Observed Temperature Gradients Research Articles

Validating Gauge-based Spatial Surface Atmospheric Temperature Datasets for Upper Benue River Basin, Nigeria

Like most other countries of Africa, one of the main problems threatening effective impact modelling in Nigeria including Upper Benue river basin, dwells in lack of high-quality in-situ observation datasets at appropriate spatiotemporal scales. Gridded meteorological variables can serve as promising alternatives to in-situ measurements in data sparse regions, but then, require validations to assess quantitatively their level of accuracies and reliabilities. As a consequence, this study makes comparative analysis of two gauge-based, spatially interpolated surface atmospheric temperature datasets with in-situ measurements in seven distinct meteorological stations covering the period of 1982-2006. Correspondingly, spatial analysis and statistical measures were used to assess the performances of the gridded datasets from the Climate Research Unit (CRU) and the Climate Prediction Centre (CPC). Results from spatial distributions depict 8, 11 and 10 °C as observed minimum temperatures and 33, 36, 42 °C as observed maximum temperatures over the Cameroon highland (Gembu), the Jos plateau and at the northern fringes of the basin respectively. Consequently, both the CRU and CPC datasets captured remarkably well the observed temperature gradients along the varying topography, though with differing margins. The interannual variabilities indicate CRU dataset to better capture the signs and magnitudes of the observed anomalies as compared to the CPC data. Moreover, the CRU data was noted to be more outstanding in representing the observed features in seasonal temperature variations over most stations. Also, the shapes of the probability density function (PDF) for both datasets in minimum and maximum temperatures measured closely the shapes of the observed PDF. Trend analysis suggests CRU datasets to better represent the warming and the cooling trends than the CPC. Overall, the CRU datasets are the most outstanding in this study and is therefore preferred for water resource application over the study area.

Thermal behavior analysis of different solar PV modules via thermographic imaging

The temperature of a photovoltaic (PV) system is a critical factor in the photovoltaic conversion process; hence, the practical performance of a PV system significantly depends on its temperature. Several different methods exist for the determination of PV module temperature. In this study, thermography was employed to investigate the thermal behavior of different solar PV modules under outdoor operating conditions. It was observed that the temperature difference across the area of a PV module could reach as high as 12.5–14.8 °C depending on the type of PV module. Hence, the trends for the lowest and highest temperature were not predictable. Glass-to-glass non-frame PV modules exhibited the highest temperature gradients compared to glass-to-Tedlar non-frame modules. The observed temperature gradients demonstrated that measuring the temperature at a single point on the module was not sufficient to accurately represent the temperature over the entirety of the PV module.

Annual and Interannual Variability in the California Current System: Comparison of an Ocean State Estimate with a Network of Underwater Gliders

AbstractA data-constrained state estimate of the southern California Current System (CCS) is presented and compared with withheld California Cooperative Oceanic Fisheries Investigations (CalCOFI) data and assimilated glider data over 2007–17. The objective of this comparison is to assess the ability of the California State Estimate (CASE) to reproduce the key physical features of the CCS mean state, annual cycles, and interannual variability along the three sections of the California Underwater Glider Network (CUGN). The assessment focuses on several oceanic metrics deemed most important for characterizing physical variability in the CCS: 50-m potential temperature, 80-m salinity, and 26 kg m−3 isopycnal depth and salinity. In the time mean, the CASE reproduces large-scale thermohaline and circulation structures, including observed temperature gradients, shoaling isopycnals, and the locations and magnitudes of the equatorward California Current and poleward California Undercurrent. With respect to the annual cycle, the CASE captures the phase and, to a lesser extent, the magnitude of upper-ocean warming and stratification from late summer to early fall and of isopycnal heave during springtime upwelling. The CASE also realistically captures near-surface diapycnal mixing during upwelling season and the semiannual cycle of the California Undercurrent. In terms of interannual variability, the most pronounced signals are the persistent warming and downwelling anomalies of 2014–16 and a positive isopycnal salinity anomaly that peaked with the 2015–16 El Niño.

Thermal Emission From Saturn's Polar Cyclones

AbstractWe have used data from the Cassini Composite Infrared Spectrometer to map the temperatures in Saturn's polar cyclones at the highest spatial resolution obtained during the Cassini mission. We find temperature contrasts of 7 K in the upper troposphere within 1.4° of both poles, roughly 50 percent larger than earlier measurements at lower spatial resolution. The polar hot spots weaken with depth, disappearing near 500 mbar. In the stratosphere, the polar hot spot becomes broader, extending 4° from the poles, and weakens with altitude disappearing near 1 mbar. A thermal relaxation model shows that the tropospheric hot spot is consistent with adiabatic heating from subsidence with a vertical velocity of about −0.05 mm/s above 500 mbar. The observed temperature gradients imply that the winds in the polar cyclone decay with increasing altitude over roughly three pressure scale heights above the 200‐mbar level.

EDITORIAL

The editorial of Engenharia Térmica of this issue continues the discussion on scientific research needs in vital areas in which thermal engineering has important participation. The main goal is to motivate the readers, within their specialties, to identify possible subjects for their future research. With the development of modern high resolution infrared cameras, the utilization of thermal imaging exams has gained new appeal in medical practice, although the method has been applied for the first time more than 60 years ago. The technique is noninvasive, there is no ionizing radiation emission, low cost, fast in image capturing and of easy application. However, there are some aspects such as method imprecision due to the individual metabolism and surrounding ambient temperature that interfere in precise results, making the method subjective. In Engineering it is a well established field, mainly for the detection of heat leaks in boilers, hot fluid pipes, and other equipment, in which high temperatures are observed, thus with high temperature gradients with respect to the ambient, that are much above measurements uncertainties, what allows for well conclusive analyses. On the other hand, surface temperatures on human skin are close to the ambient temperature, therefore the observed temperature gradients are small, what makes the analyses less conclusive. In sum, there is need for the development of structured methodologies for adequate selection of human body surface temperatures that are related to diverse diseases. Expected normality ranges could be established based on infrared imaging temperature measurements of volunteers without complaints. It is expected that measurements in patients previously diagnosed with traditional techniques (e.g., biopsy) fall out of such ranges. The main objective would be to concretely demonstrate that infrared imaging has potential for utilization as a noninvasive screening exam for people with complaints, what would indicate whether or not the individual should be submitted to a more complex exam. The mission of Engenharia Térmica is to document the scientific progress in areas related to thermal engineering (e.g., energy, oil and renewable fuels). We are confident that we will continue to receive articles’ submissions that contribute to the progress of science.

Investigating the thermophysical properties of the ice–snow interface under a controlled temperature gradient Part II: Analysis

In order to develop a more intuitive understanding of the physical mechanisms and processes responsible for enhanced kinetic snow metamorphism at the ice–snow interface, we have performed a detailed and quantitative analysis of the in situ micro-thermocouple data originally presented in Part I of this study. In our detailed analysis, we have focused primarily on the observed temperature gradients from within one millimeter above and below the ice–snow interface, as measured in our laboratory prepared specimen. Our findings show via a simple one-dimensional model for energy balance that thermal contact resistance followed by decreases in the effective thermal conductivity are the primary contributors to the dramatic increases in the local temperature gradient near the ice–snow interface. Additional mechanisms for heat and mass transfer are also reviewed in our analysis, including the water vapor flux and latent heat flux.

Electron energetics in the expanding solar wind via Helios observations

AbstractWe present an observational analysis of electron cooling/heating rates in the fast and slow solar wind between 0.3 and 1 AU. We fit electron velocity distribution functions acquired in situ by Helios 1 and 2 spacecraft by a three‐component (core‐halo‐strahl) analytical model. The resulting radial profiles of macroscopic characteristics (density, temperatures, and heat fluxes) are employed to examine properties of theoretical energy balance equations and to estimate external cooling/heating terms. Our analysis indicates that in contrast to solar wind protons the electrons do not require important heating mechanisms to explain the observed temperature gradients. The electron heating rates are actually found to be negative for both the slow and fast solar wind, namely, due to the significant degradation of the electron heat flux with increasing radial distance from the Sun. Cooling mechanisms acting on electrons are found to be significantly stronger in the slow wind than in the fast wind streams.

Determination of effective thermal conductivity of beryllium pebble beds during progressive neutron irradiation up to 6000 appm He in the HIDOBE experiments

In present fusion reactors designs, beryllium pebble beds are the prime candidate for use as neutron multiplier for the helium cooled pebble bed (HCPB) breeder blankets. In the 2 HIDOBE experiments (HIgh DOse irradiation of BEryllium; [1]), performed in the High Flux Reactor (HFR) at NRG in Petten, constrained beryllium pebble bed samples are irradiated with four different target temperatures (425°C, 525°C, 650°C and 750°C) up to a doses of 3000 and 6000appm He production in Beryllium. HIDOBE-02 reached a maximum neutron fluence (E>1.0MeV) of ∼1.78×1026m−2 (±10%) in 1260 Full Power Days.In this paper a relation is described to assess the state of the pebble bed during operation, using only temperature information, together with present models for effective thermal conductivity. Observed temperature gradients across the pebble bed are measured, reconstructed, and checked/corrected for ‘external’ causes, to obtain the corresponding thermal conductivities of the pebble beds.The resulting increase in effective thermal conductivity of beryllium pebble beds is caused by changing thermal–mechanical behaviour (creep) of the constrained pebble beds, which is determined using existing correlations from out-of-pile experiments. Creep values in pebble beds under irradiation correspond well with out-of-pile experiments. One pebble bed (Tirr 525°C) shows signs of reaching a maximum creep value after a fast neutron fluence (E>1.0MeV) of ∼0.8×1026m−2.

Measurements of Momentum and Heat Transfer across the Air–Sea Interface

Abstract This study makes direct measurements of turbulent fluxes in the mixed layer in order to close heat and momentum budgets across the air–sea interface and to assess the ability of rigid-boundary turbulence models to predict mean vertical gradients beneath the ocean’s wavy surface. Observations were made at 20 Hz at nominal depths of 2.2 and 1.7 m in ∼16 m of water. A new method is developed to estimate the fluxes and the length scales of dominant flux-carrying eddies from cospectra at frequencies below the wave band. The results are compared to independent estimates of those quantities, with good agreement between the two sets of estimates. The observed temperature gradients were smaller than predicted by standard rigid-boundary closure models, consistent with the suggestion that wave breaking and Langmuir circulation increase turbulent diffusivity in the upper ocean. Similarly, the Monin–Obukhov stability function ϕh was smaller in the authors’ measurements than the stability functions used in rigid-boundary applications of the Monin–Obukhov similarity theory. The dominant horizontal length scales of flux-carrying turbulent eddies were found to be consistent with observations in the bottom boundary layer of the atmosphere and from laboratory experiments in three ways: 1) in statically unstable conditions, the eddy sizes scaled linearly with distance to the boundary; 2) in statically stable conditions, length scales decreased with increasing downward buoyancy flux; and 3) downwind length scales were larger than crosswind length scales.

Estimating mud expulsion rates from temperature measurements on Håkon Mosby Mud Volcano, SW Barents Sea

The Håkon Mosby Mud Volcano (HMMV), located on the Norwegian–Barents–Svalbard continental margin in 1250 m water depth, has been identified and described as a structure caused by upward transport of mud, pore water and gas [e.g. Eldholm, O., Sundvor, E., Vogt, P.R., Hjelstuen, B.O., Crane, K., Nilsen, A.K., Gladczenko, T.P., 1999. SW Barents Sea continental margin heat flow and Håkon Mosby Volcano. Geo-Marine Letters 19, 29–37]. During RV Polarstern expedition ARK XIX/3b in 2003, an integrated study took place to investigate the detailed morphology, biology, chemistry and geophysical aspects of HMMV [Klages, M., Thiede, J., Foucher, J.-P., 2004. The Expeditions ARK XIX 3a, 3b and 3c, Berichte zur Polarforschung, 488.]. In this paper, we describe a detailed survey involving more than 100 temperature gradient measurements in order to reveal the temperature structure of HMMV. Values of apparent heat flow up to 3000 mW/m 2 and absolute temperatures up to 25.8 °C have been detected. These enormously high heat flux values do not reflect deep-seated thermal gradients but are a result of surface mud flows. The occurrence and abundance of mud flows varies in different areas within the HMMV inner crater. A combination of very shallow, ROV-derived temperature measurements, a large number of intermediate depth temperature gradients and nine deep penetrating gravity corers allows us to reconstruct the history of activity of HMMV. Modeling of the observed temperature gradients indicates vigorous activity with very recent mud flows. Furthermore, the supply of energy and material from the HMMV is estimated to have an annual mass volume of ∼15,000 m 3. From the thermal corona of HMMV and the observed horizontal heat flux, it is possible to deduce that the long term temperature of the mud pond is stable at a temperature approximately similar to the recent maximum temperature of 25 °C.

Heat transfer in dust structures in an RF discharge plasma

Results are presented from experimental studies of heat transfer in liquid-like plasma-dust structures. The experiments were performed with aluminum oxide grains ∼3–5 μm in size in an RF discharge plasma. The heat capacity of the dust grains in plasma is measured. The thermal conductivity and thermal diffusivity of liquid-like plasma-dust structures are deduced under the assumption that the observed temperature gradients and the propagation of a thermal perturbation in a dusty plasma are related to heat conduction within the dust component. The measured temperature dependences of the thermal conductivity and thermal diffusivity are in qualitative agreement with the results of numerical simulations performed in the model of a simple single-atom liquid. It is shown that quantitative discrepancy between the experimental and numerical results is related to the energy loss of dust grains in their collisions with the neutral particles of the ambient gas.

Thermal effect at motion of gas bubbles in uniform liquid

Thermal effects related to the processes of formation and disappearance of the surface occurring during the motion of gas bubbles (droplets) in a uniform liquid are considered. Their relation to the thermocapillary motion is discussed. It is shown that for millimeter-size bubbles floating in water under the effect of Archimedes’ force, temperature drop in the front and rear parts of the bubble amounts to a few tenths of a degree and can be measured in experiments. Experimentally observed temperature gradients were shown to appear in a liquid during the motion of a bubble swarm.

Thermal conduction and reduced cooling flows in galaxy clusters

Conduction may play an important role in reducing cooling flows in galaxy clusters. We analyse a sample of sixteen objects using Chandra data and find that a balance between conduction and cooling can exist in the hotter clusters (T > 5 keV), provided the plasma conductivity is close to the unhindered Spitzer value. In the absence of any additional heat sources, a reduced mass inflow must develop in the cooler objects in the sample. We fit cooling flow models to deprojected data and compare the spectral mass deposition rates found to the values required to account for the excess luminosity, assuming Spitzer-rate heat transfer over the observed temperature gradients. The mass inflow rates found are lower than is necessary to maintain energy balance in at least five clusters. However, emission from cooling gas may be partially absorbed. We also compute the flux supplied by turbulent heat transport (Cho et al. 2003) and find conductivity profiles which follow a strikingly similar temperature dependence to the conductivity values required to prevent cooling. Finally, we show that the cluster radio luminosities vary by over five orders of magnitude in objects with X-ray luminosities differing by no more than a factor of a few. This suggests that there is unlikely to be a straightforward correlation between the mechanical power provided by the radio lobes and the rate of energy loss in cooling flow clusters.

Modified Entropy Models for the Intracluster Medium

We present a set of cluster models that link the present-day properties of clusters to the processes that govern galaxy formation. These models treat the entropy distribution of the intracluster medium as its most fundamental property. Because convection strives to establish an entropy gradient that rises with radius, the observable properties of a relaxed cluster depend entirely on its dark-matter potential and the entropy distribution of its uncondensed gas. Guided by simulations, we compute the intracluster entropy distribution that arises in the absence of radiative cooling and supernova heating by assuming that the gas-density distribution would be identical to that of the dark matter. The lowest-entropy gas would then fall below a critical entropy threshold at which the cooling time equals a Hubble time. Radiative cooling and whatever feedback is associated with it must modify the entropy of that low-entropy gas, changing the overall entropy distribution function and thereby altering the observable properties of the cluster. Using some phenomenological prescriptions for entropy modification based on the existence of this cooling threshold, we construct a remarkably realistic set of cluster models. The surface-brightness profiles, mass-temperature relation, and luminosity-temperature relation of observed clusters all naturally emerge from these models. By introducing a single adjustable parameter related to the amount of intracluster gas that can cool within a Hubble time, we can also reproduce the observed temperature gradients of clusters and the deviations of cooling-flow clusters from the standard luminosity-temperature relation.

Three‐dimensional Stereoscopic Analysis of Solar Active Region Loops. I.SOHO/EIT Observations at Temperatures of (1.0–1.5) x 106K

The three-dimensional structure of solar active region NOAA 7986 observed on 1996 August 30 with the Extreme-Ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO) is analyzed. We develop a new method of dynamic stereoscopy to reconstruct the three-dimensional geometry of dynamically changing loops, which allows us to determine the orientation of the mean loop plane with respect to the line of sight, a prerequisite to correct properly for projection effects in three-dimensional loop models. With this method and the filter-ratio technique applied to EIT 171 and 195 Å images we determine the three-dimensional coordinates [x(s), y(s), z(s)], the loop width w(s), the electron density ne(s), and the electron temperature Te(s) as a function of the loop length s for 30 loop segments. Fitting the loop densities with an exponential density model ne(h) we find that the mean of inferred scale height temperatures, Tλe=1.22 ± 0.23 MK, matches closely that of EIT filter-ratio temperatures, TEITe=1.21 ± 0.06 MK. We conclude that these cool and rather large-scale loops (with heights of h≈30-225 Mm) are in hydrostatic equilibrium. Most of the loops show no significant thickness variation w(s), but we measure for most of them a positive temperature gradient (dT/ds>0) across the first scale height above the footpoint. Based on these temperature gradients we find that the conductive loss rate is about 2 orders of magnitude smaller than the radiative loss rate, which is in strong contrast to hot active region loops seen in soft X-rays. We infer a mean radiative loss time of τrad≈40 minutes at the loop base. Because thermal conduction is negligible in these cool EUV loops, they are not in steady state, and radiative loss has entirely to be balanced by the heating function. A statistical heating model with recurrent heating events distributed along the entire loop can explain the observed temperature gradients if the mean recurrence time is ≲10 minutes. We computed also a potential field model (from SOHO/MDI magnetograms) and found a reasonable match with the traced EIT loops. With the magnetic field model we determined also the height dependence of the magnetic field B(h), the plasma parameter β(h), and the Alfvén velocity vA(h). No correlation was found between the heating rate requirement EH0 and the magnetic field Bfoot at the loop footpoints.

20th century mass balance and thermal regime change at Scott Turnerbreen, Svalbard

AbstractThe changing geometry and thermal structure of Scott Turnerbreen, a 3.3 km2 glacier located at 78° N in the Svalbard archipelago, is documented. A net mass balance of–0.58 m a–1w.e. is determined for the period 1936–93, by comparing a recent topographic survey with earlier maps. The thermal regime was investigated with multifrequency radar and borehole thermistors. Basal temperatures of–4.1° and –3.3°C were measured, and observed temperature gradients indicate that the entire bed is frozen. This interpretation is confirmed by continuous radar profiling, which demonstrates the absence of high-frequency scattering from temperate ice. However, with the reconstructed 1936 ice- thickness distribution, at least 2 km of the length of the glacier bed would be at the pressure-melting temperature. The 20th century mass-balance history of Scott Turnerbreen is likely to have been influenced by a surge occurring around 1930, which meant that the glacier was already in a state of disequilibrium before the abrupt climate perturbation marking the termination of the Little Ice Age. A significant loss of mass has been accompanied by a transition from inferred polythermal to entirely non-temperate thermal conditions. Current driving stress and velocity are very low, and the glacier has almost certainly fallen out of the surge cycle. Within 60 years, there has therefore been a wholesale transformation in the geometry, thermal structure and dynamics of Scott Turnerbreen.

Stellar Occultation Observations of Saturn's North-Polar Temperature Structure

We have observed a stellar occultation of GSC5249-01240 by Saturn's north polar region on November 20, 1995 from NASA's Infrared Telescope Facility (IRTF). This is the first recorded occultation by the polar region of a giant planet. The occulted region extends 88 km in vertical height and 660 km in horizontal length, over a region from 82.5° to 85° in planetocentric latitude and from 20° to 30° in planetocentric longitude. Based on isothermal model fits to the light curve, we find an equivalent isothermal temperature of 130 ± 10 K at a pressure level of 1.6 ± 0.1 μbar, which corresponds to a half-light latitude of 83.2 ± 0.2° and longitude of 24.1 ± 0.5°. Using numerical inversion procedures, we have retrieved the temperature profile of the occulted region, which suggests an increase in temperature (with radius) of 14.5 K between 6 and 10 μbar. We also find temperature fluctuations of 1 to 5 K along the path probed by the occultation; if the observed temperature gradients of these fluctuations apply to the vertical direction only, then this region is super-adiabatic. More likely, these thermal gradients are due to a combination of diffractive scintillations and horizontal temperature variations. Given that isothermal model fits and numerical inversions cannot separate individual contributions to observed temperature gradients, such as from vertical variations, horizontal variations, and scintillations, this occultation requires further study.

The measurement of ion acoustic turbulence and reduced thermal conductivity caused by a large temperature gradient in a laser heated plasma

An extensive account is given of experiments in which an homogeneous preformed plasma of density 6*1016 cm-3 was heated by 10.6 mu m radiation focused on 1011 W cm-2. Ruby laser scattering gave space and time resolved measurements of the resultant density and temperature, showing large temperature gradients up to lambda e mod Delta T mod /T=0.5. Enhanced low frequency turbulence was observed. When compared with a one dimensional computer code, the observed temperature gradients imply that the heat flux was limited to 4+or-2% of the free streaming limit but that the absorption was 1.1+or-0.5 times the classical inverse bremsstrahlung absorption rate. The observed Te/Ti and lambda e mod Delta T mod /T were sufficient to excite heat flux driven ion acoustic turbulence, which explains the observed low frequency turbulence. This turbulence level is shown to be large enough to account for the observed thermal conductivity.

Validity of Reported Extreme Wind Speeds in the Arctic Stratosphere at SST Altitudes

Wind speeds of more than 100 m sec−1 (sometimes exceeding 150 m sec−1) were often recorded in the Canadian stratosphere prior to the winter of 1967–68, and occasionally recorded over Alaska, Greenland and Eurasian arctic regions. For the stations at which these extreme winds occurred, all values greater than 100 m sec−1 were recorded at or near the termination level of the rawinsonde and/or at very small elevation angles, suggesting instrumentation error. Previous studies have established that the RMS wind speed error grows rapidly as elevation angles become small and as altitude of measurement increases above 20 km. Mathematical determinations of the horizontal temperature gradients at these altitudes over Canada, using the thermal wind relation and observed wind extremes, are shown to be at least 50% larger than the observed temperature gradients for distances of 150 to 300 mi. Also, speeds exceeding 100 m sec−1 in the Canadian arctic have rarely appeared in the records since the winter of 1966–67, probably a consequence of changes in Canadian upper-air sounding procedures. As a result, virtually all of these unusually strong winds which have been recorded by rawinsondes at altitudes above 20 km are considered unreliable. They should either not be used or used with extreme caution in developing climatologies related to the design and operation of the SST and other aerospace vehicles.

Surveyor vs. Refraction

Abstract While the accuracy of instruments and techniques in surveying is constantly being improved, the atmosphere through which we observe remains unchanged. In order to determine the adequacy of present methods of dealing with the bending of light rays, causes of refraction are analysed and data are assembled on the amount of bending and its variation, based on observed temperature gradients. The effects of this bending, both in magnitude and variation, are discussed in relation to trigonometric heighting, levelling, photogrammetry, triangulation, and high precision traversing, and the relevance to geodimeter and tellurometer observations is also noted.