Journal articles on the topic 'Eddy heat flux'
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1
Chinn, Brian S., and Sarah T. Gille. "Estimating Eddy Heat Flux from Float Data in the North Atlantic: The Impact of Temporal Sampling Interval." Journal of Atmospheric and Oceanic Technology 24, no. 5 (May 1, 2007): 923–34. http://dx.doi.org/10.1175/jtech2057.1.
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Abstract Acoustically tracked float data from 16 experiments carried out in the North Atlantic are used to evaluate the feasibility of estimating eddy heat fluxes from floats. Daily float observations were bin averaged in 2° by 2° by 200-db-deep geographic bins, and eddy heat fluxes were estimated for each bin. Results suggest that eddy heat fluxes can be highly variable, with substantial outliers that mean that fluxes do not converge quickly. If 100 statistically independent observations are available in each bin (corresponding to 500–1000 float days of data), then results predict that 80% of bins will have eddy heat fluxes that are statistically different from zero. Pop-up floats, such as Autonomous Lagrangian Circulation Explorer (ALACE) and Argo floats, do not provide daily sampling and therefore underestimate eddy heat flux. The fraction of eddy heat flux resolved using pop-up float sampling patterns decreases linearly with increasing intervals between float mapping and can be modeled analytically. This implies that flux estimates from pop-up floats may be correctable to represent true eddy heat flux.
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Gutierrez-Villanueva, Manuel O., Teresa K. Chereskin, and Janet Sprintall. "Upper-Ocean Eddy Heat Flux across the Antarctic Circumpolar Current in Drake Passage from Observations: Time-Mean and Seasonal Variability." Journal of Physical Oceanography 50, no. 9 (September 1, 2020): 2507–27. http://dx.doi.org/10.1175/jpo-d-19-0266.1.
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AbstractEddy heat flux plays a fundamental role in the Southern Ocean meridional overturning circulation, providing the only mechanism for poleward heat transport above the topography and below the Ekman layer at the latitudes of Drake Passage. Models and observations identify Drake Passage as one of a handful of hot spots in the Southern Ocean where eddy heat transport across the Antarctic Circumpolar Current (ACC) is enhanced. Quantifying this transport, however, together with its spatial distribution and temporal variability, remains an open question. This study quantifies eddy heat flux as a function of ACC streamlines using a unique 20-yr time series of upper-ocean temperature and velocity transects with unprecedented horizontal resolution. Eddy heat flux is calculated using both time-mean and time-varying streamlines to isolate the dynamically important across-ACC heat flux component. The time-varying streamlines provide the best estimate of the across-ACC component because they track the shifting and meandering of the ACC fronts. The depth-integrated (0–900 m) across-stream eddy heat flux is maximum poleward in the south flank of the Subantarctic Front (−0.10 ± 0.05 GW m−1) and decreases toward the south, becoming statistically insignificant in the Polar Front, indicating heat convergence south of the Subantarctic Front. The time series provides an uncommon opportunity to explore the seasonal cycle of eddy heat flux. Poleward eddy heat flux in the Polar Front Zone is enhanced during austral autumn–winter, suggesting a seasonal variation in eddy-driven upwelling and thus the meridional overturning circulation.
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Dunn-Sigouin, Etienne, and Tiffany Shaw. "Dynamics of Anomalous Stratospheric Eddy Heat Flux Events in an Idealized Model." Journal of the Atmospheric Sciences 77, no. 6 (May 28, 2020): 2187–202. http://dx.doi.org/10.1175/jas-d-19-0231.1.
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Abstract Extreme stratospheric eddy and sudden stratospheric warming (SSW) events both involve anomalous stratospheric eddy heat flux. The cause of the anomaly has been hypothesized to be due to tropospheric or stratospheric dynamics. Here, ensemble spectral nudging experiments in a dry dynamical-core model are used to quantify the role of the troposphere versus the stratosphere. The experiments focus on the wavenumber-1 heat flux since it dominates the anomalous stratospheric eddy heat flux during both events. Nudging the stratospheric zonal-mean flow does not account for the anomalous stratospheric wave-1 heat flux. Nudging either tropospheric wave-1 or higher-order wavenumbers (k ≥ 2) accounts for a large fraction of the anomalous stratospheric wave-1 heat flux. Mechanism denial experiments, whereby tropospheric eddies (wave 1 or k ≥ 2) are nudged and the zonal-mean flow is fixed to climatology, suggest the climatological stratospheric zonal-mean flow is sufficient to account for the anomalous stratospheric wave-1 heat flux and wave–wave interaction plays a role in generating the anomalous tropospheric wave-1 source. Taken together, the experiments suggest the troposphere dominates the anomalous stratospheric eddy heat flux during extreme stratospheric eddy and SSW events while the stratospheric zonal-mean flow plays secondary role.
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Wang, Lei, and Noboru Nakamura. "Covariation of Finite-Amplitude Wave Activity and the Zonal-Mean Flow in the Midlatitude Troposphere. Part II: Eddy Forcing Spectra and the Periodic Behavior in the Southern Hemisphere Summer." Journal of the Atmospheric Sciences 73, no. 12 (November 17, 2016): 4731–52. http://dx.doi.org/10.1175/jas-d-16-0091.1.
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Abstract Previously, in Part I of this study, the authors used latitude-by-latitude budgets of the vertically integrated finite-amplitude wave activity (FAWA) to describe the covariation of the zonal-mean state and eddy amplitude. In the austral summer within 40°–55°S, FAWA exhibits a marked 20–30-day periodicity driven mainly by the low-level meridional eddy heat flux, consistent with the recently identified baroclinic annular mode (BAM). The present article examines the spectra of eddy heat flux that produce the periodic behavior in the Southern Hemisphere storm track. Analysis of the ERA-Interim product reveals that the 20–30-day periodicity in raw FAWA and eddy heat flux is particularly robust during the warm season. A dry GCM is shown to reproduce qualitatively BAM-like eddy heat flux spectra if the zonal-mean state resembles that of the austral summer and if the surface thermal damping is sufficiently strong. The observed eddy heat flux cospectra in summer contain a few dominant frequencies for each of the energy-containing zonal wavenumbers (4–6). The corresponding Fourier modes are heat transporting but neutral, with slightly different meridional structures. As these modes travel at different phase speeds they interfere with each other and produce an amplitude modulation to the eddy heat flux with a periodicity consistent with the BAM. The meridionally confined baroclinic zone in the mean state of the austral summer provides a waveguide that directs the mode propagation and interference along the latitude circle. However, the processes that give rise to the quasi-discrete Fourier modes remain to be identified.
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Hogg, Andrew Mc C., Michael P. Meredith, Jeffrey R. Blundell, and Chris Wilson. "Eddy Heat Flux in the Southern Ocean: Response to Variable Wind Forcing." Journal of Climate 21, no. 4 (February 15, 2008): 608–20. http://dx.doi.org/10.1175/2007jcli1925.1.
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Abstract The authors assess the role of time-dependent eddy variability in the Antarctic Circumpolar Current (ACC) in influencing warming of the Southern Ocean. For this, an eddy-resolving quasigeostrophic model of the wind-driven circulation is used, and the response of circumpolar transport, eddy kinetic energy, and eddy heat transport to changes in winds is quantified. On interannual time scales, the model exhibits the behavior of an “eddy saturated” ocean state, where increases in wind stress do not significantly change the circumpolar transport, but instead enhance the eddy field. This is in accord with previous dynamical arguments, and a recent observational study. The instantaneous response to increased wind stress is to cool temperatures through increased northward Ekman transport of cool water. But, in the longer term, the enhanced eddy state is more efficient at transporting heat, leading to a warming of the ocean. The total eddy heat flux response is greater than the Ekman transport heat flux in this model by a factor of 2, indicating that coarse (non eddy resolving) models may fail to adequately capture the key processes. The authors also test the model response to long-term changes in wind forcing, including steadily increasing circumpolar wind strength over a 30-yr period. The model shows a response in eddy heat flux, and a change in ocean temperature not dissimilar from observed Southern Ocean warming. These findings suggest that eddy heat flux, energized by increasing wind stress, may be a significant contributor to the observed warming of the Southern Ocean.
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De Souza, João Marcos Azevedo Correia, Afonso De Moraes Paiva, and Karina Von Schuckmann. "New estimates for the heat flux across the Polar Front: spatial and temporal variability in recent years." Antarctic Science 25, no. 3 (January 9, 2013): 433–44. http://dx.doi.org/10.1017/s0954102012001113.
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AbstractTwo different methodologies are applied in order to quantify the eddy contribution to the heat flux across the Polar Front, between January 2006 and December 2009. First, the eddy fluxes are indirectly estimated through a heat balance based on geostrophic fluxes obtained from the Argo climatological temperature and salinity. Second, a parametric model based on sea level anomaly data from a merged satellite product is used to obtain a direct estimate of the eddy heat flux and its temporal and spatial variability. The results obtained through the heat balance (-80.5 ± 16.45 x 1013 W) and the parameterization (-56.2 ± 4.18 x 1013 W) are within the range established by previous studies. The eddy heat flux is observed to be concentrated in a few narrow regions, with a particularly large contribution from the Atlantic sector. A trend of intensification of the southward heat flux is observed in the study period (-0.44 x 1013 W year-1), compatible with recent modelling and observational studies.
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Watts, D. Randolph, Karen L. Tracey, Kathleen A. Donohue, and Teresa K. Chereskin. "Estimates of Eddy Heat Flux Crossing the Antarctic Circumpolar Current from Observations in Drake Passage." Journal of Physical Oceanography 46, no. 7 (July 2016): 2103–22. http://dx.doi.org/10.1175/jpo-d-16-0029.1.
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AbstractThe 4-yr measurements by current- and pressure-recording inverted echo sounders in Drake Passage produced statistically stable eddy heat flux estimates. Horizontal currents in the Antarctic Circumpolar Current (ACC) turn with depth when a depth-independent geostrophic current crosses the upper baroclinic zone. The dynamically important divergent component of eddy heat flux is calculated. Whereas full eddy heat fluxes differ greatly in magnitude and direction at neighboring locations within the local dynamics array (LDA), the divergent eddy heat fluxes are poleward almost everywhere. Case studies illustrate baroclinic instability events that cause meanders to grow rapidly. In the southern passage, where eddy variability is weak, heat fluxes are weak and not statistically significant. Vertical profiles of heat flux are surface intensified with ~50% above 1000 m and uniformly distributed with depth below. Summing poleward transient eddy heat transport across the LDA of −0.010 ± 0.005 PW with the stationary meander contribution of −0.004 ± 0.001 PW yields −0.013 ± 0.005 PW. A comparison metric, −0.4 PW, represents the total oceanic heat loss to the atmosphere south of 60°S. Summed along the circumpolar ACC path, if the LDA heat flux occurred at six “hot spots” spanning similar or longer path segments, this could account for 20%–70% of the metric, that is, up to −0.28 PW. The balance of ocean poleward heat transport along the remaining ACC path should come from weak eddy heat fluxes plus mean cross-front temperature transports. Alternatively, the metric −0.4 PW, having large uncertainty, may be high.
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Fine, Elizabeth C., Jennifer A. MacKinnon, Matthew H. Alford, and John B. Mickett. "Microstructure Observations of Turbulent Heat Fluxes in a Warm-Core Canada Basin Eddy." Journal of Physical Oceanography 48, no. 10 (October 2018): 2397–418. http://dx.doi.org/10.1175/jpo-d-18-0028.1.
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AbstractAn intrahalocline eddy was observed on the Chukchi slope in September of 2015 using both towed CTD and microstructure temperature and shear sections. The core of the eddy was 6°C, significantly warmer than the surrounding −1°C water and far exceeding typical temperatures of warm-core Arctic eddies. Microstructure sections indicated that outside of the eddy the rate of dissipation of turbulent kinetic energy ε was quite low . However, at the edges of the eddy core, ε was elevated to . Three different processes were associated with elevated ε. Double-diffusive steps were found at the eddy’s top edge and were associated with an upward heat flux of 5 W m−2. At the bottom edge of the eddy, shear-driven mixing played a modest role, generating a heat flux of approximately 0.5 W m−2 downward. Along the sides of the eddy, density-compensated thermohaline intrusions transported heat laterally out of the eddy, with a horizontal heat flux of 2000 W m−2. Integrating these fluxes over an idealized approximation of the eddy’s shape, we estimate that the net heat transport due to thermohaline intrusions along the eddy flanks was 2 GW, while the double-diffusive flux above the eddy was 0.4 GW. Shear-driven mixing at the bottom of the eddy accounted for only 0.04 GW. If these processes continued indefinitely at the same rate, the estimated life-span would be 1–2 years. Such eddies may be an important mechanism for the transport of Pacific-origin heat, freshwater, and nutrients into the Canada Basin.
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Bennett, Andrew F., and Warren B. White. "Eddy Heat Flux in the Subtropical North Pacific." Journal of Physical Oceanography 16, no. 4 (April 1986): 728–40. http://dx.doi.org/10.1175/1520-0485(1986)016<0728:ehfits>2.0.co;2.
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Rüdiger, G., P. Egorov, L. L. Kitchatinov, and M. Küker. "The eddy heat-flux in rotating turbulent convection." Astronomy & Astrophysics 431, no. 1 (February 2005): 345–52. http://dx.doi.org/10.1051/0004-6361:20041670.
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Xiao, Dong, and Hongli Ren. "Interdecadal changes in synoptic transient eddy activity over the Northeast Pacific and their role in tropospheric Arctic amplification." Climate Dynamics 57, no. 3-4 (April 3, 2021): 993–1008. http://dx.doi.org/10.1007/s00382-021-05752-6.
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AbstractArctic amplification refers to the greater surface warming of the Arctic than of other regions during recent decades. A similar phenomenon occurs in the troposphere and is termed “tropospheric Arctic amplification” (TAA). The poleward eddy heat flux and eddy moisture flux are critical to Arctic warming. In this study, we investigate the synoptic transient eddy activity over the North Pacific associated with TAA and its relationship with the subtropical jet stream, and propose the following mechanism. A poleward shift of the subtropical jet axis results in anomalies of the meridional gradient of zonal wind over the North Pacific, which drive a meridional dipole pattern of synoptic transient wave intensity over the North Pacific, referred to as the North Pacific Synoptic Transient wave intensity Dipole (NPSTD). The NPSTD index underwent an interdecadal shift in the late 1990s accompanying that of the subtropical jet stream. During the positive phase of the NPSTD index, synoptic eddy heat flux transports more heat to the Arctic Circle, and the eddy heat flux diverges, increasing Arctic temperature. This mechanism highlights the need to consider synoptic transient eddy activity over the North Pacific as the link between the mean state of the North Pacific subtropical upper jet and TAA.
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Ditchek, Sarah D., John Molinari, and David Vollaro. "Tropical Cyclone Outflow-Layer Structure and Balanced Response to Eddy Forcings." Journal of the Atmospheric Sciences 74, no. 1 (January 1, 2017): 133–49. http://dx.doi.org/10.1175/jas-d-16-0117.1.
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Abstract The ERA-Interim is used to generate azimuthally averaged composites of Atlantic basin tropical cyclones from 1979 to 2014. Both the mean state and the eddy forcing terms exhibited similar radial–vertical structure for all storm intensities, varying only in magnitude. Thus, only major hurricanes are described in detail. Radial inflow and outflow extended beyond the 2000-km radius. Warm anomalies reached 2000 km in the outflow layer. Composite eddy momentum fluxes within the outflow layer were 2.5 times larger than mean momentum fluxes, highlighting the importance of outflow–environment interactions. A balanced vortex equation was applied to understand the role of eddy heat and momentum fluxes. Dominant terms were the lateral eddy heat flux convergence, lateral eddy momentum flux, and eddy Coriolis torque. Each acted to enhance the secondary circulation. The eddy momentum flux terms produced about twice the response of heat flux terms. The circulation created by the eddy Coriolis torque arises from a vertical gradient of mean storm-relative meridional wind in the upper troposphere at outer radii. It is produced by background inertial stability variations that allow stronger outflow on the equatorward side. Overall, the fluxes drive a strengthened secondary circulation that extends to outer radii. Balanced vertical motion is strongest in the upper troposphere in the storm core. A method is proposed for evaluating the role of environmental interaction on tropical cyclone intensity change.
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Zieliński, Mariusz, Krzysztof Fortuniak, Włodzimierz Pawlak, and Mariusz Siedlecki. "Turbulent sensible heat flux in Łódź, Central Poland, obtained from scintillometer and eddy covariance measurements." Meteorologische Zeitschrift 22, no. 5 (October 1, 2013): 603–13. http://dx.doi.org/10.1127/0941-2948/2013/0448.
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Rocha, Adolpho Emanuel Quintela da, José Leonaldo de Souza, Guilherme Bastos Lyra, Ricardo Araújo Ferreira Junior, Gustavo Bastos Lyra, Laurício Endres, and Marshall Victor Chagas Santos. "Micrometeorological methods to estimate sugarcane evapotranspiration in coastal northeastern region of Brazil." Australian Journal of Crop Science, no. 13(09):2019 (September 20, 2019): 1422–28. http://dx.doi.org/10.21475/ajcs.19.13.09.p1257.
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The aim of the present work was to evaluate the performance of Bowen ratio-energy balance method, as well as the energy balance closure by Eddy covariance technique for a sugarcane crop in Brazilian northeastern region. Micrometeorological measurements were carried out between June 7th and November 17th, 2013. Latent and sensible heat fluxes were determined through Eddy covariance technique (EC) and by the Bowen ratio-energy balance method (BREB), considering two approaches. The first, estimated the air temperature and water vapour pressure gradient in two levels above the canopy. The second method measured the air temperature and water vapour pressure at the first level and the surface temperature from radiometric measurements. Latent heat flux was also estimated as energy balance residue from determinations of the sensible heat flux by Eddy covariance. The degree of energy balance closure was dependent on the time of the day considered. Bowen ratio - energy balance estimated from the first approach, showed the best agreement with the eddy covariance measurements to estimate latent heat flux, while in the second case, when the Bowen ratio was estimated using the surface temperature, the linear relationship was the most discrepant. Therefore, the Bowen ratio conventional method is more suitable for estimating latent heat flux in sugarcane.
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Tang, Xin Ying, Lin Han, and Ge Wang. "Progress in Preliminary Processing of Eddy Covariance Flux Data." Advanced Materials Research 807-809 (September 2013): 1909–14. http://dx.doi.org/10.4028/www.scientific.net/amr.807-809.1909.
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The eddy covariance (EC) technique of observation is a standard method for direct measurement of CO2, H2O and energy flux between vegetation and the atmosphere, the calculation formula of which is based on a series of assumptions. In reality, the assumed conditions are usually not satisfied, and the flux data is subject to significant deviation, thus the measured result should be corrected. The difference in data processing may lead to obvious difference in the calculated results of sensible heat flux and latent heat flux, while the universality of existing flux processing software is not verified. On the basis of domestic and foreign literature, this paper systematically summarizes and evaluates the preliminary processing of EC observation data in the aspects of principle and method of flux observation, rejection and interpolation of flux data, quality control and evaluation of flux data.
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Wehr, Richard, and Scott R. Saleska. "Calculating canopy stomatal conductance from eddy covariance measurements, in light of the energy budget closure problem." Biogeosciences 18, no. 1 (January 4, 2021): 13–24. http://dx.doi.org/10.5194/bg-18-13-2021.
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Abstract. Canopy stomatal conductance is commonly estimated from eddy covariance measurements of the latent heat flux (LE) by inverting the Penman–Monteith equation. That method ignores eddy covariance measurements of the sensible heat flux (H) and instead calculates H implicitly as the residual of all other terms in the site energy budget. Here we show that canopy stomatal conductance is more accurately calculated from eddy covariance (EC) measurements of both H and LE using the flux–gradient equations that define conductance and underlie the Penman–Monteith equation, especially when the site energy budget fails to close due to pervasive biases in the eddy fluxes and/or the available energy. The flux–gradient formulation dispenses with unnecessary assumptions, is conceptually simpler, and is as or more accurate in all plausible scenarios. The inverted Penman–Monteith equation, on the other hand, contributes substantial biases and erroneous spatial and temporal patterns to canopy stomatal conductance, skewing its relationships with drivers such as light and vapor pressure deficit.
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Karpetchko, Alexei, and Grigory Nikulin. "Influence of Early Winter Upward Wave Activity Flux on Midwinter Circulation in the Stratosphere and Troposphere." Journal of Climate 17, no. 22 (November 15, 2004): 4443–52. http://dx.doi.org/10.1175/jcli-3229.1.
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Abstract Using NCEP–NCAR reanalysis data the authors show that the November–December averaged stratospheric eddy heat flux is strongly anticorrelated with the January–February averaged eddy heat flux in the midlatitude stratosphere and troposphere. This finding further emphasizes differences between early and midwinter stratospheric wave flux behavior, which has recently been found in long-term variations. Analysis suggests that the intraseasonal anticorrelation of stratospheric heat fluxes results from changes in the upward wave propagation in the troposphere. Stronger (weaker) upward wave fluxes in early winter lead to weaker (stronger) upward wave fluxes from the troposphere during midwinter. Also, enhanced equatorward wave refraction during midwinter (due to the stronger polar night jet) is associated with weak heat flux in the early winter. It is suggested that the effect of enhanced midwinter upward wave flux from the troposphere in the years with weak early winter heat flux overcompensates the effect of increased equatorward wave refraction in midwinter, leading to a net increase of midwinter upward wave fluxes into the stratosphere.
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Zhang, Jun A., and William M. Drennan. "An Observational Study of Vertical Eddy Diffusivity in the Hurricane Boundary Layer." Journal of the Atmospheric Sciences 69, no. 11 (November 1, 2012): 3223–36. http://dx.doi.org/10.1175/jas-d-11-0348.1.
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Abstract Although vertical eddy diffusivity or viscosity has been extensively used in theoretical and numerical models simulating tropical cyclones, little observational study has documented the magnitude of the eddy diffusivity in high-wind conditions (>20 m s−1) until now. Through analyzing in situ aircraft data that were collected in the atmospheric boundary layer of four intense hurricanes, this study provides the first estimates of vertical distributions of the vertical eddy diffusivities for momentum, sensible heat, and latent heat fluxes in the surface wind speed range between 18 and 30 m s−1. In this work, eddy diffusivity is determined from directly measured turbulent fluxes and vertical gradients of the mean variable, such as wind speed, temperature, and humidity. The analyses show that the magnitudes of vertical eddy diffusivities for momentum and latent heat fluxes are comparable to each other, but the eddy diffusivity for sensible heat flux is much smaller than that for the latent heat flux. The vertical distributions of the eddy diffusivities are generally alike, increasing from the surface to a maximum value within the thermodynamic mixed layer and then deceasing with height. The results indicate also that momentum and latent heat are mainly transferred downgradient of the mean flow and that countergradient transport of the sensible heat may exist. The observational estimates are compared with the eddy diffusivities derived from different methods as used in planetary boundary layer (PBL) parameterization schemes in numerical models as well as ones used in previous observational studies.
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Tsubokura, Makoto. "Subgrid Scale Modeling of Turbulence for the Dynamic Procedure Using Finite Difference Method and Its Assessment on the Thermally Stratified Turbulent Channel Flow." Journal of Applied Mechanics 73, no. 3 (October 14, 2005): 382–90. http://dx.doi.org/10.1115/1.2150236.
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Previously proposed methods for subgrid-scale (SGS) stress modeling were re-investigated and extended to SGS heat-flux modeling, and various anisotropic and isotropic eddy viscosity/diffusivity models were obtained. On the assumption that they are used in a finite-difference (FD) simulation, the models were constructed in such a way that they are insensitive to numerical parameters on which calculated flows are strongly dependent in the conventional Smagorinsky model. The models obtained, as well as those previously proposed, were evaluated a priori in a stably stratified open channel flow, which is considered to be a challenging application of large eddy simulation and suitable for testing both SGS stress and heat-flux models. The most important feature of the models proposed is that they are insensitive to the discretized test filtering parameter required in the dynamic procedure of Germano et al. (1991, Phys. Fluids, 3, pp. 1760–1765) in FD simulation. We also found in SGS heat-flux modeling that the effect of the grid (resolved)-scale (GS) velocity gradient plays an important role in the estimation of the streamwise heat flux, and an isotropic eddy diffusivity model with the effect of the GS velocity is proposed.
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Novak, Lenka, Maarten H. P. Ambaum, and Rémi Tailleux. "The Life Cycle of the North Atlantic Storm Track*." Journal of the Atmospheric Sciences 72, no. 2 (February 1, 2015): 821–33. http://dx.doi.org/10.1175/jas-d-14-0082.1.
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Abstract The North Atlantic eddy-driven jet exhibits latitudinal variability with evidence of three preferred latitudinal locations: south, middle, and north. Here the authors examine the drivers of this variability and the variability of the associated storm track. The authors investigate the changes in the storm-track characteristics for the three jet locations and propose a mechanism by which enhanced storm-track activity, as measured by upstream heat flux, is responsible for cyclical downstream latitudinal shifts in the jet. This mechanism is based on a nonlinear oscillator relationship between the enhanced meridional temperature gradient (and thus baroclinicity) and the meridional high-frequency (periods of shorter than 10 days) eddy heat flux. Such oscillations in baroclinicity and heat flux induce variability in eddy anisotropy, which is associated with the changes in the dominant type of wave breaking and a different latitudinal deflection of the jet. The authors’ results suggest that high heat flux is conducive to a northward deflection of the jet, whereas low heat flux is conducive to a more zonal jet. This jet-deflecting effect was found to operate most prominently downstream of the storm-track maximum, while the storm track and the jet remain anchored at a fixed latitudinal location at the beginning of the storm track. These cyclical changes in storm-track characteristics can be viewed as different stages of the storm track’s spatiotemporal life cycle.
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Dawe, Jordan T., and Lu Anne Thompson. "PDO-Related Heat and Temperature Budget Changes in a Model of the North Pacific." Journal of Climate 20, no. 10 (May 15, 2007): 2092–108. http://dx.doi.org/10.1175/jcli4229.1.
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Abstract Heat and temperature budget changes in a ⅓° model of the North Pacific driven by an idealized Pacific decadal oscillation (PDO) atmospheric forcing are diagnosed to determine the roles of atmospheric heat flux and ocean dynamics in upper-ocean heat content and mixed layer temperature (MLT) changes. Changes in MLT and heat content during the transition between negative and positive PDOs are driven primarily by atmospheric heat fluxes, with contributions from ageostrophic advection and entrainment. Once the new PDO state is established, atmospheric heat flux in the central North Pacific works to mitigate the MLT change while vertical entrainment and ageostrophic advection act to enhance it. Upper-ocean heat content is affected in a similar matter, except that vertical processes are not important in the heat budget balance. At the same time, changes in wind stress curl cause the subtropical gyre to spin up and the subpolar gyre boundary to migrate southward. These circulation changes cause a large increase in the geostrophic advective heat flux in the Kuroshio region. This increase results in more heat flux to the atmosphere, demonstrating an active role for ocean dynamics in the upper-ocean heat budget. Eddy heat flux divergence along the Kuroshio Extension doubles after the transition, due to stronger eddy activity related to increased Kuroshio transport.
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Meredith, L. K., R. Commane, J. W. Munger, A. Dunn, J. Tang, S. C. Wofsy, and R. G. Prinn. "Ecosystem fluxes of hydrogen: a comparison of flux-gradient methods." Atmospheric Measurement Techniques Discussions 7, no. 3 (March 25, 2014): 2879–928. http://dx.doi.org/10.5194/amtd-7-2879-2014.
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Abstract. Our understanding of biosphere-atmosphere exchange has been considerably enhanced by eddy-covariance measurements, however there remain many trace gases, such as molecular hydrogen (H2), for which there are no suitable analytical methods to measure their fluxes by eddy covariance. In such cases, flux-gradient methods can be used to calculate ecosystem-scale fluxes from vertical concentration gradients. The budget of atmospheric H2 is poorly constrained by the limited available observations, thus the ability to quantify and characterize the sources and sinks of H2 by flux-gradient methods in various ecosystems is important. We developed an approach to make nonintrusive, automated measurements of ecosystem-scale H2 fluxes both above and below the forest canopy at the Harvard Forest in Petersham, MA for over a year. We used three flux-gradient methods to calculate the fluxes: two similarity methods that do not rely on a micrometeorological determination of the eddy diffusivity, K, based on (1) trace gases or (2) sensible heat and one flux-gradient method that (3) parameterizes K. We quantitatively assessed the flux-gradient methods on CO2 and H2O by comparison to their simultaneous independent flux measurements via eddy covariance and chambers. All three flux-gradient methods performed well in certain locations, seasons, and times of day, and the best methods were trace gas similarity above and K parameterization below the canopy. Sensible heat similarity required several independent measurements and the results were more variable, in part because those data were only available in the winter when heat fluxes and temperature gradients were small and difficult to measure. Biases were often observed between flux-gradient methods and the independent flux measurements, including at least a 26% difference in nocturnal eddy-derived Net Ecosystem Exchange (NEE) and soil chamber measurements. All flux-gradient methods used to calculate above and below canopy H2 fluxes pointed to soil uptake as the main driver of H2 exchange at Harvard Forest. H2 fluxes calculated in a summer period agreed within their uncertainty and indicated that H2 deposition velocities ranged from 0.04 to 0.1 cm s−1.
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Meredith, L. K., R. Commane, J. W. Munger, A. Dunn, J. Tang, S. C. Wofsy, and R. G. Prinn. "Ecosystem fluxes of hydrogen: a comparison of flux-gradient methods." Atmospheric Measurement Techniques 7, no. 9 (September 3, 2014): 2787–805. http://dx.doi.org/10.5194/amt-7-2787-2014.
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Abstract. Our understanding of biosphere–atmosphere exchange has been considerably enhanced by eddy covariance measurements. However, there remain many trace gases, such as molecular hydrogen (H2), that lack suitable analytical methods to measure their fluxes by eddy covariance. In such cases, flux-gradient methods can be used to calculate ecosystem-scale fluxes from vertical concentration gradients. The budget of atmospheric H2 is poorly constrained by the limited available observations, and thus the ability to quantify and characterize the sources and sinks of H2 by flux-gradient methods in various ecosystems is important. We developed an approach to make nonintrusive, automated measurements of ecosystem-scale H2 fluxes both above and below the forest canopy at the Harvard Forest in Petersham, Massachusetts, for over a year. We used three flux-gradient methods to calculate the fluxes: two similarity methods that do not rely on a micrometeorological determination of the eddy diffusivity, K, based on (1) trace gases or (2) sensible heat, and one flux-gradient method that (3) parameterizes K. We quantitatively assessed the flux-gradient methods using CO2 and H2O by comparison to their simultaneous independent flux measurements via eddy covariance and soil chambers. All three flux-gradient methods performed well in certain locations, seasons, and times of day, and the best methods were trace gas similarity for above the canopy and K parameterization below it. Sensible heat similarity required several independent measurements, and the results were more variable, in part because those data were only available in the winter, when heat fluxes and temperature gradients were small and difficult to measure. Biases were often observed between flux-gradient methods and the independent flux measurements, and there was at least a 26% difference in nocturnal eddy-derived net ecosystem exchange (NEE) and chamber measurements. H2 fluxes calculated in a summer period agreed within their uncertainty and pointed to soil uptake as the main driver of H2 exchange at Harvard Forest, with H2 deposition velocities ranging from 0.04 to 0.10 cm s−1.
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Sievers, J., T. Papakyriakou, S. E. Larsen, M. M. Jammet, S. Rysgaard, M. K. Sejr, and L. L. Sørensen. "Estimating surface fluxes using eddy covariance and numerical ogive optimization." Atmospheric Chemistry and Physics 15, no. 4 (February 26, 2015): 2081–103. http://dx.doi.org/10.5194/acp-15-2081-2015.
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Abstract. Estimating representative surface fluxes using eddy covariance leads invariably to questions concerning inclusion or exclusion of low-frequency flux contributions. For studies where fluxes are linked to local physical parameters and up-scaled through numerical modelling efforts, low-frequency contributions interfere with our ability to isolate local biogeochemical processes of interest, as represented by turbulent fluxes. No method currently exists to disentangle low-frequency contributions on flux estimates. Here, we present a novel comprehensive numerical scheme to identify and separate out low-frequency contributions to vertical turbulent surface fluxes. For high flux rates (|Sensible heat flux| > 40 Wm−2, |latent heat flux|> 20 Wm−2 and |CO2 flux|> 100 mmol m−2 d−1 we found that the average relative difference between fluxes estimated by ogive optimization and the conventional method was low (5–20%) suggesting negligible low-frequency influence and that both methods capture the turbulent fluxes equally well. For flux rates below these thresholds, however, the average relative difference between flux estimates was found to be very high (23–98%) suggesting non-negligible low-frequency influence and that the conventional method fails in separating low-frequency influences from the turbulent fluxes. Hence, the ogive optimization method is an appropriate method of flux analysis, particularly in low-flux environments.
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Cerovečki, Ivana, and John Marshall. "Eddy Modulation of Air–Sea Interaction and Convection." Journal of Physical Oceanography 38, no. 1 (January 1, 2008): 65–83. http://dx.doi.org/10.1175/2007jpo3545.1.
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Abstract Eddy modulation of the air–sea interaction and convection that occurs in the process of mode water formation is analyzed in simulations of a baroclinically unstable wind- and buoyancy-driven jet. The watermass transformation analysis of Walin is used to estimate the formation rate of mode water and to characterize the role of eddies in that process. It is found that diabatic eddy heat flux divergences in the mixed layer are comparable in magnitude, but of opposite sign, to the surface air–sea heat flux and largely cancel the direct effect of buoyancy loss to the atmosphere. The calculations suggest that mode water formation estimates based on climatological air–sea heat flux data and outcrops, which do not fully resolve ocean eddies, may neglect a large opposing term in the heat budget and are thus likely to significantly overestimate true formation rates. In Walin’s watermass transformation framework, this manifests itself as a sensitivity of formation rate estimates to the averaging period over which the outcrops and air–sea fluxes are subjected. The key processes are described in terms of a transformed Eulerian-mean formalism in which eddy-induced mean flow tends to cancel the Eulerian-mean flow, resulting in weaker residual mean flow, subduction, and mode water formation rates.
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Jiménez-Urias, Miguel A., and LuAnne Thompson. "Idealized Study on the Effect of Bottom Topography on the Seasonality of the Stability of the Iceland–Faeroe Front." Journal of Physical Oceanography 48, no. 12 (December 2018): 2989–3008. http://dx.doi.org/10.1175/jpo-d-18-0048.1.
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AbstractWe investigate the effects of bottom topography on the instability, eddy-driven heat flux, and overturning of a front that sits atop a ridge by varying the initial location of an idealized frontal outcrop with respect to a topographic ridge. The front is periodic in the along-ridge direction and unstable to both mixed layer and mesoscale baroclinic instabilities with both instabilities focused on the northern flank of the ridge where the front outcrops. We find agreement with the theoretical predictions for the development of mesoscale instability of the jet in the presence of sloping bottom topography, and we find the initial growth of surface mixed layer eddies is insensitive to topographic variations. However, during the finite amplitude phase of mixed layer instability, we find faster development of mesoscale eddies and thus a stronger cross-front eddy heat flux and residual circulation for the position of the jet where we found the faster growth of mesoscale baroclinic instability. Over an advective time scale that represents the transit time of a water parcel along the Iceland–Faeroe Ridge (IFR), the resulting eddy heat flux is greatest in the cases where the frontal jet experiences the most destabilizing bottom topography of the three cases tested, with values comparable to the heat flux associated with the mean flow. Therefore, eddy dynamics over the IFR frontal region are important contributors to the heat exchanges between the North Atlantic and Nordic Seas, with the bottom topography playing a key role in determining the largest heat fluxes, whether the initial growth is dominated by mixed layer eddies or mesoscale eddies.
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Abernathey, Ryan, John Marshall, and David Ferreira. "The Dependence of Southern Ocean Meridional Overturning on Wind Stress." Journal of Physical Oceanography 41, no. 12 (December 1, 2011): 2261–78. http://dx.doi.org/10.1175/jpo-d-11-023.1.
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Abstract An eddy-resolving numerical model of a zonal flow, meant to resemble the Antarctic Circumpolar Current, is described and analyzed using the framework of J. Marshall and T. Radko. In addition to wind and buoyancy forcing at the surface, the model contains a sponge layer at the northern boundary that permits a residual meridional overturning circulation (MOC) to exist at depth. The strength of the residual MOC is diagnosed for different strengths of surface wind stress. It is found that the eddy circulation largely compensates for the changes in Ekman circulation. The extent of the compensation and thus the sensitivity of the MOC to the winds depend on the surface boundary condition. A fixed-heat-flux surface boundary severely limits the ability of the MOC to change. An interactive heat flux leads to greater sensitivity. To explain the MOC sensitivity to the wind strength under the interactive heat flux, transformed Eulerian-mean theory is applied, in which the eddy diffusivity plays a central role in determining the eddy response. A scaling theory for the eddy diffusivity, based on the mechanical energy balance, is developed and tested; the average magnitude of the diffusivity is found to be proportional to the square root of the wind stress. The MOC sensitivity to the winds based on this scaling is compared with the true sensitivity diagnosed from the experiments.
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Chávez, JoséL, Christopher M. U. Neale, Lawrence E. Hipps, John H. Prueger, and William P. Kustas. "Comparing Aircraft-Based Remotely Sensed Energy Balance Fluxes with Eddy Covariance Tower Data Using Heat Flux Source Area Functions." Journal of Hydrometeorology 6, no. 6 (December 1, 2005): 923–40. http://dx.doi.org/10.1175/jhm467.1.
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Abstract In an effort to better evaluate distributed airborne remotely sensed sensible and latent heat flux estimates, two heat flux source area (footprint) models were applied to the imagery, and their pixel weighting/integrating functionality was investigated through statistical analysis. Soil heat flux and sensible heat flux models were calibrated. The latent heat flux was determined as a residual from the energy balance equation. The resulting raster images were integrated using the 2D footprints and were compared to eddy covariance energy balance flux measurements. The results show latent heat flux estimates (adjusted for closure) with errors of (mean ± std dev) −9.2 ± 39.4 W m−2, sensible heat flux estimate errors of 9.4 ± 28.3 W m−2, net radiation error of −4.8 ± 20.7 W m−2, and soil heat flux error of −0.5 ± 24.5 W m−2. This good agreement with measured values indicates that the adopted methodology for estimating the energy balance components, using high-resolution airborne multispectral imagery, is appropriate for modeling latent heat fluxes. The method worked well for the unstable atmospheric conditions of the study. The footprint weighting/integration models tested indicate that they perform better than simple pixel averages upwind from the flux stations. In particular the flux source area model (footprint) seemed to better integrate the resulting heat flux image pixels. It is suggested that future studies test the methodology for heterogeneous surfaces under stable atmospheric conditions.
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Solignac, P. A., A. Brut, J. L. Selves, J. P. Béteille, J. P. Gastellu-Etchegorry, P. Keravec, P. Béziat, and E. Ceschia. "Uncertainty analysis of computational methods for deriving sensible heat flux values from scintillometer measurements." Atmospheric Measurement Techniques Discussions 2, no. 3 (June 5, 2009): 1383–417. http://dx.doi.org/10.5194/amtd-2-1383-2009.
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Abstract. The use of scintillometers to determine sensible heat fluxes is now common in studies of land-atmosphere interactions. The main interest in these instruments is due to their ability to quantify energy distributions at the landscape scale, as they can calculate sensible heat flux values over long distances, in contrast to Eddy Correlation systems. However, scintillometer data do not provide a direct measure of sensible heat flux, but require additional data, such as the Bowen ratio (β), to provide flux values. The Bowen ratio can either be measured using Eddy Correlation systems or derived from the energy balance closure. In this work, specific requirements for estimating energy fluxes using a scintillometer were analyzed, as well as the accuracy of two flux calculation methods. We first focused on the classical method (used in standard software). We analysed the impact of the Bowen ratio according to both time averaging and ratio values; for instance, an averaged Bowen ratio (β) of less than 1 proved to be a significant source of measurement uncertainty. An alternative method, called the "β-closure method", for which the Bowen ratio measurement is not necessary, was also tested. In this case, it was observed that even for low β values, flux uncertainties were reduced and scintillometer data were well correlated with the Eddy Correlation results.
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Solignac, P. A., A. Brut, J. L. Selves, J. P. Béteille, J. P. Gastellu-Etchegorry, P. Keravec, P. Béziat, and E. Ceschia. "Uncertainty analysis of computational methods for deriving sensible heat flux values from scintillometer measurements." Atmospheric Measurement Techniques 2, no. 2 (November 18, 2009): 741–53. http://dx.doi.org/10.5194/amt-2-741-2009.
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Abstract. The use of scintillometers to determine sensible heat fluxes is now common in studies of land-atmosphere interactions. The main interest in these instruments is due to their ability to quantify energy distributions at the landscape scale, as they can calculate sensible heat flux values over long distances, in contrast to Eddy Covariance systems. However, scintillometer data do not provide a direct measure of sensible heat flux, but require additional data, such as the Bowen ratio (β), to provide flux values. The Bowen ratio can either be measured using Eddy Covariance systems or derived from the energy balance closure. In this work, specific requirements for estimating energy fluxes using a scintillometer were analyzed, as well as the accuracy of two flux calculation methods. We first focused on the classical method (used in standard softwares) and we analysed the impact of the Bowen ratio on flux value and uncertainty. For instance, an averaged Bowen ratio (β) of less than 1 proved to be a significant source of measurement uncertainty. An alternative method, called the "β-closure method", for which the Bowen ratio measurement is not necessary, was also tested. In this case, it was observed that even for low β values, flux uncertainties were reduced and scintillometer data were well correlated with the Eddy Covariance results. Besides, both methods should tend to the same results, but the second one slightly underestimates H while β decreases (<5%).
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Suga, K., M. Nagaoka and, and N. Horinouchi. "Application of a Higher Order GGDH Heat Flux Model to Three-Dimensional Turbulent U-Bend Duct Heat Transfer." Journal of Heat Transfer 125, no. 1 (January 29, 2003): 200–203. http://dx.doi.org/10.1115/1.1532018.
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A higher order version of the generalized gradient diffusion hypothesis (HOGGDH) for turbulent heat flux is applied to predict heat transfer in a square-sectioned U-bend duct. The flow field turbulence models coupled with are a cubic nonlinear eddy viscosity model and a full second moment closure. Both of them are low Reynolds number turbulence models. The benefits of using the HOGGDH heat flux model are presented through the comparison with the standard GGDH.
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Zurita-Gotor, Pablo, Javier Blanco-Fuentes, and Edwin P. Gerber. "The Impact of Baroclinic Eddy Feedback on the Persistence of Jet Variability in the Two-Layer Model." Journal of the Atmospheric Sciences 71, no. 1 (December 27, 2013): 410–29. http://dx.doi.org/10.1175/jas-d-13-0102.1.
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Abstract Although it is well known that the persistence of extratropical jet shifts is enhanced by a positive eddy feedback, the dynamics of this feedback is still debated. Two types of mechanisms have been proposed: barotropic mechanisms rely on changes in upper-level propagation and baroclinic mechanisms rely on the coupling between barotropic and baroclinic flow. Recent studies have suggested that barotropic models can capture key aspects of the observed jet variability but the role of baroclinic dynamics has been less explored. This study investigates the temporal relations between barotropic and baroclinic anomalies and their eddy forcings during the internal variability of the simple two-layer quasigeostrophic model. A large correlation is found between barotropic and baroclinic anomalies and between the meridional and vertical components of the Eliassen–Palm divergence, especially at low frequency. The low-frequency variability is consistent with the baroclinic mechanism: persistent upper-level eddy momentum convergence is associated with (and precedes) persistent anomalies in the poleward eddy heat flux. In contrast, at high frequency, poleward heat flux anomalies are associated with eddy momentum divergence aloft and both eddy forcings have same-sign contributions to the upper-level eddy potential vorticity (PV) flux. In this limit the eddy PV flux is associated with wave activity transience as effective diffusivity is too small to dissipate the wave–mean flow interaction term. The large correlation between barotropic and baroclinic anomalies implies that the low-frequency variability of barotropic flow may be affected by thermal damping when this damping is sufficiently strong. For example, zonal index persistence drops drastically in our model when baroclinicity shifts are prevented by strong thermal restoration.
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Zangeneh, Rozie. "Assessing IDDES-Based Wall-Modeled Large-Eddy Simulation (WMLES) for Separated Flows with Heat Transfer." Fluids 6, no. 7 (July 5, 2021): 246. http://dx.doi.org/10.3390/fluids6070246.
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The Wall-modeled Large-eddy Simulation (WMLES) methods are commonly accompanied with an underprediction of the skin friction and a deviation of the velocity profile. The widely-used Improved Delayed Detached Eddy Simulation (IDDES) method is suggested to improve the prediction of the mean skin friction when it acts as WMLES, as claimed by the original authors. However, the model tested only on flow configurations with no heat transfer. This study takes a systematic approach to assess the performance of the IDDES model for separated flows with heat transfer. Separated flows on an isothermal wall and walls with mild and intense heat fluxes are considered. For the case of the wall with heat flux, the skin friction and Stanton number are underpredicted by the IDDES model however, the underprediction is less significant for the isothermal wall case. The simulations of the cases with intense wall heat transfer reveal an interesting dependence on the heat flux level supplied; as the heat flux increases, the IDDES model declines to predict the accurate skin friction.
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Shaw, Tiffany A., Pragallva Barpanda, and Aaron Donohoe. "A Moist Static Energy Framework for Zonal-Mean Storm-Track Intensity." Journal of the Atmospheric Sciences 75, no. 6 (May 30, 2018): 1979–94. http://dx.doi.org/10.1175/jas-d-17-0183.1.
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Abstract A moist static energy (MSE) framework for zonal-mean storm-track intensity, defined as the extremum of zonal-mean transient eddy MSE flux, is derived and applied across a range of time scales. According to the framework, storm-track intensity can be decomposed into contributions from net energy input [sum of shortwave absorption and surface heat fluxes into the atmosphere minus outgoing longwave radiation (OLR) and atmospheric storage] integrated poleward of the storm-track position and MSE flux by the mean meridional circulation or stationary eddies at the storm-track position. The framework predicts storm-track decay in spring and amplification in fall in response to seasonal insolation. When applied diagnostically the framework shows shortwave absorption and land turbulent surface heat fluxes account for the seasonal evolution of Northern Hemisphere (NH) intensity; however, they are partially compensated by OLR (Planck feedback) and stationary eddy MSE flux. The negligible amplitude of Southern Hemisphere (SH) seasonal intensity is consistent with the compensation of shortwave absorption by OLR and oceanic turbulent surface heat fluxes (ocean energy storage). On interannual time scales, El Niño minus La Niña conditions amplify the NH storm track, consistent with decreased subtropical stationary eddy MSE flux. Finally, on centennial time scales, the CO2 indirect effect (sea surface temperature warming) amplifies the NH summertime storm track whereas the direct effect (increased CO2 over land) weakens it, consistent with opposing turbulent surface heat flux responses over land and ocean.
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Haklander, A. J., P. C. Siegmund, and H. M. Kelder. "Interannual variability of the stratospheric wave driving during northern winter." Atmospheric Chemistry and Physics 7, no. 10 (May 16, 2007): 2575–84. http://dx.doi.org/10.5194/acp-7-2575-2007.
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Abstract. The strength of the stratospheric wave driving during northern winter is often quantified by the January–February mean poleward eddy heat flux at 100 hPa, averaged over 40°–80° N (or a similar area and period). Despite the dynamical and chemical relevance of the wave driving, the causes for its variability are still not well understood. In this study, ERA-40 reanalysis data for the period 1979–2002 are used to examine several factors that significantly affect the interannual variability of the wave driving. The total poleward heat flux at 100 hPa is poorly correlated with that in the troposphere, suggesting a decoupling between 100 hPa and the troposphere. However, the individual zonal wave-1 and wave-2 contributions to the wave driving at 100 hPa do exhibit a significant coupling with the troposphere, predominantly their stationary components. The stationary wave-1 contribution to the total wave driving significantly depends on the latitude of the stationary wave-1 source in the troposphere. The results suggest that this dependence is associated with the varying ability of stationary wave-1 activity to enter the tropospheric waveguide at mid-latitudes. The wave driving anomalies are separated into three parts: one part due to anomalies in the zonal correlation coefficient between the eddy temperature and eddy meridional wind, another part due to anomalies in the zonal eddy temperature amplitude, and a third part due to anomalies in the zonal eddy meridional wind amplitude. It is found that year-to-year variability in the zonal correlation coefficient between the eddy temperature and the eddy meridional wind is the most dominant factor in explaining the year-to-year variability of the poleward eddy heat flux.
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Eichinger, W. E., H. E. Holder, R. Knight, J. Nichols, D. I. Cooper, L. E. Hipps, W. P. Kustas, and J. H. Prueger. "Lidar Measurement of Boundary Layer Evolution to Determine Sensible Heat Fluxes." Journal of Hydrometeorology 6, no. 6 (December 1, 2005): 840–53. http://dx.doi.org/10.1175/jhm461.1.
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Abstract The Soil Moisture–Atmosphere Coupling Experiment (SMACEX) was conducted in the Walnut Creek watershed near Ames, Iowa, over the period from 15 June to 11 July 2002. A main focus of SMACEX is the investigation of the interactions between the atmospheric boundary layer, surface moisture, and canopy. A vertically staring elastic lidar was used to provide a high-time-resolution continuous record of the boundary layer height at the edge between a soybean and cornfield. The height and thickness of the entrainment zone are used to estimate the surface sensible heat flux using the Batchvarova–Gryning boundary layer model. Flux estimates made over 6 days are compared to conventional eddy correlation measurements. The calculated values of the sensible heat flux were found to be well correlated (R2 = 0.79, with a slope of 0.95) when compared to eddy correlation measurements in the area. The standard error of the flux estimates was 21.4 W m−2 (31% rms difference between this method and surface measurements), which is somewhat higher than a predicted uncertainty of 16%. The major sources of error were from the estimates of the vertical potential temperature gradient and an assumption that the entrainment parameter A was equal to the ratio of the entrainment flux and the surface heat flux.
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Lammert, A., and F. Ament. "CO<sub>2</sub>-flux measurements above the Baltic Sea at two heights: flux gradients in the surface layer?" Earth System Science Data 7, no. 2 (November 16, 2015): 311–17. http://dx.doi.org/10.5194/essd-7-311-2015.
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Abstract. The estimation of CO2 exchange between the ocean and the atmosphere is essential to understand the global carbon cycle. The eddy-covariance technique offers a very direct approach to observe these fluxes. The turbulent CO2 flux is measured, as well as the sensible and latent heat flux and the momentum flux, a few meters above the ocean in the atmosphere. Assuming a constant-flux layer in the near-surface part of the atmospheric boundary layer, this flux equals the exchange flux between ocean and atmosphere. The purpose of this paper is the comparison of long-term flux measurements at two different heights above the Baltic Sea to investigate this assumption. The results are based on a 1.5-year record of quality-controlled eddy-covariance measurements. Concerning the flux of momentum and of sensible and latent heat, the constant-flux layer theory can be confirmed because flux differences between the two heights are insignificantly small more than 95 % of the time. In contrast, significant differences, which are larger than the measurement error, occur in the CO2 flux about 35 % of the time. Data used for this paper are published at http://doi.pangaea.de/10.1594/PANGAEA.808714.
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Lammert, A., and F. Ament. "CO<sub>2</sub>-flux measurements above the Baltic Sea at two heights: flux gradients in the surface layer." Earth System Science Data Discussions 8, no. 2 (July 13, 2015): 587–601. http://dx.doi.org/10.5194/essdd-8-587-2015.
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Abstract. The estimation of CO2 exchange between the ocean and the atmosphere is essential to understand the global carbon cycle. The eddy-covariance technique offers a very direct approach to observe these fluxes. The turbulent CO2 flux is measured as well as the sensible and latent heat flux and the momentum flux, a few meters above the ocean in the atmosphere. Assuming a constant-flux layer in the near surface part of the atmospheric boundary, this flux equals the exchange flux between ocean and atmosphere. The goal of this paper is the comparison of long-term flux measurements at two different heights above the Baltic Sea due to this assumption. The results are based on an one-and-a-half year record of quality controlled eddy covariance measurements. Concerning the flux of momentum and of sensible and latent heat, the constant-flux layer theory can be validated because flux gradients between the two heights are more than 95 % of the time insignificantly small. In contrast, significant gradients, which are larger than the measurement error, occur for the CO2 flux in nearly 35 % of the time. Data, used for this paper are published at http://doi.pangaea.de/10.1594/PANGAEA.808714.
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Rokni and, Masoud, and Bengt Sunde´n. "Investigation of a Two-Equation Turbulent Heat Transfer Model Applied to Ducts." Journal of Heat Transfer 125, no. 1 (January 29, 2003): 194–200. http://dx.doi.org/10.1115/1.1532017.
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This investigation concerns numerical calculation of fully developed turbulent forced convective heat transfer and fluid flow in ducts over a wide range of Reynolds numbers. The low Reynolds number version of a non-linear eddy viscosity model is combined with a two-equation heat flux model with the eddy diffusivity concept. The model can theoretically be used for a range of Prandtl numbers or a range of different fluids. The computed results compare satisfactory with the available experiment. Based on existing DNS data and calculations in this work the ratio between the time-scales (temperature to velocity) is found to be approximately 0.7. In light of this assumption an algebraic scalar flux model with variable diffusivity is presented.
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Buttar, Noman Ali, Hu Yongguang, Josef Tanny, M. Waqar Akram, and Abdul Shabbir. "Fetch Effect on Flux-Variance Estimations of Sensible and Latent Heat Fluxes of Camellia Sinensis." Atmosphere 10, no. 6 (June 1, 2019): 299. http://dx.doi.org/10.3390/atmos10060299.
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Precise estimation of surface-atmosphere exchange is a major challenge in micrometeorology. Previous literature presented the eddy covariance (EC) as the most reliable method for the measurements of such fluxes. Nevertheless, the EC technique is quite expensive and complex, hence other simpler methods are sought. One of these methods is Flux-Variance (FV). The FV method estimates sensible heat flux (H) using high frequency (~10Hz) air temperature measurements by a fine wire thermocouple. Additional measurements of net radiation (Rn) and soil heat flux (G) allow the derivation of latent heat flux (LE) as the residual of the energy balance equation. In this study, the Flux Variance method was investigated, and the results were compared against eddy covariance measurements. The specific goal of the present study was to assess the performance of the FV method for the estimation of surface fluxes along a variable fetch. Experiment was carried out in a tea garden; an EC system measured latent and sensible heat fluxes and five fine-wire thermocouples were installed towards the wind dominant direction at different distances (fetch) of TC1 = 170 m, TC2 = 165 m, TC3 = 160 m, TC4 = 155 m and TC5 = 150 m from the field edge. Footprint analysis was employed to examine the effect of temperature measurement position on the ratio between 90% footprint and measurement height. Results showed a good agreement between FV and EC measurements of sensible heat flux, with all regression coefficients (R2) larger than 0.6; the sensor at 170 m (TC1), nearest to the EC system, had highest R2 = 0.86 and lowest root mean square error (RMSE = 25 Wm−2). The estimation of LE at TC1 was also in best agreement with eddy covariance, with the highest R2 = 0.90. The FV similarity constant varied along the fetch within the range 2.2–2.4.
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Sekma, H., Y. H. Park, and F. Vivier. "Time-Mean Flow as the Prevailing Contribution to the Poleward Heat Flux across the Southern Flank of the Antarctic Circumpolar Current: A Case Study in the Fawn Trough, Kerguelen Plateau." Journal of Physical Oceanography 43, no. 3 (March 1, 2013): 583–601. http://dx.doi.org/10.1175/jpo-d-12-0125.1.
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Abstract The major mechanisms of the oceanic poleward heat flux in the Southern Ocean are still in debate. The long-standing belief stipulates that the poleward heat flux across the Antarctic Circumpolar Current (ACC) is mainly due to mesoscale transient eddies and the cross-stream heat flux by time-mean flow is insignificant. This belief has recently been challenged by several numerical modeling studies, which stress the importance of mean flow for the meridional heat flux in the Southern Ocean. Here, this study analyzes moored current meter data obtained recently in the Fawn Trough, Kerguelen Plateau, to estimate the cross-stream heat flux caused by the time-mean flow and transient eddies. It is shown that the poleward eddy heat flux in this southern part of the ACC is negligible, while that from the mean flow is overwhelming by two orders of magnitude. This is due to the unusual anticlockwise turning of currents with decreasing depth, which is associated with significant bottom upwelling engendered by strong bottom currents flowing over the sloping topography of the trough. The circumpolar implications of these local observations are discussed in terms of the depth-integrated linear vorticity budget, which suggests that the six topographic features along the southern flank of the ACC equivalent to the Fawn Trough case would yield sufficient poleward heat flux to balance the oceanic heat loss in the subpolar region. As eddy activity on the southern flank of the ACC is too weak to transport sufficient heat poleward, the nonequivalent barotropic structure of the mean flow in several topographically constricted passages should accomplish the required task.
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Santos, Carlos Antonio Costa dos, Bernardo Barbosa da Silva, Tantravahi Venkata Ramana Rao, and Christopher Michael Usher Neale. "Energy balance measurements over a banana orchard in the Semiarid region in the Northeast of Brazil." Pesquisa Agropecuária Brasileira 44, no. 11 (November 2009): 1365–73. http://dx.doi.org/10.1590/s0100-204x2009001100001.
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The objective of this work was to evaluate the reliability of eddy covariance measurements, analyzing the energy balance components, evapotranspiration and energy balance closure in dry and wet growing seasons, in a banana orchard. The experiment was carried out at a farm located within the irrigation district of Quixeré, in the Lower Jaguaribe basin, in Ceará state, Brazil. An eddy covariance system was used to measure the turbulent flux. An automatic weather station was installed in a grass field to obtain the reference evapotranspiration (ET0) from the combined FAO-Penman-Monteith method. Wind speed and vapor pressure deficit are the most important variables on the evaporative process in both growing seasons. In the dry season, the heat fluxes have a similar order of magnitude, and during the wet season the latent heat flux is the largest. The eddy covariance system had acceptable reliability in measuring heat flux, with actual evapotranspiration results comparing well with those obtained by using the water balance method. The energy balance closure had good results for the study area, with mean values of 0.93 and 0.86 for the dry and wet growing seasons respectively.
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Abernathey, Ryan, and Cimarron Wortham. "Phase Speed Cross Spectra of Eddy Heat Fluxes in the Eastern Pacific." Journal of Physical Oceanography 45, no. 5 (May 2015): 1285–301. http://dx.doi.org/10.1175/jpo-d-14-0160.1.
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AbstractThis study investigates the observed spectral character of eddy heat fluxes near the ocean surface, focusing on the distribution in wavenumber and phase speed space. Eddy heat fluxes in the eastern Pacific are calculated from concurrent satellite sea surface height and sea surface temperature data. A high-resolution coupled climate model is also analyzed in order to verify the physical mechanisms involved and to validate the model against observations. Wavenumber, frequency, and phase speed power spectra and cross spectra are constructed and presented as a function of latitude. These spectra reveal the dominance of coherent mesoscale eddies in both the length scale and phase speed of eddy heat fluxes. The breadths of the spectra are characterized via spectral moments; these moments show that the eddy fluxes are relatively concentrated around the dominant wavenumber and phase speed. Good agreement is found between the model and the observed spectra. The integrated heat transport and corresponding eddy diffusivity are shown to compare well with previous studies, but the results give a deeper insight into what determines the heat flux. Implications for eddy parameterization are discussed.
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Treguier, A. M., C. Lique, J. Deshayes, and J. M. Molines. "The North Atlantic Eddy Heat Transport and Its Relation with the Vertical Tilting of the Gulf Stream Axis." Journal of Physical Oceanography 47, no. 6 (June 2017): 1281–89. http://dx.doi.org/10.1175/jpo-d-16-0172.1.
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AbstractCorrelations between temperature and velocity fluctuations are a significant contribution to the North Atlantic meridional heat transport, especially at the northern boundary of the subtropical gyre. In satellite observations and in a numerical model at ⅞° resolution, a localized pattern of positive eddy heat flux is found northwest of the Gulf Stream, downstream of its separation at Cape Hatteras. It is confined to the upper 500 m. A simple kinematic model of a meandering jet can explain the surface eddy flux, taking into account a spatial shift between the maximum velocity of the jet and the maximum cross-jet temperature gradient. In the Gulf Stream such a spatial shift results from the nonlinear temperature profile and the vertical tilting of the velocity profile with depth. The numerical model suggests that the meandering of the Gulf Stream could account, at least in part, for the large eddy heat transport (of order 0.3 PW) near 36°N in the North Atlantic and for its compensation by the mean flow.
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Messager, C., and S. Swart. "Significant Atmospheric Boundary Layer Change Observed above an Agulhas Current Warm Cored Eddy." Advances in Meteorology 2016 (2016): 1–7. http://dx.doi.org/10.1155/2016/3659657.
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The air-sea impact of a warm cored eddy ejected from the Agulhas Retroflection region south of Africa was assessed through both ocean and atmospheric profiling measurements during the austral summer. The presence of the eddy causes dramatic atmospheric boundary layer deepening, exceeding what was measured previously over such a feature in the region. This deepening seems mainly due to the turbulent heat flux anomaly above the warm eddy inducing extensive deep and persistent changes in the atmospheric boundary layer thermodynamics. The loss of heat by turbulent processes suggests that this kind of oceanic feature is an important and persistent source of heat for the atmosphere.
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Schemm, Sebastian, and Gwendal Rivière. "On the Efficiency of Baroclinic Eddy Growth and How It Reduces the North Pacific Storm-Track Intensity in Midwinter." Journal of Climate 32, no. 23 (November 14, 2019): 8373–98. http://dx.doi.org/10.1175/jcli-d-19-0115.1.
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Abstract This study investigates the efficiency of baroclinic eddy growth in an effort to better understand the suppression of the North Pacific storm-track intensity in winter. The efficiency of baroclinic eddy growth depends on the magnitude and orientation of the vertical tilt of the eddy geopotential isolines. The eddy efficiency is maximized if the orientation of the vertical tilt creates an eddy heat flux that aligns with the mean baroclinicity (defined as minus the temperature gradient divided by a stratification parameter) and if the magnitude of the vertical tilt is neither too strong nor too weak. The eddy efficiency is, in contrast to most other eddy measures, independent of the eddy amplitude and thus useful for improving our mechanistic understanding of the effective eddy growth. During the midwinter suppression, the eddy efficiency is reduced north of 40°N over a region upstream of the main storm track, and baroclinic growth is reduced despite a maximum in baroclinicity. Eulerian diagnostics and feature tracking suggest that the reduction in eddy efficiency is due to a stronger poleward tilt with height of eddies entering the Pacific through the northern seeding branch, which results in a more eastward-oriented eddy heat flux and a reduced alignment with the baroclinicity. The stronger poleward tilt with height is constrained by the eddy propagation direction, which is more equatorward when the subtropical jet moves equatorward in winter. In addition, the westward tilt with height is too strong. South of 40°N, the eddy efficiency increases during midwinter but in a region far away from the main storm track.
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Marzahn, Philip, Linda Flade, and Arturo Sanchez-Azofeifa. "Spatial Estimation of the Latent Heat Flux in a Tropical Dry Forest by Using Unmanned Aerial Vehicles." Forests 11, no. 6 (May 26, 2020): 604. http://dx.doi.org/10.3390/f11060604.
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In this paper, we address the retrieval of spatially distributed latent heat flux ( λ E) over a tropical dry forest using multi-spectral and thermal unmanned aerial vehicle (UAV) imagery. The study was carried out in the Santa Rosa National Park Environmental Monitoring Super-Site, Costa Rica, in June 2016. The triangle method was used to derive λ E from the UAV imagery and the results were compared to λ E measurements of an eddy covariance system within the coincident eddy flux tower footprint. The tower footprint was derived using a two-dimensional parameterization model for flux footprint prediction. The comparisons with the flux tower measurements showed a mean relative difference of 10.98% with a slight overestimation of the UAV-based flux retrievals by nearly 7.7 Wm − 2 . The results are in good agreement with satellite-based retrievals, as provided by the literature, for which the triangle method was initially developed and mostly used so far. This study proved to be a promising approach for transferring the triangle method to UAV imagery in ecosystems such as tropical dry forests. With the presented approach, new details in spatially distributed latent heat flux estimates at ultra-high resolution are now possible, thereby potentially closing the gap in spatial resolution between satellites and flux towers. Even more, it allows tracing the latent heat flux from single trees at leaf level. Besides, this approach also opens new perspectives for the monitoring of latent heat fluxes in tropical dry forests.
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Houghton, Robert W., and Christian Colin. "Wind-driven meridional eddy heat flux in the Gulf of Guinea." Journal of Geophysical Research 92, no. C10 (1987): 10777. http://dx.doi.org/10.1029/jc092ic10p10777.
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Morrison, A. K., O. A. Saenko, A. McC Hogg, and P. Spence. "The role of vertical eddy flux in Southern Ocean heat uptake." Geophysical Research Letters 40, no. 20 (October 17, 2013): 5445–50. http://dx.doi.org/10.1002/2013gl057706.
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Martínez-Cob, Antonio. "Adequacy of Villalobos method to adjust eddy covariance latent heat flux." Irrigation Science 20, no. 4 (October 2001): 175–88. http://dx.doi.org/10.1007/s002710100044.
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