Surface Temperature Evolution Research Articles

Influence of sea surface temperature on the intraseasonal variability of the South China Sea summer monsoon

The objective of this study is to examine, based on recently available high resolution satellite and observational data, the evolution and role of sea surface temperature (SST) in influencing the intraseasonal variability of the South China Sea (SCS) summer monsoon (SM). The study focuses on the 30–60 day timescale when the northward propagating anomalies are dominant over the SCS. Composite analysis of the SST maximum events during SCS SM shows that increased SST anomalies over the SCS are significantly influenced by the downward shortwave radiation flux anomalies, with the suppressed surface latent heat flux anomalies supplementing to it. A thermal damping of the positive SST anomalies induces positive upward heat fluxes, which then destabilize the lower atmosphere between 1,000 and 700 hPa. The positive SST anomalies lead the positive precipitation anomalies over the SCS by 10 days, with a significant correlation (r = 0.44) between the SST-precipitation anomalies. The new findings here indicate an ocean-to-atmosphere effect over the SCS, where underlying SST anomalies tend to form a favorable condition for convective activity and sustain enhanced precipitation during the SCS SM. It is also argued, based on our observations, that the negative sea level pressure anomalies induced by the positive SST anomalies play a role in enhancing the northward propagation of the intraseasonal anomalies over the SCS.

Pre-Observational Evolution of Surface Temperature in Romania as Inferred from Borehole Temperature Measurements

Temperature data from nine boreholes in the Carpathian orogen in Romania were used to obtain information on the ground surface temperature history (GSTH) in the last 250 years. The temperature measurements were taken with a thermistor probe (sensitivity in the 10 mK range) using the stop-and-go technique, at 10 m intervals, in the depth range of 20–580 m. The least squares inverse modelling approach of Tarantola and Valette (J Geophys 50:159–170, 1982) was used to infer the GSTH. Long-term air temperature records available from the Romanian weather station network were used as a comparison term for the first 100–150 years of the GSTH, and as a forcing function in a POM-SAT model that combines borehole temperature profiles (BTPs) and meteorological time series (surface air temperature, SAT) to produce information on the so-called pre-observational mean (POM). Results from a global circulation model for the Romanian area are incorporated in the discussion as well.

Thermography as a technique for monitoring early age temperatures of hardening concrete

The exothermal character of cement hydration reactions causes concrete to endure temperature changes during the first days after casting, with associated volumetric deformations that may induce undesired cracking. The capability to predict temperature evolution in concrete since casting is thus important to back decisions that avoid detrimental thermal cracking in concrete structures. Even though several approaches exist to model the early age behavior of concrete, the laboratory or in situ verification of numerical predictions is scarce, and mostly done with embedded temperature sensors, with limited sampling points. The present research intends to evaluate the performance of the thermography technique in the continuous monitoring of surface temperatures of a hydrating 0.40 × 0.40 × 0.40 m 3 concrete cube, in which embedded thermal sensors are also used. By using thermography, simultaneous monitoring of the visible surfaces of the specimen is possible, thus providing comprehensive information regarding the evolution of surface temperatures. The temperatures monitored with the thermography, as well as with the embedded temperature sensors, are finally used as a benchmark example for validation of a 3D finite element numerical code for thermal analysis developed by the authors. The use of thermography images for validation of finite element results is rather more advantageous than the use of standard single point temperature measurements, in view of the large facility and wide range of comparison provided by the simultaneous visualization of temperature surface color maps (measured and simulated).

Study of pyrolysis and upward flame spread on charring materials—Part I: Experimental study

AbstractIn this paper, we describe the results from an experimental campaign, focused on vertical upward flame spread over a charring material. First, for validation purposes of simulation tools, we report on cone calorimeter results for square (9.8cm×9.8cm), 1.65 cm thick, medium density fibre samples, mounted horizontally. Temperature is shown at the surface and at different depths. The mass of the sample is continuously measured. From the raw data, we derive the temporal evolution of the mass loss rate due to pyrolysis. Different externally imposed heat fluxes are investigated (20, 30 and 50kW/m2), onto dry and wet material. Afterwards, for the configuration of two particle board plates (0.025 m thick, 0.4 m wide and 2.5 m high), vertically mounted face to face is considered. Two different horizontal spacing distances between the two plates are studied (30.5 and 10.5 cm). The purpose of this set‐up is to investigate the vertical upward flame spread with strong radiative heat feedback. To that purpose, the temporal evolution of surface temperature is measured over the height of the plates. The measurement data are used to test a pyrolysis model in numerical simulations. Copyright © 2010 John Wiley & Sons, Ltd.

Snow/atmosphere coupled simulation at Dome C, Antarctica

AbstractUsing a snow/atmosphere coupled model, the evolution of the surface and near-surface snow temperature is modeled at Dome C, Antarctica, during the period 20–30 January 2010. Firstly, the detailed multilayer snow model Crocus is run in stand-alone mode, with meteorological input forcing data provided by local meteorological observations. The snow model is able to simulate the evolution of surface temperature with good accuracy. It reproduces the observed downward propagation of the diurnal heatwave into the upper 50 cm of the snowpack reasonably well. Secondly, a fully coupled 3-D snow/atmosphere simulation is performed with the AROME regional meteorological model, for which the standard single-layer snow parameterization is replaced by Crocus. In spite of a poor simulation of clouds, the surface and near-surface snow temperatures are correctly simulated, showing neither significant bias nor drifts during the simulation period. The model reproduces particularly well the average decrease of the diurnal amplitude of air temperature from the surface to the top of the 45 m instrumented tower. This study highlights the potential of snow/atmosphere coupled models over the Antarctic plateau and the need to improve cloud microphysics and data assimilation over polar regions.

EXPERIMENTAL INVESTIGATION AND PERFORMANCE ANALYSES OF CBN INSERT IN HARD TURNING OF COLD WORK TOOL STEEL (D3)

Long-term wear tests on the CBN tool behaviour during hard turning of AISI D3 (60 HRC) have been investigated. The evolution of surface roughness, cutting forces and temperature has been studied according to the cutting parameters and tool wear. Results show that CBN is resistant to wear despite of aggressiveness of AISI D3 steel. A great part of heat generated is mainly dissipated throughout the chip; at a cutting speed of 320 m/min the chip temperature is found to be 14 times higher than that recorded in the workpiece. The cutting speed range of 90 to 240 m/min has been found suitable to cut this material. The former speed range is appropriate to respect the cutting constraints, whereas beyond 240 m/min a drastic increase in tool wear occurs, causing a remarkable drop in tool life. Roughness measurements reveal a dependence on CBN tool wear. However, although the wear rises up to the allowable flank wear of value 0.3 mm, roughness Ra remains around 1.0 μm. The feed rate remains the most affecting factor on the roughness values. The proposed statistical models are based on the response surface methodology correlating the cutting parameters together with roughness, cutting forces and tool life.

Hydrodynamic modeling of Lake Ontario: An intercomparison of three models

The solutions of three lake hydrodynamic models, namely, Princeton Ocean Model (POM), Canadian Version of Diecast Model, and Estuary, Lake, and Coastal Ocean Model, are compared with each other and with observations in Lake Ontario. The models have the same horizontal resolution and are forced with meteorological observations during mid‐April to early October of 2006. The three models obtained qualitatively similar results, although they have differences in physical parameters, numerical scheme, and vertical discretization. Comparison with observations shows that the models can reproduce the time evolution of lake surface temperature reasonably well. All the models produced shallower mixed layers than observations at midlake stations, causing significant errors in simulating the temperatures in the thermocline but performed better near the coast. All the models also reproduced the characteristics of the time variability of the surface currents but quantitatively had substantial errors at subsurface levels. The three models all reproduced the observed spatial pattern of the summer mean near‐surface temperatures, with upwelling (colder temperatures) along the north shore and downwelling (warmer temperatures) along the southeastern shore. The models simulated a lake‐wide cyclonic circulation occupying a large portion of the lake, consistent with the observed climatology, but showed distinct differences in simulating the smaller gyre in the western corner of the lake. Although POM has half‐vertical layers compared to z level models, its performance is comparable or slightly better than other models in most of the measures. During a strong easterly wind event, the performances of the models are similar in simulating the upwelling and downwelling processes in the lake and agree with the expected dynamic response to the strong wind forcing.

Contrasting evolution of sea surface temperature in the Benguela upwelling system under natural and anthropogenic climate forcings

We present alkenone‐derived Sea Surface Temperature (SST) records from three marine cores collected within the southern Benguela Upwelling System (BUS) spanning the last 3 ka. The SST evolution over the last 3 millennia is marked by aperiodic millennial‐scale oscillations that broadly correspond to climatic anomalies identified over the North Atlantic region. The BUS SST data further suggest cooling and warming trends opposite to the temperature evolution in the Moroccan upwelling region and in Antarctica. In contrast, the last decades are marked by a cooling of unprecedented magnitude in both the Benguela and Moroccan upwelling systems, which is not observed in the Antarctic record. These contrasted responses in Atlantic upwelling systems triggered by natural and anthropogenic forcings shed light on how different climatic mechanisms are mediated by ocean‐atmosphere interactions and transmitted to the geological records of past and present climate changes.

Mean seasonal cycle and evolution of the sea surface temperature from satellite and in situ data in the English Channel for the period 1986–2006

A night-time series of sea surface temperature (SST) of the advanced very high-resolution radiometer (AVHRR) sensors provided by the AVHRR/Pathfinder was analysed over the period 1986–2006 in the English Channel. The studied area is characterized by a strong influence of the bathymetry on the mixing of the water column, mostly through the action of the tide and waves, leading to regional patterns in the SST fields. Another specific aspect of the area is the relatively large number of in situ measurements available from coastal stations. The remotely sensed SST data with fine spatial resolution and high-frequency measurements made at coastal stations have been analysed using a common model. The long-term evolution of SST has been defined in this study through a linear trend while the seasonal evolution has been described through two harmonic functions. The daily satellite SST fields have been estimated over the period 1986–2006 by applying the kriging method to the anomalies calculated from the model. These interpolated temperatures were compared with in situ data, including many coastal stations unreachable at the sensor resolution. To use those coastal stations for comparison and to complement the satellite-derived data set, we defined transfer functions established from fine analysis of the in situ gradients along cross shore transects. The study showed the existence of a long-term warming and that this trend was not homogeneous in the area studied. The central part of the English Channel and the Western part of Brittany show an increase in temperature of about 0.6°C and the Northern part of the Irish and Baltic Sea, included in the studied area, show a maximum increase in the temperature of 1.6°C over the period 1986–2006.

Oxygen-driven surface segregation of lithium from single-wall carbon nanotubes

We have investigated the effects of oxygen exposure on lithium-intercalated single-wall carbon nanotube bundles at room temperature, and the evolution of surface configuration versus temperature. X-ray and ultraviolet photoelectron spectroscopy measurements show a remarkable increase of surface lithium concentration, associated to modifications suffered by both core-level O 1 s line shape and valence band spectra. These results have been attributed to the occurrence of lithium surface segregation induced by interaction with oxygen species. Moreover, lithium oxide and peroxide related features are observed indicating that lithium oxidation takes place at the nanotube bundle surface.

Tropical Pacific Ocean and the Madden‐Julian Oscillation: Role of wind and buoyancy forcing

A global ocean circulation model is used to examine the dynamical response of the tropical Pacific Ocean to forcing associated with the Madden‐Julian Oscillation (MJO). Model sensitivity experiments first reveal that MJO‐related changes in sea level are caused primarily by changes in wind stress. Further, the MJO‐related changes in sea surface temperature (SST) are mainly caused by buoyancy (heat) flux in the Indian Ocean, by wind stress in the central tropical Pacific, and by both buoyancy flux and wind stress in the eastern tropical Pacific. Additional model sensitivity studies quantify the tropical Pacific Ocean response to MJO wind forcing. The simulations reveal that the subsurface temperature variations associated with the MJO propagate eastward along the thermocline and rise to the surface in the eastern Pacific. Zonal advection plays a dominant role in SST variation in the central Pacific; vertical advection plays an important role in the evolution of subsurface and surface temperatures in the eastern Pacific. Finally, it is shown that MJO wind forcing can rectify SST variations through nonlinear interactions of the intraseasonal variations of the zonal currents and the zonal SST gradient.

Formation history and physical properties of sediments from the Mount Elbert Gas Hydrate Stratigraphic Test Well, Alaska North Slope

The synthesis of available geological information and surface temperature evolution in the Alaska North Slope region suggests that: biogenic and deeper thermogenic gases migrated through fault networks and preferentially invaded coarse-grained layers that have relatively high hydraulic conductivity and low gas entry pressures; hydrate started forming before the beginning of the permafrost; eventually, the permafrost deepened and any remaining free water froze so that ice and hydrate may coexist at some elevations. The single tested specimen (depth 620.47–620.62 m) from the D unit consists of uncemented quartzitic fine sand with a high fraction of fines (56% by mass finer than sieve #200). The as-received specimen shows no evidence of gas present. The surface texture of sediment grains is compatible with a fluvial-deltaic sedimentation environment and shows no signs of glacial entrainment. Tests conducted on sediments with and without THF hydrates show that effective stress, porosity, and hydrate saturation are the major controls on the mechanical and geophysical properties. Previously derived relationships between these variables and mechanical/geophysical parameters properly fit the measurements gathered with Mount Elbert specimens at different hydrate saturations and effective stress levels. We show that these measurements can be combined with index properties and empirical geomechanical relationships to estimate engineering design parameters. Volumetric strains measured during hydrate dissociation vanish at 2–4 MPa; therefore, minimal volumetric strains are anticipated during gas production at the Mount Elbert well. However, volume changes could increase if extensive grain crushing takes place during depressurization-driven production strategies, if the sediment has unexpectedly high in situ porosity associated to the formation history, or if fines migration and clogging cause a situation of sustained sand production.

Thermal and tribological study of a periodic contact under braking conditions

The present work concerns the tribological and thermal studies of periodic contact obtained during successions of railway stop-brakings. Tests with heat accumulation, performed on a braking tribometer, permit the observation of a modification of the friction coefficient, a wear increase and the presence of a large compacted third body layer on the pad surface. An analytic model of thermal conduction is developed for the determination of the disc surface temperature evolution during the succession of stop-brakings. The results obtained using mass temperature measurements during the succession are compared with those estimated by pyrometry; a good agreement is found.

Life prediction of metals undergoing fatigue load based on temperature evolution

Fatigue failure of metals undergoing cyclic load is evaluated based on the evolution of surface temperature. Aluminum Alloy 6061 and Stainless Steel 304 are selected as testing materials and specimens are subjected to completely reversed torsion load. A thermographic technique is used to measure the temperature increase of the specimen due to hysteresis heating during the fatigue testing. Experimental results indicate that the initial rate of temperature rise as a function of time can be utilized as an index for prediction of fatigue life. An empirical correlation of the form N f = c 1 R θ c 2 with constants c 1 and c 2 is derived that relates the rate of temperature rise, R θ , at the beginning of the test to the number of cycles to failure, N f . It is shown that c 1 is dependent upon the material properties and stress state whilst c 2 is a constant. Experimental results are consolidated into a single curve which gives the time to failure as a function of initial slope of temperature rise, thereby enabling fast prediction of fatigue failure.

The influence of stratospheric potential vorticity on baroclinic instability

AbstractThis article examines the dynamical coupling between the stratosphere and troposphere by considering the effect of direct perturbations to stratospheric potential vorticity on the evolution of midlatitude baroclinic instability in a simple extension of an Eady model. A simulation in which stratospheric potential vorticity is exactly zero is used as a control case, and both zonally symmetric and asymmetric perturbations to the stratospheric potential vorticity are then considered, the former representative of a strong polar vortex, the latter representative of the stratospheric state following a major sudden warming. Both types of stratospheric perturbation result in significant changes to the synoptic‐scale evolution of surface temperature, as well as to zonally and globally averaged tropospheric quantities. In the case of a zonally symmetric perturbation, the linear growth rate of all unstable modes decreases with increasing perturbation amplitude. Initial growth rates in cases with significant asymmetric perturbations are also weaker than those of the control case, but final eddy kinetic energy values are much larger due to the growth of low zonal wavenumbers triggered by the initial stratospheric perturbation. A comparison of the zonally symmetric and asymmetric perturbations gives some insight into the possible influence of pre‐ or post‐sudden‐warming conditions on tropospheric evolution. Copyright © 2009 Royal Meteorological Society

A Modeling and Observational Framework for Diagnosing Local Land–Atmosphere Coupling on Diurnal Time Scales

AbstractLand–atmosphere interactions play a critical role in determining the diurnal evolution of both planetary boundary layer (PBL) and land surface temperature and moisture states. The degree of coupling between the land surface and PBL in numerical weather prediction and climate models remains largely unexplored and undiagnosed because of the complex interactions and feedbacks present across a range of scales. Furthermore, uncoupled systems or experiments [e.g., the Project for the Intercomparison of Land-Surface Parameterization Schemes (PILPS)] may lead to inaccurate water and energy cycle process understanding by neglecting feedback processes such as PBL-top entrainment. In this study, a framework for diagnosing local land–atmosphere coupling is presented using a coupled mesoscale model with a suite of PBL and land surface model (LSM) options along with observations during field experiments in the U.S. Southern Great Plains. Specifically, the Weather Research and Forecasting Model (WRF) has been coupled to the Land Information System (LIS), which provides a flexible and high-resolution representation and initialization of land surface physics and states. Within this framework, the coupling established by each pairing of the available PBL schemes in WRF with the LSMs in LIS is evaluated in terms of the diurnal temperature and humidity evolution in the mixed layer. The coevolution of these variables and the convective PBL are sensitive to and, in fact, integrative of the dominant processes that govern the PBL budget, which are synthesized through the use of mixing diagrams. Results show how the sensitivity of land–atmosphere interactions to the specific choice of PBL scheme and LSM varies across surface moisture regimes and can be quantified and evaluated against observations. As such, this methodology provides a potential pathway to study factors controlling local land–atmosphere coupling (LoCo) using the LIS–WRF system, which will serve as a test bed for future experiments to evaluate coupling diagnostics within the community.

Wear mechanisms of WC–Co cutting tools from high-speed tribological tests

In machining processes, surface roughness and dimensional accuracy of machined parts depend on tool wear. Cemented carbide based cutting tools remain widely used in machining processes for their wear resistance. The aim of this paper is to study wear mechanisms of a WC–Co cutting tool grade under tribological conditions. Dry friction experiments are carried out on a high-speed pin-on-disc tribometer considering WC–Co pins against steel discs made of an AISI 1045 grade. Furthermore, two type-K thermocouples are embedded in WC–Co pins in order to estimate the contact temperature during sliding tests. A large sliding speed range is considered: from 60 up to 600 m/min. Results deal with wear rate versus tribological conditions, evolution of friction coefficient and temperature versus sliding speed and evolution of wear mechanisms. WC–Co tribological pins exhibit different wear mechanisms: abrasion, adhesion, transgranular WC micro-cracking and WC/WC debonding. Circulation of debris in the friction contact depends on sliding speed and on test duration. The evolution of surface temperature versus friction coefficient is studied too. Furthermore, a particular attention is paid on the relationship between the thermal energy in the pin and the mechanical energy in the contact. The thermal energy is calculated from the temperature values of K-thermocouples and the mechanical energy dissipated in the pin is calculated from friction coefficient evolutions. Relationships are established through modelling approaches.

Tribological, physicochemical and thermal study of the abrupt friction transition during carbon/carbon composite friction

Due to their thermo-mechanical performances maintained at high temperature, C/C composites demonstrate their advantages in high energy aeronautical braking. During friction a typical tribological behavior was observed. At first, an abrupt transition of friction coefficient takes place systematically from a weak value (∼0.15) to a high value (∼0.35). Before this transition, an extremely weak wear rate is associated to a weak friction coefficient value and no gas exchanges occur in the contact, this regime being called non-reactive. From the abrupt transition, a very high wear rate and strong gas exchanges associated to the high friction value occur (reactive regime). In this paper, for a better understanding of the mechanisms governing the abrupt transition during C/C composites tribological, mechanical, thermal and physico-chemical data are analyzed. Friction tests are performed on a 3D C/C composite consisting of PAN-based fibers and CVI pyrocarbon matrix in using a pin-on-disc tribometer equipped with a mass spectrometer allowing the in situ gas exchange analysis (CO 2 production, O 2 consumption) in the contact. To follow the disc surface temperature evolution before, during and after the transition, a thermal infrared camera is used. After friction, worn surfaces and interfaces are characterized by optical microscopy and scanning electron microscopy. In a final analysis, a mechanism is proposed to explain the abrupt transition.

The Characterization of Defects in Multi-Layered Composite Materials by Thermal Tomography Methods

The idea of thermal tomography is slicing a work piece for some in-depth layers which exhibit the distribution of thermal properties in materials by the analogy with X-ray tomography. Thermal tomography is based on the analysis of the surface temperature evolution which follows thermal stimulation of test samples. In this paper, some experimental results of applying the dynamic thermal tomography algorithm to a carbon flbre reinforced plastic sample are presented. The e‐ciency of few data processing methods is discussed.

Code development for ITER edge modelling – SOLPS5.1

Most ITER divertor modelling work to date used the B2–EIRENE (SOLPS4) code package, coupling a 2D fluid description of the charged plasma species (B2) to a Monte-Carlo kinetic description of the neutrals (EIRENE). In recent years, the emphasis at ITER has been on completing the neutral model, including neutral-neutral collisions, opacity effects, radiation transport, etc. Elsewhere, new physics, numerics, and algorithmic improvements, such as E × B and diamagnetic drifts, electric currents, ion and neutral heat and particle flux limits, wall material mixing and surface temperature evolution, and bundling of heavy ions species, as well as switching to cell-centred velocities and using an internal energy instead of a total energy equation, gave birth to the B2.5 code, combined with EIRENE as SOLPS5. We report on work in progress to merge these advances with the ITER-specific model of the edge and divertor.