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This article demonstrates the importance of making explicit different conceptions of movement for the philosophy of sport. In addition to the mechanistic and the Aristotelian approaches, this article presents a third, underexplored view of movement, namely that of Lucretius as interpreted by Karl Marx and Michel Serres. By exploring the similarities between Marx’s motion of repulsion and Serres’s turbulent flux, it will be argued that a Lucretian view offers a philosophy of movement that uniquely does not rely on stasis. This Lucretian perspective is illustrated through Serres’s elaborations on the body and sport. It is concluded that sport is not primarily a rational, rule-guided practice but arises from moving and sensuous bodies that are always deviating from their standard trajectory. [ABSTRACT FROM AUTHOR]

In vegetated flows a reliable estimation of flow scales is crucial to understand and model mixing processes. This study presents velocity maps obtained using particle image velocimetry (PIV) within a cylinder array (diameters 4≤d≤20 mm) designed to mimic real emergent vegetation. Tests were undertaken over a comprehensive range of stem Reynolds numbers (100≤Red≤900), intended to characterize time-dependent hydrodynamic features, including their interactions. Time-averaged flow heterogeneities are found to be independent of Red. Vortex dynamics are seen to dominate turbulent fluxes of momentum, and are the relevant coherent structures driving mass transport. The range of characteristic time- and length-scales from these coherent structures was quantified and shown to be determined by the distribution of spaces between cylinders. This is due to: (1) neighboring cylinders forming clusters, leading to larger flow structures, and (2) the maximum size of the flow structures being constrained by the inter-stem space. It is concluded that the Delaunay criterion provides practitioners with a good approximation to the distribution of flow scales in vegetated flows. Practical Applications: This study presents the quantification of the scales of flow structures generated in a vegetated flow. These structures play an important role in the quantification of mass transport processes, and estimates of the sizes of these flow structures are necessary to understand the rate of solute transport and therefore provide reliable models for pollutant mixing in vegetated flows. Using state-of-the-art equipment to characterize velocity fields, the present study found that the size of these flow structures is determined by the spacing between cylinders. The authors recommend that for practical applications, engineers quantify the spacing between plant stems using the criteria presented in this paper. [ABSTRACT FROM AUTHOR]

Stratification and turbulent mixing have an immense impact on biogeochemical regimes and ecosystem dynamics in stratified large lakes. This study investigates the physical properties of the epi‐ and metalimnion of Lake Biwa (Japan), focusing on the persistent vertical diffusive fluxes due to turbulent mixing in the lower metalimnion and their effects on upward nitrate transport. We conducted 24‐h observations at an offshore station in the summer for three consecutive years to examine the temporal and vertical variations of stratification and turbulence. A mooring system provided long‐term data on stratification and current velocity, while thermal profiles along two offshore transects were collected to investigate lateral changes. Our findings revealed strong stratification in the upper metalimnion, where vertical diffusive fluxes were essentially suppressed. Distinct turbulent mixing layers were identified near the water surface and within the moderately stratified lower metalimnion. Field data and numerical model suggested that the turbulence in the lower metalimnion was driven by shear instability, straining, and/or wave–wave interactions linked with the persistent internal waves that occur even during weak winds. Vertical eddy diffusivity of > 10−5 m2 s−1 in the lower metalimnion was associated with rather strong turbulence, which has not been reported in other large lakes. The elevated turbulence resulted in an upward nitrate flux of 0.2 mmol N m−2 d−1 across the lower metalimnion, indicating that the upward nutrient transport could support primary productivity and play an important ecological role in deep stratified lakes. [ABSTRACT FROM AUTHOR]

Extratropical disturbances are known to impact the genesis and intensification of Mixed Rossby‐Gravity waves (MRGW) in the Western Hemisphere (WH). The study provides observational evidence supporting the wave resonance (WR) theory which attempts to explain the intensification of MRGW by extratropical forcing. Wavenumber‐frequency cospectral analysis and a bulk measure of growth of MRGW estimated using reanalysis data reveal that the extratropical forcing manifested in the form of eddy momentum flux convergence can create eddy kinetic energy (EKE) and aid the intensification of MRGW via WR mechanism during boreal winter season. However, the WR mechanism does not hold during boreal summer season as the extratropical forcing tends to dampen the MRGW. The analysis also reveals that the Doppler‐shifted eastward propagating MRGW in the WH during boreal winter season are not maintained by extratropical forcing, marking another highlight of this study. Plain Language Summary: Mixed Rossby‐Gravity waves (MRGW) are a key component of tropical dynamics and extratropical forcing has been considered as an important factor in governing the growth of MRGW. Wave resonance (WR) theory, as proposed by previous theoretical studies, offers a compelling framework for understanding how extratropical forcing influences MRGW. This study seeks to provide observational evidence supporting the intensification of MRGW by extratropical forcing using the WR framework. Analyses conducted using reanalysis data show that the interaction between MRGW and extratropical forcing generates eddy kinetic energy, which intensifies the MRGW during boreal winter. In contrast, this interaction leads to the attenuation of MRGW during boreal summer season, highlighting the seasonal variability in these dynamics. Interestingly, while Doppler‐shifted eastward propagating MRGW are observed over the Western Hemisphere during boreal winter season, their presence cannot be attributed to extratropical forcing. Overall, this study underscores the importance of extratropical forcing as a crucial factor in modulating the MRGW. Key Points: The study provides observational evidences supporting the growth of Mixed Rossby‐Gravity waves by tropical‐extratropical wave resonanceExtratropical eddy momentum forcing enhances Mixed Rossby‐Gravity wave growth in boreal winter while dampens its growth in boreal summerExtratropical eddy momentum forcing does not explain the existence of Doppler shifted eastward propagating Mixed Rossby‐Gravity waves [ABSTRACT FROM AUTHOR]

Heat waves (HW) are prolonged periods of excessively hot weather that can cause severe socioeconomic and environmental impacts. This study aims to evaluate the differences in stored heat and turbulent flux partitioning during a heat wave event in Mexico City, using observations from an eddy covariance tower during the period from 14 June to 21 June 2023. During this period, net radiation (Rn) and sensible heat flux (H) increased significantly, particularly from noon to evening, reflecting stable atmospheric conditions. The air temperature showed a noticeable increase in the afternoon and evening, whereas absolute humidity decreased. We found that during the heat wave, the Bowen ratio (β) increased by 80% during daylight hours and 65% over a full 24-hour period compared to the pre-heat wave period. This heat release at night prolonged warm conditions, intensifying heat stress. The partitioning of net radiation for latent heat (LE), sensible heat (H), and heat storage (ΔQs) showed significant changes; during the heat wave, 51% of Rn was allocated to H and 34% to ΔQs, compared to pre-heat wave values of 49% and 27%, respectively. This study introduces a new characterization of heat waves in terms of energy, emphasizing the significant shifts in energy flux partitioning and storage. The new characterization highlights the critical role of urban heat storage and its release in exacerbating heat stress during and after heat wave events. This approach provides a comprehensive understanding of the energy dynamics during heat waves, which is essential for developing effective mitigation strategies to combat the adverse effects of extreme heat in urban environments. [ABSTRACT FROM AUTHOR]

Internal climate variability (ICV) creates a range of climate trajectories, which are superimposed upon the forced response. A single climate model realization may not represent forced change alone and may diverge from other realizations, as well as observations, due to ICV. We use an initial-condition large ensemble of simulations with the Community Earth System Model (CESM2) to show that ICV produces a range of outcomes in the terrestrial carbon cycle. Trends in gross primary production (GPP) from 1991 to 2020 differ among ensemble members due to the different climate trajectories resulting from ICV. We quantify how ICV imparts on GPP trends and apply our methodology to the observational record. Observed changes in GPP at two long-running eddy covariance flux towers are consistent with ICV, challenging the understanding of forced changes in the carbon cycle at these locations. A probabilistic framework that accounts for ICV is needed to interpret carbon cycle trends. [ABSTRACT FROM AUTHOR]

The meridional displacements of the East Asian westerly jet (EAJ) exhibit remarkable interannual variability characteristics, significantly modulating the weather and climate over East Asia. Our study aims to refine the thermal‐driven (angular momentum transport) and dynamically driven (atmospheric eddy activities) processes that dominate the interannual meridional motion of the wintertime EAJ. We employ the recently proposed three‐pattern decomposition of global atmospheric circulation (3P‐DGAC) theory to decompose the zonal momentum equation for the purpose of diagnosing the zonal momentum budget of the EAJ from three‐dimensional (3D) horizontal, meridional and zonal circulation perspectives. Results indicate that, in addition to the widely recognised driving mechanisms of angular momentum transported by thermal direct meridional Hadley circulation and horizontal eddy momentum flux convergence, the previously neglected role of local zonal circulation in transporting angular momentum significantly impacts the meridional shift of EAJ. The uneven accumulation of angular momentum transported by asymmetric zonal circulations emerges on the northern and southern sides of EAJ axis, causing an abnormal meridional displacement of EAJ. Notably, the local zonal circulation rising from the Tibetan Plateau and descending across the North Pacific Ocean transported angular momentum to the core and downstream regions of EAJ, thereby significantly accelerating zonal winds and pushing the EAJ northward. Further investigation into the potential mechanisms suggests that anomalous snow depth on the southern Tibetan Plateau is the main factor causing abnormal local zonal circulation. Our study addresses the deficiency in traditional two‐dimensional (2D) circulation decomposition methods that neglect the significant role of zonal circulation in the thermal‐driven process of EAJ, complements the understanding of 3D angular momentum transport mechanisms and reveals potential nonlinear synergies of 3D circulations related to the interannual meridional displacement of EAJ. [ABSTRACT FROM AUTHOR]

High latitudes, including the Bering Sea, are experiencing unprecedented rates of change. Long-term Bering Sea warming trends have been identified, and marine heatwaves (MHWs), event-scale elevated sea surface temperature (SST) extremes, have also increased in frequency and longevity in recent years. Recent work has shown that variability in air–sea coupling plays a dominant role in driving Bering Sea upper-ocean thermal variability and that surface forcing has driven an increase in the occurrence of positive ocean temperature anomalies since 2010. In this work, we characterize the drivers of the anomalous surface air–sea heat fluxes in the Bering Sea over the period 2010–22 using ERA5 fields. We show that the surface turbulent heat flux dominates the net surface heat flux variability from September to April and is primarily a result of near-surface air temperature and specific humidity anomalies. The airmass anomalies that account for the majority of the turbulent heat flux variability are a function of wind direction, with southerly (northerly) wind advecting anomalously warm (cool), moist (dry) air over the Bering Sea, resulting in positive (negative) surface turbulent flux anomalies. During the remaining months of the year, anomalies in the surface radiative fluxes account for the majority of the net surface heat flux variability and are a result of anomalous cloud coverage, anomalous lower-tropospheric virtual temperature, and sea ice coverage variability. Our results indicate that atmospheric variability drives much of the Bering Sea upper-ocean temperature variability through the mediation of the surface heat fluxes during the analysis period. Significance Statement: A long-term ocean warming trend and a recent increase in marine heatwaves in the Bering Sea have been identified. Previous work showed that anomalies in the exchange of heat between the ocean and the atmosphere were the primary driver of Bering Sea temperature variability, but the processes responsible for the heat exchange anomalies were unknown. In this work, we show that the atmosphere is the primary driver of anomalies in the Bering Sea air–sea heat exchange and therefore plays an important role in altering the thermal state of the Bering Sea. Our results highlight the importance of understanding more about how the ocean and the atmosphere interact at high latitudes and how this relationship will be affected by future climate change. [ABSTRACT FROM AUTHOR]

This study investigates the causes of shifts in the subsiding edge of the boreal winter Hadley cell (HC) in response to a comprehensive treatment of ocean surface albedo (OSA) in the fully coupled CESM2. The focus is on an in‐depth understanding of the atmospheric dynamical processes that influence the HC subsiding edge. Two sets of experiments were performed: one utilizing the default OSA, and the other employing the comprehensive OSA that accounts for realistic physical mechanisms. The results show that implementing the comprehensive OSA simulates an El Niño‐like warming pattern in reference to the default experiment, which leads to an HC contraction. Examination of zonal mean momentum dynamics in the upper troposphere reveals that variations in meridional winds, crucial for determining the HC extent, are primarily driven by the differences in the horizontal eddy momentum flux derivative. The findings indicate that the equatorward shift in meridional temperature gradients enhances subtropical zonal winds and baroclinicity along their equatorial flanks, amplifying equatorward‐propagating Rossby waves. This, in turn, alters the eddy momentum flux, reshaping the pattern of the derivatives of horizontal eddy momentum flux, constraining meridional winds, and resulting in the equatorward movement of the HC subsiding edge. A scaling theory further supports the results of the HC contraction, showing that the increased subtropical zonal winds and the equatorward shift of the Intertropical Convergence Zone (ITCZ) elevate the atmospheric angular momentum and eventually limit the expansion of the HC. Plain Language Summary: The Hadley cell (HC) is a large‐scale tropical circulation system that exerts a substantial influence on global and regional climates. However, it is necessary to further explain the mechanisms that control the HC edge. This study investigates how the HC descending edge shifts when a comprehensive ocean surface albedo (OSA), including more realistic physical processes, is used in a fully coupled climate model. Two sets of simulations were conducted: one using the default OSA, which neglects certain physical processes, and the other using the comprehensive OSA. The comprehensive OSA experiment simulated an El Niño‐like warming climate in contrast to the default simulation, with equatorward movement of the HC edge. The present study finds that the equatorward shift in the air meridional temperature gradient results in the intensification of the subtropical zonal winds and baroclinic instability along their equatorial flanks, enhancing equatorward Rossby wave activities and affecting the pattern of the horizontal eddy momentum flux. This constrains the meridional winds, causing the HC edge to move equatorward. A scaling theory supports these findings by showing that the stronger subtropical winds and the equatorward shift of the Intertropical Convergence Zone (ITCZ) increase the atmospheric angular momentum and subsequently prevent the HC expanding. Key Points: The El Niño‐like warming pattern due to considering ocean surface albedo physics comprehensively is demonstratedEquatorward shift in temperature gradients alters eddy momentum flux, limits meridional winds, and contracts the Hadley Cell (HC)A scaling theory supports HC contraction with stronger subtropical zonal winds, enhancing angular momentum and limiting its extent [ABSTRACT FROM AUTHOR]

Rewetting peatlands is required to limit carbon dioxide (CO2) emissions, however, raising the groundwater level (GWL) will strongly increase the chance of methane (CH4) emissions which has a higher radiative forcing than CO2. Data sets of CH4 from different rewetting strategies and natural systems are scarce, and quantification and an understanding of the main drivers of CH4 emissions are needed to make effective peatland rewetting decisions. We present a large data set of CH4 fluxes (FCH4) measured across 16 sites with eddy covariance on Dutch peatlands. Sites were classified into six land uses, which also determined their vegetation and GWL range. We investigated the principal drivers of emissions and gapfilled the data using machine learning (ML) to derive annual totals. In addition, Shapley values were used to understand the importance of drivers to ML model predictions. The data showed the typical controls of FCH4 where temperature and the GWL were the dominant factors, however, some relationships were dependent on land use and the vegetation present. There was a clear average increase in FCH4 with increasing GWLs, with the highest emissions occurring at GWLs near the surface. Soil temperature was the single most important predictor for ML gapfilling but the Shapley values revealed the multi‐driver dependency of FCH4. Mean annual FCH4 totals across all land uses ranged from 90 ± 11 to 632 ± 65 kg CH4 ha−1 year−1 and were on average highest for semi‐natural land uses, followed by paludiculture, lake, wet grassland and pasture with water infiltration system. The mean annual flux was strongly correlated with the mean annual GWL (R2 = 0.80). The greenhouse gas balance of our sites still needs to be estimated to determine the net climate impact, however, our results indicate that considerable rates of CO2 uptake and long‐term storage are required to fully offset the emissions of CH4 from land uses with high GWLs. [ABSTRACT FROM AUTHOR]

Peatlands are a critical component of the global carbon cycle. Within Canada, the Hudson Bay Lowlands (HBL) has accumulated an estimated 33 Gt of carbon as peat because of a small but persistent difference between gross primary productivity (GPP) and ecosystem respiration over millennia. However, the impacts of disturbance and climate change on GPP are difficult to monitor across the HBL due to its vast size and remote location. This study evaluates the potential for random forest regression models to estimate GPP at five HBL eddy covariance flux monitoring sites using only optical data from MODIS (500 m, 8 day) or harmonized Landsat/Sentinel (HLS; 30 m, 16 day or more frequent). The results show that spatial resolution has less impact on modeled daily GPP compared to temporal resolution across model configurations. Using MODIS data, individual sites' daily GPP could be simulated with minimal bias, R2 up to 0.89 and mean absolute error as low as 0.37 g C m−2 day−1. For annual GPP, MODIS (R2 = 0.84; mean absolute error 40.5 g C m−2 year−1) also outperformed the HLS models (R2 = 0.46; mean absolute error 86.4 g C m−2 year−1). [ABSTRACT FROM AUTHOR]

Estimating daily continuous evapotranspiration (ET) can significantly enhance the monitoring of crop stress and drought on regional scales, as well as benefit the design of agricultural drought early warning systems. However, there is a need to verify the models' performance in estimating the spatiotemporal continuity of long-term daily evapotranspiration (ETd) on regional scales due to uncertainties in satellite measurements. In this study, a thermal-based two-surface energy balance (TSEB) model was used concurrently with Terra/Aqua MODIS data and the ERA5 atmospheric reanalysis dataset to calculate the surface energy balance of the soil–canopy–atmosphere continuum and estimate ET at a 1 km spatial resolution from 2000 to 2022. The performance of the model was evaluated using 11 eddy covariance flux towers in various land cover types (i.e., savannas, woody savannas, croplands, evergreen broadleaf forests, and open shrublands), correcting for the energy balance closure (EBC). The Bowen ratio (BR) and residual (RES) methods were used for enforcing the EBC in the EC observations. The modeled ET was evaluated against unclosed ET and closed ET (ETBR and ETRES) under clear-sky and all-sky observations as well as gap-filled data. The results showed that the modeled ET presented a better agreement with closed ET compared to unclosed ET in both Terra and Aqua datasets. Additionally, although the model overestimated ETd across all different land cover types, it successfully captured the spatiotemporal variability in ET. After the gap-filling, the total number of days compared with flux measurements increased substantially, from 13,761 to 19,265 for Terra and from 13,329 to 19,265 for Aqua. The overall mean results including clear-sky and all-sky observations as well as gap-filled data with the Aqua dataset showed the lowest errors with ETRES, by a mean bias error (MBE) of 0.96 mm.day−1, an average mean root square (RMSE) of 1.47 mm.day−1, and a correlation (r) value of 0.51. The equivalent figures for Terra were about 1.06 mm.day−1, 1.60 mm.day−1, and 0.52. Additionally, the result from the gap-filling model indicated small changes compared with the all-sky observations, which demonstrated that the modeling framework remained robust, even with the expanded days. Hence, the presented modeling framework can serve as a pathway for estimating daily remote sensing-based ET on regional scales. Furthermore, in terms of temporal trends, the intra-annual and inter-annual variability in ET can be used as indicators for monitoring crop stress and drought. [ABSTRACT FROM AUTHOR]

In this paper we study the influence of atmospheric and oceanic resolutions on the sea surface temperature (SST) under climate change and the related mechanisms. To this end, a set of historical period and future simulations in which two different atmospheric resolutions are combined with two different oceanic resolutions, one of them eddy-permitting, are used. We found that the magnitude of the warming is more dependent on atmospheric resolution, while the influence of oceanic resolution is stronger on the spatial pattern of SST changes, leading to the enhancement of the climate change signal in coastal regions in the higher resolution configuration. The mechanisms related to these changes involve both the atmosphere and the ocean, with the latter playing the main role. We found that changes in upwelling are the primary drivers of SST changes in regions close to the coast, and these changes in SST exhibit a clear seasonal pattern, precisely associated with the marked seasonality of the Benguela upwelling system. The radiative and turbulent fluxes adjust to the increase of greenhouse gases and are also influenced by the resolution and SST patterns. Additionally, the net longwave fluxes into the ocean increase, while the shortwave fluxes decrease due to the formation of low clouds. [ABSTRACT FROM AUTHOR]

Changes in the global and annual Intertropical Convergence Zone (ITCZ) during the mid-Holocene are quantified in this study, using simulations from the Paleoclimate Modelling Intercomparison Project Phase 4. We find an ensemble mean northward migration of ITCZ position by 0.2 ∘ , 0.3 ∘ , and 0.8 ∘ using three different metrics, which is consistent with proxy evidence of a slight (within one degree) northward shift during the mid-Holocene. The width of the ITCZ exhibits no changes during this period, while the strength has a minor weakening by 0.9% and 0.6% based on precipitation and streamfunction metrics, respectively. Moreover, there is an ensemble mean increase in northern-to-southern hemisphere precipitation (4.6%) and ω ratio indices (12%) during the mid-Holocene, suggesting a more uneven and right-skewed meridional structure of the ITCZ with a greater asymmetry. Additionally, the moisture budget analysis indicates the eddy flux term and dynamic term primarily enhance the inter-hemispheric asymmetry of precipitation and poleward migration of both the northern and the southern rain belts within the ITCZ. Further investigation reveals that the northward migration of annual rainfall within the ITCZ predominantly occurs over terrestrial regions, which therefore dominate the change towards more asymmetric structure of the zonally averaged ITCZ. Moisture budgets for land and ocean separately indicate that the land-sea difference in the annual rainfall changes is primarily due to different changes in evaporation. [ABSTRACT FROM AUTHOR]

It is frequently observed in field experiments that the eddy-covariance heat fluxes are systematically underestimated compared to the available energy, a phenomenon known as the surface energy balance (SEB) closure problem. A large-eddy simulation (LES) study is presented that investigates the behavior of turbulent organized structures (TOS) and their impact on the SEB closure problem. LES experiments are conducted for the daytime atmospheric boundary layer heated over a flat surface with atmospheric stability parameters - z i / L ranging from 8 to 130. Local imbalance is defined as the deviation of the 'observed' heat flux at a grid point from the regionally 'representative' heat flux; systematic imbalance is defined as the horizontally averaged local imbalance. A thorough analysis of the correlation between local imbalance and various local variables is conducted. Local imbalance exhibited the most significant correlation with the variance of potential temperature, implying its potential usefulness in parameterizing local imbalance. In characterizing the vertical variation of systematic imbalance, the spatial variances of mean vertical velocity and potential temperature play key roles. Results reveal that TOS induced a correlation between the mean vertical velocity and potential temperature in a horizontal space, resulting in systematic imbalance. The local imbalance is further contributed by the inhomogeneous distribution of the observed heat flux. Our results advance the understanding of the SEB closure problem and pave a possible way for the development of parameterization schemes. [ABSTRACT FROM AUTHOR]

Accurate representation of the turbulent exchange of carbon, water, and heat between the land surface and the atmosphere is critical for modelling global energy, water, and carbon cycles in both future climate projections and weather forecasts. Evaluation of models' ability to do this is performed in a wide range of simulation environments, often without explicit consideration of the degree of observational constraint or uncertainty and typically without quantification of benchmark performance expectations. We describe a Model Intercomparison Project (MIP) that attempts to resolve these shortcomings, comparing the surface turbulent heat flux predictions of around 20 different land models provided with in situ meteorological forcing evaluated with measured surface fluxes using quality-controlled data from 170 eddy-covariance-based flux tower sites. Predictions from seven out-of-sample empirical models are used to quantify the information available to land models in their forcing data and so the potential for land model performance improvement. Sites with unusual behaviour, complicated processes, poor data quality, or uncommon flux magnitude are more difficult to predict for both mechanistic and empirical models, providing a means of fairer assessment of land model performance. When examining observational uncertainty, model performance does not appear to improve in low-turbulence periods or with energy-balance-corrected flux tower data, and indeed some results raise questions about whether the energy balance correction process itself is appropriate. In all cases the results are broadly consistent, with simple out-of-sample empirical models, including linear regression, comfortably outperforming mechanistic land models. In all but two cases, latent heat flux and net ecosystem exchange of CO2 are better predicted by land models than sensible heat flux, despite it seeming to have fewer physical controlling processes. Land models that are implemented in Earth system models also appear to perform notably better than stand-alone ecosystem (including demographic) models, at least in terms of the fluxes examined here. The approach we outline enables isolation of the locations and conditions under which model developers can know that a land model can improve, allowing information pathways and discrete parameterisations in models to be identified and targeted for future model development. [ABSTRACT FROM AUTHOR]

The recent development of low-cost optical particle counters (OPCs) presents new opportunities for improving spatial coverage of particle concentration in the atmosphere as they are more affordable, compact, and consume less power than traditional OPCs. In particular, these OPCs could improve our ability to quantify dust emissions in complex environments during aeolian soil erosion. The high frequency sampling capacity (1 Hz) of some sensors may make them suitable for estimating dust emissions using the eddy-covariance method. Here, the capability of the low-cost OPC-N3 from Alfasense to estimate the size-resolved dust flux using the eddy-covariance method is evaluated. During the Jordan Wind Erosion and Dust Investigation (J-WADI) experiment, we tested one OPC-N3 against traditional reference OPCs. The OPCs were located in close proximity to a sonic anemometer, enabling the correlation of dust concentration and vertical velocity fluctuations for estimating dust fluxes. Despite the high temperature and dusty wind conditions of the campaign, the N3 monitored the dynamics and magnitude of dust concentration with reasonable precision. The turbulence characteristics of the dust concentration fluctuations measured by the N3 were similar to those from the reference OPC. After calibrating the N3 dust concentration, the N3 accurately estimated the dust emission flux, with differences of less than 30 % compared to the reference OPC. Our results confirm the potential of low-cost OPCs for dust-erosion research. Nonetheless, further evaluation of low-cost OPCs is still needed across different environments and weather conditions. [ABSTRACT FROM AUTHOR]

Roll vortices can have a significant influence on the exchanges of momentum, sensible heat and moisture throughout the boundary layer. They have been shown to reinforce air‐sea interactions under strong wind conditions. This raises the question of how air‐sea exchanges can, in turn, affect the roll vortices. However, representing surface turbulent fluxes during extreme wind conditions is a major challenge in numerical weather prediction and can lead to large uncertainties in surface wind speed. The sensitivity of rolls to different representations of surface fluxes is investigated using large eddy simulations. The study focuses on Mediterranean windstorm Adrian, where rolls are responsible for the transport of strong winds to the surface. Considering the effects of sea spray increases surface heat fluxes and significantly influences the roll morphology. The rolls become narrower and extend over a greater height, while the downward transport of momentum is intensified and results in higher wind speed near the surface. Roll vortices vanish within a few minutes in the absence of momentum fluxes, which maintain the wind shear necessary for their organization. They also quickly weaken without sensible heat fluxes, which sustain the near‐neutral stratification required for their development. In contrast, latent heat fluxes play a minor role. These findings emphasize the necessity of precisely representing the processes occurring at the air‐sea interface, which do not only affect the thermodynamic surface conditions but also the vertical transport of momentum within the windstorm. Plain Language Summary: Roll vortices are coherent and organized swirls that are often observed in the atmospheric boundary layer (the lowest part of the atmosphere). They are important because they can carry strong winds from higher in the atmosphere through the boundary layer toward the surface. For this study, roll vortices are simulated at high spatial resolution in a numerical model for a Mediterranean windstorm. The existence of roll vortices requires significant exchange of both heat and momentum between the sea and the atmosphere. The morphology of roll vortices is highly dependent on air‐sea exchanges, which can be difficult to represent in numerical models under strong wind conditions. In particular, the evaporation of water droplets ejected by strong wind action on the waves may reinforce heat exchanges. When this effect is taken into account, the roll vortices are stronger, taller and narrower. Consequently, the wind speed increases near the surface. These findings highlight the need to better understand the interactions at the air‐sea interface under windstorm conditions, because they act on the formation of damaging winds. Key Points: Large eddy simulations reveal the existence of roll vortices transporting strong winds to the surface in a Mediterranean windstormIncluding the effects of sea spray in surface sensible heat fluxes reduces the size of rolls and increases momentum transportThe results may constrain the representation of turbulent fluxes at the air‐sea interface, which is uncertain under strong wind conditions [ABSTRACT FROM AUTHOR]

Atmospheric turbulence over the Arctic sea‐ice surface has been understudied due to the lack of observational data. In this study, we focus on the turbulence kinetic energy (TKE) over sea ice and distinguish its two different vertical structures, the "Surface" type and the "Elevated" type, using observations during the Multidisciplinary drifting Observatory for the Study of Arctic Climate expedition (MOSAiC). The "Surface" type has the maximum TKE near the surface (at 2 m), while the "Elevated" type has the maximum TKE at a higher level (6 m). The TKE budget analysis indicates that the "Elevated" type is caused by the increased shear production of TKE at 6 m. In addition, spectral analysis reveals that the contribution to TKE by horizontal large eddies is enhanced in the "Elevated" type. Finally, how the vertical structure of TKE affects the parameterization of turbulent momentum flux is discussed. Plain Language Summary: In recent years, the Arctic near‐surface temperature has increased at a rate that is 3–4 times faster than the global average, which has significant impacts on the global climate. Explaining this phenomenon and predicting future scenarios are urgently needed. Turbulent motions within the Arctic atmospheric boundary layer over the sea‐ice surface play an important role in determining near‐surface temperature variations, but these turbulent motions and their impacts are not thoroughly understood. To enhance our understanding of the turbulent characteristics of the Arctic boundary layer, the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) was conducted in the central Arctic and collected a wealth of data. Based on the MOSAiC observational data, we investigate the vertical structures of turbulence kinetic energy (TKE) in the surface layer and two different vertical structures of TKE are distinguished. We then compare the production of TKE between these two vertical structures. In addition, we evaluate the performance of parameterization schemes for momentum flux under different vertical TKE structures. Key Points: The vertical structures of turbulence kinetic energy (TKE) over the Arctic sea‐ice surface are investigated using MOSAiC dataBudget analysis and spectral analysis are used to analyze TKE vertical structures near the Arctic sea‐ice surfaceThe TKE vertical structures affect the performance of commonly used turbulence parameterizations [ABSTRACT FROM AUTHOR]

Sea surface temperature anomaly (SSTA) of ocean eddies induces an anomalous air‐sea turbulent heat flux that acts to dampen SSTA. A two‐dimensional SSTA model explores the effect of air‐sea turbulent heat flux, parameterized as SSTA damping, in shaping eddy SSTA patterns. Increased SSTA damping transitions the SSTA pattern from a monopole to dipole, indicating the balance between eddy stirring of the background SST gradient and SSTA damping. The SSTA dipole pattern increases the correlation of eddy velocity and SSTA, but SSTA damping weakens the SSTA, resulting in an optimal damping rate maximizing lateral eddy surface heat transport. Globally, the SSTA damping rate increases toward the equator. In mid‐latitude and high‐latitude regions (e.g., the Kuroshio, the Gulf Stream, and the Southern Ocean), eddy SSTAs are monopoles, while the tropics and subtropics exhibit dipole SSTA patterns due to higher damping rates, facilitating greater lateral eddy heat transport when the SSTA is large. Plain Language Summary: Mesoscale ocean eddies, ranging from tens to hundreds of kilometers, exhibit distinct sea surface temperature anomaly (SSTA) patterns. In regions like the Kuroshio, the Gulf Stream, and the Southern Ocean, eddy SSTA exhibits a monopole pattern, with a single warm or cold core within the eddy. At lower latitudes, a dipole‐like pattern emerges, characterized by a pair of opposite‐sign SSTA surrounding the eddy. Previous studies attribute these SSTA patterns to the lateral stirring of background SST gradients by eddies. We develop a simplified SSTA model to highlight the role of eddy‐induced air‐sea turbulent heat flux in shaping eddy SSTA patterns. Eddy stirring of the background SST gradient generates SSTA, which induces anomalous sensible and latent heat flux that dampens SSTA. In the tropics and subtropics, effective SSTA damping balances the positive and negative SSTA generated by eddy stirring, resulting in a dipole‐like pattern. Conversely, at high latitudes, where SSTA damping is weaker, SSTA maintains its signature, yielding a monopole pattern. The transition from a monopole to a dipole pattern is facilitated by air‐sea heat flux, enhancing the correlation of eddy SSTA and velocity, while reducing SSTA variance, leading to an optimal damping rate that maximizes eddy heat transport. Key Points: Ocean eddies generate a dipole sea surface temperature anomaly (SSTA) pattern when air‐sea turbulent heat flux dampens SSTA counteracting eddy stirring of the background SSTThe dipole pattern enhances lateral eddy heat transport due to increased correlation between the eddies' horizontal velocity and SSTAThe SSTA damping rate due to air‐sea heat flux decreases toward the poles, maximizing lateral eddy heat transport in the subtropics [ABSTRACT FROM AUTHOR]

The Hadley circulation (HC) has been expanding poleward in recent decades. The Coupled Model Intercomparison Project Phase 6 (CMIP6) models predict that the expansion will accelerate in the future, more so in the Southern Hemisphere (SH). However, the extent of the expansion varies widely among the models. We investigate the mechanisms driving the intermodel spread in SH HC expansion predictions. The intermodel spread is obtained by an empirical orthogonal function analysis on the SH HC trend patterns of 16 CMIP6 model simulations using the historical and shared socioeconomic pathway 5–8.5 scenarios. The leading mode, showing a mean meridional stream function anomaly at the poleward SH HC extent, explains 49.73% of the variance and significantly correlates (r = 0.94) with the SH HC expansion. By analyzing the extended Kuo‐Eliassen equation, we find that the intermodel difference in the representation of diabatic heating is responsible for about 14% of the intermodel spread. The meridional eddy momentum and heat fluxes contribute to about 21% and 18% of the intermodel spread, respectively. The models simulating a relatively large SH HC expansion tend to show increased precipitation in the Southern Pacific Convergence Zone, reduced baroclinic instability in the subtropics, and an enhanced poleward shift of jet stream in the midlatitudes. This suggests that the uncertainty in the HC projection may be constrained by reducing the bias in the trend of the mean fields. Plain Language Summary: The Hadley circulation (HC), which affects global climate patterns, is expanding toward the poles. However, different climate models predict varying extents of this expansion, especially in the Southern Hemisphere (SH). We aim to understand why. By analyzing climate model data, we identified key factors influencing the spread in SH HC expansion. Our findings suggest that factors like diabatic heating and meridional eddy momentum play significant roles. Models showing greater SH HC expansion tend to simulate increased precipitation in specific regions and shifts in atmospheric jet streams. Addressing these model biases could help reduce uncertainty in future HC projections. Key Points: The first intermodel stream function trend mode effectively captures the spread of the Southern Hemisphere Hadley Circulation expansionThe intermodel spread in expansion is explained by the spread of the meridional eddy momentum, heat fluxes, and diabatic heatingThe spread of the eddy fluxes and diabatic heating are linked with the changes in precipitation, jet, and static stability [ABSTRACT FROM AUTHOR]

Greenhouse gas monitoring is important to ensure climate goals are being achieved. This study unveils the potential of using atmospheric tall towers in direct flux measurements, bridging the gap between atmospheric and ecosystem monitoring networks. The ICOS Cities (PAUL) project aims to monitor CO2 emissions in urban areas, where concentrated emissions make them key targets for climate change mitigation. This study explores the synergy between ICOS atmospheric and ecosystem networks by utilizing slow-response analysers (∼ 3 s) on tall atmospheric towers for ecosystem studies using the eddy covariance method. A standard setup with an ultrasonic anemometer and an infrared (IR) fast-response CO2 analyser was installed and compared with measurements from an existing cavity ring-down spectroscopy (CRDS) analyser measuring CO2, CO, and CH4. Deployed on the 100 m Saclay tower near Paris, covering a 43.9 km2 80 % footprint with heavy traffic roads, a nearby heating plant, and a forest, the setup addressed technical challenges and height-induced complexities. Corrections for flux attenuation by high-frequency losses were limited to < 20 % on average for all stabilities and around 11 % for unstable conditions. Elevated mean fluxes for CO2 (10 µmolm-2s-1) and CH4 (200 µmolm-2s-1) were observed from the heating plant wind direction during December and January. Conversely, the forest direction exhibited the strongest sink among all wind directions, with - 4 µmolm-2s-1 during July and August. Storage and vertical advection were estimated using the routine three-level profile measurements done in ICOS atmospheric towers. Storage term was of the same magnitude as turbulent flux, increasing at night and de-stocking during the first half of the day. Vertical advection averaged zero on a monthly basis. These results demonstrate the feasibility and versatility of utilizing atmospheric towers for urban emission monitoring, offering valuable insights for emission monitoring strategies worldwide. [ABSTRACT FROM AUTHOR]

Although evidence of recovery in Antarctic stratospheric ozone has been found, evidence of recovery in Arctic ozone is still elusive, even though 25 years have passed since the peak in ozone depleting substances. Here we have used a Dynamic Linear Model to derive time-varying trends over 20-year periods in the Arctic ozone time series, measured in-situ by ozonesondes from 6 stations, from 1994 to 2022. The model accounts for seasonality, external forcing and 1st-order correlation in the residuals. As proxies for the external forcing, we have used tropopause pressure (replaced with Arctic Oscillation in the troposphere), eddy heat flux, the volume of polar stratospheric clouds multiplied by effective equivalent stratospheric chlorine, and solar radio flux at 10.7 cm for the 11-year solar cycle. Our results indicate that the ozone recovery in the lower Arctic stratosphere is not detectable. Though significant positive trends have been detected prior to 2017 at some stations, there are no statistically significant positive trends after 2017. Moreover, at a number of stations the trends after 2019 are rather negative and significant, varying between − 0.30 ± 0.25 and − 1.00 ± 0.85% per decade. Furthermore, the Arctic troposphere exhibited only statistically significant negative trends over 20-year periods ending in 2017 or later, varying between − 0.31 ± 0.27 and − 1.76 ± 0.41% per decade. These results highlight the importance of continued monitoring of the Arctic ozone. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO2) flux measurements were conducted throughout the year 2022 utilizing the eddy covariance technique in this study to investigate the characteristics of carbon fluxes and their influencing factors in the Chenhu wetland, a representative subtropical lake-marsh wetland located in the middle reaches of the Yangtze River in China. The results revealed that the mean daily variation of CO2 flux during the growing season exhibited a U-shaped pattern, with measurements ranging from −12.42 to 4.28 μmolCO2·m−2·s−1. The Chenhu wetland ecosystem functions as a carbon sink throughout the growing season, subsequently transitioning to a carbon source during the non-growing season, as evidenced by observations made in 2022. The annual CO2 absorption was quantified at 21.20 molCO2·m−2, a figure that is lower than those documented for specific subtropical lake wetlands, such as Dongting Lake and Poyang Lake. However, this measurement aligns closely with the average net ecosystem exchange (NEE) reported for wetlands across Asia. The correlation between daytime CO2 flux and photosynthetically active radiation (PAR) can be accurately represented through rectangular hyperbola equations throughout the growing season. Vapor pressure deficit (VPD) acts as a constraining factor for daytime NEE, with an optimal range established between 0.5 and 1.5 kPa. Furthermore, air temperature (Ta), relative humidity (RH), and vapor pressure difference (VPD) are recognized as the principal determinants affecting NEE during the nocturnal period. The association between Ta and NEE during the non-growing season conforms to the van't Hoff model, suggesting that NEE increases in response to elevated Ta during this timeframe. [ABSTRACT FROM AUTHOR]

The present study offers a twofold contribution on counter-gradient transport (CGT) of turbulent scalar flux. First, by examining turbulent scalar mixing through synchronized particle image velocimetry and planar laser-induced fluorescence on an inclined jet in cross-flow, we clarify the previously unexplained phenomenon of CGT, revealing key flow structures, their spatial distribution and modelling implications. Statistical analysis identifies two distinct CGT regions: local cross-gradient transport in the windward shear layer and non-local effects near the wall after injection. These behaviours are driven by specific flow structures, namely Kelvin–Helmholtz vortices (local) and wake vortices (non-local), suggesting that scalar flux can be decomposed into a gradient-type term for gradient diffusion and a term for large-eddy stirring. Second, we propose a new approach for reconstruction of turbulent mean flow and scalar fields using continuous adjoint data assimilation (DA). By rectifying model-form errors through anisotropic correction under observational constraints, our DA model minimizes discrepancies between experimental measurements and numerical predictions. As expected, the introduced forcing term effectively identifies regions where traditional models fall short, particularly in the jet centreline and near-wall regions, thereby enhancing the accuracy of the mean scalar field. These enhancements occur not only within the observation region but also in unseen regions, underscoring present DA approach's reliability and practicality for reproducing mean flow behaviours from limited data. These findings lay a solid foundation for adjoint-based model-consistent data-driven methods, offering promising potential for accurately predicting complex flow scenarios like film cooling. [ABSTRACT FROM AUTHOR]

This study investigates the correlation between the fluctuating wall heat flux, and the distribution and transport of Reynolds shear stress and turbulent heat flux in compressible boundary layers at Mach number 5.86 and friction Reynolds number 420, with a relatively weaker and a stronger wall cooling imposed. As illustrated from the probability density functions of the wall-heat-flux perturbations, with increasing wall cooling, the extreme wall heat flux is intensified and tends to be more negatively skewed. To examine the role of the extreme events in the transport of the momentum and heat, conditional analysis of the extreme positive and negative wall-heat-flux-perturbation events is conducted. In most regions of the boundary layer, the positive events are predominantly associated with an increase in Reynolds shear stress and a decrease in turbulent heat flux. Joint probability density functions of velocity and wall-heat-flux perturbations in the near-wall region indicate that the extreme positive events tend to be more correlated with ejections, which is particularly evident in the stronger wall-cooling case. To further shed light on the underlying mechanisms of the connections between wall heat flux and transport budgets, a transport equation for turbulent heat flux is derived, in a similar manner to that for Reynolds shear stress. The energy balance is inspected, with conditional analysis applied to budget terms and mean flow properties so as to quantify the correlation between wall-heat-flux fluctuations and energy evolution. [ABSTRACT FROM AUTHOR]

A good understanding of land-atmosphere exchange processes is essential for developing sustainable land management practices in Africa, in order to enhance food security and strengthen the resilience against climate change and extremes in this vulnerable region. In this study, we explore the energy balance closure (EBC) of three eddy covariance (EC) sites implemented along a land use gradient (pristine savanna forest, cropland, and degraded grassland) in the Sudanian savanna of West Africa. Our results show that the EBC strongly varies over the monsoon season and the EC sites. However, the best EBC is observed at the pristine site, which has the most homogenous vegetation. Thus, landscape heterogeneity seems to play an important role in the quality of the EC measurements. Moreover, we develop a novel post-closure method based on a quantile-mapping technique conditioned on monsoonal circulation patterns specifically determined for the West African Monsoon. This method is also compared to two well-established methods, the Bowen-ratio (BR) correction and a pure quantile-mapping using various bias measures. Our results show that the novel post-closure method outperforms the other methods and, therefore, leads to better elimination of the underestimation of the turbulent fluxes at the three savanna sites. In addition, specific characteristics of turbulent fluxes, like their strong diurnal cycle, are well represented by the new correction method. [ABSTRACT FROM AUTHOR]

The eddy covariance (EC) technique is currently the most widely used method for measuring carbon exchange between terrestrial ecosystems and the atmosphere at the ecosystem scale. Using this technique, a regional carbon flux network comprising a total of 34 sites has been established in the Heihe River Basin (HRB) in Northwest China. This network has been measuring the net ecosystem exchange (NEE) of CO2 for a variety of vegetation types. In this study, we compiled and post-processed half-hourly flux data from these 34 EC flux sites in the HRB to create a continuous, homogenized time series dataset. We employed standardized processing procedures to fill data gaps in meteorological and NEE measurements at half-hourly intervals. NEE measurements were also partitioned into gross primary production (GPP) and ecosystem respiration (Reco). Furthermore, half-hourly meteorological and NEE data were aggregated to daily, weekly, monthly, and yearly timescales. As a result, we produced a continuous carbon flux and auxiliary meteorological dataset, which includes 18 sites with continuous multi-year observations and 16 sites observed only during the 2012 growing season, amounting to a total of 1,513 site-months. Using the post-processed dataset, we explored the temporal and spatial characteristics of carbon exchange in the HRB. In the diurnal variation curve, GPP, NEE, and Reco peak later for ecosystems in the artificial oasis (cropland and wetland) compared to those outside the artificial oasis (grassland, forest, woodland, and Gobi/desert). Seasonal NEE, GPP, and Reco peak in early July for grassland, forest, woodland, and cropland but remain close to zero throughout the year for gobi/desert. In the last decade, NEE of wetlands significantly increased, while NEE for other ecosystems did not exhibit significant trends. Annual NEE, GPP, and Reco are significantly higher for sites inside the artificial/natural oasis compared to those outside the oasis. This post-processed carbon flux dataset has numerous applications, including exploring the carbon exchange characteristics of alpine and arid ecosystems, analyzing ecosystem responses to climate extremes, conducting cross-site synthesis from regional to global scales, supporting regional and global upscaling studies, interpreting and calibrating remote sensing products, and evaluating and calibrating carbon cycle models. [ABSTRACT FROM AUTHOR]

The relationship between precipitation and evapotranspiration (ET) is critical to understanding water cycle related dynamics in ecosystems, including crops. Existing studies of bioenergy crops have primarily focused on annual or seasonal ET rates, with less attention given to the immediate ET response following precipitation events. This study examines the variation in ET rates in the days subsequent to precipitation events across various bioenergy crops—corn, switchgrass, and prairies—utilizing 13 years (2010–2022) of growing season data. Meteorological and eddy covariance flux data were collected from seven eddy covariance flux towers as part of the GLBRC scale-up experiment at the Kellogg Biological Station Long Term Ecological Research sites. The analysis revealed that average ET peaked the day after precipitation and declined linearly over the following days, with a statistically significant relationship (p -value = 0.00027, R2 = 0.96). Neither the type of biofuel vegetation nor the historical land use significantly influenced ET post-precipitation events (p -values = 0.53 and 0.153, respectively). Key predictors of ET following precipitation events include shortwave radiation, season, day of the year, ambient temperature, vapor pressure deficit (VPD), long-wave radiation, precipitation amount, soil moisture, and annual variability. These findings enhance our comprehension of ET responses in bioenergy crop systems, with implications for water management in sustainable agriculture. [ABSTRACT FROM AUTHOR]

Mesoscale convective systems (MCSs) occasionally develop over the East China Sea (ECS) in the Baiu frontal zone under both the atmospheric and oceanic influence. The factors that determine their predictability have not been fully understood yet. This study investigates the uncertainties affecting two MCSs observed by research vessels on 19 June 2022 using regional ensemble simulations. These MCSs have contrasting features: the first was triggered by an atmospheric mesoscale disturbance, while the second was induced by the boundary layer destabilization over the warm Kuroshio current. The first MCS shows high variability in the synoptic-scale uncertainties detected by the breeding ensemble. The best-performing member successfully represents the strong meso-ß -scale cyclone and the frontal structure with deep moist layers. The ensemble simulations are less skillful for the second MCS than the first. The enhanced surface turbulent heat flux in the sea surface temperature (SST) frontal zone is found to be significantly correlated to the precipitation due to the second MCS despite the cold bias of SST that is commonly imposed on all members. The dense upper-air information from the vessels significantly improves the representation of the sharp frontal structure associated with the first MCS, but has little impact on the second MCS probably due to the underestimation of the boundary layer moistening. This case study indicates that the predictability of MCSs over the ECS depends on their development mechanisms, and that the incorporation of uncertainties in both the atmosphere and ocean are important for the ensemble forecasting of these MCSs. [ABSTRACT FROM AUTHOR]

The turbulent transport dissimilarity between momentum and scalars and the transport similarity among scalars have been widely investigated in unstable atmospheric boundary layers (ABLs). Although buoyancy and mechanically driven turbulence, along with variations in scalar sources and sinks, are recognized as key factors influencing transport similarity, the specific roles of local thermal plume-generated and nonlocal bulk shear-generated large eddies under varying stability conditions are less explored. This study utilized over four years of eddy covariance data sampled 50 m above a complex suburban canopy to characterize the influence of buoyancy and wind shear on flux transport similarity in an unstable ABL. The time threshold τ method was applied to detect large coherent events, with wind shear enhancing their intensity, while buoyancy primarily affected the ejection–sweep asymmetry of scalars. The dynamics between buoyancy and wind shear were analyzed through separate momentum, heat, and joint transport events. The results show that strong wind shear enhances nonlocal large eddies, reducing momentum–heat transport similarity, whereas strong buoyancy supports localized turbulence. As stability varies, the shift between nonlocal and local eddies alters the trends in co-transport duration and intensity, revealing distinct patterns in the water vapor intensity from that of the sensible heat owing to local sources and sinks. [ABSTRACT FROM AUTHOR]

We present direct eddy covariance measurements of the surface heat flux in sea ice over a wide range of conditions across the Arctic Ocean made during two research cruises. Photographic imagery of the surface around the ship provides a local, in situ estimate of the ice fraction. Aerodynamically rough conditions prevail for the majority of the time in the consolidated pack ice. The results are analyzed in the framework of a recently-developed parameterization scheme in which the exchange coefficients over ice are functions of a roughness Reynolds number, R*, hence account for aerodynamic roughness variability. This parameterization accurately represents the measured fluxes under all conditions, while under aerodynamically rough conditions the existing parameterizations from both the Met Office Unified Model, and ECMWF Integrated Forecast System overestimate the fluxes. The results corroborate those of a previous airborne study over the marginal ice zone, and encompass a wider range of atmospheric stability conditions. [ABSTRACT FROM AUTHOR]

This study addresses the need to investigate footprint function features in urban areas and establish a validation database for numerical methods. Concentration and its flux footprints of a block-arrayed urban model were measured in a wind tunnel with a neutrally stratified boundary layer. The velocity and concentration were simultaneously measured by an X-probe hot wire anemometer and a fast-response flame ionization detector to evaluate the vertical flux. Experimental results highlighted the influence of the measurement heights on footprint distributions. Because the sensors were immersed in the roughness sublayer, their footprints showed strong heterogeneity across horizontal positions caused by building configurations. It was found that turbulent flux contributes up to 70% of total flux footprints, emphasizing the importance of accurate turbulent dispersion estimation in numerical methods. Furthermore, measured footprints were compared to those modeled by a widely used analytical method (Kormann and Meixner in Boundary-Layer Meteorol 99:207–224, 2001, https://doi.org/10.1023/ A:1018991015119). The measured footprints extended further along the streamwise direction and their spanwise dispersions were constrained by the rows of blocks, which failed to be reproduced in the analytical method. This indicates the significant effects of building configurations on footprint functions in urban areas. [ABSTRACT FROM AUTHOR]

Turbulent transport in magnetically confined fusion plasma has conventionally been analyzed at the ion gyroradius scale based on the microturbulence theory. However, ion-scale turbulence analysis sometimes fails to predict the turbulent transport flux observed experimentally. Microturbulence at the electron gyroradius scale and cross-scale interactions between disparate-scale turbulences are possible mechanisms to resolve this issue. This overview discusses the recent progress in multiscale turbulence studies and presents future perspectives from recent experimental, theoretical, and numerical investigations. The following aspects are highlighted: (1) the importance of electron-scale effects in experiments, (2) the physical mechanisms of cross-scale interactions, (3) modeling electron-scale effects in quasilinear transport models, and (4) the impacts of cross-scale interactions on burning plasmas. Understanding multiscale turbulence is necessary to improve performance prediction and explore optimal operations for future burning plasmas. [ABSTRACT FROM AUTHOR]

Tropical cyclones are rare in the South Atlantic Ocean. Hurricane Catarina (2004), developed from a tropical transition, was the first documented case, followed by Iba (2019), which had a purely tropical genesis. In February 2024, the southeastern South Atlantic recorded its third tropical cyclone, Akará, initially a subtropical system. Due to the specific conditions required for tropical cyclones to develop in this ocean basin, the main purpose of this study is to describe the physical mechanisms that triggered the genesis of Akará's precursor and its tropical transition. Data from various sources and methodologies, including the cyclone phase space diagram, are used in this study. Results show that the passage of a cold front created an environment with horizontal wind shear, contributing to most of the cyclonic relative vorticity in the genesis region. This was the primary driver of cyclogenesis at 1200 UTC on 15 February, along with other secondary processes. The tropical transition occurred as the vertical shear weakened, and turbulent heat fluxes from the ocean to the atmosphere increased, enhancing diabatic processes that warmed the atmosphere. This led to the tropical transition at 0600 UTC on 17 February. [ABSTRACT FROM AUTHOR]

The formation of cold, dense waters south of the Antarctic Circumpolar Current (ACC) is one of the main drivers of the global overturning circulation, with major effects on the earth's climate. A key region where dense waters are formed is the Ross Sea, which is separated from the ACC by the Ross Gyre. The strength and variability of the Ross Gyre circulation impacts the formation and export of dense water, but observations of the Ross Gyre circulation are limited because of its remote location, severe weather conditions, and ice cover that has limited the application of remote sensing techniques. Quantitative estimates of the gyre's total strength are difficult to obtain from hydrographic observations alone due to the limited sampling and the relatively weak stratification. In this paper, we use a combination of observations and modeling studies to estimate the strength and variability of the Ross Gyre transport and investigate the relative contributions of the wind, buoyancy forcing, eddy fluxes, and the influence of ACC to the Ross Gyre circulation. We find that the mean transport of the Ross Gyre can be as high as about 45 Sv, more than twice the typical estimate of about 20 Sv. Sensitivity experiments to wind and buoyancy forcing, nonlinear terms, and the ACC were performed with a regional configuration of the Hybrid Coordinate Ocean Model (HYCOM). The numerical experiments show that the total Ross Gyre circulation, and its variability, are primarily wind-driven. The ACC is responsible for a small recirculation. Buoyancy and nonlinearity or eddy fluxes play a smaller role in the gyre dynamics, though they are regionally important. [ABSTRACT FROM AUTHOR]

The parameterization of suspended sediments in vegetated flows presents a significant challenge, yet it is crucial across various environmental and geophysical disciplines. This study focuses on modeling suspended sediment concentrations (SSC) in vegetated flows with a canopy density of avH ∈ [0.3, 1.0] by examining turbulent dispersive flux. While conventional studies disregard dispersive momentum flux for avH > 0.1, our findings reveal significant dispersive sediment flux for large particles with a diameter‐to‐Kolmogorov length ratio when dp/η > 0.1. Traditional Rouse alike approaches therefore must be revised to account for this effect. We introduce a hybrid methodology that combines physical modeling with machine learning to parameterize dispersive flux, guided by constraints from diffusive and settling fluxes, characterized using recent covariance and turbulent settling methods, respectively. The model predictions align well with reported SSC data, demonstrating the versatility of the model in parameterizing sediment‐vegetation interactions in turbulent flows. Plain Language Summary: This research focuses on the movement of suspended sediments in rivers, specifically in areas with vegetation. Traditional models cannot depict this process, prompting the development of a new methodology that merges conventional scientific techniques with advanced machine learning. The proposed approach has demonstrated superior performance, particularly in transitional areas between vegetated and non‐vegetated zones. The significance of this study lies in its contribution to modeling an often‐overlooked spatial term (called "turbulent dispersive flux") by showing that its magnitude is much greater than conventionally supposed. This study also advances the current methodology of including physics‐based artificial intelligence to model sediment dynamics in vegetated river systems. The proposed approach is versatile and can be included in the large‐scale transport models. Key Points: Rouse budget without dispersive flux cannot describe coarse sediment concentration in vegetated flowsA machine‐assisted physical closure for turbulent dispersive flux from spatial average is proposedPredicted sediment concentration results agree with reported experimental data in the literature [ABSTRACT FROM AUTHOR]

Diabatic heating due to latent heat release in the storm tracks plays an important but poorly understood role in the midlatitude circulation. To examine how localised diabatic heating affects the circulation, a dry model is used to apply midtropospheric perturbations to the radiative‐equilibrium temperature profile to which the model is relaxed. This allows us to isolate the one‐way causal influence of diabatic heating on the circulation without feedbacks of the circulation onto the heating. By applying switch‐on perturbations at various latitudes, the mechanisms by which an equilibrated state is reached are examined. In all cases, the equilibrated circulation exhibits a dynamically insensitive jet structure with eddies maintaining a region of self‐concentrated baroclinicity, latitudinally shifted away from the heating perturbation. However, the initial response is generally very different. For heating poleward of the jet, there is an initial thermal‐wind adjustment and weakened eddy heat fluxes, followed later by weakened eddy momentum fluxes that maintain an equilibrated equatorward jet shift. For heating equatorward of the jet, the evolution is more complex with an initial strengthening of the eddy heat fluxes that dominantly balance the imposed heating, as well as a weakening of the Hadley cell. Further, the initial thermal‐wind adjustment immediately modifies the subtropical critical lines and eddy momentum fluxes that encourage an ∼15° poleward propagation from the Subtropics to Midlatitudes, yielding an equilibrated poleward jet shift. The overall determining factor in balancing the imposed heating at equilibration is the local climatological heat budget: if the climatological eddy heat fluxes locally warm, such as in mid‐to‐high latitudes, then this effect weakens, whereas if the climatological overturning circulation locally warms, such as in the Subtropics, then this effect weakens. The insensitivity of the equilibrated jet profile to the imposed heating is remarkable given the maintenance mechanisms vary drastically according to heating latitude. [ABSTRACT FROM AUTHOR]

The relaxed eddy accumulation (REA) method is a widely‐known technique that measures turbulent fluxes of scalar quantities. The REA technique has been used to measure turbulent fluxes of various compounds, such as methane, ethene, propene, butene, isoprene, nitrous oxides, ozone, and others. The REA method requires the accumulation of scalar concentrations in two separate compartments that conditionally sample updrafts and downdraft events. It is demonstrated here that the assumptions behind the conventional or two‐compartment REA approach allow for one‐compartment sampling, therefore called a one compartment or 1‐C‐REA approach, thereby expanding its operational utility. The one‐compartment sampling method is tested across various land cover types and atmospheric stability conditions, and it is found that the one‐compartment REA can provide results comparable to those determined from conventional two‐compartment REA. This finding enables rapid expansion and practical utility of REA in studies of surface‐atmosphere exchanges, interactions, and feedbacks. Plain Language Summary: Estimates of emission inventory of chemical compounds from the biosphere remain an indispensable tool in air quality and climate science research. Such inventory requires the measurements of the number of molecules flowing from the biosphere to the atmosphere, or vice‐versa, per unit ground area per unit time. What makes these measurements challenging is that such molecules are being transported rapidly by gusts and swirling (i.e., turbulent) motion in the atmosphere. In theory, this vertical exchange can be measured by a rapidly sampled covariance between vertical velocity and concentration variations. The main drawback is that such covariance requires rapid concentration measurements that are difficult to conduct for a large number of chemical species, although it is standard practice and easier to obtain for carbon dioxide, water vapor, and air temperature. The work here offers an alternative and efficient approach that necessitates measuring the accumulation of molecules in a single compartment, supplemented by knowledge of the velocity statistics. Both velocity and accumulated concentration measurements can be conducted with available instrumentation. Thus, the work here offers a blueprint for efficient sampling of emission rates across the biosphere‐atmosphere interface that can be deployed in upcoming experiments. Key Points: Relaxed eddy accumulation (REA) is used to estimate turbulent fluxes of numerous chemical speciesThe original REA relies on sampling concentrations in two compartmentsA single‐compartment REA is proposed with no loss in accuracy [ABSTRACT FROM AUTHOR]

The parameterization of fluxes associated with representing unresolved dynamics in turbulent flows, especially in the atmosphere and ocean (which have a vast range of scales), remains a challenging task. This is especially true for Earth system models including complex biogeochemistry and requiring very long simulations. The problem of representing the dependence of the mean flux of a passive tracer in terms of the mean has a very long history; in this study, we take a somewhat different approach. We use a formalism showing that the mean flux will be a functional of the mean gradients, a formalism that can be used to calculate the structure of the functional which is non-local in both space and time. Two-dimensional turbulent simulations are used to explore the weight of nearby (in space or time) gradients. We also use stochastic velocities and iterated maps to show that the results are similar. The functional formalism provides an understanding of when non-locality needs to be considered and when a local eddy diffusivity can be a reasonably good approximation. Furthermore, the formalism provides guidance for the development of data-driven parameterizations. [ABSTRACT FROM AUTHOR]

The spontaneous formation of zonal jets is a distinctive feature of geostrophic turbulence with the phenomenon witnessed in numerous numerical studies. In such systems, strong rotation anisotropises the spectral evolution of the energy density such that zonal modes are favoured. In physical space, this manifests as eddies zonally elongating and forming into zonal jets. In the presence of large scale dissipation, the flow may reach statistical stationarity such that the zonal structure persists in the zonal and time mean, and is supported by a flux of eddy momentum. What is unclear is how the excitation of Rossby waves arranges the underlying eddy momentum stresses to support the mean flow structures. To study this, we examine a steady-state flow in the so-called 'zonostrophic' regime, in which characteristic scales of geostrophic turbulence are well separated and there are several alternating zonal jets that have formed spontaneously. We apply a geometric eddy ellipse formulation, in which momentum fluxes are cast as ellipses that encode information about the magnitude and direction of flux; the latter is described using the tilt angle. With the aid of a zonal filter, it is revealed that the scales responsible for providing the momentum fluxes associated with the jet structure are much smaller than the characteristic scales identified, and occupy a region of the energy spectrum that has been typically associated with isotropic dynamics. [ABSTRACT FROM AUTHOR]

This paper is devoted to the study of the characteristics of internal waves in the Kara Sea and their interaction with the atmosphere, in particular, their influence on the turbulent momentum and heat fluxes in the surface layer of the atmosphere. The direction and horizontal velocity of propagation of short-period internal waves in the Kara Gates Strait are calculated. Cross spectra of mesoscale fluctuations of water temperature at the sea surface, at depths of 10 and 20 m, and meteorological parameters at a height of 22 m are analyzed. Common spectral maxima at periods characteristic of the trapped internal gravity modes propagating in the thermocline layer and atmospheric gravity modes in the stably stratified layer of the lower troposphere are revealed. A possible mechanism of influence of the observed gravity modes in the thermocline layer on mesoscale fluctuations of meteorological parameters (with periods from 10 min to several hours) and turbulent fluxes of momentum and apparent and latent heat in the surface layer of the atmosphere is proposed. [ABSTRACT FROM AUTHOR]

Strategic vegetation placement can significantly alter airflow patterns and turbulence, fostering desired wind environments. By comparing scenarios where vegetation is placed upstream, downstream or absent (treeless) relative to a single building using large-eddy simulation, this study provides detailed insights into the sensitivity of flow dynamics to the positioning of the vegetation. Upstream vegetation more significantly disrupts the flow patterns around the building obstacle, altering vertical wind profiles and modifying wake circulations, compared to downstream vegetation. A small shear layer developed at the plant top for upstream vegetation markedly influences turbulent kinetic energy (TKE) on both the leeward and windward sides of the building, shifting the inflection point in vertical TKE profiles by up to 0.13 H. By contrast, smaller tree-building separations lead to an effective merging of their aerodynamic profiles, whereas larger separations confine the streamwise breadth of turbulent fluxes, amplifying flux exchanges in the spanwise direction. Spectral analyses reveal that upstream vegetation consistently results in higher power spectral densities of the streamwise turbulence in the residential area than downstream vegetation. While small-scale spanwise velocity fluctuations are found to be comparably energetic at the building's windward side for upstream vegetation, the power becomes substantially concentrated on large-scale eddies in the building wake region, providing specific insights into modulating turbulent eddy motions within the residential zone. [ABSTRACT FROM AUTHOR]

Ecosystem respiration is a key flux in the terrestrial carbon cycle and is affected substantially by temperature. This work analysed the time series data of nighttime net ecosystem exchange of carbon dioxide (NEEnight) from 196 FLUXNET2015 sites to re‐evaluate the relationships between NEEnight and temperature. A total of 93 sites (48%) were identified to have a unimodal relationship between NEEnight and temperature. Site‐specific apparent optimum temperature parameters were then estimated at these sites. We further assessed the impacts of using exponential or unimodal equations on NEEnight predictions. The predicted NEEnight values at high temperatures were substantially higher from the exponential‐type equations (mean: ~200%) than from the unimodal equation (mean: ~30%), compared to the observed NEEnight. This study calls for using a unimodal equation to predict NEEnight (often considered as nighttime ecosystem respiration, ERnight), which could substantially improve the accuracy and reduce uncertainty in ER estimates, in particular under the scenario of global warming. [ABSTRACT FROM AUTHOR]

The study of the surface energy balance characteristics of different ecosystems in the Qinghai Plateau is of great significance for a deeper understanding of land surface processes, the water cycle, and global climate change. This study aims to compare the seasonal variations in energy balance and partitioning of four typical ecosystems on the Qinghai Plateau—swamp meadows, subalpine mountain meadows, alpine shrublands, and alpine deserts. Mantel analysis and path analysis were used to explore the regulatory mechanisms of meteorological elements on energy fluxes and the Bowen ratio (β). The results showed the following: (1) Net radiation (Rn), sensible heat flux (H), and latent heat flux (LE) all exhibited a single-peak pattern of change, and the energy partitioning was closely related to the hydrothermal conditions. Swamp meadows and subalpine mountain meadows were dominated by LE throughout the year and the growing season, while H dominated in the non-growing season. Meanwhile, alpine shrublands and alpine deserts were dominated by H throughout the year. (2) β reflected the characteristics of turbulent fluxes variations and the moisture level of the underlying surface. Swamp meadows and subalpine mountain meadows were relatively moist, with the value of β all being less than 1. Alpine shrublands and deserts were comparatively arid, with the values of β all exceeding 1. The energy closure rate ranged from 48% to 90%, with better energy closure conditions observed during the growing season compared to the non-growing season. (3) Meteorological factors collectively regulated the variations in energy fluxes and its partitioning, with H and LE being primarily influenced by Rn, relative humidity (RH), and soil moisture (Ms). β was significantly affected by RH, Ms, and the saturated vapor pressure deficit (VPD). The sensitivity of the ecosystems to changes in fluxes increased with decreasing moisture, especially in alpine deserts, with Ms, VPD and RH being the most affected. Swamp meadows were significantly associated with air temperature (Ta), soil temperature (Ts), and wind speed; subalpine mountain meadows with Ta and Ts; and alpine shrublands with Ta. These results provided a basis for further analyses of the energy balance characteristics and partitioning differences of different ecosystems on the Qinghai Plateau. [ABSTRACT FROM AUTHOR]

The air–sea exchange of ozone (O 3) is controlled by chemistry involving halogens, dissolved organic carbon, and sulfur in the sea surface microlayer. Calculations also indicate faster ozone photolysis at aqueous surfaces, but the role of clouds as an ozone sink is currently not well established. Fast-response ozone sensors offer opportunities to measure eddy covariance (EC) ozone fluxes in the marine boundary layer. However, intercomparisons of fast airborne O 3 sensors and EC O 3 fluxes measured on aircraft have not been conducted before. In April 2022, the Technological Innovation Into Iodine and GV Environmental Research (TI 3 GER) field campaign deployed three fast ozone sensors (gas chemiluminescence and a combination of UV absorption with coumarin chemiluminescence detection, CID) together with a fast water vapor sensor and anemometer to study iodine chemistry in the troposphere and stratosphere over Colorado and over the Pacific Ocean near Hawaii and Alaska. Here, we present an instrument comparison between the NCAR Fast O 3 instrument (FO3, gas-phase CID) and two KIT Fast AIRborne Ozone instruments (FAIRO, UV absorption and coumarin CID). The sensors have comparable precision < 0.4 % Hz -0.5 (0.15 ppbv Hz -0.5), and ozone volume mixing ratios (VMRs) generally agreed within 2 % over a wide range of environmental conditions: 10 < O 3 < 1000 ppbv, below detection < NO x < 7 ppbv, and 2 ppmv < H 2 O < 4 % VMR. Both instrument designs are demonstrated to be suitable for EC flux measurements and were able to detect O 3 fluxes with exchange velocities (defined as positive for upward) as slow as - 0.010 ± 0.004 cm s -1 , which is in the lower range of previously reported measurements. Additionally, we present two case studies. In one, the direction of ozone and water vapor fluxes was reversed (vO3 = + 0.134 ± 0.005 cm s -1), suggesting that overhead evaporating clouds could be a strong ozone sink. Further work is needed to better understand the role of clouds as a possibly widespread sink of ozone in the remote marine boundary layer. In the second case study, vO3 values are negative (varying by a factor of 6–10 from - 0.036 ± 0.006 to - 0.003 ± 0.004 cm s -1), while the water vapor fluxes are consistently positive due to evaporation from the ocean surface and spatially homogeneous. This case study demonstrates that the processes governing ozone and water vapor fluxes can become decoupled and illustrates the need to elucidate possible drivers (physical, chemical, or biological) of the variability in ozone exchange velocities on fine spatial scales (∼ 20 km) over remote oceans. [ABSTRACT FROM AUTHOR]

Accurate evaluation of grapevine water use is essential for optimizing water management and maximizing grapevine yield and berry quality in Mediterranean climates. Understanding the water and heat flux dynamics in a vineyard during grapevine berry maturation is of utmost importance. This study focuses on evaluating sensible and latent energy fluxes at the canopy, the soil beneath the canopy, and the interrow areas. The primary objective is to develop a model framework for accurately estimating these energy fluxes, contributing to a better understanding of their behavior during berry ripening. The model's accuracy was assessed by comparing the estimated fluxes with those measured by an eddy-covariance system installed at a reference height of three meters in the experimental vineyard. This validation step was essential to confirm the model's ability to capture the intricate energy flux dynamics of the vineyard, especially during grape maturation. The results revealed a high level of agreement between the observed and estimated fluxes, confirming the model's reliability. This comprehensive evaluation of energy fluxes provides valuable insights for optimizing irrigation strategies. By doing so, this study contributes to improving grape quality, ensuring sustainable water resource use, and ultimately enhancing vineyard productivity in arid and water-scarce regions. [ABSTRACT FROM AUTHOR]

High mountain rainforests are vital in the global energy and carbon cycle. Understanding the exchange of energy and carbon plays an important role in reflecting responses to climate change. In this study, an eddy covariance (EC) measurement system installed in the high Andean Mountains of southern Ecuador was used. As EC measurements are affected by heterogeneous topography and the vegetation height, the main objective was to estimate the effect of the sloped terrain and the forest on the turbulent energy and carbon fluxes considering the energy balance closure (EBC) and the heat storage. The results showed that the performance of the EBC was generally good and estimated it to be 79.5%. This could be improved when the heat storage effect was considered. Based on the variability of the residuals in the diel, modifications in the imbalances were highlighted. Particularly, during daytime, the residuals were largest (56.9 W/m2 on average), with a clear overestimation. At nighttime, mean imbalances were rather weak (6.5 W/m2) and mostly positive while strongest underestimations developed in the transition period to morning hours (down to −100 W/m2). With respect to the Monin–Obukhov stability parameter ((z − d)/L) and the friction velocity (u*), it was revealed that the largest overestimations evolved in weak unstable and very stable conditions associated with large u* values. In contrast, underestimation was related to very unstable conditions. The estimated carbon fluxes were independently modelled with a non-linear regression using a light-response relationship and reached a good performance value (R2 = 0.51). All fluxes were additionally examined in the annual course to estimate whether both the energy and carbon fluxes resembled the microclimatological conditions of the study site. This unique study demonstrated that EC measurements provide valuable insights into land-surface–atmosphere interactions and contribute to our understanding of energy and carbon exchanges. Moreover, the flux data provide an important basis to validate coupled atmosphere ecosystem models. [ABSTRACT FROM AUTHOR]

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The South China Sea is a typical marginal sea characterized by the presence of numerous seamounts. However, the effect of seamounts on the air‐sea CO2 flux has not yet been well studied. In September 2021, the air‐sea CO2 flux was measured directly using eddy covariance (EC), and discrete waterside sampling was conducted. The results indicate that the northern South China Sea is a source of atmospheric CO2. Furthermore, EC measurements show that the seamount emits CO2 at an average rate of 0.34 mmol m−2 hr−1, nearly double that of non‐seamount areas. We suggest that the upwelling around the seamount transports deep water rich in dissolved inorganic carbon to the upper ocean, increasing the partial pressure of CO2 there. In addition, the increase in nutrients caused by the upwelling would increase the concentration of chlorophyll‐a, resulting in a productive area that emits CO2. Plain Language Summary: The South China Sea (SCS) serves as a minor CO2 source, and the air‐sea CO2 flux in its northern region demonstrates challenging spatiotemporal variations. In our investigation, we conducted underway assessments in the northern SCS and validated its emission of CO2, particularly in the vicinity of seamount ocean zones. CO2 emissions may have been intensified by the upward movement of seawater surrounding the seamount region. Key Points: The northern South China Sea emitted CO2 into the atmosphere at a mean rate of 0.28 mmol m−2 hr−1 in September 2021The CO2 flux almost doubled as the seamount was approached, indicating an increase in CO2 emissions near the seamountUpwelling releases high dissolved inorganic carbon, which increases the partial pressure of CO2 on the sea surface around the seamount [ABSTRACT FROM AUTHOR]