Subsurface Temperature Profiles Research Articles

Permanent carbon dioxide storage in deep-sea sediments.

Stabilizing the concentration of atmospheric CO(2) may require storing enormous quantities of captured anthropogenic CO(2) in near-permanent geologic reservoirs. Because of the subsurface temperature profile of terrestrial storage sites, CO(2) stored in these reservoirs is buoyant. As a result, a portion of the injected CO(2) can escape if the reservoir is not appropriately sealed. We show that injecting CO(2) into deep-sea sediments below [corrected] 3,000-m water depth and a few hundred meters of sediment provides permanent geologic storage even with large geomechanical perturbations. At the high pressures and low temperatures common in deep-sea sediments, CO(2) resides in its liquid phase and can be denser than the overlying pore fluid, causing the injected CO(2) to be gravitationally stable. Additionally, CO(2) hydrate formation will impede the flow of CO(2)(l) and serve as a second cap on the system. The evolution of the CO(2) plume is described qualitatively from the injection to the formation of CO(2) hydrates and finally to the dilution of the CO(2)(aq) solution by diffusion. If calcareous sediments are chosen, then the dissolution of carbonate host rock by the CO(2)(aq) solution will slightly increase porosity, which may cause large increases in permeability. Karst formation, however, is unlikely because total dissolution is limited to only a few percent of the rock volume. The total CO(2) storage capacity within the 200-mile economic zone of the U.S. coastline is enormous, capable of storing thousands of years of current U.S. CO(2) emissions.

Radiant smoldering ignition of plywood

This paper investigates the role of self-heating in the smoldering ignition of 18 mm (three-quarter inch) thick maple plywood exposed to radiant heat fluxes between 6 and 15 kW/m 2 in the cone calorimeter for up to 8 h. The minimum heat flux for smoldering ignition was experimentally determined to be 7.5 kW/m 2. This compares favorably to predictions made using classical self-heating theory. The role of self-heating was explored via temperature measurements distributed within the specimens. Elevated subsurface temperature profiles indicated self-heating was an important ignition factor resulting in ignition at depth with smolder propagation to the surface and into the material. The ignition depth was shown to be a function of the heat flux with the depth moving towards the surface as the heat flux increased.

Transient Burning Characteristics of JA2 Propellant Using Experimentally Determined Zel'dovich Map

Combustion characteristics of JA2 propellant were studied both experimentally and theoretically. Its steady-state burning behavior was investigated using an optical strand burner. The parameters measured were the regression rate, subsurface temperature profile, and burning surface temperature at different initial temperatures (-40<T i <80°C) and pressures (0.1<P<68 MPa). The measured burning rates r b were correlated as a function of T i and pressure up to 300 MPa. Predicted r b from the correlation are in close agreement with experimental data. The temperature sensitivity σ p was found to decrease as pressure increases, reaching an asymptotic value of 0.0024 K -1 at high pressures. Surface-temperature data were correlated as a linear function of pressure with temperature-dependent coefficients. The Zel'dovich map was constructed from the experimental data. This map was then used in a computer simulation to investigate the transient burning characteristics of JA2 under different pressurization rates. From the simulation results, it was found that JA2 propellant only exhibits a mild transient burning effect. This finding is further confirmed with the observations obtained from a parallel experimental study using an interrupted burner coupled with a real-time X-ray radiography. The reason for this finding is the low value of σ p and its rapid decay as the pressure increases for P < 20 MPa.

Initialization of an ENSO Forecast System Using a Parallelized Ensemble Filter

Abstract As a first step toward coupled ocean–atmosphere data assimilation, a parallelized ensemble filter is implemented in a new stochastic hybrid coupled model. The model consists of a global version of the GFDL Modular Ocean Model Version 4 (MOM4), coupled to a statistical atmosphere based on a regression of National Centers for Environmental Prediction (NCEP) reanalysis surface wind stress, heat, and water flux anomalies onto analyzed tropical Pacific SST anomalies from 1979 to 2002. The residual part of the NCEP fluxes not captured by the regression is then treated as stochastic forcing, with different ensemble members feeling the residual fluxes from different years. The model provides a convenient test bed for coupled data assimilation, as well as a prototype for representing uncertainties in the surface forcing. A parallel ensemble adjustment Kalman filter (EAKF) has been designed and implemented in the hybrid model, using a local least squares framework. Comparison experiments demonstrate that the massively parallel processing EAKF (MPPEAKF) produces assimilation results with essentially the same quality as a global sequential analysis. Observed subsurface temperature profiles from expendable bathythermographs (XBTs), Tropical Atmosphere Ocean (TAO) buoys, and Argo floats, along with analyzed SSTs from NCEP, are assimilated into the hybrid model over 1980–2002 using the MPPEAKF. The filtered ensemble of SSTs, ocean heat contents, and thermal structures converge well to the observations, in spite of the imposed stochastic forcings. Several facets of the EAKF algorithm used here have been designed to facilitate comparison to a traditional three-dimensional variational data assimilation (3DVAR) algorithm, for instance, the use of a univariate filter in which observations of temperature only directly impact temperature state variables. Despite these choices that may limit the power of the EAKF, the MPPEAKF solution appears to improve upon an earlier 3DVAR solution, producing a smoother, more physically reasonable analysis that better fits the observational data and produces, to some degree, a self-consistent estimate of analysis uncertainties. Hybrid model ENSO forecasts initialized from the MPPEAKF ensemble mean also appear to outperform those initialized from the 3DVAR analysis. This improvement stems from the EAKF’s utilization of anisotropic background error covariances that may vary in time.

Quasistationary field of thermal emission and near-field radiometry

We provide a theory of radiometry measurements of the quasistationary (near) field of thermal emission from a heated conducting medium. It explains why the Rytov effect, which essentially is a drastic growth of the thermal field energy near the medium surface, cannot be detected experimentally. However, we discovered a measurable near-field effect: the effective depth of formation of the received emission proves to be less than the skin-layer depth, depending on the size of the receiving antenna and its height above the surface. For such measurements highly effective antennas of a small aperture size are necessary. We developed and investigated a variety of microwave antennas whose parameters were fairly suitable for near-field radiometry. The measurements conducted with these antennas yielded experimental evidence of the fact that the quasistationary thermal field really exists. Near-field radiometry opens further opportunities for investigating media. In particular, we demonstrate here a technique for retrieval of the subsurface temperature profile in water with the help of near-field measurements.

Estimation of ocean subsurface thermal structure from surface parameters: A neural network approach

Satellite remote sensing provides diverse and useful ocean surface observations. It is of interest to determine if such surface observations can be used to infer information about the vertical structure of the ocean's interior, like that of temperature profiles. Earlier studies used either sea surface temperature or dynamic height/sea surface height to infer the subsurface temperature profiles. In this study we have used neural network approach to estimate the temperature structure from sea surface temperature, sea surface height, wind stress, net radiation, and net heat flux, available from an Arabian Sea mooring from October 1994 to October 1995, deployed by the Woods Hole Oceanographic Institution. On the average, 50% of the estimations are within an error of ±0.5°C and 90% within ±1.0°C. The average RMS error between the estimated temperature profiles and in situ observations is 0.584°C with a depth‐wise average correlation coefficient of 0.92.

Estimating the nucleus density of Comet 19P/Borrelly

The nucleus bulk density of Comet 19P/Borrelly has been estimated by modeling the sublimation-induced non-gravitational force acting upon the orbital motion, thereby reproducing the empirical perihelion advance (i.e., the shortening of the orbital period). The nucleus has been modeled as a prolate ellipsoid, covered by various surface activity maps which reproduce the observed water production rate. The theoretical water production rate of active areas has been obtained by applying a sophisticated thermophysical model. This model takes into account net sublimation of ice and thermal reradiation from the surface, solid state conductivity, sub-surface sublimation and recondensation, mass and heat transport by diffusing gas, layer absorption of solar energy, a full treatment of local time-dependent illumination conditions, and a detailed consideration of nucleus/coma interaction mechanisms. The outgassing properties of the modeled nucleus are physically consistent with the gas kinetic structure of the innermost coma since the molecular backflux and surface gas density required in the thermophysical model (as functions of the nucleus surface temperature and the sub-surface temperature profile) have been obtained from Direct Simulation Monte Carlo modeling of inelastic intermolecular collisions in the cometary Knudsen layer. The calculation of local normal forces acting on the nucleus due to outgassing has been made within the same framework—recoil and/or impact momentum transfer to the nucleus caused by sublimating molecules and by recondensing and/or scattered coma molecules is therefore evaluated in accordance with local nucleus/coma conditions. According to this model, the density is found to be 100–300 kg m −3 , depending on the applied spin axis orientation and surface activity map. This range can be narrowed down to 180–300 kg m −3 by also requiring that the empirical changes (per orbital revolution) of the argument of perihelion and the longitude of the ascending node are reproduced.

A practical tool for simulating the presence of gas comae in thermophysical modeling of cometary nuclei

A longstanding problem in thermophysical modeling of cometary nuclei has been to accurately formulate the boundary conditions at the nucleus/coma interface. A correct treatment of the problem, where the Knudsen layer gas just above the cometary surface (which is not in thermodynamic equilibrium) is modeled in parallel with the nucleus, is extremely time-consuming and has so far been avoided. Instead, simplifying assumptions regarding the coma properties are used, e.g., the surface gas density is assumed equal to zero or set to the local saturation value, and the coma backflux is neglected or given some realistic but approximate value. The resulting inaccuracy regarding the exchange of mass, energy, and momentum between the nucleus and the coma, may introduce significant errors in the calculated nucleus temperature profiles, gas production rates, and momentum transfer efficiencies. In this paper, we present a practical, accurate, and time-efficient tool which makes it possible to consider the nucleus and the innermost coma of a comet (the former assumed to consist of a porous mixture of crystalline water ice and dust) as a coupled, physically consistent system. The tool consists of interpolation tables for the surface gas density and pressure, the recondensing coma backflux, and the cooling energy flux due to diffusely scattered coma molecules. The tables cover a wide range of surface temperatures and sub-surface temperature profiles, and can be used to improve the boundary conditions used in thermophysical models. The interpolation tables have been obtained by calculating the transmission distribution functions of gas emerging from sublimating porous ice/dust mixtures with various temperature profiles, which then are used as source functions in a Direct Simulation Monte Carlo model of inelastic intermolecular collisions in the Knudsen layer.

Latitude variation of the subsurface lunar temperature: Lunar Prospector thermal neutrons

Planetary thermal neutron fluxes provide a sensitive proxy for mafic and feldspathic terranes and are also necessary for translating measured gamma‐ray line strengths to elemental abundances. Both functions require a model for near‐surface temperatures and a knowledge of the dependence of thermal neutron flux on temperature. We have explored this dependence for a representative sample of lunar soil compositions and surface temperatures using the Monte Carlo N‐Particle Code (MCNP™)(MNCP is a trademark of the Regents of the University of California, Los Alamos National Laboratory). For all soil samples, the neutron density is found to be independent of temperature, in accord with neutron moderation theory. The thermal neutron flux, however, does vary with temperature in a way that depends on Δ, the ratio of macroscopic absorption to energy‐loss cross sections of soil compositions. The weakest dependence is for the largest Δ (which corresponds to the Apollo 17 high‐Ti basalt in our soil selection), and the largest dependence is for the lowest Δ (which corresponds to ferroan anorthosite, [FAN] in our selection). For the lunar model simulated, the depth at which the thermal neutron population is most sensitive to temperature is ∼30 g cm−2. These simulations were compared with the flux of thermal neutrons measured using the Lunar Prospector neutron spectrometer over the lunar highlands using a subsurface temperature profile that varies with latitude, λ, as Cos1/4λ. Model results assuming equatorial temperatures of 200 and 250 K are in reasonable agreement with measured data. This range of equatorial temperatures is not inconsistent with the average temperature measured below the diurnal thermal wave at the equator, Tmeas = 252 ± 3 K [Langseth and Keihm, 1977].

INVERSE PROBLEMS OF THE NEAR-FIELD RADIOTHERMOMETRY

It is shown that the one-dimensional problem of near-field microwave radiometry in the case of a smoothly inhomogeneous medium can be reduced to an integral equation similar to the well-known solution of the radiation transfer equation. The kernel of this integral equation depends on only one parameter determined experimentally. This makes it possible to determine the subsurface temperature profiles by using a set of near-field antennas of arbitrary design for which the sounding-depth range is overlapped by the effective depth of formation of the radiation received by these antennas. In the case of near-field measurements, the previously obtained joint solution of the radiation transfer equation and the thermal diffusion equation can also be modified and applied for monitoring the subsurface temperature profile using the temporal dependence of the received signal.

Thermal Near Field and the Possibilities of Its Use for In-Depth Temperature Diagnostics of Media

We discover experimentally the effect of an electromagnetic thermal near field of a lossy medium. The effective depth deff of the layer in which the received signal is formed is found to be less than the skin-layer depth dsk and is a function of the size D of the receiving antenna and its height h above the medium surface. The dependence deff(D,h) is obtained from measurements of the emission from a temperature-stratified water medium at a wavelength of 31 cm using a specially developed, electrically small antenna. The results of experimental studies of radiophysical parameters of the antenna are presented. We propose to use measurements of the dependence of the received emission on D and h as a new source of information on the in-depth temperature distribution. Methods for solving the corresponding inverse problems are developed, and the first results of retrieval of the subsurface temperature profile of a water medium are obtained.

The generation of subsurface temperature profiles for Kuwait

A predicted profile of the periodic variation of subsurface temperature with depth is presented for the soil conditions of the State of Kuwait. The generation of the profile is based on Labs’ equation for subterranean temperatures, which takes into account the thermal and physical properties of the soil. These subsurface temperatures are then compared with the ambient dry-bulb temperature. The profiles are then used to analyse the seasonal variations in subsurface temperatures at different depths and the time lags produced when compared with air temperatures. The resulting charts and graphs should be a useful tool for those interested in the energy conservation potential of earth-sheltered and earth-bermed structures in Kuwait.

A method to invert MUPUS. Temperature recordings for the subsurface temperature field of P/Wirtanen

The thermal sensors on the penetrator of the MUPUS experiment package selected for the ESA Rosetta mission will enable us to determine the near-surface energy balance of the nucleus of comet P/Wirtanen by measuring the subsurface temperature profile and the thermal conductivity of the near-surface layers. Model calculations suggest that the penetrator itself will perturb the ambient temperature field such that the temperature profile will be smoothed if the thermal diffusivity of the nucleus is significantly smaller than that of the penetrator tube. It is possible, however, to calculate the undisturbed temperature profile from the data using a method based on a solution of the transient inverse heat conduction problem. Our model calculations show that a satisfactory estimate of the undisturbed temperature field can be obtained in comparatively little computing time by calculating the temperature distribution in the model volume from temperature histories at discrete points representing the penetrator temperature sensors.

Ground temperature history in Romania inferred from borehole temperature data

Geothermal observations (temperature-depth data and thermal property measurements) from a suite of boreholes in the Romanian Carpathians area are used to infer ground surface temperature (GST) history. Temperature observations in boreholes are combined with meteorological data at nearby weather stations to test that temperature in the earth's subsurface contains a record of recent climate change. The subsurface temperature profiles are consistent with the air temperature records. The GST histories that can be extracted by inversion of perturbed temperature data from boreholes ranging in depth between 190 and 520 m cover the past 200–400 years. Results of inversion indicate for the last 150 years a cooler episode for the inner region of the Carpathian Mts. and a warmer time in the Carpathian foreland. The GST histories for this southeastern part of Europe are slightly different from those obtained in western and central Europe. These differences are consistent with the spatial variability of climatic trends.

INSTANTANEOUS REGRESSION BEHAVIOR OF HTPB SOLID FUELS BURNING WITH GOX IN A SIMULATED HYBRID ROCKET MOTOR

An experimental investigation using a high−pressure hybrid motor analog has been conducted to provide detailed solid fuel regression rate data at realistic operating conditions for both model validation and correlation development. The 2−D motor operated at a maximum pressure of 9 MPa (1300 psi) with maximum injected gaseous oxygen mass fluxes of 420 kg/m2·s (0.6 lbm/in2·s). Hydroxyl−Terminated Polybutadiene (HTPB, R−45 M) cured with Isonate 2143L was used as the baseline solid fuel. Either carbon black powder or ultra−fine aluminum (UFAL) powder was added to the HTPB fuel during the processing stage for some tests. Both ultrasonic pulse−echo and real−time X−ray radiography techniques were used to determine the instantaneous regression rate. An array of fine−wire thermocouples was used to determine fuel surface temperatures and subsurface temperature profiles. The deduced instantaneous regression rates displayed a complex dependency on axial location and flow conditions. Close to the sample leading edge, the regression rate, governed by the mixing motion of the entering GOX flow, did not vary with time. Following this region, the regression rates exhibited strong dependency on both axial location and flow structure. When the GOX mass fluxes were below 140 kg/m2·s (0.2 lbm/in2·s), gas−phase radiative heat transfer to the fuel surface was found to play a more important role in the regression of solid fuel. Solid fuel regression rates were found to correlate well with the injected oxidizer mass flux, chamber pressure, axial location, and port height. The addition of carbon black had no effect on regression behavior. Addition of 20% of UFAL powder, however, was found to increase the mass burning rate by 70%.

Palaeoclimate and structure: the most important factors controlling subsurface temperatures in crystalline rocks. A case history from Outokumpu, eastern Finland

SUMMARY The present work contributes to the study of heat-transfer mechanisms in crystalline bedrock. We present evidence from a thoroughly investigated case history in Outokumpu, eastern Finland, in the Fennoscandian (or Baltic) Shield, which shows that the subsurface temperature field is controlled by the thermal conductivity structure and downward diffusion of palaeoclimatic ground-temperature variations. The subsurface temperature profiles from three continuously cored boreholes (790-1 100 m deep) were used for a detailed 2-D modelling of structural, hydrogeological and palaeoclimatic effects on the subsurface temperature field. The boreholes are situated in a subdued topography and they intersect Early Precambrian folded lithologies, such as mica gneisses, black schists, skarn rocks, quartzites and serpentinite-talc rocks. Finitedifference techniques were used in the numerical solution of the heat- and masstransport equations. The 2-D models of thermal conductivity and hydraulic permeability that were compiled were based on an extensive set of data relating to geological structure, in situ hydraulic permeability, groundwater composition and thermal conductivity of drill-core samples down to about 1 km depth. It was found that the thermal effect of topographically driven groundwater convection is very small, with Peclet numbers typically of the order of 10-4-10-5. The effect of anisotropy of thermal conductivity was found to be one order of magnitude smaller than the effects of heatflow refraction in the inclined rock layers which produce horizontal components of heat-flow density ranging from - 15 to 5 mW m-' (basal heat flow 35 mW m-'). Since the advective heat transfer could be neglected, we tried to find a palaeoclimatic groundtemperature history that would explain the measured data. First, an inversion algorithm based on heat conduction in laterally homogeneous media was used for the reconstruction of palaeoclimatic ground-temperature history, but it yielded spurious results because of the strong 2-D conductivity effects. The only means to reconstruct the past ground-temperature changes was forward modelling using a conductive transient 2-D model with time-dependent surface-temperature variations. The surface temperatures at different times (between 100000 yr BP and the present) and the basal heat-flow density were varied in order to reach a reasonable fit between the modelled and measured borehole temperatures. To reach this goal, the ground-temperature history must include the main climatic events during the last 100000 yr, such as the last glacial epoch and the Little Ice Age (from about 1300 AD to 1700 AD), followed by warmer temperatures in more recent times. Our results suggests that subsurface temperatures in conditions similar to those of the Outokumpu case can yield a wealth of palaeoclimatic information when an appropriate approach for modelling heat transfer in the bedrock is chosen.

Records of climatic change in the Canadian Arctic: towards calibrating oxygen isotope data with geothermal data

Borehole temperature-depth data have been combined with oxygen isotope data from an ice core at a nearby location in the Canadian Arctic to calibrate the oxygen isotope data to ground temperature histories. The relationship of oxygen isotope data to ground surface temperature history is δ 18O = 0.42 ΔT g and this reproduces the main features of the observed subsurface temperature profile measured at the borehole site. These results suggests that oxygen isotope data are a good representation of the regional, long term climatic variations at these latitudes. Discrepancies between the observed subsurface profile and the theoretical profile calculated from the calibrated oxygen isotope time series may be explained in terms of the different character of the records, in particular snow cover, and active layer processes.

Inferring past climate change from subsurface temperature profiles: some problems and methods

This paper traces the history of the interest in the effect of past climate change on subsurface temperatures and the later interest in the inverse problem. Consideration is given to some of the problems that have to be solved to obtain a ground surface temperature history (GSTH) that is sufficiently accurate and reliable for the anthropogenic contribution to be determined, problems such as the detection and correction for other sources of subsurface perturbations. Finally, some advantages and disadvantages of the modern methods now being developed are briefly discussed.

Inferring past climate change from subsurface temperature profiles: some problems and methods

This paper traces the history of the interest in the effect of past climate change on subsurface temperatures and the later interest in the inverse problem. Consideration is given to some of the problems that have to be solved to obtain a ground surface temperature history (GSTH) that is sufficiently accurate and reliable for the anthropogenic contribution to be determined, problems such as the detection and correction for other sources of subsurface perturbations. Finally, some advantages and disadvantages of the modern methods now being developed are briefly discussed.

Combining borehole temperature and meteorologic data to constrain past climate change

Geothermal observations from a suite of boreholes in western Utah, USA, combined with meteorologic data at nearby weather stations are used to test the hypothesis that temperatures in the earths subsurface contain an accurate record of recent climate change. The change in air temperature over the last hundred years successfully predicts detailed subsurface temperature profiles to better than ±0.05°C, indicating that ground temperatures tract air temperatures over long periods and that climate change signals are conducted into, and recorded in, the solid earth by the process of heat conduction. We combine borehole temperature data with meteorologic data from the nearest weather station to determine the time averaged difference between surface ground temperature and surface air temperature for borehole-weather station pairs and to infer the long term mean air temperature prior to the observational record. For our western Utah sites the preobservational mean temperature is close to the average surface air temperature for this century suggesting that up to 0.5°C of warming deduced from the last 100 years of weather station data may be attributed to recovery from a cool period at the turn of the century.