Vertical Heat Flux Research Articles

Upper Ocean Thermodynamic Response to Coupling Currents to Wind Stress over the Gulf Stream

We use high-resolution coupled atmosphere–ocean model simulations over the Gulf Stream extension region during a winter season to examine the upper ocean thermodynamic response to including current feedback to atmospheric wind stress. We demonstrate that a model that includes current feedback leads to significant changes in the structure and transport of heat throughout the upper ocean in comparison to the same model without current feedback. We find that including the current feedback leads to changes in the upper ocean temperature pattern that match the vorticity pattern. Areas with cyclonic ocean vorticity, typically north of the Gulf Stream extension, correspond to areas with warmer temperatures throughout the water column. Areas with anticyclonic ocean vorticity, typically south of the Gulf Stream extension, correspond to areas with cooler temperatures throughout the water column. We also find that including current feedback leads to an overall reduction in the submesoscale vertical heat flux spectra across all spatial scales, with differences in the submesoscale vertical heat flux corresponding to SST minus mixed layer temperature differences. The direct impact of current feedback on the thermodynamic structure within the upper ocean also has indirect impacts on other aspects of the ocean, such as the energy transfer between the ocean and the atmosphere, ocean stratification, and acoustic parameters.

The Impact of Turbulent Transport Efficiency on Surface Vertical Heat Fluxes in the Arctic Stable Boundary Layer Predicted from Similarity Theory and Machine Learning

Abstract We analyzed 14 days of observations from sonic anemometry and high-resolution fiber-optic distributed sensing collected in the stable boundary layer (SBL). The study sought to evaluate if and under which conditions the sensible heat flux is related to the temperature gradient. Machine learning methods were employed to identify drivers of and model heat fluxes. We found the recently proposed coupling metric Ω defined as the ratio of the buoyancy length scale and measurement height to delineate physically meaningful transport regimes. The regime transition marks the point where static stability, in addition to the vertical turbulence strength, controls the heat transport, which is rather gradual than abrupt. The maximum downward heat flux is reached when one-third of turbulent eddies exceed the opposing buoyancy forces in the SBL. We found evidence that even for large Ω a substantial fraction of the turbulent transport is nonequilibrium. The nondimensional temperature gradient is better explained by variations in Ω than ζ = zL−1 from Monin–Obukhov similarity theory. Its continuous organization with Ω across stabilities suggests that the vertical heat transport always remains coupled to the surface, but its efficiency and the resulting flux vary. Forty-three percent of the total enthalpy is exchanged during conditions of limited transport efficiency in the very SBL despite the small flux magnitude of ≤7 W m−2, which underlines the importance of quantifying the weak surface exchange for polar regions. When predicting sensible heat fluxes using mean quantities from weather stations, the net longwave radiative forcing and the horizontal wind speed are the most important predictors representing stratification and bulk shear. Significance Statement Climate warming is amplified in polar regions, but quantifying heat transfer is complicated since mixing is weak and sporadic. We aim to understand when and why measurements taken in the lowest meters above snow can be used to quantify the surface heat transfer and if common modeling concepts are valid. We found that the measured heat transfer for weak winds and clear skies is connected to the snow surface only to a small degree in 66% of all cases at a much (−65%) reduced magnitude compared to strong wind or cloudy cases. However, 43% of the total heat is exchanged during these conditions and thus must be included in surface heat budgets. Classic modeling concepts systematically underpredicted the exchanged heat budget by 12% across all conditions which limits their utility in polar regions.

Effects of the internal temperature on vertical mixing and on cloud structures in ultra-hot Jupiters

The vertical mixing in hot-Jupiter atmospheres plays a critical role in the formation and spacial distribution of cloud particles in their atmospheres. This affects the observed spectra of a planet through cloud opacity, which can be influenced by the degree of cold trapping of refractory species in the deep atmosphere. We aim to isolate the effects of the internal temperature on the mixing efficiency in the atmospheres of ultra-hot Jupiters (UHJs) and the spacial distribution of cloud particles across the planet. We combined a simplified tracer-based cloud model, a picket fence radiative-transfer scheme, and a mixing length theory to the Exo-FMS general circulation model. We ran the model for five different internal temperatures at typical UHJ atmosphere system parameters. Our results show the convective eddy diffusion coefficient remains low throughout the vast majority of the atmosphere, with mixing dominated by advective flows. However, some regions can show convective mixing in the upper atmosphere for colder interior temperatures. The vertical extent of the clouds is reduced as the internal temperature is increased. Additionally, a global cloud layer gets formed below the radiative--convective boundary (RCB) in the cooler cases. Convection is generally strongly inhibited in UHJ atmospheres above the RCB due to their strong irradiation. Convective mixing plays a minor role compared to advective mixing in keeping cloud particles aloft in UHJs with warm interiors. Higher vertical turbulent heat fluxes and the advection of potential temperature inhibit convection in warmer interiors. Our results suggest that isolated upper atmosphere regions above cold interiors may exhibit strong convective mixing in isolated regions around Rossby gyres, allowing aerosols to be better retained in these areas.

Seasonality of Submesoscale Vertical Heat Transport Modulated by Oceanic Mesoscale Eddies in the Kuroshio Extension

AbstractEnergetic mesoscale eddies are often accompanied by strong submesoscale variability, which plays a significant role in connecting mesoscale and turbulent motions in the ocean and leads to strong vertical motions. The product of a high‐resolution (1/48°) oceanic numerical model, the LLC4320, is employed to investigate the seasonal variations of vertical heat transport induced by submesoscale processes within multiple mesoscale eddies in the Kuroshio Extension (KE) region. In different seasons, the submesoscale vertical heat transport exhibits a consistent upward pattern, with notably higher magnitudes observed during winter. In winter, the maxima value of submesoscale vertical heat flux (SVHF) can account for approximately 60% of the total vertical heat flux (VHF). This is equivalent to the average net sea surface heat flux in a single eddy region. In summer and autumn, the maxima absolute value of submesoscale vertical heat flux can account for approximately 30% of the total VHF. Energy analysis reveals that baroclinic instability associated with vertical buoyancy flux has a crucial effect on generating submesoscale processes within the eddy region. The submesoscale motions are influenced by the mixed layer instability, strain‐induced frontogenesis, turbulent thermal wind and turbulent thermal wind‐induced frontogenesis within the upper mixed layer, while they are largely associated with the strain‐induced frontogenesis in the ocean interior. Furthermore, the upward low‐frequency submesoscale vertical heat transport is generated by submesoscale secondary circulation at eddy peripheries.

Air–Sea Coupling Feedbacks over Tropical Instability Waves

Abstract Tropical instability waves (TIWs) are oceanic features that form around the equatorial Pacific cold tongue and influence the large-scale circulation and coupled climate variability including El Niño–Southern Oscillation. Local air–sea coupling over TIWs is thought to play an important role in the atmosphere and ocean’s energy and tracer budgets but is not well captured in coarse-resolution models. In this study, we isolate the impacts of TIW thermal (sea surface temperature–driven) and current (surface current–driven) feedbacks by removing TIW signatures in air–sea coupling fields in a high-resolution regional coupled model. The thermal feedback is found to damp TIW temperature variance by a factor of 2, associated both with the direct dependence of surface heat fluxes on SST (∼74%) and indirect impacts on surface winds (∼35%) and air temperature and humidity (∼−9%). These changes lead to cooling of the cold tongue SST by up to 0.1°C through reduced TIW-driven meridional heat fluxes and associated small changes in atmospheric circulation. The current feedback is decomposed into TIW (i.e., mesoscale) and mean (i.e., large-scale) components using separate experiments, with both having distinct impacts on TIWs and the mean state. The mesoscale current feedback reduces TIW eddy kinetic energy (EKE) by 22% through the eddy wind work, while the mean current feedback induces a further reduction of 8% by extracting energy from the mean currents and thus reducing barotropic EKE shear production. An improved understanding of small-scale tropical Pacific processes is needed to address biases in coarse-resolution models that impact their predictions and projections of Pacific climate variability and change. Significance Statement Tropical instability waves (TIWs) are oceanic features with ∼1000-km wavelengths that propagate westward on either side of the eastern equatorial Pacific cold tongue. TIWs drive lateral and vertical heat fluxes that impact several aspects of El Niño–Southern Oscillation. While climate models with a moderate, 1/4° ocean resolution can capture some TIW variability, they fail to properly represent many associated processes such as the impact of TIWs on the overlying atmosphere. Using sensitivity studies performed using a high-resolution regional coupled model, we study the impact of TIW air–sea coupling on the eastern Pacific climate system. Increased understanding of small-scale processes from studies such as this is essential to understand and address biases in models used for seasonal climate predictions and projections in the Pacific region.

A Method for Interpreting the Role of Parameterized Turbulence on Global Metrics in the Community Earth System Model

AbstractThe parameterization of subgrid‐scale processes such as boundary layer (PBL) turbulence introduces uncertainty in Earth System Model (ESM) results. This uncertainty can contribute to or exacerbate existing biases in representing key physical processes. This study analyzes the influence of tunable parameters in an experimental version of the Cloud Layers Unified by Binormals (CLUBBX) scheme. CLUBB is the operational PBL parameterization in the Community Atmosphere Model version 6 (CAM6), the atmospheric component of the Community ESM version 2 (CESM2). We perform the Morris one‐at‐a‐time (MOAT) parameter sensitivity analysis using short‐term (3‐day), initialized hindcasts of CAM6‐CLUBBX with 24 unique initial conditions. Several input parameters modulating vertical momentum flux appear most influential for various regionally‐averaged quantities, namely surface stress and shortwave cloud forcing (SWCF). These parameter sensitivities have a spatial dependence, with parameters governing momentum flux most influential in regions of high vertical wind shear (e.g., the mid‐latitude storm tracks). We next evaluate several experimental 20‐year simulations of CAM6‐CLUBBX with targeted parameter perturbations. We find that parameter perturbations produce similar physical mechanisms in both short‐term and long‐term simulations, but these physical responses can be muted due to nonlinear feedbacks manifesting over time scales longer than 3 days, thus causing differences in how output metrics respond in the long‐term simulations. Analysis of turbulent fluxes in CLUBBX indicates that the influential parameters affect vertical fluxes of heat, moisture, and momentum, providing physical pathways for the sensitivities identified in this study.

Turbulent fluxes of aerosol and heat in a desertified area during intermittent emission of dust aerosol

Based on fluctuations measurement results in the components of wind speed, air temperature and concentration of aerosol particles on a desertified area in the Astrakhan region under conditions of intermittent emission of dust aerosol, vertical turbulent fluxes of dust aerosol and heat were determined. Using spectral analysis, the temporal variability of the horizontal and vertical components of wind speed, air temperature and concentration of dust aerosol particles was characterized. It is shown that the intermittent emission of the dust aerosol is determined by low-frequency convective-induced variations in the horizontal component of wind speed when the threshold saltation speed is exceeded. Significant differences in the spatiotemporal variability of vertical heat transfer and dust aerosol were revealed. The 30-minute average values of heat fluxes (90–158 W/m2) and dust aerosol (7.2–27.5 cm–2cm–1), as well as the rate of heat removal (14–21 cm/s) and dust aerosol (10–16 cm/s).

Simulation-Directed Construction of Bamboo-Forest-Like Heat Conduction Networks to Enhance Silicon Rubber Composites' Heat Conduction Properties.

Highly vertically thermally conductive silicon rubber (SiR) composites are widely used as thermal interface materials (TIMs) for chip cooling. Herein, inspired by water transport and transpiration of Moso bamboo-forests extensively existing in south China, and guided by filler self-assembly simulation, bamboo-forest-like heat conduction networks, with bamboo-stems-like vertically aligned polydopamine-coated carbon fibers (VA-PCFs), and bamboo-leaves-like horizontally layered Al2O3(HL-Al2O3), are rationally designed and constructed. VA-PCF/HL-Al2O3/SiR composites demonstrated enhanced heat conduction properties, and their through-plane thermal conductivity and thermal diffusivity reached 6.47W(mK)-1 and 3.98mm2s-1 at 12vol% PCF and 4vol% Al2O3 loadings, which are 32% and 38% higher than those of VA-PCF (12vol%) /SiR composites, respectively. The heat conduction enhancement mechanisms of VA-PCF/HL-Al2O3 networks on their SiR composites are revealed by multiscale simulation: HL-Al2O3 bridges the separate VA-PCF heat flow channels, and transfers more heat to the matrix, thereby increasing the vertical heat flux in composites. Along with high volume resistivity, low compression modulus, and coefficient of thermal expansion, VA-PCF/HL-Al2O3/SiR composites demonstrate great application potential as TIMs, which is proven using multiphysics simulation. This work not only makes a meaningful attempt at simulation-driven biomimetic material structure design but also provides inspiration for the preparation of TIMs.

Multiscale mushy layer model for Arctic marginal ice zone dynamics

Perhaps the most dynamic component of the Arctic sea ice cover is the marginal ice zone (MIZ), the transitional region between dense pack ice to the north and open ocean to the south. It widens by a factor of four while seasonally migrating more than 1600 km poleward in the Bering–Chukchi Sea sector, impacting climate dynamics, ecological processes, and human accessibility to the Arctic. Here we showcase a transformative mathematical modeling approach to understanding changes in MIZ location and width, focusing on their seasonal cycles as observed by satellites. We view the MIZ as a liquid-solid phase transition region, or mushy zone, on the scale of the Arctic Ocean. Invoking the physics of phase changes, the MIZ is modeled as a dynamic, multiscale composite material layer; this model captures 96% of the annual cycle of MIZ location and 78% of the annual cycle of MIZ width. Temperature in the upper ocean is described by a nonlinear heat equation with effective parameters obtained using homogenization theory for a random medium of ice floes in a sea water host. Observations and simulations together indicate that MIZ location closely tracks the below-ice 273 K isotherm while the width of the MIZ follows vertical heat flux convergence, but with a three-week lag.

Surface Quasi Geostrophic Reconstruction of Vertical Velocities and Vertical Heat Fluxes in the Southern Ocean: Perspectives for SWOT

AbstractMesoscale currents account for 80% of the ocean's kinetic energy, whereas submesoscale currents capture 50% of the vertical velocity variance. SWOT's first sea surface height (SSH) observations have a spatial resolution an order of magnitude greater than traditional nadir‐looking altimeters and capture mesoscale and submesoscale features. This enables the derivation of submesoscale vertical velocities, crucial for the vertical transport of heat, carbon and nutrients between the ocean interior and the surface. This work focuses on a mesoscale energetic region south of Tasmania using a coupled ocean‐atmosphere simulation at km‐scale resolution and preliminary SWOT SSH observations. Vertical velocities (w), temperature anomalies and vertical heat fluxes (VHF) from the surface down to 1,000 m are reconstructed using effective surface Quasi‐Geostrophic (sQG) theory. An independent method for reconstructing temperature anomalies, mimicking an operational gridded product, is also developed. Results show that sQG reconstructs 90% of the modeled w and VHF rms at scales down to 30 km just below the mixed layer and 50%–70% of the rms for scales larger than 70 km at greater depth, with a spatial correlation of 0.6. The reconstruction is spectrally coherent for scales larger than 30–40 km at the surface, slightly degrading ( 0.55) at depth. Two temperature anomaly data sets yield similar results, indicating the dominance of w on VHF. The RMS of sQG and VHF derived from SWOT are twice as large as those derived from conventional altimetry, highlighting the potential of SWOT for reconstructing energetic meso and submesoscale dynamics in the ocean interior.

How advection affects the surface energy balance and its closure at an irrigated alfalfa field

Orbiting around the non-closure problem in eddy covariance, a new generation of high-resolution thermal imagery has revealed that advection may be more common than previously expected. To investigate this, we conducted an extensive study over an irrigated alfalfa field that experienced heat and moisture advection. Over the course of five analysis periods (37 days total), multiple tower arrays and profile measurements were deployed to measure the horizontal advection and vertical heat flux divergence. Latent heat flux (λE) measured at the anchor tower showed an enhancement (i.e., increase) due to both local and non-local processes. Locally, as a result of the upwind λE, advection humidified the atmosphere and increased stomatal opening, enhancing the downwind λE. Simultaneously, with lowered atmospheric demand, λE was suppressed downwind. Our results suggest that stomatal regulation played a dominant role in the enhancement, but not by itself. Spectral analysis revealed that low frequency (i.e., large) eddies contributed high heat and moisture via advection. In combination with thermal remote sensing observations from ECOSTRESS and Landsat 8/9, we found that these large eddies were generated over the upwind surface, and they were independent of the local boundary layer conditions. Consequently, spatiotemporal heterogeneity in land-surface conditions induced large eddies, further enhancing λE through non-local transport of heat and moisture. Lastly, by conditionally including the advective fluxes, the energy balance closure improved from 89 % to 97 % (r2 = 0.97, p < 0.001) over the five analysis periods. Results from this improved energy balance closure suggest an alternative approach for developing validation datasets for remote sensing evapotranspiration (ET) models rather than forcing closure with Bowen-ratio. Furthermore, our findings provide insights for algorithms that may improve remote sensing ET products that treat pixels as isolated columns rather than also considering the lateral effects of heat and moisture transport.

Investigation on the restrain effect of air curtain to the spilled flame and its heat flux of a compartment-facade fire

This paper investigates the restrain effect of air curtain to the spilled flame and its heat flux of a compartment-facade fire. A compartment model of 1.2 m × 0.9 m × 0.9 m is established in this study, and an air curtain is facilized at the compartment opening for fire protection. The air curtain jet velocity, the heat release rate as well as the opening dimension are changed as representative to typical fire scenarios. Flame behavior and heat flux profile of spill plume are captured by CCD cameras and water-cooled heat flux gauge for discussion. Results show that the air curtain jet could have a substantial impact on the flame behavior of spilled plumes from a compartment-facade fire. Compared to that of free condition without air curtain, the flame height becomes 20 % lower as the jet velocity to be 2 m/s, while it becomes 60 % lower as the jet velocity to be 5 m/s. At the meantime, the spilled plume is noticeably influenced by the “restricting effect” of the air curtain and thus flame trajectory is significantly flattened by the inertia force of the air curtain but also pushed farther from the facade wall, resulting in an increasing of flame depth. The decreasing in flame height plus the increasing flame depth would result in the reduction of heat flux intensity upon the facade wall, which is helpful for the fire protection of the facade wall. Then, a normalized factor of Υ is further proposed to the new correlation of flame height under various air curtain jet conditions at the opening. Regarding to different ejected flame behavior at the presence of air curtain jet, the heat flux upon the facade wall is quantitative analyzed to evaluate the thermal impact of spilled plume from the compartment fire. Finally, new correlations of the vertical heat flux upon the facade wall could be well achieved by a function of normalized height factor Z/Zf, v.

Effect of mass ratio on flame propagation behaviors and thermal radiation performance of Al–AlH3 composite dust

Aluminum (Al) is a high-energy density fuel additive commonly used in solid composite propellants. However, Al dust will form a dense oxide layer, which will reduce activity. Aluminum hydride (AlH3) can release hydrogen, destroying the oxide film structure and releasing more energy. In this paper, the flame and thermal radiation characteristics of Al–AlH3 composite dust explosion with different mass ratios were studied experimentally. The results indicate that under the same mass ratio, the propagation height, velocity, and flame surface temperature of the composite system show a trend of first increasing and then decreasing. With the decrease of Al, the propagation height, velocity, and flame surface temperature increase gradually, with maximum values of 420 mm, 17.9 m⋅s−1, and 2033 °C, respectively. With the increase of AlH3 content, the composite system releases more H2, which lead to the enhancement of reaction intensity. Based on experimental and semi-empirical static models, the heat radiation flux is calculated. Compared with the quasi-static process on the tube side, the experimental value of vertical heat flux is greater than the calculated value. Therefore, the model is modified by introducing λ. It provides a theoretical basis for the flame and thermal radiation of dust explosions confined by vertical tubes.

Diffusive‐Convection Staircase Merger Events Mediated by Subsurface Eddies in the Canada Basin

AbstractDiffusive‐convection (DC) staircases, characterized by interleaving well‐mixed layers and high‐gradient interfaces of thermohaline properties, are commonly observed in the Canada Basin, Arctic. Previous studies suggested a quasi‐steady state of the thermohaline structures of these staircases. In this work, we employ mooring and Ice‐Tethered Profiler (ITP) data to show emergent merger events of staircases mediated by subsurface eddies with warm cores located at 300–500 m depths in 2005, 2007 and 2009. Two types of merger events, the B‐merger (resulting from strengthening of stronger interfaces at the expense of weaker ones) and the H‐merger (produced by vertical drift and collision of staircase interfaces), are documented during the passage of subsurface eddies. The merging staircases are located at 320–450 m depths, with layers of up to 70 m thick and high‐gradient interfaces thinner than 5 m. Mooring measurements reveal the emergence of staircase mergers associated with a background Richardson number dropping from a typical magnitude of – to , indicating the persistence of DC staircases in the presence of strong shears. In parallel, ITP data suggest the formation of B‐mergers (H‐mergers) to be favored within the eddy core (flank). The vertical heat fluxes associated with the B‐merger (H‐merger) staircases are estimated to be ∼3 W/m2 (∼1.5 W/m2), which substantially exceed the typical staircase‐driven heat fluxes of W/m2. These observations imply the significance of subsurface eddies in shaping the halocline structures and thus the vertical heat fluxes in the Arctic Ocean, particularly in a warming climate.

Increases in the Local Eddy Energetics of the Extratropical Atmosphere over the Last Four Decades

Abstract Changes in the vertical and meridional temperature gradients of the atmosphere drive competing influences on storm-track activity. We apply local eddy energetics to the ERA5, JRA-55, MERRA-2, and NCEP-2 reanalyses during 1980–2020 to determine the locations, magnitudes, and trends of the energy transfer mechanisms for synoptic-scale eddies. Eddy kinetic energy (EKE) increases more rapidly in the Southern Hemisphere at all altitudes and seasons, with larger increases during austral winter and spring. In the Northern Hemisphere, increases occur within the Atlantic and Pacific storm tracks at pressures below 300 hPa but only during boreal winter and spring and confined within a narrow zonal band; EKE decreases during boreal summer and fall. Most EKE changes correspond with trends in baroclinic energy conversion upstream of storm tracks and appear to align with increases in the growth rate of the most unstable baroclinic mode. Barotropic energy conversion of EKE to the mean flow becomes locally more intense downstream of the storm tracks. Conversion of EKE to long-period eddies plays a minor role averaged over a hemisphere but can be important locally. The primary strengthening pathway for removal of EKE is a combination of surface friction and viscous dissipation. The increased baroclinic conversion in the Southern Hemisphere appears related to upper-level tropical temperature increases. In the Northern Hemisphere, increased baroclinic conversion is enabled by a combination of increased vertical heat fluxes and a region of temperature increases within 30°–60°N. Significance Statement Traveling atmospheric disturbances arrange into storm tracks that determine the weather in the midlatitudes. Storm tracks are evolving in time due to anthropogenic warming; however, the location and strength of temperature changes compete for influence on the storm tracks. A framework to quantify the mechanisms of generation of kinetic energy contained by eddies pinpoints the extent of storm-track evolution. Storm tracks generally strengthen across the planet but have increased the most in the Southern Hemisphere. Strengthening in the Northern Hemisphere is limited to the winter in a narrow latitudinal band, because of warming in the Arctic that reduces the primary instability that drives eddies. The locations of northern warming and storm-track strengthening suggest a role for tropical dynamics.

Research on effective thermal conductivity of hollow glass microspheres under vacuum at low temperature

As insulation materials with excellent thermal insulation properties, high robustness, and low maintenance costs, hollow glass microspheres (HGM) are gradually being applied in large liquid hydrogen storage tanks. However, the low-temperature insulation mechanism of HGMs is still unknown, and the insulation effect of HGMs of different types under various conditions has been neglected in recent decades. In this study, an existing theoretical model was improved by considering the gas thermal conductivity equations under various pressure intervals, and an experimental platform was built based on the steady vertical heat flux method to measure the effective thermal conductivities of three commercially available HGM models. The effective thermal conductivities of HGM models K1, T15, and HL20 at 0.1 Pa were 10, 8.9, and 7.6 mW/(m·K), respectively. The values decreased to 2.5, 2.9, and 2.0 mW/(m·K), respectively, when the cold boundary temperature was 90 K. To analyse the effect of the HGM physical parameters and environment on the HGM insulation, the thermal conductivities were calculated using the derived theoretical model. It was found that continuing to reduce the pressure after the ambient pressure reached 10 Pa hardly improved the insulation performances of the HGMs. The radiative heat transfer was very sensitive to temperature changes and jointly dominated the heat transfer with integrated thermal conductivity in the low-temperature region. In summary, HGMs are advanced vacuum-insensitive insulation materials, which have great potential in the field of cryogenic liquid storage and transportation.

Influence of the Summer Changes in Large-scale Atmospheric Circulation on the Vertical Fluxes of Heat and Moisture in Russian Landscape Zones

Influence of the Summer Changes in Large-scale Atmospheric Circulation on the Vertical Fluxes of Heat and Moisture in Russian Landscape Zones

SEAFRAME time series from the Southern Shelf reveal a neglected major upwelling mechanism

ABSTRACT In this era of climate change, it is important to have a reference state. For this purpose, an array of 12 port-based SEAFRAME gauges was established by Professor Geoffrey Lennon, through the Flinders University of South Australia, around the Australian coastline between 1991 and 1993. In addition to changes in sea level, they also record air and water temperature and wind velocity. We provide a method to extract the daily temperature anomaly between atmospheric and oceanic temperature recorded in the SEAFRAME gauge system. Thus, a fine-resolution record of the coastal ocean temperature structure can be obtained, which is a direct index of the vertical coastal heat flux that characterises both downwelling and upwelling. Results are presented for four gauges on the Southern Shelf for 2005, and for the ocean temperature anomaly time series during 2001–2010 at Portland, which monitors the structure of the Bonney Coast upwelling. This time series is also compared with that from an ECMWF model, and with that at Esperance which monitors an upwelling of similar strength on a wider shelf. The analysis reveals a second upwelling process in addition to the Ekman upwelling, which we have called the Flinders upwelling. The Ekman upwelling is due to a vertical velocity at the base of the mixed layer. The Flinders upwelling is due to a vertical velocity at the top of the mixed layer, which has been previously ignored. Along the Southern Shelf, the SEAFRAME data suggest that the Flinders upwelling is the dominant process.

Polydisperse sea spray effect on the vertical momentum transport in hurricanes

Abstract This study focuses on the influence of the sea spray polydispersity on the vertical transport of momentum in a turbulent marine atmospheric boundary layer in high-wind conditions of a hurricane. The Eulerian multifluid model treating air and spray droplets of different sizes as interacting inter-penetrating continua is developed and its numerical solutions are analyzed. Several droplet size distribution spectra and correlation laws relating wind speed and spray production intensity are considered. Polydisperse model solutions have confirmed the difference between the roles small and large spray droplets play in modifying the turbulent momentum transport that have been previously identified by monodisperse spray models. The obtained results have also provided a physical explanation for the previously unreported phenomenon of the formation of thin low-eddy-viscosity “sliding” layers in strongly turbulent boundary layer flows laden with predominantly fine spray.

Heat transfer and phase interface dynamics during impact and evaporation of subcooled impinging droplets on a heated surface

A comprehensive understanding of heat transfer mechanisms and hydrodynamics during droplet impingement on a heated surface and subsequent evaporation is crucial for improving heat transfer models, optimizing surface engineering, and maximizing overall effectiveness. This work showcases findings related to heat transfer mechanisms and simultaneous tracking of the moving contact line (MCL) for subcooled impinging droplets across a range of surface temperatures, utilizing a custom MEMS device, at multiple impact velocities. Experimental results show that heat flux caused by droplet impingement has a weaker dependence on surface temperature than receding MCL heat transfer due to evaporation, which is significantly surface temperature dependent. The measurements also demonstrate that when a droplet impacts a heated surface and evaporates, the process can be divided into two segments based on the effective heat transfer rate: an initial conduction-dominated segment followed by another segment dominated by surface evaporation. For subcooled impinging droplets, the effect of oscillatory motion is found to be negligible, unlike in a superheated regime; hence, heat conduction into the droplet entirely governs the first segment. Results also show that heat flux at the solid-liquid interface of an impinging droplet increases with the rise of either impact velocity or surface temperature. In the subcooled regime, droplets impacting a heated surface have approximately 1.6 times higher vertical heat flux values than gently deposited droplets. Furthermore, this study quantifies the contributions of buoyancy and thermocapillary convection within the droplet to the overall heat transfer.