Eddy Flux Research Articles

A time-average ocean: Thermal wind and flow spirals

Using a 26-year average of a dynamically consistent ECCO state-estimate, an effort is made to find a few simple descriptive, but quantitative, patterns of properties of the ocean circulation that are near-globally applicable outside the Arctic regions. The conceptual assumption is made that such an average is physically meaningful. Even with a 26-year average, complex spatial variations in the flow field remain, particularly below about 2000 m where the intricate structure of the underlying topography becomes manifest. Nonetheless, certain constructs do describe the great bulk of the ocean. These constructs consist of thermal wind balance (quasi-geostrophy), spiral-like flow behavior in the near-surface boundary layers with orientation analogous to that of an Ekman layer—abruptly changing sign across the equator. In contrast, evidence for beta-spirals is very thin, consistent with the spatially complex meridional and vertical velocities. As expected, integration so as to remove spatial dependence in one coordinate (e.g. zonal) does produce much simplified structures, albeit in the process suppressing diverse dynamical regimes. Predominantly zonal structures persist in the zonal velocity at depth, and are presumed sensitive to the (parameterized) mean eddy fluxes. An unanswered question, and one perhaps unanswerable at the present time, is whether a much longer averaging interval would significantly further simplify the upper-ocean circulation. The abyssal circulation almost everywhere appears dominated by the topography and slopes and whose structure likely would persist in averages of arbitrary duration.

A Beginner's Guide to Eddy Covariance: Methodology and Its Applications to Photosynthesis.

The eddy covariance technique, commonly applied using flux towers, enables the investigation of greenhouse gas (e.g., carbon dioxide, methane, nitrous oxide) and energy (latent and sensible heat) fluxes between the biosphere and the atmosphere. Through measuring carbon fluxes in particular, eddy covariance flux towers can give insight into how ecosystem scale photosynthesis (i.e., gross primary productivity) changes over time in response to climate and management. This chapter is designed to be a beginner's guide to understanding the eddy covariance method and how it can be applied in photosynthesis research. It introduces key concepts and assumptions that apply to the method, what materials are required to set up a flux tower, as well as practical advice for site installation, maintenance, data management, and postprocessing considerations. This chapter also includes examples of what can go wrong, with advice on how to correct these errors if they arise. This chapter has been crafted to help new users design, install, and manage the best towers to suit their research needs and includes additional resources throughout to further guide successful eddy covariance research activities.

Modulation of Equatorial Currents and Tropical Instability Waves During the 2021 Atlantic Niño

AbstractIn the boreal summer of 2021, the equatorial Atlantic experienced the strongest warm event, that is, Atlantic Niño, since the beginning of satellite observations in the 1970s. Such events have far‐reaching impacts on large‐scale wind patterns and rainfall over the surrounding continents. Yet, developing a paradigm of how Atlantic Niño interacts with the upper‐ocean currents and intraseasonal waves remains elusive. Here we show that the equatorial Kelvin wave associated with the onset of the 2021 Atlantic Niño modulated both the background flow and the eddy flux of the equatorial upper‐ocean circulation, causing an extremely weak and delayed tropical instability wave (TIW) season. TIW‐induced variations of sea surface temperature (SST), sea surface salinity, sea surface height, and eddy temperature advection were exceptionally weak during May to July, the climatological peak of TIW activity, but rebounded in August when higher than normal variability was observed. Moored velocity data at 23°W show that during the peak of the 2021 Atlantic Niño from June to August, the Equatorial Undercurrent was deeper and stronger than usual. An anomalously weak eddy momentum flux strongly suppressed barotropic energy conversion north of the equator from May to July, likely contributing to low TIW activity. Reduced baroclinic energy conversion also might have played a role, as the meridional gradient of SST was sharply reduced during the Atlantic Niño. Despite extremely weak TIW velocities, modest intraseasonal variability of chlorophyll‐a (Chl‐a) was observed during the Atlantic Niño, due to pronounced meridional Chl‐a gradients that partly compensated for the weak TIWs.

Improved Modeling of Gross Primary Production and Transpiration of Sugarcane Plantations with Time-Series Landsat and Sentinel-2 Images

Sugarcane croplands account for ~70% of global sugar production and ~60% of global ethanol production. Monitoring and predicting gross primary production (GPP) and transpiration (T) in these fields is crucial to improve crop yield estimation and management. While moderate-spatial-resolution (MSR, hundreds of meters) satellite images have been employed in several models to estimate GPP and T, the potential of high-spatial-resolution (HSR, tens of meters) imagery has been considered in only a few publications, and it is underexplored in sugarcane fields. Our study evaluated the efficacy of MSR and HSR satellite images in predicting daily GPP and T for sugarcane plantations at two sites equipped with eddy flux towers: Louisiana, USA (subtropical climate) and Sao Paulo, Brazil (tropical climate). We employed the Vegetation Photosynthesis Model (VPM) and Vegetation Transpiration Model (VTM) with C4 photosynthesis pathway, integrating vegetation index data derived from satellite images and on-ground weather data, to calculate daily GPP and T. The seasonal dynamics of vegetation indices from both MSR images (MODIS sensor, 500 m) and HSR images (Landsat, 30 m; Sentinel-2, 10 m) tracked well with the GPP seasonality from the EC flux towers. The enhanced vegetation index (EVI) from the HSR images had a stronger correlation with the tower-based GPP. Our findings underscored the potential of HSR imagery for estimating GPP and T in smaller sugarcane plantations.

Long-term eddy modulation affects the meridional asymmetry of the halocline in the Beaufort Gyre

Abstract. Against the background of wind-forcing change along with Arctic sea ice retreat, the mesoscale processes undergoing distinct variation in the Beaufort Gyre (BG) region are increasingly important to oceanic transport and energy cascades, and these changes subsequently put oceanic stratification into a new state. Here, the varying number and strength of eddies in the central Canada Basin (CB) and Chukchi–Beaufort continental slope are obtained based on mooring observations (2003–2018), altimetry measurements (1993–2019), and reanalysis data (1980–2020). In this paper, the variability in the BG halocline, representing the adjustment of stratification in the upper layer, is shown in order to analyse how variability occurs under changing mesoscale processes. We find that over almost the last 2 decades the halocline depth has deepened by ∼ 40 m in the south of the central gyre, while that in the north has deepened by ∼ 70 m according to multiple datasets. Surrounding the central gyre, the asymmetry of the halocline, with much steeper and deeper isopycnals over the southern continental slope, reduced after 2014. In the meantime, eddy activities in the upper layer from the southern margin of the BG to the abyssal plain have been enhanced. Moreover, the convergence of the eddy lateral flux has increased as the halocline structures on either side, which is at least 120 km from the central gyre, have reached a nearly identical and stable regime. It has been clarified that long-term dynamic eddy modulation through eddy fluxes, facilitating the freshwater redistribution, affects the meridional asymmetry of the BG halocline. Our results provide a better understanding of the eddy modulation processes and their influence on the halocline structure.

An axial flux eddy current sensor with perpendicular coils for speed measurement

This paper presents an axial flux eddy current sensor with a compact and simple structure for measuring the rotating speed of iron shafts. The sensor structure is optimized for high sensitivity with a novel configuration of the coils positioned perpendicularly to each other. The sensor comprises two D-shaped excitation coils and two D-shaped pick-up coils in a double-layer structure. A disc-shaped magnetic shield or core shields the coils. Two iron shafts with different material properties are considered. A new cup-shaped configuration of nonmagnetic copper and aluminum caps mounted on iron shafts improves sensitivity and suppresses susceptibility to shaft material properties and airgap variation. 2D and 3D finite element methods are utilized for the performance analysis of the sensor. The measurements are performed at speeds up to ± 3000 rpm and different excitation frequencies from 400 Hz to 4 kHz. The eddy current speed sensor has excellent linearity characteristics with a nonlinearity error of 0.15%. The geometry of the coils is further optimized and improved for maximum sensitivity and compactness. The fault-tolerant capability of the sensor is also evaluated.

On the Contribution of Transient Diabatic Processes to Ocean Heat Transport and Temperature Variability

Abstract Time-varying processes contribute to ocean heat transport and are important to understand for accurate climate modeling. While past studies have quantified time-varying contributions to advective transport, less attention has been given to diabatic processes such as surface forcing and mixing. Using a global eddy-permitting ocean model we quantify the contribution of time-variable processes to meridional and diathermal (warm to cold) heat transport at different time scales using a temporal eddy-mean decomposition performed in the temperature–latitude plane. Time-varying contributions to meridional heat transport occur predominantly at mesoscale eddy-dominated midlatitudes and in the tropics, associated with the seasonal cycle and tropical instability waves. The seasonal cycle is a dominant driver of surface flux– and mixing-driven diathermal heat transports. Nonseasonal (and nondiurnal) processes contribute up to about 10% of the total. We show that transient contributions to diathermal heat transport can be interpreted as sources of Eulerian temperature variance. We thus extend recent work on the drivers of temperature variability by evaluating the role of mixing. Mixing dampens seasonal and diurnal temperature variability, except near the equator where it can be a source of seasonal variability. At mesoscale time scales mixing drives variability within and near the base of the boundary layer, the mechanisms of which are explored using a column model. We suggest that climate models that do not resolve the mesoscale may be missing the rectified heat transport associated with high-frequency diabatic processes, in addition to the adiabatic eddy fluxes that are commonly parameterized. Significance Statement Ocean heat transport plays a key role in determining how the climate responds to changes in forcing. This transport is influenced by a range of processes that vary with time. Previous research has quantified time-varying sources of lateral heat transport, such as mesoscale eddies and overturning circulation cells. However, time-varying “diabatic processes,” such as surface forcing and unresolved turbulent mixing, have received less attention. Here, we quantify these effects using a global ocean model. We find a dominant role for the seasonal cycle in driving diabatic heat transport, but processes on shorter time scales also contribute. Our results suggest that temporal variations in turbulent mixing are an important contributor to heat transport but may not be resolved in coarse-resolution climate models.

Collaborative Use of Sensor Networks and Cyberinfrastructure to Understand Complex Ecosystem Interactions in a Tropical Rainforest: Challenges and Lessons Learned.

Collaborations between ecosystem ecologists and engineers have led to impressive progress in developing complex models of biogeochemical fluxes in response to global climate change. Ecology and engineering iteratively inform and transform each other in these efforts. Nested data streams from local sources, adjacent networks, and remote sensing sources together magnify the capacity of ecosystem ecologists to observe systems in near real-time and address questions at temporal and spatial scales that were previously unobtainable. We describe our research experiences working in a Costa Rican rainforest ecosystem with the challenges presented by constant high humidity, 4300 mm of annual rainfall, flooding, small invertebrates entering the tiniest openings, stinging insects, and venomous snakes. Over the past two decades, we faced multiple challenges and learned from our mistakes to develop a broad program of ecosystem research at multiple levels of integration. This program involved integrated networks of diverse sensors on a series of canopy towers linked to multiple belowground soil sensor arrays that could transport sensor data streams from the forest directly to an off-site location via a fiber optic cable. In our commentary, we highlight three components of our work: (1) the eddy flux measurements using canopy towers; (2) the soil sensor arrays for measuring the spatial and temporal patterns of CO2 and O2 fluxes at the soil-atmosphere interface; and (3) focused investigations of the ecosystem impact of leaf-cutter ants as "ecosystem engineers" on carbon fluxes.

A comparison of moderate and high spatial resolution satellite data for modeling gross primary production and transpiration of native prairie, alfalfa, and winter wheat

Although agroecosystems have a significant potential to offset carbon dioxide (CO2), the amount of CO2 captured can vary significantly depending on management practices. Accurate estimation of gross primary production (GPP) and transpiration (T) of agroecosystems at the field scale are essential for the study of food security and water resource management. To date, the carbon and water fluxes data products for commercial agroecosystems are limited, mostly at the moderate spatial resolution (MSR, hundreds of meters), which cannot be used to assess the temporal dynamics of GPP and T at the field scale. This study used the vegetation photosynthesis model (VPM) and vegetation transpiration model (VTM) to estimate field-level daily GPP (GPPVPM) and T (TVTM), respectively, in native prairie, alfalfa (Medicago sativa L.), and winter wheat (Triticum aestivum L.) in central Oklahoma, USA. We evaluated the reliability and advantages of vegetation indices (enhanced vegetation index, EVI and land surface water index, LSWI) in monitoring the land surface phenology using moderate spatial resolution data from Moderate Resolution Imaging Spectroradiometer (MODIS) and high spatial resolution (HSR, tens of meters) data from Landsat and Sentinel-2. The accuracy of GPPVPM and TVTM estimates at different spatial scales was evaluated using GPP (GPPEC) and evapotranspiration (ETEC) from the eddy flux tower sites, respectively. Results demonstrate the capacity of VPM and VTM to estimate the field-level carbon and water flux dynamics and their responses to weather conditions. The use of HSR vegetation indices helped to address certain challenges faced by MSR indices, especially in capturing the crop phenology in smaller areas with conservation measures or disturbances. The findings highlight the importance of using HSR GPP estimates to reduce uncertainty in quantifying CO2 fluxes for croplands and grasslands. The findings also demonstrate the ability of the models to track field-level vegetation phenology, carbon uptake, and water use in agroecosystems under different management practices.

Spatial and Temporal Variations of Carbon Dioxide Fluxes in Urban Ecosystems of Changsha, China

Understanding the spatial and temporal variations of urban carbon dioxide fluxes (FCO2) and their influencing factors is crucial for solving urban climate problems and promoting the development of low-carbon cities. In this study, the carbon dioxide flux (FCO2) in Changsha City, China, was analyzed using the eddy covariance technique and flux footprint model. The results showed that the extent of the flux footprint within the observation site was mostly limited to 500 m. Diurnal variation of FCO2 showed a regular pattern influenced by plant photosynthesis and traffic flow. Meanwhile, photosynthesis was directly regulated by photosynthetically active radiation and indirectly regulated by air temperature and water vapor pressure differences. The average value of FCO2 was lower during the daytime than at night, indicating the high vegetation cover (43.5%) in the study area. In addition, there were spatial characteristics of FCO2 in each wind direction due to different surface land use in the study area. Notably, a decreasing trend in carbon dioxide content was observed after the area covered by vegetation was 1.8 times the area of buildings and major roads combined. These findings guide climate management, urban planning, and sustainable development toward a low-carbon society.

Profile constraint in toroidal plasmas and methodologies to break leading to transport barrier

Internal transport barriers (ITBs) observed in magnetically confined toroidal plasmas are promising for achieving high-performance burning plasmas, which are established from low-confinement L-mode plasmas dominated by anomalous transport exhibiting strong profile constraints. We studied the origin causing such L-mode plasmas using flux-driven gyro-kinetic based global toroidal simulations covering from core to edge. The simulations are incorporated with real space based statistical probability density function (PDF) approach, which directly measures the heat flux eddy distribution across the entire torus to identify the non-diffusive nature of turbulent transport with different spatio-temporal scales, such as micro-scale avalanches, macro-scale bursts, meso-scale E × B shear layers, etc., as the origin causing the constraints. Based on studies of such L-mode plasmas, we present a methodology to overcome such constraints and demonstrate ITB formations by the control of quasi-stationary global radial E × B shear through the toroidal plasma rotation driven by either externally using momentum injection and intrinsically using both ions and electron simultaneous heating.

Seasonal variations and drivers of energy fluxes and partitioning along an aridity gradient in temperate grasslands of Northern China

Surface energy exchange is vital because it affects microclimate, water cycle and biogeochemical processes in the canopy-atmosphere interface. In this study, seasonal variations and regulators of energy fluxes and partitioning were investigated based on a long-term eddy flux observation dataset (12 towers, 82 site-years in total) along an aridity gradient in temperate grasslands of Northern China. Our results showed that the net radiation (Rn) and all energy components, including latent heat (LE), sensible heat (H) and ground heat (G0) fluxes, presented unimodal seasonal patterns across different grassland types, with Rn and LE peaked in the middle growing season but H and G0 at the beginning of the growing season. The energy partitioning shifted from the H-dominated to the LE-dominated period accompanied vegetation phenological development, thus a U-shaped seasonal pattern of Bowen ratio (β, H/LE) was observed. Prolonged LE-dominated period and great peak of LE flux enhanced LE/Rn proportion and decreased β from desert steppes to typical steppes and meadow steppes. Climate and vegetation factors co-regulated the seasonal patterns of energy fluxes and partitioning, with enhanced effects of LAI and canopy surface conductance (gc) from desert steppes to typical and meadow steppes, but a reverse pattern of land-atmosphere coupling via vegetation physiological regulation. Meanwhile, enhanced sensitivity of β in response to variations of climate and vegetation factors was also observed with increasing aridity. Our founding highlighted the role of vegetation especially physiological regulation in determining the seasonal patterns of energy fluxes and partitioning in water-limited grasslands. Whereas, the great sensitivity of energy partitioning to vegetation changing with increasing aridity also emphasized that it is vital to pay attention to the response of energy exchange in the desert steppes to the greening trend in Northern China under future climate scenarios.

Lumped model for the calculation of harmonic eddy current losses in permanent magnets for homogeneous flux distributions considering eddy current reaction flux

This is the first of a series of papers on novel methods for the calculation of eddy current losses in permanent magnets (PMs) and the shortcomings of previously conducted analyses. Eddy current losses in PMs and their mitigation are significant factors when designing inverter-fed electric drives. Especially with the need for drives with high power density, a trend toward increased rotational speeds and, therefore, higher fundamental frequencies and inverter switching frequencies are observable. Higher harmonic frequency components of concentrated windings and fractional slot windings are widely taken into account when designing rare sintered earth magnets for permanent magnet synchronous machines (PMSMs). However, inverter-related losses are rarely simulated in Finite Element Method (FEM) co-simulations and can contribute as a major factor to the power losses in PMSMs. In the worst case, this neglection can lead to the thermal demagnetization of the permanent magnets. Segmentation provides an effective measure to limit eddy current losses. However, not every kind of segmentation proves effective in a drive application. Depending on the frequency behavior of the magnetic flux in a permanent magnet, segmentation can increase eddy current losses within the magnet compared to a non-segmented magnet. This behavior is due to the reaction to the flux caused by the eddy currents within the magnet. The reaction of the eddy currents is often neglected [1, 2], and, in other cases, the vicinity of ferromagnetic material is neglected in analytical calculations [3] but proves crucial for the exact calculation of higher frequency losses [4, 5]. In this paper, an analytical solution to calculate harmonic eddy current losses in permanent magnets, including the reaction flux with homogeneous excitation, is given.

Combining local model calibration with the emergent constraint approach to reduce uncertainty in the tropical land carbon cycle feedback

Abstract. The role of the land carbon cycle in climate change remains highly uncertain. A key source of the projection spread is related to the assumed response of photosynthesis to warming, especially in the tropics. The optimum temperature for photosynthesis determines whether warming positively or negatively impacts photosynthesis, thereby amplifying or suppressing CO2 fertilisation of photosynthesis under CO2-induced global warming. Land carbon cycle models have been extensively calibrated against local eddy flux measurements, but this has not previously been clearly translated into a reduced uncertainty in terms of how the tropical land carbon sink will respond to warming. Using a previous parameter perturbation ensemble carried out with version 3 of the Hadley Centre coupled climate–carbon cycle model (HadCM3C), we identify an emergent relationship between the optimal temperature for photosynthesis, which is especially relevant in tropical forests, and the projected amount of atmospheric CO2 at the end of the century. We combine this with a constraint on the optimum temperature for photosynthesis, derived from eddy covariance measurements using the adjoint of the Joint UK Land Environment Simulator (JULES) land surface model. Taken together, the emergent relationship from the coupled model and the constraint on the optimum temperature for photosynthesis define an emergent constraint on future atmospheric CO2 in the HadCM3C coupled climate–carbon cycle under a common emissions scenario (A1B). The emergent constraint sharpens the probability density of simulated CO2 change (2100–1900) and moves its peak to a lower value of 497 ± 91 compared to 607 ± 128 ppmv (parts per million by volume) when using the equal-weight prior. Although this result is likely to be model and scenario dependent, it demonstrates the potential of combining the large-scale emergent constraint approach with a parameter estimation using detailed local measurements.

On the interpretation of changes in the subtropical oxygen minimum zone volume off Chile during two La Niña events (2001 and 2007)

Oxygen minimum zones (OMZs) are extended oceanic regions for which dissolved oxygen concentration is extremely low. They are suspected to be expanding in response to global warming. However, currently, the mechanisms by which OMZ varies in response to climate variability are still uncertain. Here, the variability of the subtropical OMZ off central Chile of a regional coupled physical–biogeochemical regional model simulation was analyzed for the period 2000–2008, noting that its fluctuations were significant despite the relatively weak amplitude of the El Niño/Southern Oscillation (ENSO). In particular, the interannual variability in the OMZ volume (OMZVOL, defined as the volume with dissolved oxygen concentration (DO) ≤ 45μM) was approximately 38% larger than that of the seasonal cycle, with maximum and minimum anomalies of OMZVOL taking place during two cold La Niña (LN) years (2001 and 2007). The model analyses further reveal that these anomalies resulted from a combined effect of changes in (1) the oxygen-poor waters poleward transport by the Peru–Chile undercurrent (PCUC), (2) the intensity of quasi-zonal jets influencing the transport of water to and from the OMZ, and (3) the zonal DO transport related to mesoscale eddy activity. Specifically, the interannual variability of the PCUC modulated primarily the DO contents of the OMZ core [(DO) ≤ 20μM] and secondarily the OMZVOL, while cross-shore DO transport by the zonal jets and the eddy fluxes played a major role in ventilating and shaping the offshore extent of the OMZ. When the OMZVOL was maximum (minimum), the PCUC transport was slightly increased (reduced), which was associated with a reduction (increase) in the ventilation of the OMZ through negative (positive) anomalies of zonal advection and DO eddy fluxes. Our results demonstrate that significant natural interannual variability in the subtropical OMZ off Chile originates from the interplay between oceanic equatorial teleconnection (PCUC transport) and local non-linear dynamics (the zonal jets and mesoscale eddies).

Combination of Vegetation Indices and SIF Can Better Track Phenological Metrics and Gross Primary Production

AbstractAccurate phenological extraction is important for estimating carbon uptake in terrestrial ecosystems under climate change. The emergence of remotely sensed vegetation indices (VIs) and solar‐induced chlorophyll fluorescence (SIF) provides multiple approaches for extracting land surface phenology. However, there is lacking studies to track phenological metrics via multiple VIs and SIF. Therefore, the advantage of combining VIs and SIF to estimate more accurate phenology requires exploration. In this study, we combined the advantages of the normalized difference, enhanced, green‐red, near‐infrared reflectance vegetation indices from MCD43A4 data set, and SIF from CSIF data set to estimate hybrid phenology at 20 eddy flux sites in North America. Results showed that the hybrid phenology derived from the best‐performing start (SOS) and end (EOS) of the growing season among multiple VIs and SIF for each plant functional type and site were both more consistent with those derived from gross primary production (GPP). Specifically, the R2 of hybrid phenology increased by 0.11–0.4 (0.04–0.4) for SOS, 0.01–0.24 (0.09–0.22) for EOS, 0.01–0.7 (0.05–0.34) for the length of the growing season (LOS) based on Gaussian (logistic) method. Moreover, hybrid phenology can improve the explanation of the seasonal and annual variations in GPP. The explanatory power of hybrid phenology for GPP variations increased by 0.05–0.15 (0.02–0.23) for SOS, 0–0.36 (0.11–0.27) for EOS, 0.01–0.51 (0.03–0.4) for LOS, 0.04–0.18 (0.04–0.16) for LOS seasonal GPP maximum based on Gaussian (logistic) method. These findings highlight the potential of combining high‐spatiotemporal structural and coarse‐spatiotemporal physiological vegetation indicators in tracking phenology and GPP.

A Multifaceted Isoneutral Eddy Transport Diagnostic Framework and Its Application in the Southern Ocean

AbstractWe propose an isoneutral eddy transport diagnostic framework and apply it in the Southern Ocean to analyze eddy potential vorticity (PV) transport dynamics. We leverage a thickness‐weighted spatiotemporal scale separation to define the generalized eddy flux. A local sampling method is employed and validated to estimate the transport tensor. We introduce Leonard's decomposition in Large Eddy Simulations (LES) to split the process into the Reynolds and non‐Reynolds parts. We also use the stationary‐transient decomposition. The non‐Reynolds term and the stationary effect contribute significantly to the transport properties. The Reynolds and transient parts have distinctions, that show oceanic mesoscale dynamics are not synergistic in time and spatial scales. We investigate the spatial scale dependence of each part and find that the transient and stationary components of the Reynolds (non‐Reynolds) term have consistent (dissimilar) scale dependence. The scale dependence of the generalized eddy flux and the transport eigenvalues is controlled by the non‐Reynolds term. We further investigate the eigenvalues in terms of the potential enstrophy and anisotropy. The potential enstrophy in the Southern Ocean holistically has a forward cascade on the researched scales. The Reynolds and transient effects efficiently promote the forward enstrophy cascade. The non‐Reynolds and stationary effects stimulate drastically anisotropic eddy transport. The PV gradient barrier mechanism dominates the drastic anisotropic case. When the anisotropy is weak, a special anisotropic case with a locally balanced potential enstrophy budget overwhelms the case of real isotropy. We also introduce several LES concepts, hoping to enlighten any potential ocean modeling and parameterization.

A dataset of carbon and water fluxes of the typical grasslands in Duolun County, Inner Mongolia during 2006-2015

Grassland is an important terrestrial ecosystem for the exchange of mass and energy between land and atmosphere, playing an important role in global carbon cycle. However, the direction and size of its carbon sink are still in dispute. The eddy covariance technique can be sued to continuously determine ecosystem-level carbon, water and energy exchanges between vegetation and atmosphere. The long-term observations of carbon and water fluxes can help quantify the carbon sequestration capability of grassland ecosystems and its response to climate change. This dataset consists of two half-hourly data files, including the carbon, water and heat fluxes data file and the meteorological variables data file. All of the flux data were processed according to the flux data processing procedure specified by ChinaFLUX. The observational quality of this dataset is good, with a complete data observation integrity of over 95% throughout the year and a high energy balance ratio (1.04 ± 0.07). This decadal flux dataset from 2006 to 2015 provides a high-quality and continuous long-term eddy flux observation data valuable for the research of diurnal dynamics, seasonal and interannual variations of carbon and water fluxes, which is significant for evaluating the role of China’s temperate typical grasslands in regional and global carbon and water cycles.

A dataset of carbon and water fluxes of mowing grasslands in Xilinhot, Inner Mongolia during 2006-2015

Grassland is one of the most widely distributed vegetation types around the world, and play an important role in the global carbon and water cycle. As a common type of land use in Inner Mongolia, mowing has profoundly affected plant growth and ecosystem functioning of grasslands. However, the influences of mowing on the carbon and water cycle processes in grassland ecosystems are still unclear. A lack of long-term and continuous observation flux data is one of the important reasons. According to the flux data processing procedure by ChinaFLUX, we collected the carbon and water fluxes and conventional meteorological data of typical grassland ecosystems in Xilinhot, Inner Mongolia from 2006 to 2015. This dataset provides a high-quality and continuous long-term eddy flux observation valuable for the research of temporal variations and mechanisms of carbon and water fluxes. Meanwhile, it is important for optimizing grassland management practices and evaluating the role of grassland in regional and global carbon and water cycles.

The Impact of Fine-Scale Currents on Biogeochemical Cycles in a Changing Ocean.

Fine-scale currents, O(1-100 km, days-months), are actively involved in the transport and transformation of biogeochemical tracers in the ocean. However, their overall impact on large-scale biogeochemical cycling on the timescale of years remains poorly understood due to the multiscale nature of the problem. Here, we summarize these impacts and critically review current estimates. We examine how eddy fluxes and upscale connections enter into the large-scale balance of biogeochemical tracers. We show that the overall contribution of eddy fluxes to primary production and carbon export may not be as large as it is for oxygen ventilation. We highlight the importance of fine scales to low-frequency natural variability through upscale connections and show that they may also buffer the negative effects of climate change on the functioning of biogeochemical cycles. Significant interdisciplinary efforts are needed to properly account for the cross-scale effects of fine scales on biogeochemical cycles in climate projections.