scholarly journals Oceanic eddy-induced modifications to air–sea heat and CO2 fluxes in the Brazil-Malvinas Confluence

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Luciano P. Pezzi ◽  
Ronald B. de Souza ◽  
Marcelo F. Santini ◽  
Arthur J. Miller ◽  
Jonas T. Carvalho ◽  
...  
Keyword(s):  
Vertical Mixing ◽  
Sampling Period ◽  
Heat Fluxes ◽  
Observation System ◽  
Transfer Velocity ◽  
Eddy Covariance Method ◽  
Brazil Current ◽  
Southwestern Atlantic Ocean ◽  
Ocean Atmosphere ◽  
Momentum And Heat Fluxes

AbstractSea surface temperature (SST) anomalies caused by a warm core eddy (WCE) in the Southwestern Atlantic Ocean (SWA) rendered a crucial influence on modifying the marine atmospheric boundary layer (MABL). During the first cruise to support the Antarctic Modeling and Observation System (ATMOS) project, a WCE that was shed from the Brazil Current was sampled. Apart from traditional meteorological measurements, we used the Eddy Covariance method to directly measure the ocean–atmosphere sensible heat, latent heat, momentum, and carbon dioxide (CO2) fluxes. The mechanisms of pressure adjustment and vertical mixing that can make the MABL unstable were both identified. The WCE also acted to increase the surface winds and heat fluxes from the ocean to the atmosphere. Oceanic regions at middle and high latitudes are expected to absorb atmospheric CO2, and are thereby considered as sinks, due to their cold waters. Instead, the presence of this WCE in midlatitudes, surrounded by predominantly cold waters, caused the ocean to locally act as a CO2 source. The contribution to the atmosphere was estimated as 0.3 ± 0.04 mmol m−2 day−1, averaged over the sampling period. The CO2 transfer velocity coefficient (K) was determined using a quadratic fit and showed an adequate representation of ocean–atmosphere fluxes. The ocean–atmosphere CO2, momentum, and heat fluxes were each closely correlated with the SST. The increase of SST inside the WCE clearly resulted in larger magnitudes of all of the ocean–atmosphere fluxes studied here. This study adds to our understanding of how oceanic mesoscale structures, such as this WCE, affect the overlying atmosphere.

scholarly journals Vertical Mixing and the Temperature and Wind Structure of the Tropical Tropopause Layer

2014 ◽  
Vol 71 (5) ◽  
pp. 1609-1622 ◽  
Author(s):  
Thomas J. Flannaghan ◽  
Stephan Fueglistaler
Keyword(s):  
Zonal Wind ◽  
Vertical Mixing ◽  
Heat Fluxes ◽  
Temperature Perturbation ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Wind Structure ◽  
Linear Perturbations ◽  
Potential Impact ◽  
Momentum And Heat Fluxes

Abstract Vertical mixing may lead to significant momentum and heat fluxes in the tropical tropopause layer (TTL) and these momentum and heat fluxes can force large climatological temperature and zonal wind changes in the TTL. The climatology of vertical mixing and associated momentum and heat fluxes as parameterized in the Interim ECMWF Re-Analysis (ERA-Interim) and as parameterized by the mixing scheme currently used in the ECMWF operational analyses are presented. Each scheme produces a very different climatology showing that the momentum and heat fluxes arising from vertical mixing are highly dependent on the scheme used. A dry GCM is then forced with momentum and heat fluxes similar to those seen in ERA-Interim to assess the potential impact of such momentum and heat fluxes. A significant response in the TTL is found, leading to a temperature perturbation of approximately 4 K and a zonal wind perturbation of approximately 12 m s−1. These temperature and zonal wind perturbations are approximately zonally symmetric, are approximately linear perturbations to the unforced climatology, and are confined to the TTL between approximately 10°N and 10°S. There is also a smaller-amplitude tropospheric component to the response. The results presented herein indicate that vertical mixing can have a large but uncertain effect on the TTL and that the choice and impact of the vertical mixing scheme should be an important consideration when modeling the TTL.

scholarly journals Seasonal and diurnal variations in moisture, heat and CO2 fluxes over a typical steppe prairie in Inner Mongolia, China

2009 ◽  
Vol 13 (7) ◽  
pp. 987-998 ◽  
Author(s):  
Z. Gao ◽  
D. H. Lenschow ◽  
Z. He ◽  
M. Zhou
Keyword(s):  
Inner Mongolia ◽  
Surface Albedo ◽  
Sensible Heat Flux ◽  
Experimental Period ◽  
Diurnal Variations ◽  
Heat Fluxes ◽  
Co2 Fluxes ◽  
Sensible Heat ◽  
Eddy Covariance Method ◽  
Seasonal And Diurnal Variations

Abstract. In order to examine energy partitioning and CO2 exchange over a steppe prairie in Inner Mongolia, China, fluxes of moisture, heat and CO2 in the surface layer from June 2007 through June 2008 were calculated using the eddy covariance method. The study site was homogenous and approximately 1500 m×1500 m in size. Seasonal and diurnal variations in radiation components, energy components and CO2 fluxes are examined. Results show that all four radiation components changed seasonally, resulting in a seasonal variation in net radiation. The radiation components also changed diurnally. Winter surface albedo was higher than summer surface albedo because during winter the snow-covered surface increased the surface albedo. The seasonal variations in both sensible heat and CO2 fluxes were stronger than those of latent heat and soil heat fluxes. Sensible heat flux was the main consumer of available energy for the entire experimental period. The energy imbalance problem was encountered and the causes are analyzed.

scholarly journals Options to correct local turbulent flux measurements for large-scale fluxes using a LES-based approach

2021 ◽  
Author(s):  
Matthias Mauder ◽  
Andreas Ibrom ◽  
Luise Wanner ◽  
Frederik De Roo ◽  
Peter Brugger ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Large Scale ◽  
Heat Fluxes ◽  
Eddy Covariance Method ◽  
Boundary Layer Height ◽  
Secondary Circulations ◽  
Low Pass ◽  
Measurement Height ◽  
Flux Measurements ◽  
Dispersive Fluxes

Abstract. The eddy-covariance method provides the most direct estimates for fluxes between ecosystems and the atmosphere. However, dispersive fluxes can occur in the presence of secondary circulations, which can inherently not be captured by such single-tower measurements. In this study, we present options to correct local flux measurements for such large-scale transport based on a non-local parametric model that has been developed from a set of idealized LES runs for three real-world sites. The test sites DK-Sor, DE-Fen, and DE-Gwg, represent typical conditions in the mid-latitudes with different measurement height, different terrain complexity and different landscape-scale heterogeneity. Different ways to determine the boundary-layer height, which is a necessary input variable for modelling the dispersive fluxes, are applied, either from operational radio-soundings and local in-situ measurements for the flat site or from backscatter-intensity profile obtained from collocated ceilometers for the two sites in complex terrain. The adjusted total fluxes are evaluated by assessing the improvement in energy balance closure and by comparing the resulting latent heat fluxes with evapotranspiration rates from nearby lysimeters. The results show that not only the accuracy of the flux estimates is improved but also the precision, which is indicated by RMSE values that are reduced by approximately 50 %. Nevertheless, it needs to be clear that this method is intended to correct for a bias in eddy-covariance measurements due to the presence of large-scale dispersive fluxes. Other reasons potentially causing a systematic under- or overestimation, such as low-pass filtering effects and missing storage terms, still need to be considered and minimized as much as possible. Moreover, additional transport induced by surface heterogeneities is not considered.

Regional oceanic and biogeochemical modeling strategy :forced or coupled model ?

2021 ◽  
Author(s):  
Véra Oerder ◽  
Pierre-Amaël Auger ◽  
Joaquim Bento ◽  
Samuel Hormazabal
Keyword(s):  
High Resolution ◽  
Wind Stress ◽  
Coupled Model ◽  
Heat Fluxes ◽  
Atmospheric Conditions ◽  
Coupled Simulation ◽  
Biogeochemical Modeling ◽  
Ocean Atmosphere ◽  
The Impact ◽  
Oceanic Model

<p><span> Regional high resolution biogeochemical modeling studies generaly use an oceanic model forced by prescribed atmospheric conditions. The computational cost of such approach is far lower than using an high resolution ocean-atmosphere coupled model. However, forced oceanic models cannot represent adequately the atmospheric reponse to the oceanic mesoscale (~10-100km) structures and the impact on the oceanic dynamics.</span></p><p><span>To assess the bias introduce by the use of a forced model, we compare here a regional high resolution (1/12º) ocean-atmosphere coupled model with oceanic simulations forced by the outputs of the coupled simulation. Several classical forcing strategies are compared : bulk formulae, prescribed stress, prescribed heat fluxes with or without Sea Surface Temperature (SST) restoring term, .... We study the Chile Eastern Boundary Upwelling System, and the oceanic model includes a biogeochemical component,</span></p><p><span>The coupled model oceanic mesoscale impacts the atmosphere through surface current and SST anomalies. Surface currents mainly affect the wind stress while SST impacts both the wind stress and the heat fluxes. In the forced simulations, mesoscale structures generated by the model internal variability does not correspond to those of the coupled simulation. According to the forcing strategy, the atmospheric conditions are not modified by the forced model mesoscale, or the modifications are not realistic. The regional dynamics (coastal upwelling, mesoscale activity, …) is affected, with impact on the biogeochemical activity.</span></p><p> </p><p> </p><p><em>This work was supported by the FONDECYT project 3180472 (Chile), with computational support of the NLHPC from the Universidad de Chile, the HPC from the Pontificia Universidad Catolica de Valparaiso and the Irene HPC from the GENCI at the CEA (France).</em></p>

Climate Response of Linear and Quadratic Functionals Using the Fluctuation–Dissipation Theorem

2008 ◽  
Vol 65 (9) ◽  
pp. 2824-2841 ◽  
Author(s):  
Andrey Gritsun ◽  
Grant Branstator ◽  
Andrew Majda
Keyword(s):  
General Circulation ◽  
Atmospheric General Circulation Model ◽  
Circulation Model ◽  
Heat Fluxes ◽  
Heat Sources ◽  
State Variables ◽  
Fluctuation Dissipation ◽  
Fluctuation Dissipation Theorem ◽  
Low Pass ◽  
Momentum And Heat Fluxes

Abstract A generalization of the fluctuation–dissipation theorem (FDT) that allows generation of linear response operators that estimate the response of functionals of system state variables is tested for a system defined by an atmospheric general circulation model (AGCM). A sketch of the proof of this generalization is provided, followed by comparison of response estimates based on the theory and actual responses of the AGCM for various idealized anomalous equatorial heat sources. Tested response quantities include precipitation, variances of bandpass and low-pass streamfunction, and momentum and heat fluxes. The solutions from the FDT operators are very similar to the AGCM solutions in terms of structure while overestimating response amplitudes by about 20%. As an example of an application of such response operators, the FDT operator that estimates the response of bandpass upper-tropospheric streamfunction variance is used to find the most efficient means of disturbing the Atlantic storm tracks by tropical heating. The results of the study suggest that the generalized FDT is an attractive method for systematically studying response attributes of the climate system that are of interest to climate scientists and society.

scholarly journals Characterization of mixing errors in a coupled physical biogeochemical model of the North Atlantic: implications for nonlinear estimation using Gaussian anamorphosis

Ocean Science ◽  
2010 ◽  
Vol 6 (1) ◽  
pp. 247-262 ◽  
Author(s):  
D. Béal ◽  
P. Brasseur ◽  
J.-M. Brankart ◽  
Y. Ourmières ◽  
J. Verron
Keyword(s):  
North Atlantic ◽  
Chlorophyll Concentration ◽  
Vertical Mixing ◽  
Wind Forcing ◽  
Observation System ◽  
Biogeochemical Model ◽  
Significant Information ◽  
The North ◽  
Biogeochemical Models ◽  
The North Atlantic

Abstract. In biogeochemical models coupled to ocean circulation models, vertical mixing is an important physical process which governs the nutrient supply and the plankton residence in the euphotic layer. However, vertical mixing is often poorly represented in numerical simulations because of approximate parameterizations of sub-grid scale turbulence, wind forcing errors and other mis-represented processes such as restratification by mesoscale eddies. Getting a sufficient knowledge of the nature and structure of these errors is necessary to implement appropriate data assimilation methods and to evaluate if they can be controlled by a given observation system. In this paper, Monte Carlo simulations are conducted to study mixing errors induced by approximate wind forcings in a three-dimensional coupled physical-biogeochemical model of the North Atlantic with a 1/4° horizontal resolution. An ensemble forecast involving 200 members is performed during the 1998 spring bloom, by prescribing perturbations of the wind forcing to generate mixing errors. The biogeochemical response is shown to be rather complex because of nonlinearities and threshold effects in the coupled model. The response of the surface phytoplankton depends on the region of interest and is particularly sensitive to the local stratification. In addition, the statistical relationships computed between the various physical and biogeochemical variables reflect the signature of the non-Gaussian behaviour of the system. It is shown that significant information on the ecosystem can be retrieved from observations of chlorophyll concentration or sea surface temperature if a simple nonlinear change of variables (anamorphosis) is performed by mapping separately and locally the ensemble percentiles of the distributions of each state variable on the Gaussian percentiles. The results of idealized observational updates (performed with perfect observations and neglecting horizontal correlations) indicate that the implementation of this anamorphosis method into sequential assimilation schemes can substantially improve the accuracy of the estimation with respect to classical computations based on the Gaussian assumption.

scholarly journals The Modification of Bottom Boundary Layer Turbulence and Mixing by Internal Waves Shoaling on a Barrier Reef

2011 ◽  
Vol 41 (11) ◽  
pp. 2223-2241 ◽  
Author(s):  
Kristen A. Davis ◽  
Stephen G. Monismith
Keyword(s):  
Boundary Layer ◽  
Internal Waves ◽  
Fast Response ◽  
Heat Fluxes ◽  
Bottom Boundary Layer ◽  
Mixing Efficiency ◽  
Florida Shelf ◽  
Bottom Boundary ◽  
Boundary Layer Turbulence ◽  
Momentum And Heat Fluxes

Abstract Results are presented from an observational study of stratified, turbulent flow in the bottom boundary layer on the outer southeast Florida shelf. Measurements of momentum and heat fluxes were made using an array of acoustic Doppler velocimeters and fast-response temperature sensors in the bottom 3 m over a rough reef slope. Direct estimates of flux Richardson number Rf confirm previous laboratory, numerical, and observational work, which find mixing efficiency not to be a constant but rather to vary with Frt, Reb, and Rig. These results depart from previous observations in that the highest levels of mixing efficiency occur for Frt < 1, suggesting that efficient mixing can also happen in regions of buoyancy-controlled turbulence. Generally, the authors find that turbulence in the reef bottom boundary layer is highly variable in time and modified by near-bed flow, shear, and stratification driven by shoaling internal waves.

scholarly journals Ocean–Atmosphere Feedback during Extreme Rainfall Events in Eastern Northeast Brazil

2018 ◽  
Vol 57 (5) ◽  
pp. 1211-1229 ◽  
Author(s):  
Thiago Luiz do Vale Silva ◽  
Doris Veleda ◽  
Moacyr Araujo ◽  
Pedro Tyaquiçã
Keyword(s):  
Transport Model ◽  
Inversion Layer ◽  
Lower Troposphere ◽  
Extreme Rainfall ◽  
Atmospheric Model ◽  
Heat Fluxes ◽  
Northeast Brazil ◽  
Extreme Rainfall Events ◽  
Rainfall Events ◽  
Ocean Atmosphere

AbstractThe coupled ocean–atmosphere–wave–sediment transport model and the Weather Research and Forecasting (WRF) atmospheric model were used to simulate extreme rainfall events from 10 to 25 June 2010 in eastern Northeast Brazil (ENEB). The simulations aimed at investigating the improvements from using a coupled ocean–atmospheric model of meteorological systems as the ocean–atmosphere interactions intensified during the period when flood events occurred in ENEB. In June 2010, the sea surface temperature (SST) was warmer than 28.5°C in the western tropical South Atlantic Ocean with anomalies above 1°C, which are characteristics of a warm pool. The sensible and latent heat fluxes acted to moisten the lower troposphere and affected the height of the trade winds inversion layer (TWIL). The meteorological system that occurred at the low–midlevels during the period favored the weakening and even the breakdown of the TWIL. These atmospheric disturbances were associated with convergence, cyclonic vorticity, and upward water vapor motion to the midtroposphere levels. When the disturbances reached the coast of ENEB, they favored convection and intense rainfall over the region. Both coupled and uncoupled modeling experiments were performed with the same physical parameterizations and validated with in situ atmospheric and oceanic measurements. The results highlight that the predictions of extreme rainfall events were greatly improved with the coupled model.

scholarly journals A theory for surface-layer scaling of thermally-driven slope flows

2021 ◽  
Author(s):  
Dino Zardi
Keyword(s):  
Boundary Layer ◽  
Surface Layer ◽  
Sensible Heat Flux ◽  
Viscous Sublayer ◽  
Transport Processes ◽  
Heat Fluxes ◽  
Night Time ◽  
Slope Winds ◽  
Thermally Driven ◽  
Momentum And Heat Fluxes

<p>Sloping terrains of any inclination favour the development, under the daily cycle of day time surface heating and night time cooling, of thermally-driven organised flows, displaying peculiar boundary layer structures, and eventually triggering the development of atmospheric convection.</p><p>The ubiquitous occurrence over the Earth of variously tilted surfaces - from gently sloping plains to steep cliffs, or valley and basin sidewalls – makes the understanding of such flows of utmost importance in view of the appropriate forecasting of the associated boundary layer transport processes. Also, they display a highly conceptual relevance, as they represent a prototypal situations for many other thermally driven-flows over complex terrain.   </p><p>An appropriate surface-layer scaling for slope wind is derived extending the classical analysis for flat horizontal terrain situations to the cover inclines. In the former, momentum and heat fluxes at the surface are two independent quantities, and vertical profiles of velocity and temperature can only be connected to them by means  of similiarity relationships, as fluxes are nearly invariant with height.</p><p>Instead, equations governing slope winds show that the mean wind and temperature profiles are closely connected to the flux structure normal to the slope, as this is not constant. Also, surface values of momentum flux and sensible heat flux are shown to be proportional to each other.</p><p>Based on the above relationships, suitable expressions are derived for the slope-normal profiles of velocity and temperature, both in the viscous sublayer and in the fully turbulent surface layer, as well as for the appropriate scaling factors in the two regions.</p>

Sign in / Sign up

Export Citation Format

Share Document