scholarly journals Physical changes within a large tropical hydroelectric reservoir induced by wintertime cold front activity

2014 ◽  
Vol 18 (8) ◽  
pp. 3079-3093 ◽  
Author(s):  
M. P. Curtarelli ◽  
E. H. Alcântara ◽  
C. D. Rennó ◽  
J. L. Stech
Keyword(s):  
Weather Forecasting ◽  
Cold Front ◽  
Three Dimensional ◽  
Remote Sensing Data ◽  
Turbulent Energy ◽  
Heat Fluxes ◽  
Physical Processes ◽  
Tropical Reservoir ◽  
The Difference

Abstract. We investigated the influence of wintertime cold front activity on the physical processes within a large tropical reservoir located in Brazil. The period chosen for this study consisted of 49 days between 28 April 2010 and 15 July 2010. This period was defined based on information from the Brazilian Center for Weather Forecasting and Climate Studies (CPTEC), data collected in situ and the interpretation of remotely sensed images. To better understand the governing processes that drive changes in the heat balance, differential cooling and mixing dynamics, a simulation was performed that utilized a three-dimensional hydrodynamic model enforced with in situ and remote sensing data. The results showed that during a cold front passage over the reservoir, the sensible and latent heat fluxes were enhanced by approximately 77 and 16%, respectively. The reservoir's daily averaged heat loss was up to 167% higher on the days with cold front activity than on the days without activity. The cold front passage also intensified the differential cooling process; in some cases the difference between the water temperature of the littoral and pelagic zones reached up to 8 °C. The occurrence of cold front passages impacted the diurnal mixed layer (DML), by increasing the turbulent energy input (∼54%) and the DML depth (∼41%). Our results indicate that the cold front events are one of the main meteorological disturbances driving the physical processes within hydroelectric reservoirs located in tropical South America during the wintertime. Hence, cold front activity over these aquatic systems has several implications for water quality and reservoir management in Brazil.

scholarly journals Modeling the effects of cold front passages on the heat fluxes and thermal structure of a tropical hydroelectric reservoir

2013 ◽  
Vol 10 (7) ◽  
pp. 8467-8502 ◽  
Author(s):  
M. P. Curtarelli ◽  
E. H. Alcântara ◽  
C. D. Rennó ◽  
J. L. Stech
Keyword(s):  
Heat Loss ◽  
Weather Forecasting ◽  
Cold Front ◽  
Thermal Structure ◽  
Three Dimensional ◽  
Cumulative Effect ◽  
High Heat ◽  
Heat Fluxes ◽  
Tropical Reservoir ◽  
Cold Fronts

Abstract. We study the influence of cold fronts on the heat fluxes and thermal structure of a tropical reservoir located in Brazil. The period chosen for this study consisted of 49 days between 28 April 2010 and 15 July 2010 and was defined based on information from the Brazilian Centre for Weather Forecasting and Climate Studies (CPTEC), data collected in situ and the interpretation of remotely sensed images. During the selected time period, five cold front passages were identified, allowing us to analyze the cumulative effect of cold fronts and the reservoir's resilience on the days that elapsed between the passages. To better understand the physical processes that drive changes in heat fluxes and thermal structure, a simulation was performed that utilized a three-dimensional hydrodynamic model. The results showed that during the cold front days, the sensible and latent heat fluxes were enhanced by approximately 24% and 19%, respectively. The daily average heat loss was up to 167% higher on the cold front days than on the non-cold front days. The high heat loss and the increased wind intensity that occurred during the cold front passages destabilized the water column and provided partial or complete mixing. The colder waters of the Paranaíba River contributed to reestablish the thermal stratification following the passages of the cold fronts. These results suggest that cold front passages play an important role in the stratification and mixing regimes of Brazilian reservoirs located in southern and southeastern regions.

Modelling the surface circulation and thermal structure of a tropical reservoir using three-dimensional hydrodynamic lake model and remote-sensing data

2013 ◽  
Vol 28 (4) ◽  
pp. 516-525 ◽  
Author(s):  
Marcelo Pedroso Curtarelli ◽  
Enner Alcântara ◽  
Camilo Daleles Rennó ◽  
Arcilan Trevenzoli Assireu ◽  
Marie Paule Bonnet ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Thermal Structure ◽  
Three Dimensional ◽  
Remote Sensing Data ◽  
Tropical Reservoir ◽  
Sensing Data ◽  
Surface Circulation ◽  
Lake Model

scholarly journals Estimation and Mapping of Hurricane Turbulent Energy Using Airborne Doppler Measurements

2010 ◽  
Vol 138 (9) ◽  
pp. 3656-3670 ◽  
Author(s):  
Sylvie Lorsolo ◽  
Jun A. Zhang ◽  
Frank Marks ◽  
John Gamache
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Turbulent Energy ◽  
Vertical Shear ◽  
Horizontal Wind ◽  
Horizontal Shear ◽  
Retrieval Method ◽  
Hurricane Boundary Layer

Abstract Hurricane turbulent kinetic energy (TKE) was computed using airborne Doppler measurements from the NOAA WP-3D tail radars, and TKE data were retrieved for a variety of storms at different stages of their life cycle. The geometry of the radar analysis coupled with the relatively small beam resolution at ranges <8 km allowed for the estimation of subkilometer turbulent processes. Two-dimensional profiles of TKE were constructed and revealed that the strongest turbulence was generally located in convective regions, such as the eyewall, with magnitudes often exceeding 15 m2 s−2 and in the boundary layer with values of 5–10 m2 s−2 in the lowest kilometer. A correlation analysis showed that the strong turbulence was generally associated with strong horizontal shear of vertical and radial wind components in the eyewall and strong vertical shear of horizontal wind in the boundary layer. Mean vertical profiles of TKE decrease sharply above the hurricane boundary layer and level off at low magnitude for all regions outside the radius of maximum wind. The quality of the retrieval method was evaluated and showed very good agreement with TKE values directly calculated from the three-dimensional wind components of in situ measurements. The method presented here provides a unique opportunity to assess hurricane turbulence throughout the storm, especially in high-wind regions, and can be applied on extensive datasets of past and future airborne hurricane penetrations.

scholarly journals Modeling Evapotranspiration during SMACEX: Comparing Two Approaches for Local- and Regional-Scale Prediction

2005 ◽  
Vol 6 (6) ◽  
pp. 910-922 ◽  
Author(s):  
H. Su ◽  
M. F. McCabe ◽  
E. F. Wood ◽  
Z. Su ◽  
J. H. Prueger
Keyword(s):  
Remote Sensing ◽  
Surface Energy ◽  
Regional Scale ◽  
Remote Sensing Data ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
High Quality ◽  
Sensing Data ◽  
Mean Square Errors

Abstract The Surface Energy Balance System (SEBS) model was developed to estimate land surface fluxes using remotely sensed data and available meteorology. In this study, a dual assessment of SEBS is performed using two independent, high-quality datasets that are collected during the Soil Moisture–Atmosphere Coupling Experiment (SMACEX). The purpose of this comparison is twofold. First, using high-quality local-scale data, model-predicted surface fluxes can be evaluated against in situ observations to determine the accuracy limit at the field scale using SEBS. To accomplish this, SEBS is forced with meteorological data derived from towers distributed throughout the Walnut Creek catchment. Flux measurements from 10 eddy covariance systems positioned on these towers are used to evaluate SEBS over both corn and soybean surfaces. These data allow for an assessment of modeled fluxes during a period of rapid vegetation growth and varied hydrometeorology. Results indicate that SEBS can predict evapotranspiration with accuracies approaching 10%–15% of that of the in situ measurements, effectively capturing the temporal development of surface flux patterns for both corn and soybean, even when the evaporative fraction ranges between 0.50 and 0.90. Second, utilizing high-resolution remote sensing data and operational meteorology, a catchment-scale examination of model performance is undertaken. To extend the field-based assessment of SEBS, information derived from the Landsat Enhanced Thematic Mapper (ETM) and data from the North American Land Data Assimilation System (NLDAS) were combined to determine regional surface energy fluxes for a clear day during the field experiment. Results from this analysis indicate that prediction accuracy was strongly related to crop type, with corn predictions showing improved estimates compared to those of soybean. Although root-mean-square errors were affected by the limited number of samples and one poorly performing soybean site, differences between the mean values of observations and SEBS Landsat-based predictions at the tower sites were approximately 5%. Overall, results from this analysis indicate much potential toward routine prediction of surface heat fluxes using remote sensing data and operational meteorology.

Direct simulations of a rough-wall channel flow

2007 ◽  
Vol 571 ◽  
pp. 235-263 ◽  
Author(s):  
TOMOAKI IKEDA ◽  
PAUL A. DURBIN
Keyword(s):  
Friction Velocity ◽  
Three Dimensional ◽  
Turbulent Energy ◽  
High Energy ◽  
Rough Wall ◽  
Roughness Sublayer ◽  
Wall Friction ◽  
Turbulence Structure ◽  
The Difference ◽  
Grain Roughness

In this study, we performed simulations of turbulent flow over rectangular ribs transversely mounted on one side of a plane in a channel, with the other side being smooth. The separation between ribs is large enough to avoid forming stable vortices in the spacing, which exhibits k-type, or sand-grain roughness. The Reynolds number Reτ of our representative direct numerical simulation case is 460 based on the smooth-wall friction velocity and the channel half-width. The roughness height h is estimated as 110 wall units based on the rough-wall friction velocity. The velocity profile and kinetic energy budget verify the presence of an equilibrium, logarithmic layer at y≳2h. In the roughness sublayer, however, a significant turbulent energy flux was observed. A high-energy region is formed by the irregular motions just above the roughness. Visualizations of vortical streaks, disrupted in all three directions in the roughness sublayer, indicate that the three-dimensional flow structure of sand-grain roughness is replicated by the two-dimensional roughness, and that this vortical structure is responsible for the high energy production. The difference in turbulence structure between smooth- and rough-wall layers can also be seen in other flow properties, such as anisotropy and turbulence length scales.

scholarly journals Variability of Precipitation along Cold Fronts in Idealized Baroclinic Waves

2017 ◽  
Vol 145 (8) ◽  
pp. 2971-2992 ◽  
Author(s):  
Jesse Norris ◽  
Geraint Vaughan ◽  
David M. Schultz
Keyword(s):  
Roughness Length ◽  
Cold Front ◽  
Thermal Structure ◽  
Surface Wind ◽  
Three Dimensional ◽  
Lower Troposphere ◽  
Equation Model ◽  
Vertical Shear ◽  
Cold Fronts ◽  
The Difference

Precipitation patterns along cold fronts can exhibit a variety of morphologies including narrow cold-frontal rainbands and core-and-gap structures. A three-dimensional primitive equation model is used to investigate alongfront variability of precipitation in an idealized baroclinic wave. Along the poleward part of the cold front, a narrow line of precipitation develops. Along the equatorward part of the cold front, precipitation cores and gaps form. The difference between the two evolutions is due to differences in the orientation of vertical shear near the front in the lower troposphere: at the poleward end the along-frontal shear is dominant and the front is in near-thermal wind balance, while at the equatorward end the cross-frontal shear is almost as large. At the poleward end, the thermal structure remains erect with the front well defined up to the midtroposphere, hence updrafts remain erect and precipitation falls in a continuous line along the front. At the equatorward end, the cores form as undulations appear in both the prefrontal and postfrontal lighter precipitation, associated with vorticity maxima moving along the front on either side. Cross-frontal winds aloft tilt updrafts, so that some precipitation falls ahead of the surface cold front, forming the cores. Sensitivity simulations are also presented in which SST and roughness length are varied between simulations. Larger SST reduces cross-frontal winds aloft and leads to a more continuous rainband. Larger roughness length destroys the surface wind shift and thermal gradient, allowing mesovortices to dominate the precipitation distribution, leading to distinctive and irregularly shaped, quasi-regularly spaced precipitation maxima.

scholarly journals Data assimilation of in-situ and satellite remote sensing data to 3D hydrodynamic lake models

2019 ◽  
Author(s):  
Theo Baracchini ◽  
Philip Yifei Chu ◽  
Jonas Šukys ◽  
Gian Lieberherr ◽  
Stefan Wunderle ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Data Assimilation ◽  
Satellite Remote Sensing ◽  
Three Dimensional ◽  
Model Performance ◽  
Remote Sensing Data ◽  
Temporal Scales ◽  
Localization Scheme ◽  
Spatio Temporal

Abstract. The understanding of lakes physical dynamics is crucial to provide scientifically credible information for ecosystem management. We show how the combination of in-situ data, remote sensing observations and three-dimensional hydrodynamic numerical simulations is capable of delivering various spatio-temporal scales involved in lakes dynamics. This combination is achieved through data assimilation (DA) and uncertainty quantification. In this study, we present a flexible framework for DA into lakes three-dimensional hydrodynamic models. Using an Ensemble Kalman Filter, our approach accounts for model and observational uncertainties. We demonstrate the framework by assimilating in-situ and satellite remote sensing temperature data into a three-dimensional hydrodynamic model of Lake Geneva. Results show that DA effectively improves model performance over a broad range of spatio-temporal scales and physical processes. Overall, temperature errors have been reduced by 54 %. With a localization scheme, an ensemble size of 20 members is found to be sufficient to derive covariance matrices leading to satisfactory results. The entire framework has been developed for the constraints of operational systems and near real-time operations (e.g. integration into http://meteolakes.ch).

scholarly journals Turbulent flow over transitionally rough surfaces with varying roughness densities

2016 ◽  
Vol 804 ◽  
pp. 130-161 ◽  
Author(s):  
M. MacDonald ◽  
L. Chan ◽  
D. Chung ◽  
N. Hutchins ◽  
A. Ooi
Keyword(s):  
Turbulent Flows ◽  
Reynolds Shear Stress ◽  
Three Dimensional ◽  
Turbulent Energy ◽  
Rough Wall ◽  
Momentum Balance ◽  
Wall Flows ◽  
Roughness Elements ◽  
The Difference ◽  
Near Wall

We investigate rough-wall turbulent flows through direct numerical simulations of flow over three-dimensional transitionally rough sinusoidal surfaces. The roughness Reynolds number is fixed at $k^{+}=10$, where $k$ is the sinusoidal semi-amplitude, and the sinusoidal wavelength is varied, resulting in the roughness solidity $\unicode[STIX]{x1D6EC}$ (frontal area divided by plan area) ranging from 0.05 to 0.54. The high cost of resolving both the flow around the dense roughness elements and the bulk flow is circumvented by the use of the minimal-span channel technique, recently demonstrated by Chung et al. (J. Fluid Mech., vol. 773, 2015, pp. 418–431) to accurately determine the Hama roughness function, $\unicode[STIX]{x0394}U^{+}$. Good agreement of the second-order statistics in the near-wall roughness-affected region between minimal- and full-span rough-wall channels is observed. In the sparse regime of roughness ($\unicode[STIX]{x1D6EC}\lesssim 0.15$) the roughness function increases with increasing solidity, while in the dense regime the roughness function decreases with increasing solidity. It was found that the dense regime begins when $\unicode[STIX]{x1D6EC}\gtrsim 0.15{-}0.18$, in agreement with the literature. A model is proposed for the limit of $\unicode[STIX]{x1D6EC}\rightarrow \infty$, which is a smooth wall located at the crest of the roughness elements. This model assists with interpreting the asymptotic behaviour of the roughness, and the rough-wall data presented in this paper show that the near-wall flow is tending towards this modelled limit. The peak streamwise turbulence intensity, which is associated with the turbulent near-wall cycle, is seen to move further away from the wall with increasing solidity. In the sparse regime, increasing $\unicode[STIX]{x1D6EC}$ reduces the streamwise turbulent energy associated with the near-wall cycle, while increasing $\unicode[STIX]{x1D6EC}$ in the dense regime increases turbulent energy. An analysis of the difference of the integrated mean momentum balance between smooth- and rough-wall flows reveals that the roughness function decreases in the dense regime due to a reduction in the Reynolds shear stress. This is predominantly due to the near-wall cycle being pushed away from the roughness elements, which leads to a reduction in turbulent energy in the region previously occupied by these events.

Correlated Studies of Cellular Interactions Using TEM, Freeze Etching, and SEM

1974 ◽  
Vol 32 ◽  
pp. 320-321
Author(s):  
J. P. Revel
Keyword(s):  
Developmental Stages ◽  
Three Dimensional ◽  
Cell Movement ◽  
Cellular Interactions ◽  
Serial Sections ◽  
Cell Sheets ◽  
Freeze Etching ◽  
Early Developmental

Movement of individual cells or of cell sheets and complex patterns of folding play a prominent role in the early developmental stages of the embryo. Our understanding of these processes is based on three- dimensional reconstructions laboriously prepared from serial sections, and from autoradiographic and other studies. Many concepts have also evolved from extrapolation of investigations of cell movement carried out in vitro. The scanning electron microscope now allows us to examine some of these events in situ. It is possible to prepare dissections of embryos and even of tissues of adult animals which reveal existing relationships between various structures more readily than used to be possible vithout an SEM.

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