Horizontal Mixing Research Articles

Tropical Cyclone Potential Size

Abstract A model for tropical cyclone (TC) potential size (PS), which is capable of predicting the equilibrium outer radius of a TC solely from environmental parameters, is proposed. The model combines an updated Carnot cycle model with a physical model for the wind profile, which serve as energetic and dynamic constraints, respectively, on the minimum pressure. Physically, the Carnot cycle model defines how much the surface pressure can be dropped energetically, and the wind profile model defines how large the steady-state storm needs to be to yield that pressure drop for a given maximum wind speed. The model yields an intrinsic length scale VCarnot/f, with f the Coriolis parameter, VCarnot similar to the potential intensity Vp, but without a dependence on the surface exchange coefficients of enthalpy Ck and momentum Cd. Analytic tests with the theory varying outflow temperature, sea surface temperature (SST), and f demonstrate that the model predictions are qualitatively consistent with the Vp/f scaling for outer size found in past work. The model also predicts a weak dependence of outer size on Cd, Ck, and horizontal mixing length lh of turbulence, consistent with numerical simulation results. Idealized numerical simulation experiments with varied tropopause temperature, SST, f, Cd, Ck, and lh show that the model performs well in predicting the simulated outer radius. The VCarnot/f scaling also better captures the dependence of simulated TC size on SST than Vp/f. Overall, the model appears to capture the essential physics that determine equilibrium TC size on the f plane.

Synergistic Effect of Atmospheric Boundary Layer and Regional Transport on Aggravating Air Pollution in the Twain-Hu Basin: A Case Study

The impact of structural variations in the atmospheric boundary layer (ABL) during the regional transport of air pollutants on its local pollution changes deserves attention. Based on multi-source ABL detection and numerical simulation of air pollutants over the Twain-Hu Basin (THB) during 4–6 January 2019, the mechanism of the rapid growth of atmospheric pollutant concentrations in Xianning by the synergistic effect of regional transport and ABL evolution is explored, and the main conclusions are obtained as follows. The vertically stratified atmosphere is noticeable at nighttime, and the heavy humidity of near-surface fog within the stable boundary layer (SBL) promoted the generation and cumulative growth of secondary PM2.5 components during the pollution formation stage. The horizontal transport characteristics of atmospheric pollutant concentration peak were observed in the residual layer (RL) of 500–600 m. At the pollution maintenance stage, the convective boundary layer (CBL) developed during the daytime, and northerly wind transported high-concentration pollutants from the north to the THB. Under the combined action of horizontal transport and turbulent mixing, the high-concentration atmospheric pollutants in the mixing layer (ML) from the ground to the 500 m height were mixed uniformly and maintained accumulation growth. The next day, the strong vertical turbulent mixing caused the downward transport of high-concentration pollutants in the RL during nighttime due to the development of the CBL again, resulting in a doubling of near-surface pollutant concentration in a short time. With the development of ABL turbulence, local pollution dissipated rapidly without the continuous input of pollutants from external regions. This study emphasizes the importance of multi-scale processes impact on pollution variation, that is, regional transport of atmospheric pollutants at the CBL development stage for the rapid growth of PM2.5 concentration in the ML.

Prospects for acoustic remote sensing and acoustic system performance in the Beaufort Gyre region

In the Beaufort Gyre region north of Alaska, the vertical interleaving of the near-surface temperature maximum, the warm Pacific Summer Water (PSW), the cool Pacific Winter Water, and the Atlantic layer make for unusual acoustic conditions. The dynamics of these upper ocean layers cause typical complex and turbulent-like oceanic flow that causes geographically variable heat content and acoustics. A sound duct in the PWW, below the PSW and above the Atlantic Layer, filling ∼75 to 225 m depth, is prominent but not universal. Erosion of the PSW warm layer by either vertical or horizontal mixing processes often breaks the duct, with an additional seasonal cycle of ducting effectiveness, and allows sound to escape to interact with the scattering and attenuating surface. The duct enables communication and navigation signaling, but with that interruption caveat. It also allows passive sensing, best for sound that enters the duct and moves through it. A challenge is to utilize sound that exists outside the duct. This includes sounds emitted outside the duct by mammals, fracturing ice, or anything else. This sound will either cycle through the duct at steep angle, or stay above the duct and repeatedly reflect from the top boundary. The combination of unducted sound being subject to strong attenuation by ice or wave interaction (the typical high-latitude situation) and high variability of the duct effectiveness, imposes limitations on the usefulness of the otherwise convenient duct.

Characterizing the Impacts of Turbulence Closures on Real Hurricane Forecasts: A Comprehensive Joint Assessment of Grid Resolution, Horizontal Turbulence Models, and Horizontal Mixing Length

AbstractHurricanes are highly complex geophysical flows that have caused billions of dollars in damage in recent years. Despite the significance of these extreme weather events, the turbulence mechanisms that derive the dynamics of hurricane flow systems are poorly understood and ineffectively parameterized in numerical weather prediction (NWP) models. The objective of this study is to bridge these knowledge gaps by assessing the accuracy and deficiencies of existing horizontal turbulence models in NWPs for hurricane forecasts. In particular, the Weather and Research Forecasting (WRF) Model is employed to conduct 135 simulations of five real hurricanes by varying the grid resolution, turbulence models, and horizontal mixing length values. Decreasing the default horizontal mixing length values both in low and high resolution WRF simulations significantly improves the wind intensity forecasts. This result indicates that the existing horizontal diffusion parameterizations are overly dissipative for hurricane flows, and thus, generate a weaker vortex compared to observations. These deficiencies are shown to stem from the horizontal mixing‐length parameterization in WRF that is prescribed as a function of grid size without considering the physics of the flows (e.g., rotation). The paper provides notable insights into the role of turbulent fluxes in simulated hurricane evolutions that can be useful to advance the turbulence parameterizations of NWP models for hurricane forecasts.

Erratum: Grid of pseudo-2D chemistry models for tidally locked exoplanets – I. The role of vertical and horizontal mixing

Erratum: Grid of pseudo-2D chemistry models for tidally locked exoplanets – I. The role of vertical and horizontal mixing

Effect of Temperature on Properties of Concrete in Stirring Process

Taking composite silicate concrete as the research object, the double horizontal shaft mixing method is used to mix concrete. The setting time, strength and workability tests are carried out to study the influence of temperature on the mechanical properties of concrete in the ordinary mixing process. The results show that the temperature has great influence on the setting time, compressive strength and splitting strength of concrete. Reasonable control of cement temperature has important guiding significance and theoretical basis in practical construction application.

Toward Super Temporal Resolution by Suppression of Mixing Effects of Electrons

The theoretical temporal resolution limit of silicon (Si) image sensors is 11.1 ps. The super temporal resolution (STR) is defined as a frame interval less than this limit. The temporal resolution of burst image sensors is significantly affected by “mixing” of signal electrons traveling from different starting positions. For example, the penetration depths of photons incident to a surface of a photodiode (PD) disperse exponentially, resulting in mixing of the photoelectrons from different depths at the other end, which causes a distribution of the arrival times. The temporal resolution is proportional to the standard deviation of the arrival time. Toward STR imaging, this article proposes measures to suppress various mixing phenomena during the travel of the signal electrons: 1) a germanium (Ge) PD for visible light to practically eliminate the effect of vertical mixing caused by the distribution of the penetration depth; 2) an inverted pyramid PD to efficiently suppress the horizontal mixing, keeping a 100% fill factor; 3) a standard column PD with negative potential on the vertical walls to squeeze the trajectory bundle of electrons falling on the guide gate on the front side; and 4) a resistive guide gate to linearize the potential profile to maximize the horizontal drift velocity to minimize the mixing together with the squeezed electron bundle.

Applications of generalized vertical coordinates in ocean circulation models

Two types of generalized vertical coordinates are introduced to reduce model errors in calculating the baroclinic pressure gradient (BPG), advection term and horizontal mixing in tracer equations in a three-dimensional (3D) ocean circulation model. These two types of vertical coordinates are defined as the generalized terrain-following coordinate (GTC) and generalized piecewise terrain-following coordinate (GPTC). The main feature of the GTC is the use of a series of constant-depth levels in the water column above the sea bottom. The GPTC differs from the GTC in which the depth differences between two adjacent grids are reduced, especially in the bottom layer over steep topography. Performances of these two vertical coordinate systems are assessed first in two types of idealized numerical experiments with a tall seamount and continuously varying bottom slope respectively. The model results in the tall seamount experiment demonstrate that both the GTC and GPTC perform well in reducing the model errors in the BPG over the steep topography, and greatly alleviate the spurious diapycnal mixing in terrain-following coordinate models. In the continuously varying bottom slope experiment, both the GTC and GPTC perform better than the z-level coordinate in simulating the 3D currents. The performances of the GTC and GPTC are further assessed by examining prognostic simulations of 3D currents and hydrography in the Yellow and East China Seas with realistic external forcing and bottom topography. The model results in the third experiment demonstrate that the GPTC restrains the overestimated upward climbing of the bottom cold water in comparison with other coordinates. The GPTC also performs better than the GTC and the conventional sigma-layer coordinate in simulating the shoreward intrusion of relatively high-salinity subsurface waters, intermediate low-salinity waters and the Yellow Sea bottom cold waters. By comparison, the GTC simulates the Kuroshio, the Slope Counter-Current and their seasonal variability significantly better than other coordinates.

Diagnosis of Second-Order Turbulent Properties of the Surface Layer for Three-Dimensional Flow Based on the Mellor–Yamada Model

Abstract Accurate representation of heterogeneous surface layer processes is essential for numerical weather prediction (NWP) with sub-kilometer grid spacing. NWP models such as the Weather Research and Forecasting (WRF) Model generally use second-moment turbulent models for parameterizing the planetary boundary layer (PBL). The most common parameterizations follow Mellor–Yamada and account for the vertical turbulent mixing only; that is, standard PBL parameterizations are one-dimensional (1DPBL). The horizontal diffusion of momentum is parameterized based on Smagorinsky’s model for numerical stability. Although the combination of 1DPBL and 2D Smagorinsky parameterizations is successful at coarse grid resolutions (e.g., grid-size dx ∼ 12–2 km), it does not represent well the effect of horizontal turbulence as gridcell size decreases (<1 km). To reconcile the representation of vertical and horizontal turbulent mixing, a full three-dimensional PBL scheme (3DPBL) based on the Mellor–Yamada model was implemented in WRF. The 3DPBL uses the horizontal and vertical turbulent fluxes diagnosed from the flow gradients to handle the turbulent mixing. These gradients cannot be directly calculated near the surface. Therefore, the 3DPBL parameterization is coupled herein to a second-order diagnostic model of the three-dimensional turbulent fluxes in the surface layer. Several adjustments to the original Mellor–Yamada model, including a modified length scale, were introduced to capture flow anisotropy and dependence on stability conditions. The results are compared against data from the Wind Forecast Improvement Project 2 (WFIP2) for different weather regimes and using different grid resolutions to examine stability and scale dependency.

Radium-Derived Water Mixing and Associated Nutrient in the Northern South China Sea

Nutrients play an important role as biogenic elements in modulating marine productivity, and water mixing usually facilitates the transportation of nutrients in the coastal ocean. In this study, the distributions of naturally occurring radioisotopes 226Ra and 228Ra in the surface and water column of the northern South China Sea (NSCS) have been investigated to estimate oceanic mixing and nutrient supplies. We identified three masses of the South China Sea Warm Current (SCSWC), the South China Sea Branch of the Kuroshio (SCSBK), and shelf water in the summer of June 2015, but only SCSWC and SCSBK were observed in the spring of March 2017. The fraction of the SCSBK in summer was estimated to be an average of 0.25 ± 0.16, which was lower than that in the spring of 0.57 ± 0.32 in our study area. The horizontal mixing from the Pearl River plume revealed eddy diffusion of (1.2 ± 0.79) × 105 cm2/s and advection velocity ω of 0.25 ± 0.16 cm/s in the slope region. In the water column, the best-fit exponential curve gradient of 228Ra led to a vertical diffusion coefficient of 0.43 ± 0.33 cm2/s that went down to the subsurface of the upper 1,000 m, and an upward vertical diffusion coefficient was revealed as 18 ± 9.9 cm2/s from the near-bottom. Combining the nutrient distributions, horizontal mixing from the Pearl River plume carried (5.6 ± 4.9) × 102 mmol N/m2/d, 2.2 ± 2.0 mmol P/m2/d, and (4.1 ± 3.9) × 102 mmol Si/m2/d in the very surface layer, suggesting that shelf water plays a significant role in the nutrient sources of the slope of the NSCS during June 2015. The upward vertical mixing supplied 2.7 ± 1.6 mmol N/m2/d, 0.18 ± 0.11 mmol P/m2/d, and 15 ± 8.4 mmol Si/m2/d to the upper layer, which appeared more important than atmospheric deposition and rivaled submarine groundwater discharge.

Summertime Transport Pathways and Dynamics From Northern India and Tibetan Plateau to the Lower Stratosphere: Insights From Idealized Tracer Experiments

AbstractWe use the idealized tracer experiments and investigate the summertime transport from the surface region of northern India and Tibetan Plateau to the lower stratosphere. It is found that the transport, compared to other surrounding regions, has an overall younger modal age in the northern lower stratosphere away from the tropopause. Analysis of the tracer budget reveals that the tracer is transported to the tropical lower stratosphere rapidly in the first 5 days due to vertical eddy transport and afterward in a month or two advection associated with the Brewer‐Dobson circulation. Meanwhile the tracer is also transported to the northern extratropical lower stratosphere in the first 3 months due to horizontal eddy mixing. The results highlight the uniqueness of the northern India region in the summertime transport to the lower stratosphere and implications for the transport of short‐lived chemical species in the destruction of stratospheric ozone.

Freshwater transport by eddies within the Bay of Bengal's central axis

The excess of freshwater from rivers and precipitation delivered to the Bay of Bengal (BoB) must be exported to the neighboring ocean in order to establish a quasi-steady state salinity field. The BoB's sea surface salinity is approximately 3 PSU less than that of the Arabian Sea, which experiences net evaporation, a difference reflecting the efficiency of exchange between the two embayments (Gordon et al., 2019). Using Argo salinity profiles from 2003 to 2018 along the BoB's central axis, we investigate the significance of eddies in the removal of excess freshwater injected into the northern BoB by rivers. Southwestward freshwater volume flux is estimated by combining horizontal freshwater (salinity) gradients, as a function of latitude, depth, and season, with a realistic estimate of the horizontal mixing coefficient. The ratio of these fluxes for 0–50 m: 50–100 m: 100–300 m depth slabs is 5.68 : 1.75: 1 in the 15 ± 2° N (northern) study box and 4.61 : 2.24: 1 in the 10 ± 2° N (southern) study box, highlighting the importance of the upper 50 m in the removal of river runoff. In the northern BoB, boreal winter experiences the highest freshwater eddy flux, a consequence of the accumulated freshwater from the previous summer monsoon season. Lower latitudes reach their peak freshwater flux in the summer, a delayed response due to the time required to transport the freshwater southward. Southwestward eddy freshwater flux in the top 300 m can account for almost all of the export of the 0.094 Sv (Sv = 106 m3/s) river runoff into the northern BoB.

Destratification of a Eutrophic Reservoir in South Korea Using a Novel Convectional Water Circulation System (CWCS)

Replication of natural mixing through artificial water circulation techniques, such as convectional water circulation systems (CWCS), can break thermal stratification in stagnant water and suppress algal blooms. Here, the field performance of a novel CWCS was evaluated in a eutrophic reservoir (Shingal reservoir, South Korea) for three seasons between September 2016 and September 2018. The CWCS was deployed in a corner of stagnated water in the reservoir. The changes in water temperature and dissolved oxygen (DO) concentrations at different water depths were examined at the deployment site and two control sites within the stagnant area during the 2016 and 2017 seasons. In 2018, the performance of the CWCS in replicating natural mixing was assessed by monitoring water temperature changes at different depths at the CWCS unit deployment site and a comparison site with natural water flow. The differences in water temperature and DO concentrations between the epilimnion and the hypolimnion were significantly smaller at the deployment site than at the control sites, demonstrating the effectiveness of the CWCS in vertical and horizontal mixing as well as in oxygen transfer. The findings of the field study revealed that the CWCS effectively induced natural-like mixing without disturbing the hypolimnion.

Sensitivity of Global Ocean Deoxygenation to Vertical and Isopycnal Mixing in an Ocean Biogeochemistry Model

AbstractLarge‐scale loss of oxygen under global warming is termed “ocean deoxygenation” and is caused by the imbalance between physical supply and biological consumption of oxygen in the ocean interior. Significant progress has been made in the theoretical understanding of ocean deoxygenation; however, many questions remain unresolved. The oxygen change in the tropical thermocline is poorly understood, with diverging projections among different models. Physical oxygen supply is controlled by a suite of processes that transport oxygen‐rich surface waters into the interior ocean, which is expected to weaken due to increasing stratification under global warming. Using a numerical model and a series of sensitivity experiments, the role of ocean mixing is examined in terms of effects on the mean state and the response to a transient warming. Both vertical and horizontal (isopycnal) mixing coefficients are systematically varied over a wide range, and the resulting oxygen distributions in equilibrated and transient simulations are examined. The spatial patterns of oxygen loss are sensitive to both vertical and isopycnal mixing, and the sign of tropical oxygen trend under climate warming can reverse depending on the choice of mixing parameters. An elevated level of isopycnal mixing disrupts the vertical advective‐diffusive balance of the tropical thermocline, increasing the mean state oxygen as well as the magnitude of the transient oxygen decline. These results provide first‐order explanations for the diverging behaviors of simulated tropical oxygen with respect to ocean mixing parameters.

On the Resolution‐Dependence of Anvil Cloud Fraction and Precipitation Efficiency in Radiative‐Convective Equilibrium

AbstractTropical anvil clouds are an important player in Earth's climate and climate sensitivity, but simulations of anvil clouds are uncertain. Here we identify and investigate one source of uncertainty by demonstrating a marked increase of anvil cloud fraction with resolution in cloud‐resolving simulations of radiative‐convective equilibrium. This increase in cloud fraction can be traced back to the resolution dependence of horizontal mixing between clear and cloudy air. A mixing timescale is diagnosed for each simulation using the cloud fraction theory of Seeley, Jeevanjee, Langhans, and Romps (2019) (https://doi.org/10.1029/2018GL080747) and is found to scale linearly with grid spacing, as expected from a simple scaling law. Thus mixing becomes more efficient with increasing resolution, generating more evaporation in middle and lower tropospheric updrafts. This decreases their precipitation efficiency (PE), thereby increasing their overall mass flux, leading to greater detrainment at the anvil level and hence higher anvil cloud fraction. The decrease in PE also yields a marked increase in relative humidity with resolution.

Large Increase in Dissolved Inorganic Carbon in the East Sea (Japan Sea) From 1999 to 2019

The East Sea (also known as the Japan Sea; hereafter, EJS) has its own deep overturning circulation, that operates over a centurial timescale compared with a millennial timescale in the ocean. This allows the EJS to be used as a natural laboratory for investigating potential future changes in the oceanic system. Dissolved inorganic carbon (DIC), total alkalinity (TA), and pH were measured in 2019 in a wide area of the EJS to investigate the characteristics and changes of the carbonate system since the last extensive survey in 1999. In the layer below ∼1,000 m, DIC and apparent oxygen utilization (AOU) was uniform implying rapid horizontal mixing within a few years. Since 1999, DIC concentration increased by ∼11 μmol kg–1 in the layer deeper than 500 m. This increase accompanied a commensurate increase in AOU with the canonical ratio of 1.3, indicating that the accumulation of DIC was supplied from organic matter decomposition. This observation is consistent with a previous study suggesting that the slowed deep water ventilation was the cause of the increase in AOU and fast acidification. In the EJS, increase in DIC from the surface water to deep waters is much higher than that in TA, which is caused by high primary productivity and export production together with low rates of CaCO3 export. Thus, the DIC/TA ratio of deep waters, an indicator of vulnerability to acidification, is high. A recently reported change in deep water ventilation, namely, re-initiation of deep water formation reaching deeper depths to the Deep Water and the Bottom Water, implies that unexpected changes in the carbonate system may be detected in the future, which needs to be further monitored.

Моніторинг технічного стану ЗПРК за керівними матеріалами на їх експлуатацію

The efficiency of use and increase the reliability of agricultural machinery depends on the regulatory and technical documentation governing the requirements for its technical condition and operation. The analysis of the existing normative-technical and guiding documents on ensuring the reliability of means for preparation and distribution of fodder is given. To effectively carry out maintenance and repair of means for the preparation and distribution of feed should know: the criteria for disability; maximum and permissible parameters of technical condition; indicators of the transition of equipment from working to inoperable condition. The article presents the monitoring of instructions for maintenance and operation of machines, guide materials for use from the standpoint of their informativeness on the implementation of reliability requirements. Monitoring of technical condition was carried out for foreign samples of means for preparation and distribution of feed with horizontal mixing and grinding mechanisms. The mechanisms are analyzed from the standpoint of the availability of information about the features of the structure, the characteristic faults and failures, the main ways to restore efficiency. Ensuring reliability includes several activities throughout the life cycle. The main provisions for assessing the technical condition and improving the reliability of machines when using guide materials. The provisions include: information on the reliability of machines, mechanisms, working bodies; periodicity of maintenance and repair of machines, restoration of working bodies; information on the complexity of maintenance and repair of machines, restoration of working bodies; schemes of assembly and disassembly of mechanisms; information on typical failures and the sequence of their elimination; information on the limit state criteria; technologies for the restoration of working bodies; information on installation requirements. The current normative documents of the system of general technical requirements for the means for the preparation and distribution of feed do not fully meet the organizational and methodological aspects of ensuring their reliability.

Long‐Distance/Time Surf‐Zone Tracer Evolution Affected by Inner‐Shelf Tracer Retention and Recirculation

AbstractThe evolution of a surf‐zone released tracer ( Liter over 4 hr) was observed for h. Surf‐zone tracer was transported alongshore (y) with relatively steady mean speed vSZ ≈ 0.18 m s−1, consistent with obliquely incident wave forcing. Maximum in situ surf‐zone tracer concentration decayed exponentially with 1.6 km alongshore e‐folding length scale, that is, 2.5 hr advective time scale. Surf‐zone tracer time‐series evolved downstream of the release from a top‐hat structure for y ≤ 1 km to increasingly skewed farther downstream. Within km of the northward propagating tracer front, inner‐shelf tracer was confined to onshore of (surf‐zone width LSZ ≈ 100 m) and was alongshore patchy. A coupled surf‐zone/inner‐shelf tracer advection‐diffusion‐exchange box model reproduces the observed surf‐zone downstream max concentration decay and temporal skewness, with surf‐zone flushing time h. A weaker inner‐shelf unidirectional‐exchange rate kIS ≈ kSZ/2 indicates reduced horizontal mixing outside the surf‐zone. Surf‐zone temporal skewness is linked to inner‐shelf tracer storage, differential surf‐zone/inner‐shelf advection, and recirculation, that is, non‐asymptotic shear dispersion. On the inner‐shelf (), tracer vertical structure differed in the morning versus afternoon suggesting internal tide and solar forced thermal modulation. Model parameters representing surf‐zone processes are well constrained by existing observations and scales. However, the many overlapping inner‐shelf processes make a single process based generalization of inner‐shelf cross‐shore exchange rate (i.e., kIS) and alongshore transport difficult.

Controlling Eutrophication via Surface Aerators in Irregular-Shaped Urban Ponds

Surface aerators have often been introduced in urban ponds for esthetics, but their roles in remediating water quality are less understood. Effects of surface aerators on controlling eutrophication were examined in two urban ponds, in which anaerobic odors and cyanobacterial blooms had occurred and several aerators had been installed. In one of the ponds, a dramatic improvement in dissolved oxygen (DO) (from 1.8 to 8.1 mg L−1) and total phosphorus (TP) (from 1.6 to 0.4 mg L−1) was evident based on the comparison before and after the aeration. Although cyano-bloom did not occur, phytoplankton was dominated by cyanobacteria Microcystis species in both periods. Chlorophyll a (Chl-a) increased (from 29 to 51 μg L−1) and water transparency decreased (from 81 to 27 cm) after the aeration. In the other pond with an irregular shape, water quality was monitored two years after the installation to examine seasonal variation in trophic state and its spatial variation associated with aerator distribution. The water was mixed vertically well for the whole pond, as indicated by small surface-to-bottom differences in temperature. DO decreased in summer after rainfall but was always >5.7 mg L−1. Total nitrogen (TN) and TP were 0.8–2.3 and 0.03–0.07 mg L−1, respectively, and no cyano-blooms were observed across sites throughout the year. Phytoplankton was dominated by green algae and diatom species, which may be favored by the lower phosphorus level of the pond. Chl-a was higher and transparency was lower in the north side, which had more aerators and less shade from trees and buildings. These results suggest that surface aerators increased DO by vertical and horizontal mixing of water, reduced phosphorus release from sediment, and prevented cyano-bloom occurrence, but they did not improve Chl-a level and transparency. Rather, aeration can promote algal growth, and thus, additional purifying measures such as filtration and contact oxidation are required to further improve the trophic state of these ponds.

Stratospheric Adiabatic Mixing Rates Derived From the Vertical Gradient of Age of Air

AbstractThe circulation of the stratosphere transports important trace gases, including ozone, and can be thought of as having a fast horizontal mixing component and a slow meridional overturning component. Measuring the strength of the circulation directly is not possible, and so it must be inferred from tracer measurements. Long‐lived trace gases can be related to the idealized tracer age of air, which describes how long an air parcel has been in the stratosphere. In this paper, we derive a quantitative relationship between the vertical gradient of age and the horizontal mixing between the tropics and the extratropics using a “leaky pipe” framework in isentropic coordinates. Mixing rates of air into and out of the tropics are related to the vertical gradient of age in the tropics and in the extratropics, respectively. The derivation is repeated with the hemispheres separated so that the vertical structure of the mixing in the two hemispheres can be compared directly. These theories are applied to output from an idealized model of the stratosphere and from a realistic chemistry‐climate model to test our assumptions and calculate the mixing rates in the models. We then perform a quantitative comparison of the mixing rates in the Northern and Southern hemispheres along with an examination of where such a separation is valid. Finally, we perform a very preliminary calculation of mixing efficiency with satellite data to demonstrate the use of the mixing metric to compare mixing in models and data.