scholarly journals Large-Eddy Simulation of a Coastal Ocean under the Combined Effects of Surface Heat Fluxes and Full-Depth Langmuir Circulation

2016 ◽  
Vol 46 (8) ◽  
pp. 2411-2436 ◽  
Author(s):  
Rachel Walker ◽  
Andrés E. Tejada-Martínez ◽  
Chester E. Grosch
Keyword(s):  
Water Column ◽  
Stable Stratification ◽  
Coastal Ocean ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Surface Heating ◽  
Surface Cooling ◽  
Surface Heat Fluxes ◽  
Wide Range ◽  
Large Eddy

AbstractResults are presented from the large-eddy simulations (LES) of a wind-driven flow representative of the shallow coastal ocean under the influences of Langmuir forcing and surface heating and cooling fluxes. Langmuir (wind and surface gravity wave) forcing leads to the generation of Langmuir turbulence consisting of a wide range of Langmuir circulations (LCs) or parallel, counterrotating vortices that are aligned roughly in the direction of the wind. In unstratified, shallow coastal regions, the largest of the LCs reach the bottom of the water column. Full-depth LCs are investigated under surface waves with a significant wave height of 1.2 m and a dominant wavelength of 90 m and wave period of 8 s, for a wind speed of 7.8 m s−1 in a 15-m-deep coastal shelf region. Both unstable and stable stratification are imposed by constant surface heat fluxes and an adiabatic bottom wall. Simulations are characterized by Rayleigh and Richardson numbers representative of surface buoyancy forcing relative to wind forcing. For the particular combination of Langmuir forcing parameters studied, although surface cooling is able to augment the strength of LC, a significantly high cooling flux of 560 W m−2 (such that the Rayleigh number is Raτ = 1000) is required in order for turbulence kinetic energy generation by convection to exceed Langmuir production. Such a transition is expected at a lower heat flux for weaker wind and wave conditions and thus weaker LCs than those studied. Furthermore, a surface heating flux of approximately 281 W m−2 (such that the Richardson number is Riτ = 500) is able to inhibit vertical mixing of LC, particularly in the bottom half of the water column, allowing stable stratification to develop.

Convective Boundary Layers Driven by Nonstationary Surface Heat Fluxes

2011 ◽  
Vol 68 (4) ◽  
pp. 727-738 ◽  
Author(s):  
Robert van Driel ◽  
Harm J. J. Jonker
Keyword(s):  
Boundary Layer ◽  
Mixed Layer ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Layer Model ◽  
Convective Boundary ◽  
Surface Heat Fluxes ◽  
Large Eddy ◽  
Convective Boundary Layers ◽  
Mixed Layer Model

In this study the response of dry convective boundary layers to nonstationary surface heat fluxes is systematically investigated. This is relevant not only during sunset and sunrise but also, for example, when clouds modulate incoming solar radiation. Because the time scale of the associated change in surface heat fluxes may differ from case to case, the authors consider the generic situation of oscillatory surface heat fluxes with different frequencies and amplitudes and study the response of the boundary layer in terms of transfer functions. To this end both a mixed layer model (MLM) and a large-eddy simulation (LES) model are used; the latter is used to evaluate the predictive quality of the mixed layer model. The mixed layer model performs generally quite well for slow changes in the surface heat flux and provides analytical understanding of the transfer characteristics of the boundary layer such as amplitude and phase lag. For rapidly changing surface fluxes (i.e., changes within a time frame comparable to the large eddy turnover time), it proves important to account for the time it takes for the information to travel from the surface to higher levels of the boundary layer such as the inversion zone. As a follow-up to a 1997 study by Sorbjan, who showed that the conventional convective velocity scale is inadequate as a scaling quantity during the decay phase, this paper addresses the issue of defining, in (generic) transitional situations, a velocity scale that is solely based on the surface heat flux and its history.

scholarly journals Evidence for the Influence of Surface Heat Fluxes on Turbulent Mixing of Microplastic Marine Debris

2016 ◽  
Vol 46 (3) ◽  
pp. 809-815 ◽  
Author(s):  
Tobias Kukulka ◽  
Kara L. Law ◽  
Giora Proskurowski
Keyword(s):  
Turbulent Transport ◽  
Surface Heat ◽  
Transport Processes ◽  
Heat Fluxes ◽  
Marine Debris ◽  
Surface Boundary ◽  
Heating Cycle ◽  
Surface Cooling ◽  
Surface Boundary Layer ◽  
Surface Heat Fluxes

AbstractBuoyant microplastic marine debris (MPMD) is a pollutant in the ocean surface boundary layer (OSBL) that is submerged by wave-driven turbulent transport processes. This study analyzes observed MPMD surface concentrations in the Atlantic and Pacific Oceans to reveal a significant increase in concentrations during surface heating and a decrease during surface cooling. Turbulence-resolving large-eddy simulations of the OSBL for an idealized diurnal heating cycle suggest that turbulent downward fluxes of buoyant tracers are enhanced at night, facilitating deep submergence of plastics, and suppressed in heating conditions, resulting in surface-trapped MPMD. Simulations agree better with observations if enhanced mixing due to wave-driven Langmuir turbulence (LT) is included. The simulated time-dependent OSBL response results in hysteresis effects so that surface concentrations depend also on the phase of the diurnal heating cycle. The results demonstrate the controlling influence of surface heat fluxes and LT on turbulent transport in the OSBL and on vertical distributions of buoyant marine particles.

scholarly journals Large-eddy simulations of marine boundary-layer clouds associated with cold air outbreaks during the ACTIVATE campaign– part 1: Case setup and sensitivities to large-scale forcings

2021 ◽  
Author(s):  
Xiang-Yu Li ◽  
Hailong Wang ◽  
Jingyi Chen ◽  
Satoshi Endo ◽  
Geet George ◽  
...  
Keyword(s):  
Large Scale ◽  
Field Measurements ◽  
Reanalysis Data ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Turbulent Heat ◽  
Liquid Water Path ◽  
Surface Heat Fluxes ◽  
Large Eddy ◽  
Turbulent Heat Fluxes

Abstract Large-eddy simulation (LES) is able to capture key boundary-layer (BL) turbulence and cloud processes. Yet, large-scale forcing and surface turbulent fluxes of sensible and latent heat are often poorly prescribed for LES simulations. We derive these quantities from measurements and reanalysis obtained for two cold air outbreak (CAO) events during Phase I of the Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE) in February-March 2020. We study the two contrasting CAO cases by performing LES and test the sensitivity of BL structure and clouds to large-scale forcings and turbulent heat fluxes. Profiles of atmospheric state and large-scale divergence and surface turbulent heat fluxes obtained from the reanalysis data ERA5 agree reasonablywell with those derived fromACTIVATE field measurements for both cases at the sampling time and location. Therefore, we adopt the time evolving heat fluxes, wind and advective tendencies profiles from ERA5 reanalysis data to drive the LES.We find that large-scale thermodynamic advective tendencies and wind relaxations are important for the LES to capture the evolving observed BL meteorological states characterized by the hourly ERA5 reanalysis data and validated by the observations. We show that the divergence (or vertical velocity) is important in regulating the BL growth driven by surface heat fluxes in LES simulations. The evolution of liquid water path is largely affected by the evolution of surface heat fluxes. The liquid water path simulated in LES agrees reasonably well with the ACTIVATE measurements. This study paves the path to investigate aerosol-cloud-meteorology interactions using LES informed and evaluated by ACTIVATE field measurements.

Trends of land surface heat fluxes on the Tibetan Plateau from 2001 to 2012

2017 ◽  
Vol 37 (14) ◽  
pp. 4757-4767 ◽  
Author(s):  
Cunbo Han ◽  
Yaoming Ma ◽  
Xuelong Chen ◽  
Zhongbo Su
Keyword(s):  
Tibetan Plateau ◽  
Land Surface ◽  
Surface Heat ◽  
Heat Fluxes ◽  
The Tibetan Plateau ◽  
Surface Heat Fluxes ◽  
Land Surface Heat Fluxes

On the Hyperbolicity of the Bulk Air–Sea Heat Flux Functions: Insights into the Efficiency of Air–Sea Moisture Disequilibrium for Tropical Cyclone Intensification

2021 ◽  
Vol 149 (5) ◽  
pp. 1517-1534
Author(s):  
Benjamin Jaimes de la Cruz ◽  
Lynn K. Shay ◽  
Joshua B. Wadler ◽  
Johna E. Rudzin
Keyword(s):  
Tropical Cyclone ◽  
Surface Wind ◽  
Heat Content ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Ocean Heat Uptake ◽  
Surface Heat Fluxes ◽  
Heat Uptake ◽  
Moisture Fluxes ◽  
New Perspective

AbstractSea-to-air heat fluxes are the energy source for tropical cyclone (TC) development and maintenance. In the bulk aerodynamic formulas, these fluxes are a function of surface wind speed U10 and air–sea temperature and moisture disequilibrium (ΔT and Δq, respectively). Although many studies have explained TC intensification through the mutual dependence between increasing U10 and increasing sea-to-air heat fluxes, recent studies have found that TC intensification can occur through deep convective vortex structures that obtain their local buoyancy from sea-to-air moisture fluxes, even under conditions of relatively low wind. Herein, a new perspective on the bulk aerodynamic formulas is introduced to evaluate the relative contribution of wind-driven (U10) and thermodynamically driven (ΔT and Δq) ocean heat uptake. Previously unnoticed salient properties of these formulas, reported here, are as follows: 1) these functions are hyperbolic and 2) increasing Δq is an efficient mechanism for enhancing the fluxes. This new perspective was used to investigate surface heat fluxes in six TCs during phases of steady-state intensity (SS), slow intensification (SI), and rapid intensification (RI). A capping of wind-driven heat uptake was found during periods of SS, SI, and RI. Compensation by larger values of Δq > 5 g kg−1 at moderate values of U10 led to intense inner-core moisture fluxes of greater than 600 W m−2 during RI. Peak values in Δq preferentially occurred over oceanic regimes with higher sea surface temperature (SST) and upper-ocean heat content. Thus, increasing SST and Δq is a very effective way to increase surface heat fluxes—this can easily be achieved as a TC moves over deeper warm oceanic regimes.

Boundary Surface Heat Fluxes in a Square Enclosure with an Embedded Design Element

2010 ◽  
Vol 24 (4) ◽  
pp. 845-849 ◽  
Author(s):  
M. Ajith ◽  
Ranjan Das ◽  
Ramgopal Uppaluri ◽  
Subhash C. Mishra
Keyword(s):  
Boundary Surface ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Design Element ◽  
Surface Heat Fluxes ◽  
Square Enclosure ◽  
Embedded Design
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