Vertical Mass Transport Research Articles

Relationship between Fine Layering of Stratified Water Environment and Vertical Turbulent Mass Transport

Relationship between Fine Layering of Stratified Water Environment and Vertical Turbulent Mass Transport

Influence of Radiation Stress on Upper-Layer Ocean Temperature under Geostrophic Condition

Wave-induced radiation stress (RS), as a primary driver of ocean currents influenced by waves, plays an important role in the response of upper ocean temperatures under typhoons. Previous studies have mainly focused on wave-generated currents and coastal currents in nearshore areas. This paper incorporates the geostrophic effect into the wave-induced radiation stress of wave-current interaction, and the effect of waves on the changes in upper ocean temperature (including sea surface temperature (SST) and mixed layer temperature) under typhoon Nanmadol (2022) is studied. The FVCOM-SWAVE model is used to conduct a preliminary numerical study in the western Pacific Ocean. The RS with the geostrophic effect increased the horizontal and vertical components, leading to an enhancement in turbulent mixing and a decrease in SST by up to 1.0 °C to 1.4 °C, which is closer to the SST obtained by OISST remote sensing fusion observation data. In the strong divergence domain, the direction of the vortex flow exhibits a more pronounced turn to the right, accompanied by an increase in water velocity. The vertical temperature profile of the ocean shows that the water below is perturbed by the RS component of the geostrophic effect, and the depth of the mixed layer increases by about 2 m, which is closer to the depth of the mixed layer observed by the Argo floats, indirectly enhancing the vertical mass transport of the ocean. In general, this shows that RS, which takes into account geostrophic effects, enhances the effect of waves on the water below, indirectly leading to lower temperatures in the upper ocean, and the simulated results align more closely with the observed data, offering valuable insights for enhancing marine numerical forecasting accuracy.

Linking turbulent waves and bubble diffusion in self-aerated open-channel flows: two-state air concentration

High-Froude-number flows become self-aerated when the destabilizing effect of turbulence overcomes gravity and surface tension forces. Traditionally, the resulting air concentration profile has been explained using single-layer approaches that invoke solutions of the advection–diffusion equation for air in water, i.e. bubbles’ dispersion. Based on a wide range of experimental evidence, we argue that the complete air concentration profile shall be explained through the weak interaction of different canonical turbulent flows, namely a turbulent boundary layer (TBL) and a turbulent wavy layer (TWL). Motivated by a decomposition of the streamwise velocity into a pure wall flow and a free-stream flow (Krug et al., J. Fluid Mech., vol. 811, 2017, pp. 421–435), we present a physically consistent two-state formulation of the structure of a self-aerated flow. The air concentration is mathematically built upon a modified Rouse profile and a Gaussian error function, resembling vertical mass transport in the TBL and the TWL. We apply our air concentration theory to over 500 profiles from different data sets, featuring excellent agreement. Finally, we show that the turbulent Schmidt number, characterizing the momentum-mass transfer, ranges between 0.2 and 1, which is consistent with previous mass-transfer experiments in TBLs. Altogether, the proposed flow conceptualization sets the scene for more physically based numerical modelling of turbulent mass diffusion in self-aerated flows.

Effect of morphology and an upstream tall building on the mean turbulence statistics of a street canyon flow

The effects on turbulent street canyon flow of the morphological model and the existence of an upstream tall building are investigated in a wind tunnel, using Stereoscopic Particle Image Velocimetry (S-PIV) measurements on two orthogonal vertical planes. The cathedral in the “Rue de Strasbourg, (Nantes, France)” morphological model is regarded as a local tall building and is tested and then replaced by generic, square planform buildings of 4 different heights. The cathedral induces an asymmetrical wake while no obvious different influence on the street canyon flow can be identified, in comparison with a generic building of the same height. A strong along-canyon flow occurs which may be due to the intersections, while the along-canyon ventilation decreases with increasing building height. The higher the building, the stronger its sheltering effect, leading to a reduction of the vertical ventilation and mass transport across the canyon opening, at least in the canyon portion directly downstream of the building.

Divergence Observation in a Mesoscale Eddy during Chla Bloom Revealed in Submesoscale Satellite Currents

Oceanic mesoscale eddies continuously regulate the horizontal and vertical transport of mass, heat, salt, carbon, and nutrients throughout the ocean system owing to their ubiquity, three-dimensionality, and long-term persistence. Although satellites have been the main platforms used to observe mesoscale eddies and chlorophyll-a (Chla) distributions, they cannot support submesoscale physical–biological interactions. Contemporary satellite observations of Eulerian velocity fields are unable to resolve submesoscale processes that govern vertical migration and mixing, which are crucial for controlling the nutrients and light for phytoplankton in the surface layer. We explored the physical–biological interaction between the anticyclonic mesoscale eddy and the Chla secondary bloom that occurred after the spring bloom in the East/Japan Sea using the Geostationary Ocean Color Imager (GOCI). The GOCI currents were generated using GOCI Chla data and were used to map streamlines, vorticity, and divergence to characterize the surface current near the eddy. In the early spring bloom period, the eddy interior showed Chla depletion as the eddy was trapped externally. We found that the second bloom period coincided with a higher divergence or upwelling period in the eddy core, and a sharp Chla peak was observed when wind-induced Ekman suction was pronounced. This study describes the first satellite observation of surface layer divergence inside an anticyclonic mesoscale eddy with internal Chla blooms, utilizing a submesoscale-permitting GOCI-based surface current.

Intercomparison of Planetary Boundary Layer Heights Using Remote Sensing Retrievals and ERA5 Reanalysis over Central Amazonia

The atmospheric boundary layer height (zi) is a key parameter in the vertical transport of mass, energy, moisture, and chemical species between the surface and the free atmosphere. There is a lack of long-term and continuous observations of zi, however, particularly for remote regions, such as the Amazon forest. Reanalysis products, such as ERA5, can fill this gap by providing temporally and spatially resolved information on zi. In this work, we evaluate the ERA5 estimates of zi (zi-ERA5) for two locations in the Amazon and corrected them by means of ceilometer, radiosondes, and SODAR measurements (zi-experimental). The experimental data were obtained at the remote Amazon Tall Tower Observatory (ATTO) with its pristine tropical forest cover and the T3 site downwind of the city of Manaus with a mixture of forest (63%), pasture (17%), and rivers (20%). We focus on the rather typical year 2014 and the El Niño year 2015. The comparison of the experimental vs. ERA5 zi data yielded the following results: (i) zi-ERA5 underestimates zi-experimental daytime at the T3 site for both years 2014 (30%, underestimate) and 2015 (15%, underestimate); (ii) zi-ERA5 overestimates zi-experimental daytime at ATTO site (12%, overestimate); (iii) during nighttime, no significant correlation between the zi-experimental and zi-ERA5 was observed. Based on these findings, we propose a correction for the daytime zi-ERA5, for both sites and for both years, which yields a better agreement between experimental and ERA5 data. These results and corrections are relevant for studies at ATTO and the T3 site and can likely also be applied at further locations in the Amazon.

Hidden Upwelling Systems Associated With Major Western Boundary Currents

AbstractWestern boundary currents (WBCs) play an essential role in regulating global climate. In contrast to their widely examined horizontal motions, less attention has been paid to vertical motions associated with WBCs. Here, we examine vertical motions associated with the major WBCs by analyzing vertical velocity from five ocean synthesis products and one eddy‐resolving ocean simulation. These data reveal robust and intense subsurface upwelling systems, which are primarily along isopycnal surfaces, in five major subtropical WBC systems. These upwelling systems are part of basin‐scale overturning circulations and are likely driven by meridional pressure gradients along the western boundary. Globally, the WBC upwelling contributes significantly to the vertical transport of water mass and ocean properties and is an essential yet overlooked branch of the global ocean circulation. In addition, the WBC upwelling intersects the oceanic euphotic and mixed layers, and thus likely plays an important role in ocean biological and chemical processes by transporting nutrients, carbon and other tracers vertically inside the ocean. This study calls for more research into the dynamics of the WBC upwelling and their role in the ocean and climate systems.

Crucial Role of Mesoscale Convective Systems in the Vertical Mass, Water, and Energy Transports of the South Asian Summer Monsoon

AbstractConvective vertical transport is critical in the monsoonal overturning, but the relative roles of different convective systems are not well understood. This study used a cloud classification and tracking technique to decompose a convection-permitting simulation of the South Asian summer monsoon (SASM) into subregimes of mesoscale convective systems (MCSs), non-MCS deep convection (non-MCS), congestus, and shallow convection/clear sky. Isentropic analysis is adopted to quantify the contributions of different convective systems to the total SASM vertical mass, water, and energy transports. The results underscore the crucial roles of MCSs in the SASM vertical transports. Compared to non-MCSs, the total mass and energy transports by MCSs are at least 1.5 times stronger throughout the troposphere, with a larger contributing fraction from convective updrafts compared to upward motion in stratiform regions. Occurrence frequency of non-MCSs is around 40 times higher than that of MCSs. However, per instantaneous convection features, the vertical transports and net moist static energy (MSE) exported by MCSs are about 70–100 and 58 times stronger than that of non-MCSs. While these differences are dominantly contributed by differences in the per-feature MCS and non-MCS area coverage, MCSs also show stronger transport intensities than non-MCSs over both ocean and land. Oceanic MCSs and non-MCSs show more obvious top-heavy structures than their inland counterparts, which are closely related to the widespread stratiform over ocean. Compared to the monsoon break phase, MCSs occur more frequently (~1.6 times) but their vertical transport intensity slightly weakens (by ~10%) during the active phases. These results are useful for understanding the SASM and advancing the energetic framework.

Intermittent Intense Thermocline Shear Associated With Wind‐Forced Near‐Inertial Internal Waves in a Summer Stratified Temperate Shelf Sea

AbstractThermocline shear (i.e., velocity shear in the thermocline) lies at the heart of stratified shelf sea systems, regulating the vertical mixing and transport of mass and biogeochemical constituents. Based on year‐long moored ADCP measurements in the southern Yellow Sea (YS), the baroclinic kinetic energy and thermocline shear are investigated in this study. The rotary spectra analysis of the velocity measurements and numerical simulations with the slab model demonstrate that the wind‐forced near‐inertial internal waves (NIWs) contribute most of the baroclinic kinetic energy (50%) and thermocline shear (55%) in this stratified temperate shelf sea. The NIWs are mostly in the first two modes and are frequently generated during the warm season, associated with the presence of strong stratification and disturbances from extratropical cyclones. Most interestingly, the observed thermocline shear shows intermittent enhanced near‐inertial shear in the YS for the first time. Further analysis reveals that the thermocline shear is in the form of a clockwise rotating vector with the shear maxima (hereafter the shear spike) occurring at an angle of ∼90° to the right of the wind vector. These shear spikes, which prevail in warm seasons, are further demonstrated to be related to the wind‐shear‐alignment mechanism through comparing with a theoretical shear production model. Given the prevalence of shear spikes in warm seasons, this process is believed to have important implications in inducing thermocline mixing, which may further modulate nutrients cycling and help the maintenance of primary productivity in seasonally stratified shelf seas.

Investigation of near-global daytime boundary layer height using high-resolution radiosondes: first results and comparison with ERA5, MERRA-2, JRA-55, and NCEP-2 reanalyses

Abstract. The planetary boundary layer (PBL) governs the vertical transport of mass, momentum, and moisture between the surface and the free atmosphere, and thus the determination of PBL height (BLH) is recognized as crucial for air quality, weather, and climate analysis. Although reanalysis products can provide important insight into the global view of BLH in a seamless way, the BLH observed in situ on a global scale remains poorly understood due to the lack of high-resolution (1 or 2 s) radiosonde measurements. The present study attempts to establish a near-global BLH climatology at synoptic times (00:00 and 12:00 UTC) and in the daytime using high-resolution radiosonde measurements over 300 radiosonde sites worldwide for the period 2012 to 2019, which is then compared against the BLHs obtained from four reanalysis datasets, including ERA5, MERRA-2, JRA-55, and NCEP-2. The variations in daytime BLH exhibit large spatial and temporal dependence, and as a result the BLH maxima are generally discerned over the regions such as the western United States and western China, in which the balloon launch times mostly correspond to the afternoon. The diurnal variations in BLH are revealed with a peak at 17:00 local solar time (LST). The most promising reanalysis product is ERA5, which underestimates BLH by around 130 m as compared to radiosondes released during daytime. In addition, MERRA-2 is a well-established product and has an underestimation of around 160 m. JRA-55 and NCEP-2 might produce considerable additional uncertainties, with a much larger underestimation of up to 400 m. The largest bias in the reanalysis data appears over the western United States and western China, and it might be attributed to the maximal BLH in the afternoon when the PBL has risen. Statistical analyses further indicate that the biases of reanalysis BLH products are positively associated with orographic complexity, as well as the occurrence of static instability. To our best knowledge, this study presents the first near-global view of high-resolution radiosonde-derived boundary layer height and provides a quantitative assessment of the four frequently used reanalysis products.

A Numerical Study of Cirrus Bands and Low Static-stability Layers associated with Tropical Cyclone Outflow

AbstractProminent cirrus cloud banding occurred episodically within a northern cirrus canopy of Typhoon Talim (2017) during its recurvature. The generation mechanisms of the cirrus bands and low static-stability layers that support the bands are investigated using a numerical simulation with the Advanced Research Weather Research and Forecasting Model. Inspection of model output reveals that thin layers of near-neutral to weakly unstable static stability are persistently present in the upper and lower parts of the upper-level outflow, and shallow convection aligned along the vertical shear vector is prevalent in these layers. The cirrus banding occurs as the lowered outflow from the weakening storm ascends slantwise over a midlatitude baroclinic zone, and updrafts of the preexisting shallow convection in the upper part of the outflow layer become saturated. It is shown that the strong outflow resulting from violation of gradient-wind balance in the core region, by itself, creates the low static-stability layers. Analyses of potential temperature and static stability budgets show that the low static-stability layers are created mainly by the differential radial advection of radial thermal gradients on the vertical edges of the outflow. The radial thermal gradients occur in response to the outward air parcel acceleration in the core region and deceleration in the outer region, which, by inducing compensating vertical mass transport into and out of the outflow, act to tilt the isentropes within the shear layers. The effects of environmental flow and cloud radiative forcing on the cirrus banding are also addressed.

Revisiting the Entrainment Relationship of Convective Plumes: A Perspective From Global Observations

AbstractEntrainment is an important process affecting convective transport and is a key parameter in convection modeling. For over half a century, an inverse relationship between entrainment rate (λ) and convective core size (R) has been used in modeling convective clouds. This short letter revisits the λ‐R relation using multiple years of CloudSat observations. Results show that the inverse relationship between λ and R is robust. However, they are not scaled by a simple constant. Global satellite observations provide some guidance for choosing the range of the scaling parameter. Further, our analysis shows that continental convective clouds tend to have smaller λ and larger R compared to oceanic convective clouds, suggesting that vertical mass transport by continental convection is more efficient. The satellite‐based study of the λ‐R relation has the potential to become a new diagnostic metric for assessing the representation of convection in weather and climate models.

Sensitivity of organized convective storms to model grid spacing in current and future climates.

Mesoscale convective systems (MCSs) are complexes of thunderstorms that become organized and cover hundreds of kilometres over several hours. MCSs are prolific rain producers in the tropics and mid-latitudes and are the major cause of warm-season flooding. Traditionally, climate models have difficulties in simulating MCSs partly due to the misrepresentation of complex process interactions that operate across a large range of scales. Significant improvements in simulating MCSs have been found in kilometre-scale models that explicitly simulate deep convection. However, these models operate in the grey zone of turbulent motion and have known deficiencies in simulating small-scale processes (e.g. entrainment, vertical mass transport). Here, we perform mid-latitude idealized ensemble MCS simulations under current and future climate conditions in three atmospheric regimes: hydrostatic (12 km horizontal grid spacing; Δx), non-hydrostatic (Δx = 4, 2 and 1 km) and large eddy scale (Δx = 500 m and 250 m). Our results show a dramatic improvement in simulating MCS precipitation, movement, cold pools, and cloud properties when transitioning from 12 km to 4 km Δx. Decreasing Δx beyond 4 km results in modest improvements except for up- and downdraft sizes, average vertical mass fluxes, and cloud top height and temperature, which continue to change. Most important for climate modelling is that Δx = 4 km simulations reliably capture most MCS climate change signals compared to those of the Δx = 250 m runs. Significantly different climate change signals are found in Δx = 12 km runs that overestimate extreme precipitation changes by up to 100%.This article is part of a discussion meeting issue ‘Intensification of short-duration rainfall extremes and implications for flash flood risks’.

Kinematic Subduction Rate Of Labrador Sea Water From an Eddy‐Permitting Numerical Model

AbstractWe use an eddy‐permitting, 1/12° regional configuration of the Nucleus for European Modelling of the Ocean (NEMO) model to examine water mass subduction rates in the Labrador Sea for the 2002–2013 period. An instantaneous kinematic subduction approach is implemented to calculate the subduction rate of Labrador Sea Water (LSW). By following the outcrop positions of a given isopycncal range, we calculate the vertical transport of a water mass from the mixed layer into the permanent thermocline over the course of a year. We examine the importance of the various terms in this approach, including the evolution of the Mixed Layer Depth (MLD), the advection across the base of the Mixed Layer (ML), and the vertical velocity at the base of the ML. We find that the subduction rate is not greatly affected by the definition of the MLD, as long as the integration time is long enough for the subduction‐obduction processes to balance each other. The total LSW subduction rate is ∼4–5 Sv, with similar rates for both Upper (ULSW) and Classical LSWs (CLSW), (∼2–2.5 Sv). After 2008, a shift in the LSW density is found in the simulation. CLSW reaches a maximum rate of 6 Sv in 2008, which is mainly inferred by the instantaneous ML change.

Facilitating All‐Inorganic Halide Perovskites Fabrication in Confined‐Space Deposition

Abstract2D all‐inorganic halide perovskites (2D AIHP) have attracted huge attention for their excellent optoelectronic properties and superior atmospheric stability for organic–inorganic halide perovskites. 2D AIHP has been fabricated by varied strategies, whereas a satisfied way to simultaneously reach good quality, dimensions, and uniformity is still far from achieved yet. Here, a direct thermal deposition method to synthesize 2D AIHP of lateral length up to ≈30 µm and uniform thickness down to ≈10 nm, which shows excellent optoelectronic performance comparable to the reported top‐level 2D AIHP, is proposed. A vertical mass transport instead of conventional horizontal mode is adopted, significantly enhancing the deposition stability. Furthermore, the morphologies of AIHP are switchable between nanowires and nanoflakes under the control of deposition temperature. This method may pave the way for uniform fabrication of 2D AIHP or AIHP‐based 2D heterostructures for various applications.

Tropical cyclone enhanced vertical transport in the northwestern South China Sea I: Mooring observation analysis for Washi (2005)

Using mooring-observed horizontal velocities and temperature from July 28 to August 2, 2005, this study analyzes the temporal-vertical variation of the diagnostic vertical velocity and mass transport during passage of tropical storm Washi (2005) over the northwestern continental shelf of the South China Sea (SCS). The results show that the total vertical velocity is of the order of O(1×10−4) m s−1 in the mixed layer above 25 m, and of O(1×10−5) m s−1 in the lower layer. Dynamically, the geostrophic advection and unsteady behavior of density induced by near-inertial oscillation are dominant factors in the upper and lower layers, respectively. As tropical storm Washi (2005) passed by from July 29 to 31, 2005, the upward vertical velocity was dominant and significantly enhanced to the order of O(1×10−3) m s−1. The diagnosed vertical velocity in the upper layer is one order greater than the averaged Ekman pumping velocity, which occurred one day earlier. The vertical advection transport calculated from the diagnosed vertical velocity reaches O(1×10−5) kg s−1m−3, one order greater than that induced by turbulent mixing. Time-averaged transports by vertical advection and mixing are both upward in the layer above the thermocline during the storm passage.

Significant Contribution of Mesoscale Overturning to Tropical Mass and Energy Transport Revealed by the ERA5 Reanalysis

Key Points The multiscale atmospheric overturning in the ERA5 and ERA‐Interim global reanalyses is compared using isentropic analysis Observed outgoing longwave radiation suggests that the mesoscale overturning in the tropics is better captured by ERA5 than ERA‐Interim Mesoscale overturning plays a comparable role to large‐scale overturning in vertical mass and energy transport over the tropics

Labrador Sea Water Formation Rate and Its Impact on the Local Meridional Overturning Circulation

AbstractThis paper investigates the link between the Labrador Sea Water (LSW) formation rate and the strength of the Atlantic Meridional Overturning Circulation within the Labrador Sea. LSW is formed in the Labrador Sea through deep wintertime ocean convection and is then carried out of the basin by, among other currents, the Deep Western Boundary Current (DWBC) that flows southward along the east coast of Canada. We used an eddy‐permitting simulation (at 1/12°, horizontal resolution) with an Arctic and Northern Hemisphere Atlantic configuration of the Nucleus for European Modeling of the Ocean (NEMO) model that covers the period from 2002 to 2017. In this study, the formation rate of LSW is estimated using an instantaneous kinematic subduction approach by analyzing the vertical transport of a water mass through the base of the mixed layer. We computed the local Meridional Overturning Circulation (MOC) index and the transport of LSW within the DWBC at the Atlantic Repeat hydrographic section 7 West (AR7W). Results show that an increase in the formation rate of LSW entails an increase in the LSW transport in the DWBC within 1 year. This is followed by an enhancement of the overturning in the Labrador Sea.

Numerical evaluation of urban green space scenarios effects on gaseous air pollutants in Tehran Metropolis based on WRF-Chem model

Although positive environmental aspects of increasing urban vegetative spaces are undeniable, using predefined or unmanaged long-term green programs may cause undesirable and unexpected impacts on the air quality in megacities. In this study, the mitigation potential of three green spaces development scenarios (expansion of surface vegetative area, Green Roof development and combination of surface and roof greenery) on three gaseous air pollutants (O3, SO2 and NO2) concentrations in Tehran Metropolis in an early summertime period is analyzed using coupled Weather Research and Forecasting model with chemistry (WRF/Chem), single-layer urban canopy model (SLUCM) and biogenic emission from Model of Emissions of Gases and Aerosols from Nature (MEGAN). Current results indicate that general patterns of diurnal distribution of SO2 and NO2 are totally controlled by the location of anthropogenic sources of pollutants in the south and the city center, beside the prevailing wind field over the city of Tehran. Ozone distribution follows the diurnal advection from the northern and eastern sub-urban areas and distribution of primary pollutants such as NO2. By conducting green scenarios, reduction in the wind speed, variations in pollutants dry deposition velocities which are directly affected by the boundary layer and surface properties, and pollutants deposition fluxes are observed. Alterations in deposition fluxes are not uniform across the city area and clearly conform to changes in pollutants concentrations. In addition, the shallower (deeper) boundary layer height and the buoyancy forcing due to the reduction (increase) in near-surface air temperature cause less (more) vertical mass transport during the day (night), which in both situations could have negative impacts on the air quality since under lower wind speed condition and less convective upward transfer, polluted air near the surface can be trapped. The defined scenarios have shown different impacts over the city of Tehran with the complex urban morphology so, suggestion of the most efficient summertime green policy with the minimum negative feedbacks is not conceivable.

Transport by deep convection in basin-scale geostrophic circulation: turbulence-resolving simulations

Direct numerical simulations are used to investigate the nature of fully resolved small-scale convection and its role in large-scale circulation in a rotating $f$-plane rectangular basin with imposed surface temperature difference. The large-scale circulation has a horizontal geostrophic component and a deep vertical overturning. This paper focuses on convective circulation with no wind stress, and buoyancy forcing sufficiently strong to ensure turbulent convection within the thermal boundary layer (horizontal Rayleigh numbers $Ra\approx 10^{12}{-}10^{13}$). The dynamics are found to depend on the value of a convective Rossby number, $Ro_{\unicode[STIX]{x0394}T}$, which represents the strength of buoyancy forcing relative to Coriolis forces. Vertical convection shifts from a mean endwall plume under weak rotation ($Ro_{\unicode[STIX]{x0394}T}>10^{-1}$) to ‘open ocean’ chimney convection plus mean vertical plumes at the side boundaries under strong rotation ($Ro_{\unicode[STIX]{x0394}T}<10^{-1}$). The overall heat throughput, horizontal gyre transport and zonally integrated overturning transport are then consistent with scaling predictions for flow constrained by thermal wind balance in the thermal boundary layer coupled to vertical advection–diffusion balance in the boundary layer. For small Rossby numbers relevant to circulation in an ocean basin, vertical heat transport from the surface layer into the deep interior occurs mostly in ‘open ocean’ chimney convection while most vertical mass transport is against the side boundaries. Both heat throughput and the mean circulation (in geostrophic gyres, boundary currents and overturning) are reduced by geostrophic constraints.