Horizontal Flux Research Articles

Dynamics of CO2, CH4, and N2O in Ria Formosa coastal lagoon (southwestern Iberia) and export to the Gulf of Cadiz

A first characterization of greenhouse gases had been carried out to study their role and impact in a productive transitional coastal system of the southern Portugal – Ria Formosa lagoon. To this purpose, the partial pressure of CO2 (pCO2) and the concentration of dissolved CH4 and N2O have been measured. Two surveys were carried out during 2020, at low tide under typical conditions of Spring (March) and end of Summer (October). The samplings sites were distributed along the costal lagoon covering: i) inner areas with strong human impact (influence of different flows of treated wastewater discharges); and ii) main channels in connection with the main inlets to study the exchanges with the ocean. In general, the highest values of the three greenhouse gases were found at the inner studied areas, especially affected by the disposal of treated effluents from wastewater treatment plans, in October. The mean water - atmosphere fluxes of the CO2, CH4 and N2O are positive, showing that the study area acts as a source of these gases to the atmosphere. On the other hand, it was calculated a rough estimation of the three gases globally exported from Ria Formosa to the ocean, through the main six inlets to evaluate the magnitude of the supply of these gases from Ria Formosa to the adjacent ocean. The mean CO2, CH4 and N2O horizontal water fluxes exported from all the inlets of Ria Formosa to the Gulf of Cadiz for both seasons, during low water, are 8.7 ± 3.9 mmol m−2 s−1, 8.0 ± 3.5 μmol m−2 s−1 and 3.2 ± 1.5 μmol m−2 s−1, which corresponds to a mass transport through the inlets section of 0.7 ± 0.7 kg s−1, 0.2 ± 0.2 g s−1 and 0.2 ± 0.3 g s−1 respectively. From these estimates, as expected, the higher mass transport was found at the larger and deeper inlets (Faro-Olhão and Armona).

Ammonia volatilization measured with the IHF method in a rainfed arable crop: Evaluation of tillage intensity and the number of experimental replicates

Ammonia (NH3) volatilization losses have severe impacts on human health, climate change and natural environments, but the effect of tillage intensity on these emissions has been barely evaluated in field conditions, particularly using micrometeorological methods, which require large surfaces. In this context, a field experiment in a barley (Hordeum vulgare L.) crop was set up in central Spain, in which NH3 volatilization losses from non-tilled plots (NT) were compared with those from conventionally tilled (T) plots, using the integrated horizontal flux (IHF) technique with three replicates. Ancillary soil and meteorological measurements were taken to explain NH3 fluxes, and the effect of the number of replicates on the results was statistically addressed. The highest NH3 emissions were obtained in NT plots after both basal (40 kg N ha−1 applied as urea) and top-dressing (120 kg N ha−1 applied as urea) fertilization events, while NH3 emission factors were higher after basal fertilization, in comparison with top-dressing application. Considering the sum of both periods, NT significantly increased NH3 emissions by 63 % with respect to T. We observed a notable influence of the number of replicates, since only two of the nine combinations of two replicates led to rejecting the null hypotheses. No tillage requires the optimized management of N (timing, rate and particularly source) to abate the potential side effects regarding NH3 volatilization, while the use of robust measurement methods (e.g. IHF) should be implemented with enough replicates to increase the precision in estimating differences.

Horizontal flux of ozone in the planetary boundary layer in Hong Kong using wind LiDAR measurements

While the crucial roles of ozone (O3) transport in the planetary boundary layer (PBL) have been acknowledged for some time, there is currently limited knowledge about this aspect primarily due to the limited availability of measurements to determine the characteristics of the PBL. In this study, measurements from a wind Light Detection and Ranging (LiDAR) system were taken to monitor vertical profile of wind pattern at an urban site in Hong Kong in September 2022, a period when the city was frequently impacted by tropical cyclones and experienced severe O3 pollution levels. The PBL height was identified based on the vertical profile of wind speed shear. By combining information on the PBL height, vertical wind profile, and O3 concentration, we performed a cross-sectional analysis to explore the total horizontal flux (THF) of O3 across the PBL in Hong Kong. Throughout the entire study month, the THF of O3 exhibited a predominant easterly component. However, during the O3 pollution episodes, the THF of O3 exhibited a predominant westerly component, indicating an increased regional transport from Greater Bay Area (GBA). The westerly winds between 240° and 300° contributed 61.2% to the total flux of O3 in the PBL during these episodes. In addition, clockwise veering winds were observed from the ground to the top of the PBL, which can be attributed to the Ekman spiral. As a result, during the O3 pollution episodes, the wind with the peak O3 flux shifted from westerly to northwesterly as the height increased in the PBL. The northwesterly THF of O3 between 290° and 300° reached its peak at 600 m above ground level during these episodes. These findings enhance our understanding of the 3D pollutant transports for both long-term averages and short-term pollution episodes in the GBA and Hong Kong.

Tropical tropospheric warming pattern explained by shifts in convective heating in the Matsuno–Gill model

AbstractHorizontal temperature gradients in the tropical free troposphere are fairly weak, and tropical tropospheric warming is usually treated as uniform. However, we show here that projected tropospheric warming is spatially inhomogeneous in Coupled Model Intercomparison Project Phase 6 models, as well as in a storm‐resolving climate model. We relate the upper tropospheric warming pattern to sea‐surface temperature changes that reorganise convection and thereby cause spatial shifts in convective heating. Using the classical Gill model for tropical circulation and forcing it with precipitation changes that arise due to greenhouse gas warming, we can understand and reproduce the different warming patterns simulated by a range of global climate models. Forcing the Gill model with precipitation changes from a certain region demonstrates how local tropospheric temperature changes depend on local changes in convective heating. Close to the Equator, anomalous geopotential gradients are balanced by the dissipation term in the Gill model. The optimal dissipation time‐scale to reproduce the warming pattern varies depending on the Coupled Model Intercomparison Project Phase 6 model, and is between 1 and 10 days. We demonstrate that horizontal advection and eddy momentum fluxes have large enough equivalent dissipation time‐scales to balance the gradients in geopotential and thereby shape the warming pattern. Though climate models show a large spread in projections of tropical sea‐surface temperature and precipitation changes, our results imply that, once these predictions improve, our confidence in the predicted upper tropospheric warming pattern should also increase.

Organic Matter Export Rates and the Pathways of Nutrient Supply in the Ocean

AbstractMultiyear estimates of organic matter (OM) export based primarily on oxygen and dissolved inorganic carbon surface layer budgets applied basin‐wide for the Pacific, Atlantic, and S. Indian Oceans yield an inter‐basin range from 1 to 3 mol C/m2/yr with a global mean of 2.0 mol C/m2/yr (8.5 Gt C/yr). OM export rates per area in the Pacific and Atlantic oceans are twice than that in the Indian Ocean. The supply of nutrients from the Southern Ocean can potentially support ∼70% of the observed OM export in the ocean based on observed surface current velocities and PO4 distributions. Horizontal flux of PO4 and dissolved organic phosphorous in the surface layer can support ∼50%, 20%, and 15% of observed OM export in the Pacific, S. Indian and Atlantic oceans, respectively, with the remainder being supplied vertically from the subsurface. Potential utilization of unused surface PO4 in the subtropical gyre yields ∼0.1 mol C/m2/yr increase in OM export in the Pacific and Atlantic oceans but a ∼0.8 mol C/m2/yr increase in the S. Indian ocean suggesting that stronger nutrient limitation contributes to lower export rates observed in the Indian ocean.

High-Resolving modeling of the surface semidiurnal M<sub>2</sub> tide in the East-Siberian Sea

In the framework of a high-resolving version of the 3D finite-element hydrostatic model QUODDY-4 we have simulated the fields of dynamic characteristics (amplitudes and phases of tidal elevations and barotropic tidal velocity ellipses) corresponding to the surface semidiurnal M2 tide in the no-ice East-Siberian Sea. It is shown that the obtained tidal chart has a complex structure, determined by 4 real amphidromes of left rotation which are induced by interference of counter-coming progressive Poincare waves in the southern part of the sea, 1 fake amphidrome with the center upon the Novaya Sibir Isl. and 4 small-scale amphidromes caused by interference of counter-coming Kelvin waves, from which 3 are formed in the narrow straits in the region of Bolshoy and Maly Lyahovsky Isls. and 1 near the entrance of the Chaunskaya Guba. Tidal amplitudes in the vicinity of the Novaya Sibir Isl. achieve 20–30 cm, whereas in the remaining part of the sea they are comparatively small and do not exceed 5–10 cm. Accordingly, the field of barotropic tidal velocities in the north-western part of the sea basically consists of high values (they are tens of cm/s), but in the other parts of the sea barotropic velocities are small (lower then 10 cm/s) and their field has a band structure. The fields of the averaged (over a tidal cycle) integrated in depth constituents of the barotropic tidal energy budget (namely, the barotropic tidal energy density, the advective transport and the horizontal wave flux per unit length of this energy and the rate of its dissipation due to the bottom friction) are presented. Also, a comparison of predicted tidal elevations with the mareographic level measurement data states that an estimate of their agreement may be considered as satisfactory taking into account that the tidal amplitudes in the sea as a whole are small.

Sensitivity of Mountain Wave Drag Estimates on Separation Methods and Proposed Improvements

Abstract Internal gravity waves (GWs) are ubiquitous in the atmosphere, making significant contributions to the mesoscale motions. Since the majority of their spectrum is unresolved in global circulation models, their effects need to be parameterized. In recent decades GWs have been increasingly studied in high-resolution simulations, which, unlike direct observations, allow us to explore full spatiotemporal variations of the resolved wave field. In our study we analyze and refine a traditional method for GW analysis in a high-resolution simulation on a regional domain around the Drake Passage. We show that GW momentum drag estimates based on the Gaussian high-pass filter method applied to separate GW perturbations from the background are sensitive to the choice of a cutoff parameter. The impact of the cutoff parameter is higher for horizontal fluxes of horizontal momentum, which indicates higher sensitivity for horizontally propagating waves. Two modified methods, which choose the parameter value from spectral information, are proposed. The dynamically determined cutoff is mostly higher than the traditional cutoff values around 500 km, leading to larger GW fluxes and drag, and varies with time and altitude. The differences between the traditional and the modified methods are especially pronounced during events with significant drag contributions from horizontal momentum fluxes. Significance Statement In this study, we highlight that the analysis of gravity wave activity from high-resolution datasets is a complex task with a pronounced sensitivity to the methodology, and we propose modified versions of a classical statistical gravity wave detection method enhanced by the spectral information. Although no optimal methodology exists to date, we show that the modified methods improve the accuracy of the gravity wave activity estimates, especially when oblique propagation plays a role.

Observed Dawn and Twilight Pressure Sudden Peaks in the Global Martian Surface and Possible Relationships With Atmospheric Tides

AbstractMultilanders and rovers on Mars have observed the diurnal variation in surface pressure with two significant peaks at dawn and twilight (around 8:00 a.m. and 8:00 p.m.) at different locations near the equinox. The Dynamic Meteorology Laboratory Martian General Circulation Model (GCM) simulates similar phase‐locked surface pressure fluctuations. The surface pressure peaks at a certain local time occur at most mid‐ and low‐latitude locations, as GCM simulations suggested. By reconstructing the surface pressure variation from the horizontal mass flux obtained in the GCM simulations, we find that the pressure fluctuations are due to the diurnal variation in the horizontal wind divergence and convergence in the Martian tropical troposphere. The diurnal variation in surface pressure corresponds to the migrating diurnal tidal wind, with the enhanced convergence due to the overlap of the 4‐hr and 6‐hr tides before 8:00 a.m. and 8:00 p.m. Although the amplitudes of the 4‐hr and 6‐hr tides are smaller than those of diurnal tides, the convergences/divergences caused by the 4‐hr/6‐hr tidal winds at different altitudes are in phase and added up together to create a mass flux comparable to that induced by diurnal/semidiurnal components and lead to rapid pressure fluctuations. The 4‐hr/6‐hr tidal amplitudes and the two pressure peaks at dawn and twilight are the strongest near the equinox.

3D-гидродинамическое моделирование потоков СО2 и CH4 в приземном слое атмосферы (На примере лесного участка «Рошни-Чу»)

Introduction: The aim of this study is to evaluate the spatial variability of carbon dioxide (CO2) and methane (CH4) fluxes at the reference site "Roshni-Chu" of the carbon measurement megasites of the Chechen Republic using modeling experiments with in-situ measurements and remote sensing data. Methods and materials: Measurements of carbon dioxide (CO2) and methane (CH4) fluxes at the soil surface at the "Roshni Chu" forest site in the mountainous forest region of the Chechen Republic were conducted using a dynamic closed chamber connected to a portable gas analyzer G4301 (Picarro, USA). Leaf photosynthesis and respiration parameters of the main edificators and sub-edificators of premontane broadleaf forests were measured using the portable photosynthetic system LI-6800 (LI-COR, USA). Landsat 8 data were used to produce digital maps of surface topography and Nor-malized Difference Vegetation Index (NDVI). A 3D process-based atmospheric transfer model was chosen to describe the spatial variability of carbon dioxide and methane fluxes within the atmospheric boundary layer. The model is based on a one-and-a-half closure scheme for the Navier-Stokes and continuity equations, solved using Reynolds averaging and the Bussiness conjecture. Results: It was shown that a three-dimensional (3D) mathematical transfer models based on the solution of the equations of thermo-hydrodynamics are among the most effective methods for estimating vertical and horizontal fluxes of greenhouse gases in the atmosphere, taking into account the heterogeneous vegetation structure and surface topography. Based on the modeling results, maps of spatial distribution of turbulent exchange coefficient and horizontal wind speed at 5 m height, and maps of spatial distribution of CO2 and CH4 methane fluxes at 5, 25 and 50 m height were created. It was revealed that the "Roshni-Chu" forest area serves as a CO2 sink from the atmosphere under warm sunny weather in summer. The greatest uptake is detected near the local elevations. The fluxes of CH4 are almost negative, the lowest values of CH4 uptake are connected with uneven topography and are observed in small depressions between the hills. Conclusions: Based on the study of the wind field and the greenhouse gas fluxes at the carbon experimental site "Roshni-Chu" in the Chechen Republic, a significant spatial heterogeneity of the vertical CO2 and CH4 fluxes was revealed. The model approach, together with field measurements and remote sensing data, can be very effective for assessing the spatial heterogeneity of greenhouse gas fluxes at sites with non-uniform topography and vegetation. The method of modeling the spatial distribution of CO2 and CH4 fluxes within the atmospheric boundary layer can be used in different forest regions of the North Caucasus to describe the regional greenhouse gas balance.

Effects of geomorphic-induced turbulence on horizontal mixing in the coastal lagoon Xiaohai in China

Geomorphic conditions and the resulting turbulence are significant factors that influence coastal lagoonal environments. In this study, a shallow-water hydrodynamic transport model was employed to investigate turbulence related to geomorphic features in a large shallow lagoon (Xiaohai Lagoon) in China and to explore the effects these features have on horizontal mixing and the dissipation of tidal energy within the lagoon. At various tidal stages, the vorticity distribution revealed the presence of large-scale turbulent structures associated with the local geomorphic features found in the downstream part of Xiaohai Lagoon, which enhanced flow shear in the affected area and governed local mixing. Increased tidal range enhanced the horizontal mixing flux in the upstream part of the lagoon during spring-neap cycles. In contrast, the mixing flux in the downstream region declined during spring tides and increased during neap tides due to phase differences between tidal flow processes and tracer concentration. In addition, tidal energy dissipation was most concentrated in the vicinity of the local geomorphic features. The rate of dissipation from the inlet to the upstream end of the deep groove accounted for 99.6% of the total in Xiaohai Lagoon, resulting in a loss of 72% of the tidal range in the upstream region, which substantially limited the upstream tidal prism and water mixing. This study suggests that turbulent mixing and energy dissipation associated with local geomorphic features are important mechanisms governing water exchange and environmental heterogeneity in lagoons and should be considered when formulating management and optimization strategies for coastal lagoons.

A contrasting seasonality of wind erosivity and wind erosion between Central and Western Sahel

Wind erosion is a major phenomenon in the Sahel, and can affect soil fertility. Studies of Sahelian aeolian erosion or erosivity are scarce and have been mainly focused on the Central Sahel. Since February 2020, the number of saltating particles and the horizontal flux of aeolian sediment were monitored in Bambey (Senegal) in combination with long-term 5-minutes wind measurements (2014–2021). These datasets enabled to assess the consistency of wind erosion and wind erosivity estimates, and thus to further analyze wind erosivity over pluriannual periods, as wind speed time-series are available over longer terms than horizontal aeolian flux. As a result, the seasonality of wind erosivity largely differs between Western and Central Sahel. In Western Sahel, wind erosivity is related to medium wind speeds during the dry season, while in Central Sahel it is mostly due to high wind speeds occurring at the monsoon onset. Additionally, horizontal flux of aeolian sediments during the dry season are of the same order in Senegal as in Western Niger, but lower than in Eastern Niger. Horizontal flux of aeolian sediments during the rainy season are lower in Senegal than in Western Niger and Eastern Niger. Altogether, annual aeolian flux thus appears significantly lower in Western than in Central Sahel, and mostly related to the dry season.

Representing Eddy Diffusion in the Surface Boundary Layer of Ocean Models With General Vertical Coordinates

AbstractThe mixing of tracers by mesoscale eddies, parameterized in many ocean general circulation models (OGCMs) as a diffusive‐advective process, contributes significantly to the distribution of tracers in the ocean. In the ocean interior, diffusive contribution occurs mostly along the direction parallel to local neutral density surfaces. However, near the surface of the ocean, small‐scale turbulence and the presence of the boundary itself break this constraint and the mesoscale transport occurs mostly along a plane parallel to the ocean surface (horizontal). Although this process is easily represented in OGCMs with geopotential vertical coordinates, the representation is more challenging in OGCMs that use a general vertical coordinate, where surfaces can be tilted with respect to the horizontal. We propose a method for representing the diffusive horizontal mesoscale fluxes within the surface boundary layer of general vertical coordinate OGCMs. The method relies on regridding/remapping techniques to represent tracers in a geopotential grid. Horizontal fluxes are calculated on this grid and then remapped back to the native grid, where fluxes are applied. The algorithm is implemented in an ocean model and tested in idealized and realistic settings. Horizontal diffusion can account for up to 10% of the total northward heat transport in the Southern Ocean and Western boundary current regions of the Northern Hemisphere. It also reduces the vertical stratification of the upper ocean, which results in an overall deepening of the surface boundary layer depth. Finally, enabling horizontal diffusion leads to meaningful reductions in the near‐surface global bias of potential temperature and salinity.

Investigation of non-uniform characteristics in a 300 MWth circulating fluidized bed with different coal feeding modes

Circulating fluidized bed (CFB) has been practised in many engineering fields, but the non-uniform characteristics deteriorate combustion performance and system control. In this study, the improvement of external-loop and in-furnace non-uniformity of a 300 MWth industrial-scale CFB with multiple cyclones by a dual-side coal feeding mode was numerically quantified. The results show that the pressure is non-uniformly distributed among three external loops, where the pressure in the middle loop seal is lower than that in the corner loop seals by 4.5 %. The pressure gradient positively correlates with the solid holdup. As compared with the traditional single-side coal feeding mode, the dual-side coal feeding mode: (i) promotes the final mixing degree by 11.15 %; (ii) extends the residence time of coal particles by 10.3 %; (iii) reduces the magnitude and fluctuation of the horizontal solid flux by 28.5 % and 77%, respectively; (iv) narrows the temperature range and reduces the mean temperature by 7 °C; (v) enhances the combustion of coal particles by consuming more O2; (vi) decreases the concentrations of SO2 and NO by 3 % and 5 %, respectively. The present study shows the superiority of the dual-side coal feeding mode to the traditional single-side coal feeding mode in the optimization of CFBs in practical industrial processes.

Multi-point in situ measurements of turbulent flow in a wind turbine wake and inflow with a fleet of uncrewed aerial systems

Abstract. The demand on wind energy for power generation will increase significantly in the next decade due to the transformation towards renewable energy production. In order to optimize the power generation of a wind farm, it is crucial to understand the flow in the wind turbine wake. The flow in the near wake close to downstream of the wind turbine (WT) is complex and highly three-dimensional. In the present study, for the first time, the SWUF-3D (Simultaneous Wind measurement with Unmanned Flight Systems in 3D) fleet of multirotor UASs (uncrewed aerial systems) is deployed for field measurements on an operating 2 MW WT in complex terrain. The UAS fleet has the potential to fill the meteorological gap of observations in the near wake with high-temporal- and high-spatial-resolution wind vector measurements plus temperature, humidity and pressure. During the experiment, the flow up- and downstream of the WT is measured simultaneously. Various flight patterns are used to investigate the near wake of the WT. The velocity deficit and the turbulence profile at different downstream distances are measured by distributed UASs which are aligned perpendicular to the flow in the near wake. The results show the expected double-Gaussian shape in the near wake under nearly stable atmospheric conditions. However, measurements in unstable atmospheric conditions with high turbulence intensity levels lead to single-Gaussian-like profiles at equal downstream distances (<1 D). Additionally, horizontal momentum fluxes and turbulence spectra are analyzed. The turbulence spectra of the wind measurement at the edge of the wake could reveal that tip vortices can be observed with the UASs.

Three-Dimensional Lattice Structure to Reduce Parasitic Inductance for WBG Power Semiconductor-Based Converters

Wide bandgap (WBG) power semiconductors can achieve high efficiency and power density due to their low on-resistance and fast switching speeds. However, the fast-switching speed induces voltage to the parasitic inductance in the circuit, causing a significant overshoot in the drain-source voltage of the devices and the ringing of the drain current due to resonance with the parasitic capacitance. Thus, minimizing parasitic inductance is necessary for driving WBG power semiconductors in a stable manner. This paper proposes a three-dimensional lattice structure that reduces parasitic inductance through horizontal and vertical magnetic flux cancellations within a printed circuit board (PCB). The relationship between the magnetic flux cancellation and the parasitic inductance is analyzed, and the magnetic flux cancellation in the proposed structure is described. In addition, a practical PCB layout design procedure based on the proposed structure is provided. Simulation results demonstrate a 55.8% reduction in parasitic inductance, and experimental results show reduced overshoot and ringing at the switching transient, resulting in a 26% reduction in switching loss. As a result, the proposed method can improve the efficiency and stability of WBG device-based power converters.

Evaluation of energy balance closure adjustment and imbalance prediction methods in the convective boundary layer – A large eddy simulation study

The non-closure of the surface energy balance is one of the greatest challenges in quantifying the atmosphere-surface exchange of energy and water. One open question associated with the energy imbalance is how to partition the residual energy, i.e., the difference between the available energy and the sum of turbulent fluxes, between the sensible and latent heat fluxes. Here, based on high-resolution large-eddy simulations (LESs), five energy balance closing methods and three imbalance prediction methods are evaluated in the convective boundary layer over idealized heterogeneous surfaces. The results show that advection fluxes are highly correlated with flux imbalances and are leading factors for the flux imbalances. Overall, the Bowen ratio closure method has a better performance than other closure methods, especially when the vertical advection flux dominates the flux imbalance where its assumption is nearly fulfilled. However, when the horizontal advection flux dominates the flux imbalance, the Bowen ratio closure method cannot correctly close the sensible and latent heat fluxes, even though it exhibits better performance than other methods. This is mainly because the heat and water vapor transported by horizontal advection originate from different sources due to surface heterogeneity, which breaks the assumption of the Bowen ratio closure method, leading to failure. Moreover, using the footprint-weighted surface true fluxes (weighted surface true fluxes within the source area of EC) calculated by the Lagrangian particle model instead of the analytical footprint models can reduce the flux imbalance and improve the performance of different closure methods. None of the existing imbalance prediction methods can correctly predict the flux imbalance for H or LE, even though the prediction method proposed over heterogeneous surfaces has a better performance than those proposed over homogeneous surfaces. Our findings provide meaningful suggestions for the selection of energy balance closing methods in practice.

Near-surface characteristics of velocity profile and momentum transport after wave-breaking in deep water

Wave-breaking plays an important role in the process of mixing in the upper ocean, which can cause wave momentum and energy flux loss, enhance near-surface turbulence, and adjust the distribution of the momentum flux at the air-sea interface. In this paper, wave-breaking was generated using a laboratory method of controllable deep water breaking waves, and flow field characteristics after wave-breaking were measured and analyzed using PIV technology and the ensemble average method. The velocity threshold was proposed for the effective influence of wave-breaking on the flow field, then the EID (Effective-Influenced-Depth) of wave-breaking, which is Dv in the paper, was quantified, and the quantitative relationship between Dv and energy loss induced by breaking was established. Velocity characteristics of the near-surface flow field and transport characteristics of horizontal momentum induced by wave-breaking were analyzed, which can contribute to the parameterization of wave-breaking. The results show that the energy injected by wave-breaking is transported downstream along the direction of wave propagation. The vertical-influenced range of wave-breaking is about 1–2 times the wave-breaking height. The time integral of horizontal momentum flux increases significantly in the depth of about 1 time the wave-breaking height near the surface and decays significantly with depth. Mass transport of the fluid near the surface induced by wave-breaking mainly occurs in the depth where momentum flux increases significantly. After about 29 times the SWWP (spectrally weighted wave period) after breaking, fluid near the surface is no longer under the action of horizontal stress induced by wave-breaking, so no mass transport occurs anymore. For parameterization of wave-breaking in circulation models, the research can provide a reference in time and space scale, as well as experimental data support for the establishment of a new influence mode.

Modeling Tool for Estimating Carbon Dioxide Fluxes over a Non-Uniform Boreal Peatland

We present a modeling tool capable of computing carbon dioxide (CO2) fluxes over a non-uniform boreal peatland. The three-dimensional (3D) hydrodynamic model is based on the “one-and-a-half” closure scheme of the system of the Reynolds-Averaged Navier–Stokes and continuity equations. Despite simplifications used in the turbulence description, the model allowed obtaining the spatial steady-state distribution of the averaged wind velocities and coefficients of turbulent exchange within the atmospheric surface layer, taking into account the surface heterogeneity. The spatial pattern of CO2 fluxes within and above a plant canopy is derived using the “diffusion–reaction–advection” equation. The model was applied to estimate the spatial heterogeneity of CO2 fluxes over a non-uniform boreal ombrotrophic peatland, Staroselsky Moch, in the Tver region of European Russia. The modeling results showed a significant effect of vegetation heterogeneity on the spatial pattern of vertical and horizontal wind components and on vertical and horizontal CO2 flux distributions. Maximal airflow disturbances were detected in the near-surface layer at the windward and leeward forest edges. The forest edges were also characterized by maximum rates of horizontal CO2 fluxes. Modeled turbulent CO2 fluxes were compared with the mid-day eddy covariance flux measurements in the southern part of the peatland. A very good agreement of modeled and measured fluxes (R2 = 0.86, p < 0.05) was found. Comparisons of the vertical profiles of CO2 fluxes over the entire peatland area and at the flux tower location showed significant differences between these fluxes, depending on the prevailing wind direction and the height above the ground.

Theoretical Foundation of the Linear Relationship between the Midlatitude Eddy Heat Flux and Fall-to-Spring Polar Ozone Buildup

Abstract It has been demonstrated that there is a globally unified linear relationship between the interannual variations of the fall-to-spring polar ozone accumulation and the winter-mean poleward eddy heat flux on the 100 hPa pressure surface. The foundation of this relationship is investigated using time-slice experiments on a chemistry–climate model with two levels of ozone-depleting substances (ODSs). The features of the transport field are interpreted by decomposing the horizontal ozone flux caused by the residual circulation into contributing processes including the eddy heat flux with the aid of the transformed Eulerian-mean momentum equation followed by rearrangement of terms. The linear relationship between the interannual variations of the fall-to-spring ozone buildup integrated poleward and above a reference point Pref on a meridional plane and the poleward eddy heat flux during the corresponding period at Pref is realized for each hemisphere implying that the interhemispheric unification should be treated with caution. This relationship is interpreted using the fact that the interannual variation of poleward ozone transport in the upper stratosphere is captured well by the vertical convergence of the constituent-based Eliassen–Palm (EP) flux (), which is defined as the product of the constituent (ozone) mixing ratio and EP flux. The eddy momentum flux contributes to the meridional ozone transport in combination with the eddy heat flux in the form of the divergence of , although it is not responsible for realizing the linear relationship. The dependence of the linearity on the location of Pref and ODS levels is discussed.

Entrainment and horizontal atmospheric transport of microplastics from soil

Soils are an important source of microplastics (MPs) to the atmosphere but the fluxes and mechanisms involved in MPs entrainment are not well understood. In the present study, a series of horizontally aligned sediment traps have been deployed at different heights within 1 m above the ground for a two-month period at various locations in an arid region (Sarakhs, Iran). MPs were isolated from sediments and were quantified and characterised according to size, colour, shape and polymer composition by established techniques. Most MPs were <250 μm in length, fibres were the most important shape, black and blue-green were the dominant colours, and polymer abundance decreased in the order polyethylene > nylon > polypropylene > polystyrene > polyethylene terephthalate. The distributions of sediment mass (range <0.01–9 g) and number of MPs (range = 0 to 21) were heterogeneous, both between sites and at the different heights sampled, and yielded median, vertically-averaged horizontal fluxes for the region of about 450 g m−2 d−1 and 2600 MP m−2 d−1, respectively. However, when data were pooled, the number of MPs normalised to sediment mass exhibited a significant inverse relationship with sediment mass, an effect attributed to the presence of ambient suspended MPs and sediment that are diluted by the suspension of soil and deposited MPs at higher wind speeds. The mechanisms of MP saltation and entrainment were not ascertained but a theoretical framework for threshold shear velocity based on regularly-shaped particles and density considerations is presented. Further experimental work is required to verify this framework, and in particular for fibrous MPs with different aerodynamic properties to soil particles.