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

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.

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Mathematical Modeling of Diurnal Patterns of Turbulent Heat Fluxes using Modified Aerodynamic Resistance Method

Asian Journal of Applied Sciences ◽

10.24203/ajas.v6i6.5568 ◽

2018 ◽

Vol 6 (6) ◽

Author(s):

R. T. Akinnubi ◽

O. O. Oketayo ◽

B. F. Akinwale ◽

M. O. Ojo ◽

A. Ikusika

Keyword(s):

Surface Temperature ◽

Aerodynamic Resistance ◽

Surface Heat ◽

Heat Fluxes ◽

Mean Bias Error ◽

Turbulent Heat ◽

Surface Heat Fluxes ◽

Diurnal Patterns ◽

Turbulent Heat Fluxes ◽

Following Error

The development of improved methods for estimating turbulent heat fluxes is important in effective monitoring of the surface energy balance for climate change prediction. However, different Â parameterized models carried out at the local site of Nigerian Micrometeorological site (NIMEX-1) did not consider the surface heat fluxes-aerodynamics resistance relationships, and these validated models cannot be incorporated into the Climate models because some of the input climate variables are not routinely available in some meteorological stations. This study therefore, aims at improving the diurnal patterns of surface heat fluxes estimates using radiometric surface temperature and aerodynamic surface-layer resistances. Hourly data of air temperature (Ta), soil temperature (Tsoil), global radiation (QL), surface temperature (Ts), wind speed (u), QH and QE were obtained from the NIMEX-1 at Ile-Ife (7.55 oN, 4.55 oE). The QH and QE were estimated using Aerodynamic Resistance Approach algorithm which was modified to reduce the large bias errors between the aerodynamic temperature and surface temperature above the ground level. The algorithms were validated and rated using the following error statistics: coefficient of determination (r2), Mean Bias Error (MBE) and Root Mean Square Error (RMSE). The RMSE and MBE for the modeled QE estimated using ARM and MAR reduced from 28.33Wm-2 to 14.33 Wm-2 and 36.93 to 10.74 Wm-2 respectively while for QH ,the RMSE and MBE reduced from 17.29 Wm-2 to 9.49 Wm-2 and 31.39 to 16.93 Wm-2 respectively. The r2 values ranged from 0.68 to 0.73 and 0.95 to 0.98 for QH and QE respectively. The MAR had the highest r2 and least error values.Â Hence, the proposed modified Aerodynamic resistance models are estimated the diurnal and seasonal turbulent heat fluxes accurately for tropical regions.

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

Journal of Physical Oceanography ◽

10.1175/jpo-d-15-0168.1 ◽

2016 ◽

Vol 46 (8) ◽

pp. 2411-2436 ◽

Cited By ~ 9

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.

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An Extremum Solution of the Monin–Obukhov Similarity Equations

Journal of the Atmospheric Sciences ◽

10.1175/2009jas3117.1 ◽

2010 ◽

Vol 67 (2) ◽

pp. 485-499 ◽

Cited By ~ 18

Author(s):

Jingfeng Wang ◽

Rafael L. Bras

Keyword(s):

Surface Layer ◽

Atmospheric Surface Layer ◽

Turbulent Transport ◽

Asymptotic Properties ◽

Field Measurements ◽

Surface Heat ◽

Heat Fluxes ◽

Obukhov Length ◽

Surface Heat Fluxes ◽

Momentum And Heat Fluxes

Abstract An extremum hypothesis of turbulent transport in the atmospheric surface layer is postulated. The hypothesis has led to a unique solution of Monin–Obukhov similarity equations in terms of simple expressions linking shear stress (momentum flux) and heat flux to mean wind shear and temperature gradient. The extremum solution is consistent with the well-known asymptotic properties of the surface layer. Validation of the extremum solution has been made by comparison to field measurements of momentum and heat fluxes. Furthermore, a modeling test of predicting surface heat fluxes using the results of this work is presented. A critical reexamination of the interpretation of the Obukhov length is given.

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Large Scale Surface Heat Fluxes

Large-Scale Oceanographic Experiments and Satellites ◽

10.1007/978-94-009-6421-1_11 ◽

1984 ◽

pp. 147-165 ◽

Cited By ~ 4

Author(s):

E. S. Sarachik

Keyword(s):

Large Scale ◽

Surface Heat ◽

Heat Fluxes ◽

Surface Heat Fluxes ◽

Scale Surface

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Convective Boundary Layers Driven by Nonstationary Surface Heat Fluxes

Journal of the Atmospheric Sciences ◽

10.1175/2010jas3643.1 ◽

2011 ◽

Vol 68 (4) ◽

pp. 727-738 ◽

Cited By ~ 31

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.

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Large-scale state and evolution of the atmosphere and ocean during PISTON 2018

Journal of Climate ◽

10.1175/jcli-d-20-0517.1 ◽

2021 ◽

pp. 1-59

Author(s):

Adam H. Sobel ◽

Janet Sprintall ◽

Eric D. Maloney ◽

Zane K. Martin ◽

Shuguang Wang ◽

...

Keyword(s):

Tropical Cyclone ◽

Large Scale ◽

Deep Convection ◽

Intraseasonal Variability ◽

Reanalysis Data ◽

The Philippines ◽

Heat Fluxes ◽

Surface Heat Fluxes ◽

Low Level ◽

The North

AbstractThe Propagation of Intraseasonal Tropical Oscillations (PISTON) experiment conducted a field campaign inAugust-October 2018. The R/V Thomas G. Thompson made two cruises in thewestern North Pacific region north of Palau and east of the Philippines. Using select field observations and global observational and reanalysis data sets, this study describes the large-scale state and evolution of the atmosphere and ocean during these cruises. Intraseasonal variability was weak during the field program, except for a period of suppressed convection in October. Tropical cyclone activity, on the other hand, was strong. Variability at the ship location was characterized by periods of low-level easterly atmospheric flow with embedded westward propagating synoptic-scale atmospheric disturbances, punctuated by periods of strong low-level westerly winds that were both connected to the Asian monsoon westerlies and associated with tropical cyclones. In the most dramatic case, westerlies persisted for days during and after tropical cyclone Jebi had passed to the north of the ship. In these periods, the sea surface temperature was reduced by a couple of degrees by both wind mixing and net surface heat fluxes that were strongly (~200Wm−2) out of the ocean, due to both large latent heat flux and cloud shading associated with widespread deep convection. Underway conductivity-temperature transects showed dramatic cooling and deepening of the ocean mixed layer and erosion of the barrier layer after the passage of Typhoon Mangkhut due to entrainment of cooler water from below. Strong zonal currents observed over at least the upper 400 meters were likely related to the generation and propagation of near-inertial currents.

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The Seasonality of Convective Events in the Labrador Sea

Journal of Climate ◽

10.1175/jcli-d-14-00009.1 ◽

2014 ◽

Vol 27 (17) ◽

pp. 6456-6471 ◽

Cited By ~ 6

Author(s):

Hao Luo ◽

Annalisa Bracco ◽

Fan Zhang

Keyword(s):

Large Scale ◽

Current System ◽

Horizontal Resolution ◽

Surface Heat ◽

Heat Fluxes ◽

Ocean Modeling ◽

Labrador Sea ◽

Boundary Current ◽

Regional Ocean Modeling System ◽

Surface Heat Fluxes

Abstract Modeling deep convection is a key challenge for climate science. Here two simulations of the Labrador Sea circulation obtained with the Regional Ocean Modeling System (ROMS) run at a horizontal resolution of 7.5 km are used to characterize the response of convection to atmospheric forcing and its seasonal variability over the period 1980–2009. The integrations compare well with the sparse observations available. The modeled convection varies in three key aspects over the 30 years considered. First, its magnitude changes greatly at decadal scales. This aspect is supported by the in situ observations. Second, the initiation and peak of convection (i.e., initiation and maximum) shift by 2–3 weeks between strong and weak convective years. Third, the duration of convection varies by approximately one month between strong and weak years. The last two changes are associated with the variability of the time-integrated surface heat fluxes over the Labrador Sea during winter and spring, while the first results from changes in both atmospheric heat fluxes and oceanic conditions through the lateral inflow of warm Irminger Water from the boundary current system to the basin interior. Changes in surface heat fluxes over the convective region are linked to large-scale modes of variability, the North Atlantic Oscillation and Arctic Oscillation. Implications for modeling the climate variability of the Labrador basin are discussed.

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