Time Evolution Of Temperature Profiles Research Articles

Time evolution of temperature profiles retrieved from 13 years of infrared atmospheric sounding interferometer (IASI) data using an artificial neural network

Abstract. The three infrared atmospheric sounding interferometers (IASIs), launched in 2006, 2012, and 2018, are key instruments to weather forecasting, and most meteorological centres assimilate IASI nadir radiance data into atmospheric models to feed their forecasts. The European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) recently released a reprocessed homogeneous radiance record for the whole IASI observation period, from which 13 years (2008–2020) of temperature profiles can be obtained. In this work, atmospheric temperatures at different altitudes are retrieved from IASI radiances measured in the carbon dioxide absorption bands (654–800 and 2250–2400 cm−1) by selecting the channels that are the most sensitive to the temperature at different altitudes. We rely on an artificial neural network (ANN) to retrieve atmospheric temperatures from a selected set of IASI radiances. We trained the ANN with IASI radiances as input and the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis version 5 (ERA5) as output. The retrieved temperatures were validated with ERA5, with in situ radiosonde temperatures from the Analysed RadioSoundings Archive (ARSA) network and with EUMETSAT temperatures retrieved from IASI radiances using a different method. Between 750 and 7 hPa, where IASI is most sensitive to temperature, a good agreement is observed between the three datasets: the differences between IASI on one hand and ERA5, ARSA, or EUMETSAT on the other hand are usually less than 0.5 K at these altitudes. At 2 hPa, as the IASI sensitivity decreases, we found differences up to 2 K between IASI and the three validation datasets. We then computed atmospheric temperature linear trends from atmospheric temperatures between 750 and 2 hPa. We found that in the past 13 years, there is a general warming trend of the troposphere that is more important at the poles and at mid-latitudes (0.5 K/decade at mid-latitudes, 1 K/decade at the North Pole). The stratosphere is globally cooling on average, except at the South Pole as a result of the ozone layer recovery and a sudden stratospheric warming in 2019. The cooling is most pronounced in the equatorial upper stratosphere (−1 K/decade). This work shows that ANN can be a powerful and simple tool to retrieve IASI temperatures at different altitudes in the upper troposphere and in the stratosphere, allowing us to construct a homogeneous and consistent temperature data record adapted to trend analysis.

Experimental validation of heat transfer models for flow through a porous medium

Unsteady heat transfer in a fluid saturated porous medium contained in a tube is studied. The porous medium is a bed of uniform diameter spheres, made of glass or steel, while the flowing fluid is water. The flow field is time invariant in the simulation as well as experiments. Step response of the bed when the temperature of the incoming water is suddenly increased, and oscillatory response when hot and cold fluids alternately flow through the tube are studied. Heat transfer models are based on thermal equilibrium between the fluid and the solid phase (one-equation) and thermal non-equilibrium (two-equation) between the two phases. The predictions of these models are compared against experiments conducted in a laboratory-scale apparatus. The comparison is in terms of time evolution of temperature profiles at selected points in the bed, as well as global properties of the temperature distribution such as attenuation and phase lag with respect to the boundary perturbations. The range of Peclet numbers considered in the study is 500–4,000, for which the flow can be considered laminar. Results show that the predictions of the two-equation model are uniformly superior to the one-equation model over the range of Peclet numbers studied. The differences among the three approaches diminish when the thermophysical properties of the solid and fluid phases are close to one another. The differences also reduce in the step response test as steady state is approached.

Nonlinear Dynamics of Reaction-Diffusion Systems: Analysis and Computations

In this paper, equilibria and dynamics of reaction-diffusion systems are studied by means of analysis and computations based on a central expansion method for radially symmetric as well as angularly asymmetric distributions. Effects of boundary conditions are included. The interplay between the different processes in the evolution of the system is considered. The investigation provides a unified description in one, two, and three dimensions. A particular application concerns the time evolution of temperature profiles in a fusion reactor plasma.

Thermal distribution and the effect on resist sensitivity in electron-beam direct write

Thermal sensitivity measurements of diazoquinone/novolac (DQN), poly-olefin sulfone/novolac (SNS), and an acid catalyzed/proprietary resin (XPR) were made by gently exposing coated wafers at 10−9 amp/cm2 on a cooled/heated stage in our e-beam exposure tool. The results were characterized by the influence of exposure temperature on blanket-exposure-dissolution rates and developed image profiles. Three-dimensional Monte Carlo absorbed-energy-density calculations have been combined with ANSYS finite-element-thermal analysis to estimate the time evolution of temperature profiles on silicon wafers, silicon membranes, and SiO2 wafers at 50 keV. Lithographic modeling system (LMS) has then combined the predicted thermal fronts with the experimentally measured resist response to predict the effects on image profiles. Thermal proximity effects in 2 μm wide lines are negligible on Si wafers, 3–5% on Si membranes, and two to three times worse on SiO2 substrates.

Time Evolution of Temperature Profiles in the Abdominal Cross Section during Hyperthermia Treatment for Deep-situated Tumors

Time Evolution of Temperature Profiles in the Abdominal Cross Section during Hyperthermia Treatment for Deep-situated Tumors

Thermal explosion and times-to-ignition in systems with distributed temperatures I. Reactant consumption ignored

Hitherto the time evolution of temperature profiles within systems capable of reacting exothermically and perhaps of exploding has only been known for the limiting case in which the temperature remains essentially uniform throughout. In this paper we consider the more difficult and general problem in which the temperature profile is not uniform. We concentrate on numerical results for the three simplest geometries (infinite slab, infinite cylinder, sphere) but our solutions are valid for arbitrary geometry. Similarly we concentrate on Arrhenius temperature-dependence; the solutions can again cope readily with general forms. The principal result of the paper is a description of the evolution of the central temperature when circumstances are marginally supercritical. When the value of Frank-Kamenetskii’s reduced reaction rate parameter ( δ ) slightly exceeds its critical value ( δ cr ), the temperature at first increases rapidly and then moves very slowly for a long while before a final, rapid acceleration leads to ignition. Times to ignition ( t ) all have the form t / t ad = M /( δ / δ cr - 1) ½ where t ad is a known time closely corresponding to the time to ignition under adiabatic conditions. The value of the constant M is readily calculated from certain simple integrals. Its variation with geometry and Biot number β is presented and discussed. The limiting form of our expressions for β → 0 is precisely the well known solution of the problem for Semenov boundary conditions. We also compare our results with an exact (numerical) solution of the time-dependent problem for a sphere with fixed surface temperature. Not only is the agreement close to criticality very good but also it yields a fair approximation up to δ ≈ 2 δ cr .

The effect of carrier diffusion on laser heating of lightly damaged semiconductors

It has been observed that the surface temperature obtained during laser heating of lightly damaged material is generally considerably lower than the temperature obtained in heavily damaged material. We develop a model which explains this observation by taking into acount the diffusion of the photoexcited carriers. The time evolution of temperature profiles was calculated for pulsed ruby and Nd : YAG illumination of silicon and ruby illumination of GaAs. The material, optical, and electronic properties were varied, according to the material quality. Surface recombination of the carriers was also taken into account. For the same laser power, the induced temperature was lower and the heating times were longer in good-quality materials than in heavily damaged materials. This is because of longer carrier difusion lengths in good-quality material. The effect of the damage on the heating was found to be much more pronounced for Nd : YAG than for ruby irradiation because a larger portion of the ruby laser energy (excess above band gap) is given rapidly to the lattice through quasithermalization inside the semiconductor energy bands. Thermal spikes are formed as the result of the preferential recombination of the carriers at the surface. For a sufficiently fast surface recombination, the temperature profile may develop a secondary maximum in the material interior.