping subsurface cooling through wind-driven circulation changes, and effective connectivity between subsurface and surface temperatures via upwelling and mixing. Consequently, none of the models approximate the observed lack of cold tongue SST warming and strengthening of zonal SST gradient across the equatorial Pacific. Further, those that come closest achieve this due to interhemispheric warming differences rather than equatorial dynamics as observed. Addressing different origins of subsurface cooling in observations and simulations, and how they connect to SST, will lead to improved understanding of tropical Pacific SST changes to date and how they will evolve in the future.

This Work has been submitted to the American Meteorological Society - Journal of Atmospheric Sciences. Copyright in this Work may be transferred without further notice.

A document by Wang Mudan. Click on the document to view its contents.

Aerodynamic roughness length (z0) fundamentally affects land surface momentum loss and wind resource simulation, but ground truth data of z0 are sparse in space, causing z0 datasets used in atmospheric models are empirically estimated from land cover types through a look-up table. In this study, we derived z0 values from 101 anemometer towers in China. Taking them as ground truth, we show that existing gridded z0 datasets determined from either a look-up table or a machine-learning method contain considerable uncertainty and fail to capture the variability of z0 within each land cover type, although the latter performs better. Even for the widely-used ERA5, its z0 is overestimated in wind-rich regions of China, causing an underestimation of near-surface wind speed. This highlights the urgency to improve z0 data in atmospheric models. Current rapidly expanding anemometer towers may substantially enrich z0 truth data and thus provide potential to improve wind resource modeling.

We model the subsurface thermal field of the Apollo 17 landing site in the Taurus-Littrow valley focusing on local topographic effects and refraction of heat. Topographic effects have been accounted for in original reports, but the refraction of heat due to local thermal conductivity contrasts has not been analyzed. Refraction of heat is evident due to the extreme thermal conductivity contrast between the regolith (0.01 – 0.02 Wm-1K-1) and underlying basaltic rocks (0.5 – 1.0 Wm-1K-1). Outcrops of basalt peeking from beneath the regolith funnel the heat flow resulting in a decrease of the heat flow in low conductivity areas and an increase in high conductivity areas, respectively. The effect is enhanced by the topographic effect in craters, which become spots of very high heat flow. Two-dimensional (width 2.5 km, height 1.7 km) and three-dimensional (6 km x 5 km x 1.7 km) finite element models of conductive heat transfer indicate the commonly accepted value of 16 mWm-2 in the Taurus-Littrow site should be increased by about 3 mWm-2, i.e. by 19% to obtain an estimate representative for the valley floor at a depth where the topographic and refraction effects have attenuated (ca. 1.7 km depth). Our modeling illustrates the challenges in interpreting point-like lunar heat flow measurements and potentially contributes to planning of future thermal studies on the Moon, Mercury and Mars.

Coupled land-atmosphere models exchange grid cell mean values of states and fluxes even as they separately simulate subgrid variability. The characteristics of atmospheric heterogeneity driven by land surface heterogeneity are examined in large eddy simulations. The degree of spatial variance in the atmosphere is highly correlated with the spatial variance of land surface fluxes, but the impacts are entirely at scales larger than 10-30 km. Between 1-10 km throughout most of the day there is no difference in power spectra over heterogeneous and homogeneous surfaces, as synoptic situations and internal dynamics associated with atmospheric turbulent transfer is insensitive to surface heterogeneity. To improve forecasts, the ability of land surface heterogeneity to organize mesoscale circulations affecting boundary layer evolution and convective development should be represented in non-cloud-resolving models, as modern convective parameterizations can account for such subgrid processes. This will require the exchange of subgrid information between land and atmosphere models.

On January 18, 2021, a blind mid-crustal Mw ~6.4 earthquake occured near San Juán, Argentina. The observation of associated ground deformation with InSAR is hidden by strong tropospheric signals. We properly correct the data and reconstruct the deformation field through InSAR timeseries approach. We show it is possible to retrieve such signal with sufficient quality to invert the fault parameters. The ground deformation can be explained by uniform slip of a single NW dipping fault plane at a depth of 19km, and the geometry of such fault supports the reactivation of inherited structures on top of the Cuyania Terrane, insinuating a direct connection and strain transfer to the active east-vergent Precordillera front.

A document by Peter Chu. Click on the document to view its contents.

• Earth system models (ESMs) have many tunable parameters that are difficult to estimate and weakly constrained by theory. • Kalman filter-based approaches are attractive options, but existing implementations require expensive offline hyperparameter selection. • We propose a new Kalman filter algorithm that estimates model parameters and its hyperparameter simultaneously.

Experimental bacteriophage addition to soil depresses bacterial respiration and alters nitrogen transformationsBenjamin D. Duval1*, Kurt E. Williamson2, Anika Baloun1, Linda C. DeVeaux11Biology Department, New Mexico Institute of Mining and Technology, Socorro, New Mexico, USA 878012Biology Department, The College of William and Mary, Williamsburg, Virginia, USA 23185*corresponding author:benjamin.duval@nmt.edu575-835-5820ORCID ID: 0000-0001-7692-4400CRediT contributor roles:BDD: conceptualization, data curation, formal analysis, methodology, project administration, supervision, writing (draft), writing (editing)KEW: conceptualization, writing (draft), writing (review & editing)AB: investigation, writing (review & editing)LCD: methodology, resources, supervision, writing (review & editing)ABSTRACTSoil heterogeneity and complex host-phage relationships impede understanding phage influence on terrestrial nutrient cycles. We performed laboratory experiments quantifying phage effects on bacterial respiration and inorganic soil N and P changes. Soil microcosms under reducing conditions were inoculated with a single bacterial host (Gordonia rubripertincta ) or with the host + phage (φ Apollonia6). Respiration declined immediately following phage introduction, and was lower in the presence of phage through time. Phage additions increased variance in N transforms. NH4+ decline did not match NO3- gain, suggesting microbial immobilization in +phage microcosms. Net NO3- accumulation was observed with phage, suggesting viral interruption of bacterial NO3- reduction. Phosphate pools declined in both treatments, likely due to cell uptake and incorporation into phage. This single host-phage system highlights phage depression of bacterial respiration and altered nutrient transformation, and can be the basis for further investigations into phage-bacteria soil interactions and their impacts on terrestrial nutrient cycling.Keywords: Ammonium uptake, bacteriophage, biogeochemistry, Gordonia rubripertincta, nitrate reduction, respiration, soilINTRODUCTIONViruses that infect bacteria (bacteriophage or phage), are ubiquitous and numerous in soil systems, with abundances as high as reported for forest soils (1). There is a presumption of biogeochemical importance with such abundances, and phage are increasingly recognized as having a regulatory role within bacteria-driven portions of carbon (C), nitrogen (N) and phosphorus (P) cycles (2–4). However, there is tremendous uncertainty about the magnitude and direction of phage effects on most terrestrial biogeochemical processes, due to the physical and chemical complexity of soils, and the numerous types of potential phage-bacteria interactions in soil (5).Kuzyakov and Mason-Jones’ (2018) review of phage influence on soil processes arrives at two important conclusions: 1) soil bacterial mortality is principally caused by phage, and 2) nucleotide metabolism involved in phage genome replication creates high N and P demand which alters the stoichiometry of necromass relative to living biomass. Thus, phage-induced mortality is expected to release qualitatively different resources into the soil system than other mechanisms of bacterial mortality, e.g., protozoan grazing or from soil perturbations such as freeze-thaw cycles (7). However, variation in phage infection outcomes (e.g., lysis, lysogeny or chronic infection), from a population level, may also produce very different biogeochemical results with respect to both bacterial mortality and nutrient demands.Phage-induced mortality could simply lower host bacterial population activity and the rate and net products of any processes performed by that population (i.e., microbial N immobilization or NO3- reduction). This could be characterized as “kill the host, kill the process”. However, bacterial mortality also liberates cell components that are subsequently recycled as C and N sources promoting growth and activity in living microbial biomass (i.e., “eat the dead, change the product”). These possibilities, coupled with observations that phage lysate typically has higher C:N and lower phosphorus (P) than living biomass, suggest that phage mortality creates an intermediate biogeochemical scenario between process interruption from host death and process enhancement from necromass nutrient fertilization (6–8). Furthermore, a significant fraction of soil phages at any given time are likely lysogenic, and infect bacteria without immediately causing cell death via lysis (9,10). Physiological stress may skew temperate phages toward lysogenic replication, in which the phage genome takes up stable residence inside of its host cell instead of generating progeny particles and inducing cell lysis (11), and we expect those lysogenized cells to continue elemental uptake and transformation. It is unclear if element processing rates would be negatively impacted by the presence of a prophage, but prophage could slow bacterial element processing by reducing bacterial metabolism, and lysogeny prevalence can correlate with sub-optimal host conditions (12,13).Given the range of potential phage impacts on bacterial functional roles, microcosm experiments are well-suited to answer questions related to mortality effects and quantifying elemental flux changes as a result of single host-phage interactions in soil. To do so, we selected a heterotrophic (organic C processing) host bacterial strainGordonia rubritincta, that has known roles in organic compound degradation and synthesis (14,15), NO3- reduction, and has substantial P demand (16). Our group has recently isolated several phages from natural and anthropogenically influenced soils that infect Gordonia (17). From that group, we selected the phage φApollonia6 for its consistent infection rate in our lab trials (Duval and DeVeaux, pre-experimental observations). The influence of this phage on Gordonia functional ecology was quantified for two key ecosystem processes, organic C mineralization/respiration and inorganic nutrient (N and P) transformation. Microcosms were designed to promote NO3- reduction by this bacterial strain (high H2O/low O2) during a medium duration (~1 month) incubation experiment.We predict that sterile soils inoculated with Gordonia would have relatively high rates of CO2 respiration compared to soils that also had phage additions; these soils are also predicted to yield lower final pools of NO3- due to denitrification. Phage additions will result in lower CO2 fluxes due to cell mortality, and as a result, NO3- pools increase due to denitrification interruption due to phage. Because virion production is implicitly P limited, we expect greater reductions of inorganic P pools (as a result of P uptake and synthesis into organic structures) in soils with phage addition (16). Alternatively, a dip in respiration from mortality may be followed by a pulse of activity from cells utilizing lysis products as energy sources and possibly nutrients (7). In that instance, we expect higher rates of CO2 emissions and lower NO3- pools with phage addition compared to bacteria-only soils. Regardless of outcome, this experiment contributes to the growing literature of phage-influenced soil N and P transformations.METHODS

Dust aerosols play a crucial role in Earth’s biogeochemical processes by modulating solar radiation and affecting terrestrial ecosystem productivity. In China, extensive arid and semi-arid regions contribute to high dust aerosol emissions, yet the long-term impact of dust aerosols on gross primary productivity (GPP) remains insufficiently quantified. This study coupled the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) and the Joint UK Land Environment Simulator (JULES) to quantify the impact of dust aerosol radiative forcing on GPP in China’s terrestrial ecosystems from 2000 to 2020. Results indicated that dust aerosols significantly alter surface solar radiation components by reducing direct radiation and enhancing diffuse radiation. The mean annual decrease in direct radiation due to dust aerosols was −8.2 ± 0.2 W m⁻², while the increase in diffuse radiation was 5.3 ± 0.1 W m⁻², leading to a net reduction in total surface solar radiation of around −2.9 W m⁻². These radiative changes resulted in an average annual increase in GPP of approximately 0.11 ± 0.024 Pg C yr⁻¹, accounting for around 2% of China’s mean annual GPP of 6.44 ± 0.18 Pg C yr⁻¹ during the study period. The enhancement was particularly pronounced in regions with high dust aerosol loads, such as northwest China, and exhibited notable interannual variability. This study underscores the complex interactions between dust aerosols and terrestrial ecosystems, highlighting the importance of considering aerosol radiative effects in carbon cycle assessments and climate models.

Airglow originating from metastable helium He(2^3S) at 1083 nm has been used to study the upper thermosphere since its discovery in 1959, yielding insights into e.g. solar EUV intensities and thermospheric photoelectron densities. However, passive airglow measurements are fundamentally limited, because they represent a vertical integration of the entire He(2^3S) layer, spanning 100s of km, and because they rely on solar illumination of the He(2^3S) layer, so temporal changes are difficult to distinguish from vertical variations. Recently, the first height-resolved measurements of He(2^3S) density were made by fluorescence lidar, opening a new window for studying the upper thermosphere. We report on a series of 51 measurements by this instrument spanning an entire winter season and extending to an altitude of 1000 km, revealing a broad He(2^3S) layer that extends to, and peaks at, higher altitudes than previously expected.

• Electron precipitation in Jupiter's northern auroral oval can increase microwave opacity at frequencies observed by the Juno MicroWave Radiometer, appearing as cold spots in brightness temperature. • Precipitation of 32 keV-10 MeV electrons results in ionization of the lower stratosphere below the methane homopause, producing short-lived hydrocarbon ions. • Rapid changes in MWR antenna temperatures over consecutive spacecraft spins highlight short-time scale temporal variations in the ionospheric medium. They imply downward electron fluxes whose fluxes vary within 10 s.

The recovery of the thermosphere after a strong geomagnetic storm on 12 May 2021 is investigated using lower and middle thermospheric temperature (Tdisk), ratio of atomic oxygen and molecular nitrogen column densities (O/N2), cooling due to Nitric Oxide (NO), and model simulations. The peak influence of the geomagnetic storm lasted about five hours and generated latitudinal gradients in Tdisk and O/N2. Following the storm, the latitudinal gradient in temperature recovered faster compared to that of O/N2. Measured NO-cooling rate and simulated NO-densities are enhanced on the storm day compared to a quiet-day, consistent with a rapid recovery in temperatures. Based on this, we conclude that the faster recovery of the Tdisk latitudinal gradient is driven by the combined effect of NO cooling and strong thermal conductivity. Furthermore, the slower recovery of the O/N2 latitudinal gradients can be attributed to the lack of poleward advection after the storm.

Retrieval of ocean surface current using single-antenna synthetic aperture radar (SAR) relies on the removal of the wind and wave signal (wind-wave bias) from the observed SAR Doppler shift. This is often performed using deterministic atmospheric and wave models input into a geophysical model function, though atmospheric models are chaotic, and their predictability is flow-dependent. 251 Sentinel-1 SAR scenes, obtained in 2023 over Skagerrak and Kattegat, are analyzed to assess the uncertainty in the radial velocity estimation caused by uncertainties in the wind speed and direction provided by MEPS, an operational regional atmospheric ensemble system. Using ensemble surface wind direction and speed from MEPS, we investigate the conditions under which the radial velocity retrieval uncertainties exceed community-guided thresholds. The maximum wind speed and direction values that meet the specified thresholds are also estimated using two approaches. Our findings show that retrievals have a higher degree of uncertainty when the wind speed uncertainty exceeds 20% of the mean field, with larger uncertainties associated with low-wind speed conditions. A strong dependency between satellite antenna-look and maximum uncertainty values is reported. Employing ensemble models on radial velocity uncertainty quantification has promising potential and may be extended to operational global products.

Surface runoff and infiltrated water interact with dynamic landscape properties en route to the stream, ranging from vegetation and microbial activities to soil and geological attributes. Stream solute concentrations are highly variable and interconnected due to these interactions, flow paths, and residence times, and often exhibit hysteresis with flow. Significant unknowns remain about how point measurements of stream solute chemistry reflect interdependent hydrobiogeochemical and physical processes, and how signatures are encapsulated as nonlinear dynamical relationships between variables. We take a machine learning approach to understand and capture these dynamical relationships and improve predictions of solutes at short and long time scales. We introduce a physical process-based ”flow-gate” into an LSTM (long short-term memory) model, which enables the model to learn hysteresis behaviors if they exist. Further, we use information-theoretic metrics to detect how solutes are interdependent, and iteratively select source solutes that best predict a given target solute concentration. The ”flow-gate LSTM” model improves model predictions (RSME values decrease from 1% to 32%) relative to the standard LSTM model for all nine solutes included in the study. The predictive improvements from the flow-gate LSTM model highlight the importance of lagged concentration and discharge relationships for certain solutes. It also indicates a potential limitation in the traditional LSTM model approach since flow rates are always provided as input sources, but this information is not fully utilized. This work provides a starting point for a predictive understanding of geochemical interdependencies using machine-learning approaches and highlights potential improvements in model architecture.