scholarly journals What determines the sign of the evapotranspiration response to afforestation in the European summer?

2020 ◽  
Author(s):  
Marcus Breil ◽  
Edouard L. Davin ◽  
Diana Rechid
Keyword(s):  
Surface Roughness ◽  
Observational Studies ◽  
Forest Type ◽  
Lower Surface ◽  
Heat Fluxes ◽  
Physical Processes ◽  
Saturation Deficit ◽  
Model Study ◽  
The Tropics ◽  
The Impact

Abstract. Uncertainties in the evapotranspiration response to afforestation constitute a major source of disagreement between model-based studies of the potential climate benefits of forests. Forests typically have higher evapotranspiration rates than grassland in the tropics, but whether this is also the case in the mid-latitudes is still debated. To explore this question and the underlying physical processes behind these varying evapotranspiration rates of forests and grasslands in more detail, a regional model study with idealized afforestation scenarios was performed for Europe. In the first experiment Europe was maximally forested and in the second one, all forests were turned into grassland. The results of this modelling study exhibit the same contradicting evapotranspiration characteristics of forests and grasslands as documented in observational studies. But by means of an additional sensitivity simulation, in which the surface roughness of forest was reduced to grassland, the mechanisms behind these varying evapotranspiration rates could be revealed. Due to the higher surface roughness of a forest, solar radiation is more efficiently transformed into turbulent sensible heat fluxes, leading to lower surface temperatures (top of vegetation) than in grassland. The saturation deficit between the vegetation and the atmosphere, which depends on the surface temperature, is consequently reduced over forests. This reduced saturation deficit counteracts the transpiration facilitating characteristics of a forest (deeper roots, a higher LAI and lower albedo values than grassland). If the impact of the reduced saturation deficit exceeds the effects of the transpiration facilitating characteristics of a forest, evapotranspiration is reduced compared to grassland. If not, evapotranspiration rates of forests are higher. The interplay of these two counteracting factors depends on the latitude and the prevailing forest type in a region.

scholarly journals What determines the sign of the evapotranspiration response to afforestation in European summer?

2021 ◽  
Vol 18 (4) ◽  
pp. 1499-1510
Author(s):  
Marcus Breil ◽  
Edouard L. Davin ◽  
Diana Rechid
Keyword(s):  
Surface Roughness ◽  
Forest Type ◽  
Lower Surface ◽  
Heat Fluxes ◽  
Physical Processes ◽  
Area Index ◽  
Saturation Deficit ◽  
Model Study ◽  
The Tropics ◽  
The Impact

Abstract. Uncertainties in the evapotranspiration response to afforestation constitute a major source of disagreement between model-based studies of the potential climate benefits of forests. Forests typically have higher evapotranspiration rates than grasslands in the tropics, but whether this is also the case in the midlatitudes is still debated. To explore this question and the underlying physical processes behind these varying evapotranspiration rates of forests and grasslands in more detail, a regional model study with idealized afforestation scenarios was performed for Europe. In the first experiment, Europe was maximally forested, and in the second one, all forests were turned into grassland. The results of this modeling study exhibit the same contradicting evapotranspiration characteristics of forests and grasslands as documented in observational studies, but by means of an additional sensitivity simulation in which the surface roughness of the forest was reduced to grassland, the mechanisms behind these varying evapotranspiration rates could be revealed. Due to the higher surface roughness of a forest, solar radiation is more efficiently transformed into turbulent sensible heat fluxes, leading to lower surface temperatures (top of vegetation) than in grassland. The saturation deficit between the vegetation and the atmosphere, which depends on the surface temperature, is consequently reduced over forests. This reduced saturation deficit counteracts the transpiration-facilitating characteristics of a forest (deeper roots, a higher leaf area index, LAI, and lower albedo values than grassland). If the impact of the reduced saturation deficit exceeds the effects of the transpiration-facilitating characteristics of a forest, evapotranspiration is reduced compared to grassland. If not, evapotranspiration rates of forests are higher. The interplay of these two counteracting factors depends on the latitude and the prevailing forest type in a region.

scholarly journals Impact of West African Monsoon convective transport and lightning NO<sub>x</sub> production upon the upper tropospheric composition: a multi-model study

2010 ◽  
Vol 10 (2) ◽  
pp. 2245-2302 ◽  
Author(s):  
B. Barret ◽  
J. E. Williams ◽  
I. Bouarar ◽  
X. Yang ◽  
B. Josse ◽  
...  
Keyword(s):  
West African Monsoon ◽  
Convective Transport ◽  
West African ◽  
Lightning Activity ◽  
African Monsoon ◽  
Model Study ◽  
Multidisciplinary Analysis ◽  
Low Concentrations ◽  
The Tropics ◽  
The Impact

Abstract. Within the African Monsoon Multidisciplinary Analysis (AMMA), we investigate the impact of nitrogen oxides produced by lightning (LiNOx) and convective transport during the West African Monsoon (WAM) upon the composition of the upper troposphere (UT) in the tropics. For this purpose, we have performed simulations with 4 state-of-the-art chemistry transport models involved within AMMA, namely MOCAGE, TM4, LMDz-INCA and p-TOMCAT. The model intercomparison is complemented with an evaluation of the simulations based on both spaceborne and airborne observations. The baseline simulations show important differences between the UT CO and O3 distributions simulated by each of the 4 models when compared to measurements of the African latitudinal transect from the MOZAIC program and to distributions measured by the Aura/MLS spaceborne sensor. We show that such model discrepancies can be explained by differences in the convective transport parameterizations and, more particularly, the altitude reached by convective updrafts (ranging between ~200–125 hPa). Concerning UT O3, the majority of models exhibit low concentrations compared to both MOZAIC and MLS observations south of the equator, with good agreement in the Northern Hemisphere. Sensitivity studies are performed to quantify the effect of deep convective transport and the influence of LiNOx production on the UT composition. These clearly indicate that the CO maxima and the elevated O3 concentrations south of the equator are due to convective uplift of air masses impacted by Southern African biomass burning, in agreement with previous studies. Moreover, during the WAM, LiNOx from Africa are responsible for the highest UT O3 enhancements (10–20 ppbv) over the tropical Atlantic between 10° S–20° N. Differences between models are primarily due to the performance of the parameterizations used to simulate lightning activity which are evaluated using spaceborne observations of flash frequency. Combined with comparisons of in-situ NO measurements we show that the models producing the highest amounts of LiNOx over Africa during the WAM (INCA and p-TOMCAT) capture observed NO profiles with the best accuracy, although they both overestimate lightning activity over the Sahel.

scholarly journals The influence of soak temperature and forging lubricant on surface properties of steel forgings

2020 ◽  
Author(s):  
S. Hill ◽  
R. P. Turner ◽  
P. Wardle
Keyword(s):  
Surface Roughness ◽  
Surface Hardness ◽  
Lower Surface ◽  
Design Parameters ◽  
Compression Tests ◽  
Molybdenum Disulphide ◽  
Small Series ◽  
Ring Compression ◽  
Water Based ◽  
The Impact

AbstractA small series of ring compression tests were performed on BS970:708M40 alloy steel. The samples were tested using a 2-factor temperature variable, and a 4-factor lubricant variable, as the design parameters. Two differing soak temperatures were used, namely 1030 °C and 1300 °C respectively. The lubricants applied at the billet to tooling interface were synthetic water–based, graphite water–based, graphite and molybdenum disulphide viscous grease, and finally, unlubricated samples were tested. The ring compression tests were performed using a traditional drop forging hammer and induction heating to minimise any unintentional process variability. The impact that the two varying process parameters have upon the compression sample was then assessed by measuring each sample’s surface hardness and surface roughness prior to and post forging with fully calibrated equipment. It was demonstrated that the higher soak temperature of 1300 °C yielded a lower surface hardness value and higher surface roughness than the lower soak temperature, 1030 °C. The two water-based lubricants offered negligible change in results compared with the unlubricated forging, strongly suggesting that the lubricants were evaporated off the surface prior to forging. However, the results from the graphite–molybdenum disulphate grease do indicate in particular higher surface roughness than other lubricants, and a non-symmetric distortion pattern.

scholarly journals Impact of SST and Surface Waves on Hurricane Florence (2018): A Coupled Modeling Investigation

2021 ◽  
Author(s):  
Joseph B. Zambon ◽  
Ruoying He ◽  
John C. Warner ◽  
Christie A. Hegermiller
Keyword(s):  
Surface Roughness ◽  
Wave Model ◽  
Ocean Waves ◽  
Atmospheric Model ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Coupled Modeling ◽  
Storm Characteristics ◽  
The Impact ◽  
Fully Coupled

AbstractHurricane Florence (2018) devastated the coastal communities of the Carolinas through heavy rainfall that resulted in massive flooding. Florence was characterized by an abrupt reduction in intensity (Saffir-Simpson Category 4 to Category 1) just prior to landfall and synoptic-scale interactions that stalled the storm over the Carolinas for several days. We conducted a series of numerical modeling experiments in coupled and uncoupled configurations to examine the impact of sea surface temperature (SST) and ocean waves on storm characteristics. In addition to experiments using a fully coupled atmosphere-ocean-wave model, we introduced the capability of the atmospheric model to modulate wind stress and surface fluxes by oceanwaves through data from an uncoupled wave model. We examined these experiments by comparing track, intensity, strength, SST, storm structure, wave height, surface roughness, heat fluxes, and precipitation in order to determine the impacts of resolving ocean conditions with varying degrees of coupling. We found differences in the storm’s intensity and strength, with the best correlation coefficient of intensity (r=0.89) and strength (r=0.95) coming from the fully-coupled simulations. Further analysis into surface roughness parameterizations added to the atmospheric model revealed differences in the spatial distribution and magnitude of the largest roughness lengths. Adding ocean andwave features to the model further modified the fluxes due to more realistic cooling beneath the stormwhich in turn modified the precipitation field. Our experiments highlight significant differences in how air-sea processes impact hurricane modeling. The storm characteristics of track, intensity, strength, and precipitation at landfall are crucial to predictability and forecasting of future landfalling hurricanes.

scholarly journals Impact of West African Monsoon convective transport and lightning NO<sub>x</sub> production upon the upper tropospheric composition: a multi-model study

2010 ◽  
Vol 10 (12) ◽  
pp. 5719-5738 ◽  
Author(s):  
B. Barret ◽  
J. E. Williams ◽  
I. Bouarar ◽  
X. Yang ◽  
B. Josse ◽  
...  
Keyword(s):  
West African Monsoon ◽  
Convective Transport ◽  
West African ◽  
Lightning Activity ◽  
African Monsoon ◽  
Model Study ◽  
Multidisciplinary Analysis ◽  
High Concentrations ◽  
The Tropics ◽  
The Impact

Abstract. Within the African Monsoon Multidisciplinary Analysis (AMMA), we investigate the impact of nitrogen oxides produced by lightning (LiNOx) and convective transport during the West African Monsoon (WAM) upon the composition of the upper troposphere (UT) in the tropics. For this purpose, we have performed simulations with 4 state-of-the-art chemistry transport models involved within AMMA, namely MOCAGE, TM4, LMDz-INCA and p-TOMCAT. The model intercomparison is complemented with an evaluation of the simulations based on both spaceborne and airborne observations. The baseline simulations show important differences between the UT CO and O3 distributions simulated by each of the 4 models when compared to measurements from the MOZAIC program and fom the Aura/MLS spaceborne sensor. We show that such model discrepancies can be explained by differences in the convective transport parameterizations and, more particularly, the altitude reached by convective updrafts (ranging between ~200–125 hPa). Concerning UT O3, the models exhibit a good agreement with the main observed features. Nevertheless the majority of models simulate low O3 concentrations compared to both MOZAIC and Aura/MLS observations south of the equator, and rather high concentrations in the Northern Hemisphere. Sensitivity studies are performed to quantify the effect of deep convective transport and the influence of LiNOx production on the UT composition. These clearly indicate that the CO maxima and the elevated O3 concentrations south of the equator are due to convective uplift of air masses impacted by Southern African biomass burning, in agreement with previous studies. Moreover, during the WAM, LiNOx from Africa are responsible for the highest UT O3 enhancements (10–20 ppbv) over the tropical Atlantic between 10° S–20° N. Differences between models are primarily due to the performance of the parameterizations used to simulate lightning activity which are evaluated using spaceborne observations of flash frequency. Combined with comparisons of in-situ NO measurements we show that the models producing the highest amounts of LiNOx over Africa during the WAM (INCA and p-TOMCAT) capture observed NO profiles with the best accuracy, although they both overestimate lightning activity over the Sahel.

scholarly journals OBSERVAÇÕES SOBRE A MODULAÇÃO DA CAMADA LIMITE ATMOSFÉRICA MARINHA DEVIDA À PASSAGEM DE UM SISTEMA FRONTAL NO ATLÂNTICO SUDOESTE

2016 ◽  
Vol 38 ◽  
pp. 388
Author(s):  
Fernando Rossato ◽  
Ronald Buss de Souza
Keyword(s):  
Heat Fluxes ◽  
Sensible Heat ◽  
Marine Atmospheric Boundary Layer ◽  
Southwestern Atlantic ◽  
Physical Processes ◽  
Southwestern Atlantic Ocean ◽  
Synoptic Conditions ◽  
Weather And Climate ◽  
Oceanographic Data ◽  
The Impact

Between 6-9 December 2012, the Oceanographic Vessel Alpha Crucis took oceanographic stations in the Southwestern Atlantic Ocean in support to both SAMOC and ACEx projects. During the research cruise, the vessel performed measurements with the release of weather balloons. From the data collected by the radiosondes, it was possible to verify the variability of the marine atmospheric boundary layer (MABL) in the area and period of study. From meteorological and oceanographic data, it was possible to estimate the latent and sensible heat fluxes from bulk parameterization. During an episode of formation of an extratropical cyclone, the results ,of this work demonstrate the impact of the synoptic conditions influencing the evolution of the MABL. During the prefrontal condition a stratification of the MABL was verified. The  latent and sensible heat fluxes directed from the ocean to the atmosphere were low or negative (from the atmosphere to the ocean). During the post frontal condition, the MABL was well developed with a 1200 m height and the latent and sensible heat fluxes from the ocean to the atmosphere  were more intense. These observations are fundamental to widen our understanding on the physical processes occurring at the ocean-atmosphere interface and have primary importance for the weather and climate forecast of the south-southwestern region of Brazil.

scholarly journals Smoothing additive manufactured parts using ns-pulsed laser radiation

2021 ◽  
Author(s):  
Florian Kuisat ◽  
Fernando Lasagni ◽  
Andrés Fabián Lasagni
Keyword(s):  
Surface Roughness ◽  
Mechanical Performance ◽  
State Of The Art ◽  
Pulsed Laser ◽  
Industrial Applications ◽  
Laser Source ◽  
Pulsed Laser Radiation ◽  
Current State ◽  
The Impact

AbstractIt is well known that the surface topography of a part can affect its mechanical performance, which is typical in additive manufacturing. In this context, we report about the surface modification of additive manufactured components made of Titanium 64 (Ti64) and Scalmalloy®, using a pulsed laser, with the aim of reducing their surface roughness. In our experiments, a nanosecond-pulsed infrared laser source with variable pulse durations between 8 and 200 ns was applied. The impact of varying a large number of parameters on the surface quality of the smoothed areas was investigated. The results demonstrated a reduction of surface roughness Sa by more than 80% for Titanium 64 and by 65% for Scalmalloy® samples. This allows to extend the applicability of additive manufactured components beyond the current state of the art and break new ground for the application in various industrial applications such as in aerospace.

scholarly journals Characterization of the subsurface urban heat island and its sources in the Milan city area, Italy

2021 ◽  
Author(s):  
Alberto Previati ◽  
Giovanni B. Crosta
Keyword(s):  
Urban Heat Island ◽  
Urban Areas ◽  
Heat Fluxes ◽  
Shallow Aquifer ◽  
Heat Island ◽  
Groundwater Temperature ◽  
City Area ◽  
Groundwater Environment ◽  
Urban Heat ◽  
The Impact

AbstractUrban areas are major contributors to the alteration of the local atmospheric and groundwater environment. The impact of such changes on the groundwater thermal regime is documented worldwide by elevated groundwater temperature in city centers with respect to the surrounding rural areas. This study investigates the subsurface urban heat island (SUHI) in the aquifers beneath the Milan city area in northern Italy, and assesses the natural and anthropogenic controls on groundwater temperatures within the urban area by analyzing groundwater head and temperature records acquired in the 2016–2020 period. This analysis demonstrates the occurrence of a SUHI with up to 3 °C intensity and reveals a correlation between the density of building/subsurface infrastructures and the mean annual groundwater temperature. Vertical heat fluxes to the aquifer are strongly related to the depth of the groundwater and the density of surface structures and infrastructures. The heat accumulation in the subsurface is reflected by a constant groundwater warming trend between +0.1 and + 0.4 °C/year that leads to a gain of 25 MJ/m2 of thermal energy per year in the shallow aquifer inside the SUHI area. Future monitoring of groundwater temperatures, combined with numerical modeling of coupled groundwater flow and heat transport, will be essential to reveal what this trend is controlled by and to make predictions on the lateral and vertical extent of the groundwater SUHI in the study area.

scholarly journals Bonding and Thermal Cycling Performances of Two (Poly)Aryl–Ether–Ketone (PAEKs) Materials to an Acrylic Denture Base Resin

Polymers ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 543 ◽  
Author(s):  
Tzu-Yu Peng ◽  
Saiji Shimoe ◽  
Lih-Jyh Fuh ◽  
Chung-Kwei Lin ◽  
Dan-Jae Lin ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Thermal Cycling ◽  
Fatigue Testing ◽  
Lower Surface ◽  
Aryl Ether ◽  
Bonding Performance ◽  
Significant Difference ◽  
Aryl Ether Ketone ◽  
Ether Ketone ◽  
Thermal Cycling Fatigue

Poly(aryl–ether–ketone) materials (PAEKs) are gaining interest in everyday dental practices because of their natural properties. This study aims to analyze the bonding performance of PAEKs to a denture acrylic. Testing materials were pretreated by grinding, sandblasting, and priming prior to polymerization with the denture acrylic. The surface morphologies were observed using a scanning electron microscope and the surface roughness was measured using atomic force microscopy. The shear bond strength (SBS) values were determined after 0 and 2500 thermal cycles. The obtained data were analyzed using a paired samples t-test and Tukey’s honestly significant difference (HSD) test (α = 0.05). The surface characteristics of testing materials after different surface pretreatments showed obvious differences. PAEKs showed lower surface roughness values (0.02–0.03 MPa) than Co-Cr (0.16 MPa) and zirconia (0.22 MPa) after priming and sandblasting treatments (p < 0.05). The SBS values of PAEKs (7.60–8.38 MPa) met the clinical requirements suggested by ISO 10477 (5 MPa). Moreover, PAEKs showed significantly lower SBS reductions (p < 0.05) after thermal cycling fatigue testing compared to Co-Cr and zirconia. Bonding performance is essential for denture materials, and our results demonstrated that PAEKs possess good resistance to thermal cycling fatigue, which is an advantage in clinical applications. The results imply that PAEKs are potential alternative materials for the removable of prosthetic frameworks.

scholarly journals The Effect of Atmosphere–Ocean Coupling on the Structure and Intensity of Tropical Cyclone Bejisa in the Southwest Indian Ocean

Atmosphere ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 688
Author(s):  
Soline Bielli ◽  
Christelle Barthe ◽  
Olivier Bousquet ◽  
Pierre Tulet ◽  
Joris Pianezze
Keyword(s):  
Tropical Cyclone ◽  
Mixed Layer ◽  
Heat Fluxes ◽  
Sea Surface ◽  
Ocean Mixed Layer ◽  
Surface Cooling ◽  
Southwest Indian Ocean ◽  
Left Hand ◽  
Sea Surface Cooling ◽  
The Impact

A set of numerical simulations is relied upon to evaluate the impact of air-sea interactions on the behaviour of tropical cyclone (TC) Bejisa (2014), using various configurations of the coupled ocean-atmosphere numerical system Meso-NH-NEMO. Uncoupled (SST constant) as well as 1D (use of a 1D ocean mixed layer) and 3D (full 3D ocean) coupled experiments are conducted to evaluate the impact of the oceanic response and dynamic processes, with emphasis on the simulated structure and intensity of TC Bejisa. Although the three experiments are shown to properly capture the track of the tropical cyclone, the intensity and the spatial distribution of the sea surface cooling show strong differences from one coupled experiment to another. In the 1D experiment, sea surface cooling (∼1 ∘C) is reduced by a factor 2 with respect to observations and appears restricted to the depth of the ocean mixed layer. Cooling is maximized along the right-hand side of the TC track, in apparent disagreement with satellite-derived sea surface temperature observations. In the 3D experiment, surface cooling of up to 2.5 ∘C is simulated along the left hand side of the TC track, which shows more consistency with observations both in terms of intensity and spatial structure. In-depth cooling is also shown to extend to a much deeper depth, with a secondary maximum of nearly 1.5 ∘C simulated near 250 m. With respect to the uncoupled experiment, heat fluxes are reduced from about 20% in both 1D and 3D coupling configurations. The tropical cyclone intensity in terms of occurrence of 10-m TC wind is globally reduced in both cases by about 10%. 3D-coupling tends to asymmetrize winds aloft with little impact on intensity but rather a modification of the secondary circulation, resulting in a slight change in structure.

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