Atmospheric radical chemistry determines the atmospheric composition, fate of trace species, secondary production including formation of organic aerosols and harmful tropospheric ozone (O3). Chlorine radicals (Cl•) have a pivotal role in air quality under contrasting urban atmospheric chemistry. Even in trace concentration Cl• is a critical oxidant in urban atmosphere.  Cl• has analogous reaction mechanism to OH• and having noted that Cl• have much faster reaction rates than initiated by OH•. The nocturnal reactions of N2O5 on Cl-rich aerosols affect NOx recycling, oxidation of VOCs and increases levels in particulate matter in winter mornings, thus posing serious threat to human population and reduces visibility. Abundance of Cl• highly depends on regional emissions and Indian region is prone to high chlorine rich PM and notably, northern India falls under most polluted regions globally.  Despite its importance, chlorine chemistry is often overlooked in atmospheric models, underestimating pollution levels.The work utilizes 3D GEOS-Chem model, integrated with anthropogenic HCl emissions coupled with heterogeneous N2O5 + Cl chemistry to evaluate the impact of chlorine chemistry on air quality over Indian region. It includes model's capability in reproducing observations and their distributions, quantifying the changes in total PM2.5 and surface O3. The model successfully reproduces observations, quantifying the effects of chlorine emissions on regional air chemistry. This study provides insights into the distribution of reactive chlorine species, limiting processes, impact on atmospheric oxidative capacity, chlorine-initiated oxidation of VOCs and changes in the levels of atmospheric pollutants. It underscores the necessity of incorporating chlorine emissions and mechanisms into models to accurately predict and understand air quality in India. Further results will be shared at the later stage providing a detailed and its potential effects regional air quality.

In the past five years, data-driven prediction models and Machine Learning techniques have revolutionized weather forecasting. Meteorological services around the world are now developing Artificial Intelligence (AI) components to enhance (or even replace) their numerical weather prediction systems. This shift creates new challenges and opportunities for universities and research centers, calling for a much closer cooperation of meteorology with mathematics and computer sciences, updates of teaching curricula, and new research infrastructures and strategies. To address these challenges, an interdisciplinary team of scientists from the Karlsruhe Institute of Technology (KIT) and the German Meteorological Service (DWD) created the TEstbed for Exploring Machine LEarning in Atmospheric Prediction (TEEMLEAP). Implemented on KIT’s supercomputer HoreKa, the TEEMLEAP testbed simulates the entire operational weather forecasting chain using ERA5 reanalysis data as pseudo-observations and DWD’s Basic Cycling environment for conducting assimilation-prediction-cycling experiments. Moreover, first steps are taken towards the integration of new data-driven components like FourCastNet and AI-based post-processing methods. The TEEMLEAP testbed allows systematic investigation of a wide range of issues related to weather forecasting such as optimizing the observational system, uncertainty quantification, and developing hybrid systems that integrate AI with physics-based models. This document outlines the testbed’s setup, demonstrates its functionality with a pilot experiment, and discusses examples of potential applications. Future plans include creating educational modules and developing a higher-resolution regional version that could be used for assimilating campaign observations.

Rising global temperatures pose significant risks to marine ecosystems, biodiversity and fisheries. Recent comprehensive assessments suggest that large-scale mitigation efforts to limit warming below crucial thresholds are falling short, and all feasible future climate projections, including those that represent ideal emissions reductions, exceed the Paris Agreement’s aspirational <1.5{degree sign}C warming target, at least temporarily. As such, there are a number of proposed climate interventions that aim to deliberately manipulate the environment at large scales to counteract anthropogenic global warming. Yet, there is a high level of uncertainty in how marine ecosystems will respond to these interventions directly as well as how these interventions may impact marine ecosystems’ responses to climate change. Due to the key role the ocean plays in regulating Earth’s climate and ensuring global food security, understanding the effects that these interventions may have on marine ecosystems is crucial. This review provides an overview of proposed intervention methodologies for solar radiation modification and marine carbon dioxide removal and outlines the potential trade-offs and knowledge gaps associated with their impacts on marine ecosystems. Climate interventions have the potential to reduce warming-driven impacts, but could also substantially alter marine food systems, biodiversity and ecosystem function. Impact assessments are thus crucial to quantify trade-offs between plausible intervention scenarios and to identify and discontinue scaling efforts or commercial implementation for those with unacceptable risks.

Over the last two years, large-scale AI weather models have reached or exceeded the accuracy of numerical weather prediction for short- and medium-range forecasts. Those predictions focus on some atmospheric variables, known to have a fast evolution, and lack land-atmosphere coupling.With the advent of foundation models, e.g., Aurora, it has been shown that AI models can be fine-tuned for diverse tasks. But land-surface hydrology has not yet been explored.In this work, we show that Aurora is stable when rolled out for at least two years. Our results also illustrate that seasonal fluctuations and long-term trends are captured by Aurora. Finally, a proof-of-concept experiment indicates that Aurora can be extended to new physics with reduced training costs by training separate decoders.

The Atlantic Meridional Overturning Circulation (AMOC) plays a crucial role in the global climate system. Various studies report both ongoing and projected reductions in AMOC strength, with important implications for climate and society. While Stratospheric Aerosol Injection (SAI) has been proposed to mitigate some impacts of a warming climate, model simulations disagree whether it could also be successful in ameliorating the projected AMOC decline. Using SAI sensitivity simulations with the Community Earth System Model, we demonstrate that whether SAI could restore AMOC depends on the details of SAI realization, particularly its latitude(s). Specifically, Northern-hemispheric SAI initially impacts upper-ocean densities in the North Atlantic through changes in surface heat flux and temperature, ultimately preventing AMOC decline. On the other hand, Southern-hemispheric SAI does not substantially impact AMOC strength even though global mean cooling is achieved. We show that different processes play different roles in determining the AMOC response between the initial (~10-15 years) and longer timescales, with the former dominated by the direct SAI effect and the latter influenced by feedbacks from AMOC adjustments. These processes may also offset each other, leading to a relatively stable evolution of AMOC under each SAI realization and a small, yet substantially different, subset of potential AMOC responses. Overall, our results demonstrate the potential for SAI to help avoid climatic tipping points, but also highlight the need to understand the dependence of the outcomes on the specific SAI realization as well as for a better process-based understanding of the many factors influencing such outcomes.

The NASA Tropospheric Emissions: Monitoring of Pollution (TEMPO) instrument is hosted on a geostationary commercial communications satellite. TEMPO is an imaging spectrometer with primary mission to measure trace-gas concentrations from the observed spectra of reflected sunlight over the Continental United States and parts of Canada, Mexico, and the Caribbean. TEMPO produces an ultraviolet (UV, 293 nm - 494 nm) and a visible (538 nm - 741 nm) spectrum for each spatial pixel. TEMPO saw first light in August 2023. At night, TEMPO can observe city lights, gas flaring, maritime lights from fishing and offshore oil platforms, clouds and snow in the moonlight, lightning, aurorae, and nightglow without interfering with its primary daytime air quality/chemistry mission. This paper describes the capabilities of TEMPO to make nighttime observations and surveys of some early results. Repetitive coverage of North America enables production of clearest-sky composites that are similar to VIIRS Day-Night Band (DNB) ”Black Marble” products. Spectra of urban areas contain spectral signatures of artificial lighting of various types that allow the radiance from each class of lighting to be estimated. Moonlight imaging of clouds provides a useful capability for discriminating clouds and fog. Lightning illuminating cloud tops from below is seen with distinct spectral features. Gas flares, associated with oil production, are observed and flare temperatures can be estimated from their spectra. Known auroral and nightglow spectral lines of atomic oxygen and molecular nitrogen are seen in the UV and visible spectra. The sodium d-layer is also observed.

Large-scale integral constraints on cloud behaviors can guide their more precise representation in present and future climates. We show theoretically that the moist static energy evaluated at cloud edge has an average value nearly equivalent to the mean saturated static energy of a horizontal slice of the entire atmospheric domain. The layer could be the cloudy troposphere as a whole, and a numerical model simulation of a deep-convective cloud field shows this equivalence for over a 10 K range in sea surface temperature. The constraint leads to a simple method for estimating the mean cloud level of neutral buoyancy, which rises linearly with increasing energy of sea surface air. Numerical simulations point to an interesting second constraint, which is that the saturated static energy profile has a maximum deviation from its tropospheric mean value that is equivalent to the mean energy of the tropospheric saturation deficit.

Analog methods for tropical cyclone (TC) rainfall prediction compare current and past TCrelated information (e.g., atmospheric fields) to estimate rainfall. However, comparing spatially distributed data like atmospheric fields is challenging, as common metrics fail to capture multiple characteristics of the data simultaneously. For example, conventional cosine similarity excels at identifying changes in pattern similarity but falls short in capturing absolute magnitude similarities. To address this challenge, we provide a proof of concept for using a perceptual-based measure-the Structural Similarity Index (SSIM)-to identify analog TCs based on atmospheric field similarity. Our study demonstrates the effectiveness of SSIM in selecting analogous atmospheric fields for TC rainfall prediction in a basin, producing results comparable to existing studies. Compared with cosine similarity, SSIM proved more effective in selecting atmospheric field-based analogs, leading to improved basin rainfall prediction performance. This study not only underscores the effectiveness of perceptual similarity metrics in meteorological forecasting but also illustrates how image processing techniques can innovatively be applied in geosciences, treating spatial data as analogous to images.

A comprehensive full-waveform inversion model of the crust and mantle covering nearly the entire tectonic domain of the western Pacific (FWP24) is developed by the using optimized many-core version of SPECFEM-GLOBE on the new generation Sunway supercomputer. Taking the global adjoint tomography model GLAD-M25 as the initial model, the three-component seismograms from 1,228 earthquakes recorded at 3,687 stations are employed in iterative gradient-based inversions for three period bands: 40-100s, 17-40s, and 10-60s. A total of 36 iterations are carried out using the conjugate gradient method to update the velocities of horizontally and vertically polarized P-waves and S-waves (Vph, Vpv, Vsh, and Vsv) in the FWP24 model. This process systematically reduces the phase difference between the synthetic and observed seismograms within the phase measurements. Compared with the existing inversion results, the FWP24 model realizes a wider, more continuous and higher resolution inversion range, including all subduction zones in the western Pacific (e.g., Kurile-Japan, Izu-Bonin-Mariana, New-Britanin-Solomon, New-Hebrides, Tonga-Kermadec, etc.). Furthermore, it reveals more detailed structures particularly in oceanic regions around the Philippine Sea Plate, the Caroline Sea Plate and the Ontong-Java Plateau by applying more seismic rays. Overall, the high-resolution and wide-range FWP24 model not only supports for the study of the deep structure of the mantle in the study area, but also offers reliable insights for the study of the subduction dynamics in the western Pacific.

Electromagnetic ion cyclotron (EMIC) waves, driven by ring current ion temperature anisotropy in the Earth’s magnetosphere, play a key role in accelerating and precipitating relativistic electrons in the radiation belts. Their excitation and saturation are significantly affected by the surrounding cold plasma. Previous studies have shown that background cold helium ions can influence the growth and saturation of EMIC waves, yet the role of cold oxygen ions in wave saturation remains less understood. In this paper, we use linear theory and nonlinear hybrid simulation to investigate the effect of cold oxygen ions in the EMIC wave growth and saturation in a homogeneous plasma containing hot and cold protons, cold helium and cold oxygen ions. Our findings reveal that increasing the cold oxygen ion concentration decreases the EMIC wave growth rate and broadens the spectral width of stop bands near the helium and oxygen gyrofrequencies. Furthermore, an increasing oxygen ion concentration notably reduces the saturation amplitude of EMIC waves in cases where the helium band is dominant, while cases with a dominant hydrogen band remain unaffected. Cold ions are heated during wave excitation, with cold helium ions heating more significantly than cold protons and oxygen ions. However, an increasing cold oxygen ion concentration reduces the heating efficiency for cold helium ions. These results offer insights into how cold plasma modifies the spectral properties and amplitudes of EMIC waves, shedding light on energy transfer from hot protons to cold plasma through EMIC waves.

In this study, we analyze the atypical ionospheric irregularity patterns observed during the geomagnetic storm of October 10-13, 2024. This analysis is based on high-resolution Rate of Total Electron Content Index (ROTI) maps derived from data collected by approximately 1,600 Global Navigation Satellite System (GNSS) stations distributed across the American continent and Antarctica, complemented by local ionospheric observations. The morphological characteristics of equatorial and polar ionospheric irregularities during this extreme event are investigated. Our findings reveal a reversed-C-shaped depletion band extending from the magnetic equator to auroral latitudes, driven by the intensification of both vertical drift velocities at the equator and zonal drift velocities near the auroral region. Thus, the polar irregularity region expanded to midlatitudes, converging with stretched Equatorial Plasma Bubble (EPB) structures near ~45{degree sign} MLAT, highlighting a dynamic coupling mechanism between these regions. Additionally, distinct longitudinal asymmetries in EPB behavior were observed, as they extended into midlatitudes and tied up with the polar irregularities along the western coast of South America (~0{degree sign} MLON) but remained confined to the equatorial region along the eastern coast (~20{degree sign} MLON). These asymmetries are attributed to variations in electric field penetration efficiency due to seasonally enhanced ionospheric conductivity. Finally, disturbance dynamo electric fields sustained F-region height, leading to an atypical occurrence of post-sunrise EPBs.

The North Atlantic Ocean circulation, fueled by winds and surface buoyancy fluxes, carries 1.25 PettaWatts of heat poleward in the subtropics, and helps in regulating global weather and climate patterns. Here, we assess the impacts of changes in winds and surface heat fluxes on the Atlantic Ocean circulation and heat transport using ocean simulations. We decompose the circulation and heat transport into warm and cold cells (resembling a subtropical gyre and the dense overturning circulation respectively), and a mixed cell capturing waters transitioning between warm and cold regions. Warm and mixed cells transport more heat poleward as wind stress increases; however, these anomalies are compensated by reductions in the cold cell’s heat transport. Warm and cold cells transport more heat poleward when we increase meridional heat flux gradients. Our findings underscore the distinct roles of winds and surface heat fluxes in controlling the Atlantic Ocean’s meridional heat transport.

The development of remote sensing of discharge algorithms has enabled us to estimate discharge without in-situ observations, yet their applicability of spatially continuous estimates of discharge is not adequately examined. This study calculated discharge for 668 continual reaches along the mainstem of the Yellow River using remotely sensed width from Landsat images and a discharge estimation algorithm based on the At-Many stations Hydraulic Geometry. Our result confirms the discharge decrease/increase at the dam/confluence points as well as the discharge reduction along the heavily irrigated areas, indicating the potential of capturing both natural and artificial discharge changes from the satellite. Moreover, the prediction fed by prior discharge, which gives the prior probability of the possible discharge values, that virtually considers the effect of water withdrawals improved the prediction accuracy, especially at downstream stations where the influence of irrigation is accumulated.

Cold air outbreaks (CAOs) enormously influence agriculture, environment, industry, and other socio-economic activities in East Asia. This study objectively identifies and categorizes CAOs in East Asia by employing 3-dimensional CAO detection algorithm and k-means clustering method. The analysis identifies a total of 106 CAOs which are classified into three distinct types based on core cold anomaly positions: South, Mixed, and North types. The South type, with the fewest occurrences and shortest lifetime, exhibits a weak warm lobe over Europe and northern Asian coast, with the coldest anomalies over southern China. The Mixed type, most frequent and longest-lived, accompanies the most extensive and coldest anomalies across Eurasia, uniformly distributed over East Asia. The North type shows the coldest anomalies in Northeast Asia with weaker effects in southern East Asia. The weakening trend in CAO intensity observed in East Asia is primarily due to long-term changes in the Mixed and North types. Temperature anomaly patterns and circulation variations are diverse, with the South type associated with a pre-existing strong stratospheric polar vortex state, and the Mixed and North types with a pre-existing week vortex state. Under those stratospheric backgrounds, even similar wave activities can result in dissimilar upper-tropospheric circulation anomalies over East Asia, leading to different extents and magnitudes of anomalous coldness. This study provides valuable insights into the diversity of East Asian CAOs, essential for forecasting and managing associated risks in East Asia.

A document by Nicholas Fogne Appiah. Click on the document to view its contents.

A document by Pardis Akbari. Click on the document to view its contents.

In the pursuit of advancing environmental monitoring technologies to measure toxic air contaminants, our research introduces a novel, cost-efficient Spark-Induced Breakdown Spectroscopy (SIBS) instrument engineered for the detection and quantification of toxic metal aerosols. This instrument, named TARTA 2.0 (Toxic metal Aerosol Real Time Analyzer version 2.0), has been developed recently with a comprehensive optimization of critical experimental parameters. Notably, our improvement includes a combined electrode holder and ground electrode with an increased surface area to improve particle collection efficiency. The intensity of the spark generated by this new system is strong enough to be directly captured by optical fibers, allowing us to remove the previously used optical lenses and create a more compact, user-friendly device. This compact device features an 8” x 10” footprint and weighs only 10 lbs, and it can be powered by a 12 VDC battery. With the new design, we have conducted experiments to optimize the observation time delay, electrode separation distance, and ablation voltage, all aimed at enhancing the instrument's analytical performance. Additionally, the efficacy of the instrument has been validated through the analysis of nebulized elemental standard solutions, showcasing its reliable capacity and sensitivity to detect critical metals with improved Limit of Detections (LODs) such as 1.736 ng/m3 for Co, 2.11ng/m3 for Cr, 1.97 ng/m3 for Li, 5.18ng/m3 for Be, 2.07ng/m3 for V, 1.037ng/m3 for Mn, 1.42 ng/m3 for Zn, 3.81 ng/m3 for Mg, and 5.9 ng/m3 for Fe in laboratory experiments. Our findings support the promising application of TARTA in field monitoring of air quality, heralding a new era of accessible and efficient monitoring of hazardous air pollutants, ultimately protecting public health against toxic metal exposure. Further research will be conducted to extend the spectrum of detectable pollutants, refine the quantification model, and validate the instrument across varied ambient environmental matrices. 

Kyoungsik Chang1, and George Constantinescu21School of Mechanical Engineering, The University of Ulsan, Ulsan, South Korea2IIHR–Hydroscience and Engineering and Department of Civil and Environmental Engineering, The University of Iowa, IA, USAAbstract3-D numerical simulations are used to investigate the formation, evolution and sediment entrainment capacity of planar, Boussinesq, compositional gravity currents propagating over a long, inclined surface reaching the free surface at a small angle. The generation of the gravity current is driven by surface cooling associated with the diurnal, periodic variation of the free surface total heat flux. Thermal convective plumes of cooler fluid generated along the free surface act as a source of buoyancy during the initial stages of propagation of the current. Simulations conducted with different magnitudes of the sinusoidal heat flux and bottom slopes show that gravity current head forms after 0.25-0.4T (T is the period of the oscillatory heat flux, time intervals are measured from the time when the heat flux becomes negative). The time interval for the total buoyancy of the current to peak is the largest for the case with a low bottom slope and a low magnitude of the heat flux. In all cases, the current reaches a regime where its front velocity is close to constant after 0.5-0.7T. Analysis of the bed shear stress distributions shows that the peak bed shear stresses do not generally occur beneath the head of the current and sediment entrained beneath the downstream part of the tail is the largest contributor to the total flux of sediment entrained from the inclined bed surface. Besides the fast fluid inside the gravity current, the interactions of the convective plumes with the inclined surface generate energetic vortical eddies and circulatory motions that also contribute to the amplification of the bed shear stress. The capacity of the current to entrain sediment peaks 0.25-0.3T after the gravity current enters the nearly constant front velocity regime. The flux of sediment entrained from the bed is increasing with both bed slope and magnitude of the heat flux, but the rates of increase are much higher when the magnitude of the heat flux is varied.1 INTRODUCTIONGravity currents forming in reservoirs, lakes and oceans are often characterized by a large capacity to erode the loose bed over which they propagate. Such gravity currents generally propagate over an inclined surface, at least until they reach the bottom part of the waterbody. For example, this is the case of turbidity currents forming on the inclined continental shelf of oceans (Birman et al., 2007). These currents are a main contributor to the formation of submarine canyons on the continental slope of oceans (Pratson & Coakley, 1996) and can carry a large amount of sediments into the deep parts of oceans. Saltwater intrusions into estuaries generate a compositional gravity current propagating over an inclined surface. As they propagate over a loose bed, compositional (e.g., salinity or temperature driven) and turbidity currents can induce lots of sediment erosion, carry large amounts of sediments over large distances and modify the local morphodynamics over time in regions where such currents form regularly.Such types of gravity currents propagating over a sloped bottom in reservoirs, lakes or oceans are generally investigated using lock-exchange laboratory experiments (e.g., Britter & Linden, 1980, Beghin et al.,1981; Maxworthy & Nokes, 2007; Maxworthy, 2010, Dai 2013b, 2013c, 2014; Dai & Huang, 2016; Martin et al., 2019; Zemach et al., 2019; De Falco et al., 2021; Maggi et al., 2023a, 2023b) in which the ambient fluid is either homogeneous (constant density) or linearly stratified. Given that the ambient fluid is at rest and the free surface is horizontal, the lock-exchange current advances in a positive mean background pressure gradient along the incline. The effect of earth rotation and associated Coriolis forces were investigated among others by Cenedese & Adduce (2008) and Negretti et al. (2021). One limitation of most of these laboratory studies was the limited length of the incline which allowed the study of the physics of such currents only during their initial stages Most numerical studies conducted using eddy-resolving techniques focused on the simpler case of a lock-exchange Boussinesq or non-Boussinesq current propagating in a channel with a free surface parallel to the bed (Blanchette et al., 2005, Birman et al., 2007; Dai, 2013a, 2013b, 2014, 2015) for which the background pressure gradient in the direction parallel to the incline is equal to zero. This case is more relevant for currents forming in rivers but there was no co-flow in the simulations. Steenhauer et al. (2017) used three-dimensional (3-D) large eddy simulation to simulate lock-exchange Boussinesq gravity currents propagating down a constant-slope incline based on the set up used in the experiments of Maxworthy (2010) conducted in a reservoir with a horizontal free surface. The angle of the incline was varied between 00 and 600 in these simulations which were conducted with a much longer length of the incline compared to the corresponding experiments.For the simplest case of a planar, finite-release lock-exchange compositional current propagating in a reservoir containing homogeneous ambient fluid at rest, experimental and numerical studies have shown that, following an acceleration phase, the front velocity starts decaying and the turbulent current transitions to a 2/3 power law regime that is similar to the buoyancy-inertia phase observed for currents propagating over a horizontal bed. At later times the current transitions to a 3/8 power-law regime corresponding to the buoyancy-viscous phase. Over this regime, the head is strongly distorted and raises from the bed such that the shear stresses beneath the bed are very small. The numerical study of Steenhauer et al. (2017) showed that the sediment entrainment capacity of such compositional currents peaks for slope angles of 300 to 400. These values are larger than the ones (200-300) corresponding to the fastest currents. For slope angles larger than 100, a large, intensified mixing vortex (IMV) forms at the back of the dissipative wake region. Its strength increases with increasing slope angle while the distance traveled by the current before this vortex forms decreases with increasing slope angle. For angles larger than 200, most of the buoyancy lost by the head is entrained into the core of the IMV vortex during the later stages of propagation of the current. The IMV has a larger capacity to entrain sediment that the head. In the case of constant-flux current propagating in a homogeneous ambient fluid, Middleton (1966a, 1966b) found that the current reaches a nearly-constant front velocity regime that varies little with the change in the slope angle. Martin et al. (2020) provide a detailed discussion of the structure of such currents.The formation mechanism for gravity currents propagating over a sloped bottom surface can be much more complex in natural environments. For example, katabatic winds form as air situated closed to a sloped bottom boundary is cooled by radiative processes near the ground (Manins and Sawford, 1979). The negative heat flux at the ground surface results in the formation of a certain amount of cool air that starts propagating along the inclined surface in fairly similar way to a lock-exchange current. However, the extent of the region containing cool air is controlled by the heat flux at the ground surface. As opposed to a lock-exchange current where a finite amount of cool air is released instantaneously, in the case of katabatic winds there is a certain amount of time needed for the cool air to accumulate and then to start propagating along the inclined ground surface as a gravity-current-like flow.Winter cascading of cold-shelf waters in a deep lake or over the continental shelves bordering the ocean basins also generates gravity-current-like flows (Hill et al., 1998; Fer et al., 2002a). Similar to the aforementioned example of katabatic winds, radiative processes control the formation of the region containing cooler, heavier fluid near the shoreline. However, in this case the driving radiative process is due to diurnal variations in the heat flux at the surface of the waterbody that induces differential cooling between the shallow and deep regions (Wells & Sherman, 2001). Shallow regions near the shoreline cool more rapidly than the deeper regions, which results in the formation of a gravity current containing colder, denser water that propagates over the inclined bottom of the waterbody. The cooling of the water along the free surface generates unstable stratification during the times the water loses heat to the atmosphere. The water column near the free surface overturns as the denser surface water starts sinking and convective plumes are generated (Marshall & Schott, 1999) that move toward the sloping bottom. Some of these plumes are also a source of buoyancy for the gravity current. In lakes, basins and reservoirs with a sloped bottom, this can lead to stratification in the lower layer, at the base of the deeper zones, and upwelling of cold water by the convective motions in the surface mixed layer, as well as strong horizontal circulation (Monismith et al., 1990; Wells & Sherman, 2001). The circulation induced by diurnal surface cooling plays an important role in nearshore dynamics (Monismith et al, 1990; Sturman et al., 1999). Laboratory experiments were conducted to understand the relationship between the volume flux of the gravity current and the surface cooling rates (Finnigan & Ivey, 1999, 2000). Experiments have also shown that an initial period of disorganized motion driven by convection from the free surface is present over the shallower region before the gravity current forms (Sturman & Ivey, 1998).Directly relevant for the present study, Fer et al. (2001, 2002a, 2002b) found evidence of the formation of such gravity currents in Lake Geneva in response to diurnal cooling and heating occurring at the free surface. These studies measured the mean velocity of propagation of the gravity current, its thickness and time of passage at several locations situated away from the shoreline and observed that several regions of higher thickness and velocity (e.g., pulses) were present behind the head of the current. Using quantitative analysis, these studies proved that the circulation associated with the passage of such gravity currents is a main mechanism for flushing nearshore shelf water during the winter season. It was estimated that the mean net volume flux carried by these gravity currents is more than one order of magnitude larger than the mean flux into Lake Geneva from rivers during the winter season. Moreover, some of the collected data suggested that the passage of these gravity currents can erode and transport important quantities of sediment into the deeper regions of the lake as well as affect the transport of dissolved oxygen, nutrients and contaminants present in the shallower regions of the lake, thus ventilating and oxygenating the deeper water regions (Fer et al, 2002b). This has important ecological and biological consequences for the lake ecosystem. Constant-flux plunging flumes over a sloping bed in Lake Geneva were studied experimentally and numerically by Shi et al. (2022). The mechanisms for the formation of pulses in constant-flux plunging flows into lakes and reservoirs are discussed in detail by Kostaschuk et al. (2018).The present numerical study uses 3-D large eddy simulations to study the physics of gravity currents forming in a triangularly-shaped reservoir (Figure 1) due to a sinusoidal heat flux of period T applied at the top boundary that approximates the diurnal total heat flux at the free surface. The temperature of the fluid is uniform inside the reservoir at the start of the simulation when the free surface heat flux per unit surface becomes negative (free surface is cooling) and stays negative over the first half period. Similar to the bathymetry of Lake Geneva in a section perpendicular to the shoreline, a short region with a bed slope angle of 1.30 is followed by the main sloped region (Figure 1). The slope of the main sloped region is constant and equal to θ. Its length is sufficiently large such that the front of the gravity current does not reach the end of this region after one period T. This allows studying the evolution of such currents under idealized conditions where the gravity current does not interact with the heavier fluid below the thermocline, generally present in lakes during the winter season. For such conditions, a surface mixed layer develops over the deeper layer containing heavier fluid in the deep region of the lake (Wells & Sherman, 2001) which induce large-scale circulatory motions affecting the evolution of the gravity current propagating over the non-uniformly sloped bottom of the lake. The constant slope of the main part of the inclined bottom and unimodal (e.g., sinusoidal) variation of the surface heat flux allow reducing the number of geometrical and flow variables affecting the evolution of such currents in the present numerical experiments.