Subsurface Temperature Field Research Articles

High-resolution simulation of monsoon variability of the Indian Ocean currents

A numerical model of the Indian Ocean circulation is developed at the Institute of Numerical Mathematics, Russian Academy of Sciences, and the results of simulation of monsoon current variability are presented. The model resolution is 1/8° in longitude, 1/12° in latitude with 21 unevenly vertical levels. The model was run for 15 years using monthly mean atmospheric data from NCEP reanalysis. The annual cycle of surface and subsurface currents, temperature and salinity fields are analysed for the final 15th year. The model reproduces the Summer Monsoon and Winter Monsoon Currents, their annual cycles, space structures and magnitudes. The modelled Somali Current has a good resemblance to observations with model velocities exceeding 2 ms−1 and the transport about 70 Sv during the Summer Monsoon. The model results show that a turn of the Somali Current from the summer to winter direction is accompanied by the generation of anticyclonic eddies that drift westward by the β -effect and dissipate in the Somalia shore and the Gulf of Aden. The monsoon variability of equatorial surface currents and equatorial undercurrents is analysed. It is shown that these currents are mainly generated by zonal wind stress, which is dominated at the equator by a semi-annual harmonic. Therefore, the equatorial surface currents and the compensating equatorial subsurface undercurrents also change directions with a semi-annual periodicity. It is found that gradient currents caused by river run-off make an important contribution to the circulation in the Bay of Bengal. The main features of quasistationary vigorous eddies like Great Whirl, Socotra High, Lakshadweep High, and Lakshadweep Low are well reproduced.

High-resolution simulation of monsoon variability of the Indian Ocean currents

A numerical model of the Indian Ocean circulation is developed at the Institute of Numerical Mathematics, Russian Academy of Sciences, and the results of simulation of monsoon current variability are presented. The model resolution is 1/8° in longitude, 1/12° in latitude with 21 unevenly vertical levels. The model was run for 15 years using monthly mean atmospheric data from NCEP reanalysis. The annual cycle of surface and subsurface currents, temperature and salinity fields are analysed for the final 15th year. The model reproduces the Summer Monsoon and Winter Monsoon Currents, their annual cycles, space structures and magnitudes. The modelled Somali Current has a good resemblance to observations with model velocities exceeding 2 ms−1 and the transport about 70 Sv during the Summer Monsoon. The model results show that a turn of the Somali Current from the summer to winter direction is accompanied by the generation of anticyclonic eddies that drift westward by the β -effect and dissipate in the Somalia shore and the Gulf of Aden. The monsoon variability of equatorial surface currents and equatorial undercurrents is analysed. It is shown that these currents are mainly generated by zonal wind stress, which is dominated at the equator by a semi-annual harmonic. Therefore, the equatorial surface currents and the compensating equatorial subsurface undercurrents also change directions with a semi-annual periodicity. It is found that gradient currents caused by river run-off make an important contribution to the circulation in the Bay of Bengal. The main features of quasistationary vigorous eddies like Great Whirl, Socotra High, Lakshadweep High, and Lakshadweep Low are well reproduced.

Estimating Darcy flow velocities from correlated anomalies in temperature logs

Fluid flow in reservoirs can be identified by its characteristic signatures in temperature logs. The method presented here is based on the great sensitivity of the subsurface temperature field with respect to heat advected by fluid flow. This requires that all other temperature perturbations are eliminated. These may be caused, for instance, by heterogeneous thermal properties or paleoclimate transients, both of which may distort an otherwise linear temperature log. We propose a simple geothermal technique for quantifying regional strata-bound flow based on a detailed analysis of borehole temperatures. Depending on the spatial data distribution and the geothermal situation, this method yields results of varying quality. In a case study with data from southern Germany, the method yields a lower bound for the flow magnitude. Another case study from northern Germany yields the magnitude of the regional flow owing to a larger data set and information of the direction of flow from additional independent information. Under optimum conditions, this method also yields an estimate of the direction of regional strata-bound groundwater flow as well as the uncertainty in magnitude and direction. Finally, the full potential of the method is illustrated using a synthetic data set.

Thermal sustainability of groundwater-source cooling in Winnipeg, Manitoba

Groundwater from the Carbonate Rock Aquifer is extensively used for cooling purposes in Winnipeg, Manitoba. This paper examines the factors affecting the magnitude and timing of temperature increases at production wells in groundwater-source cooling applications through numerical modeling and observations at a case study site. Generic simulations carried out using typical hydrogeologic parameters for the Carbonate Rock Aquifer suggested that temperature increases of a few degrees occur at a typical production well only a few years after the start of operation in a given system. Spacing of the wells and pumping rates were found to have a greater affect than material properties in a homogeneous aquifer. A case study of a thermal doublet in the Winnipeg area indicated, however, that heterogeneities are capable of causing a departure from the predicted temperatures of the generic models. The case study showed that it is possible to make reasonable predictions of the behaviour of the subsurface temperature field during thermal development of the Carbonate Rock Aquifer. Temperature records of the length used in this study will not be available in new developments, however, and efforts must be made to conduct more extensive field investigations to ensure that designs can properly account for geologic conditions.Key words: geothermal energy, fractured rock, Carbonate Rock Aquifer, Winnipeg, Manitoba, injection, heat flow.

Integrating Ocean Subsurface Temperatures in Statistical ENSO Forecasts

Abstract Subsurface characteristics of oceans have recently become of interest to climate modelers. Here subsurface information has been linked to the evolution of the El Niño–Southern Oscillation (ENSO) in a simple statistical formulation. The hypothesis proposed is that the inclusion of subsurface ocean heat content in a persistence-based representation of ENSO results in an increase in prediction skill. The subsurface temperature field is represented by anomalies in the 20°C isotherm (Z20) in the Indian and Pacific Oceans. Using a cross-validation approach, the first two empirical orthogonal functions (EOFs) of the Z20 anomalies are derived, but only the second EOF is used as a predictor. The first EOF is found to be representative of the mature ENSO signal while the second EOF shows characteristics that are precursory to an ENSO event. When included in a persistence-based prediction scheme, the second EOF enhances the skill of ENSO hindcasts up to a lead time of 15 months. Results are compared with another model that uses the second EOF of the SST anomalies in the tropical Pacific Ocean and persistence as predictors. Cross-validated hindcasts from the isotherm-based scheme are generally more skillful than those obtained from the persistence and SST-based prediction schemes. Hindcasts of cold events are particularly close to the observed values even at long lags. Major improvements occur for predictions made during boreal winter and spring months when the addition of subsurface information resulted in predictions that are not greatly affected by the damping effect of the “spring barrier.”

New subsurface temperature maps for the Tertiary Lower Rhine Basin and the adjacent Variscan Basement - Germany, The Netherlands, Belgium

AbstractThe regional subsurface temperature field at the transition between the Palaeozoic Variscan Basement and the Cenozoic Lower Rhine Basin in Dutch, German and Belgium territories was mapped up to a depth of 1000 m. Temperature data from 66 wells and 11 coal mine subcrops were available. In 46 wells, temperature logs, covering a cumulative depth interval of 6600 m, were measured for this study.

Subsurface heat flow in an urban environment

The subsurface temperature field beneath Winnipeg, Canada, is significantly different from that of the surrounding rural areas. Downward heat flow to depths as great as 130 m has been noted in some areas beneath the city and groundwater temperatures in a regional aquifer have risen by as much as 5°C in some areas. Numerical simulation of heat transport supports the conjecture that these temperature changes can be largely attributed to heat loss from buildings and the temperature at any given point is sensitive to the distance from and the age of any buildings. The effect is most noticable when buildings are closely spaced, which is typical of urban areas. Temperature measurements in areas more than a few hundred meters away from any heated structure were only a few tenths of a degree Celsius greater than those observed outside the city, suggesting that other reasons for increases in subsurface temperature, such as changes in surface cover or climate change, may be responsible for some of the some of the observed increase in temperatures. These sources of additional heat to the subsurface make it difficult to resolve information on past climates from temperatures measured in boreholes and monitoring wells. In some areas, the temperature increases may also have an impact on geothermal energy resources. This impact might be in the form of an increase in heat pump efficiency or in the case of the Winnipeg area, a decrease in the efficiency of direct use of groundwater for cooling.

A model study of the effects of climatic precipitation changes on ground temperatures

Temperature changes at the Earth surface propagate into the subsurface and leave a thermal signature in the underlying soil and rock. Inversions of subsurface temperature measurements yield reconstructions of ground surface temperature (GST) histories that provide estimates of climatic changes. A question remaining in the interpretation of reconstructed GST histories is the extent to which GST changes reflect changes principally in surface air temperature (SAT), or whether other factors may be significant. Here we use a Land Surface Processes (LSP) model to examine the influence of precipitation changes on GST and subsurface temperature and moisture fields on annual to decadal timescales. We model soil and vegetation conditions representative of a prairie region in the southern Great Plains of North America and force the model with meteorological data synthesized from a typical year in the region. Model responses are observed after changes in the amount of daily precipitation, the intensity and frequency of daily precipitation, and the diurnal and seasonal timing of precipitation. We show that: (1) increasing daily precipitation cools mean annual GST, (2) increasing the intensity and reducing the frequency of daily precipitation, while holding the annual amount of precipitation constant, cools mean annual GST, and (3) shifting maximum precipitation to occur in the warmest months cools mean annual GST. We compare modeled results to observed precipitation changes during the 20th century and conclude that the observed precipitation changes would cause only small changes to GST within the modeled region, on the order of 0.1 K or less.

Geomorphic interpretation of low‐temperature thermochronologic data: Insights from two‐dimensional thermal modeling

Low‐temperature thermochronologic data are useful for estimating mountain erosion rates because late stage cooling in mountain ranges often reflects exhumation via geomorphic erosion processes. Traditional interpretations of thermochronologic data assume steady, uniform erosion, conditions often violated in real mountain ranges. Here I examine whether unsteady or nonuniform erosion histories are detectable in patterns of erosion rate estimates made by traditional means. To do so, I numerically model the subsurface temperature field in a two‐dimensional section of Earth's crust under various illustrative geomorphic scenarios. I generate simulated cooling ages within two isotopic systems, apatite fission track (FT) and (U‐Th)/He, (He) at two landscape locations, ridge tops and valley bottoms. From these ages I make “field estimates” of erosion rates using the commonly employed elevation dependence and mineral pair methods. Calculations show that if errors on erosion rate estimates are kept small by replicate or transect sampling, many unsteady or nonuniform erosional histories do produce distinctive patterns of erosion rate estimates. For example, temporally increasing erosion rates produce poor agreement between erosion rate estimates made with a single method, while decreasing erosion rate produces good agreement between estimates made with a single method. Nonuniform erosion that decreases relief can produce erroneously high erosion rate estimates based on the elevation dependence method but also accurate and relatively precise mineral pair‐based estimates. A history of decreasing relief can be distinguished from one of steady, uniform erosion by (1) close agreement between mineral pair estimates and poor agreement between elevation dependence estimates and (2) the magnitude of the difference between FT and He ages. The insights gleaned from these analyses can guide forward modeling of topographic and thermal evolution.

On steady states in mountain belts

The dynamic system of tectonics and erosion contains important feedback mechanisms such that orogenic systems tend toward a steady state. This concept is often invoked, but the nature of the steady state is commonly not specified. We identify four types of steady state that characterize the orogenic system and illustrate these cases by using numerical-model results and natural examples. These types are (1) flux steady state, (2) topographic steady state, (3) thermal steady state, and (4) exhumational steady state: they refer to the erosional flux, the topography, the subsurface temperature field, and the spatial pattern of cooling ages, respectively. Models suggest that the topography will reach a steady mean form at the scale of an orogenic belt, but perfect topographic steady state is unlikely to be achieved at shorter length scales. Thermal steady state is a precondition for exhumational steady state and in the case of temperature-dependent deformation, topographic steady state. Exhumational steady state is characterized by reset age zones spatially nested according to closure temperature, as illustrated in natural systems from New Zealand, the Cascadia accretionary margin, and Taiwan.

Salinity Adjustments in the Presence of Temperature Data Assimilation

Abstract This paper is an evaluation of the role of salinity in the framework of temperature data assimilation in a global ocean model that is used to initialize seasonal climate forecasts. It is shown that the univariate assimilation of temperature profiles, without attempting to correct salinity, can induce first-order errors in the subsurface temperature and salinity fields. A recently developed scheme by A. Troccoli and K. Haines is used to improve the salinity field. In this scheme, salinity increments are derived from the observed temperature, by using the model temperature and salinity profiles, assuming that the temperature–salinity relationship in the model profiles is preserved. In addition, the temperature and salinity fields are matched below the observed temperature profile by vertically displacing the original model profiles. Two data assimilation experiments were performed for the 6-yr period 1993–98. These show that the salinity scheme is effective at maintaining the haline and thermal str...

Assimilation of Satellite Altimetry into a Western North Pacific Operational Model

An ocean data assimilation system, COMPASS-K (the Comprehensive Ocean Modeling, Prediction, Analysis and Synthesis System in the Kuroshio-region), has been developed at the Meteorological Research Institute (MRI). The purposes of the development are understanding ocean variability in the Kuroshio region as a local response to a global climate change with assimilated four-dimensional data sets, development of an operational system in the Japan Meteorological Agency, and for the GODAE (Global Ocean Data Assimilation Experiment) project. The model is an eddy permitting version of an MRI-OGCM. Space-time decorrelation scales of ocean variability are estimated with TOPEX I POSEIDON (TIP) altimeter data. Subsurface temperature and salinity fields are projected from the TIP altimeter data with a statistical correlation method and are assimilated into the model with a time-retrospective nudging scheme. Seasonal variation in the western North Pacific is investigated. Realistic space-time distribution of the physical quantities, the path of Kuroshio and its separation from Honshu are captured well. The Kuroshio volume transport is well reproduced in a reanalysis experiment of 1993. Preliminary predictability experiments are done in February and March, 1994. Predictability diagram shows the time scale of the predictability for temperature field is about 17 days in the Kuroshio south of Japan. This time scale is smaller than that in the North Atlantic.

Fracturing processes due to temperature and pressure nonlinear waves propagating in fluid‐saturated porous rocks

A model is proposed of rock deformation‐fracturing in the subsurface of hydrothermal systems in response to deep fluid‐rock temperature and pore fluid pressure perturbations, carried upward by hot and pressurized fluid fronts. Since during these episodes of unrest one also has to take into account that rock parameters can evolve, a model of fluid diffusivity change as a function of pore fluid pressure is described. Through reformulating the linear thermoporoelastic equations, rock deformation‐fracturing is thus thought of as being associated with migration of thermomechanical nonlinear waves, which travel upward, associated with an increase in concurrent fluid diffusivity. On dynamical grounds it is assumed that on the boundary of the two superimposed horizons the overlying rock suddenly starts rupturing, caused by the arrival of supercritical water from below, which drives up a pore fluid pressure excess. In this connection, the purpose of this analysis is to investigate the general evolution of the subsurface pressure and temperature fields, assuming that the original signal is itself strong enough to generate fracturing processes of the overburden rock on its arrival. A general formulation provides evidence of nonlinear “thermal waves,” “compensated waves,” and “residual pressure Burgers waves,” that can be found for every value of the system parameters. A mechanical analogy is also presented, which is treated analytically and numerically, allowing one to gain intuitive insight into such complex phenomena. A characteristic of these nonlinear processes is that the resulting timescales (of the order of years for the case of the Campi Flegrei and the Izu Peninsula) can be particularly small, corresponding to quick hyperthermal phenomena during the filtrating movement of fluid toward the Earth's surface.

Using MODAS to derive subsurface sound speed estimates from satellite observations

The Modular Ocean Data Assimilation System (MODAS) provides a set of tools for analysis and manipulation of ocean data. One of its functions is the estimation of subsurface temperature and salinity fields from satellite observations of height deviation and temperature. A two-dimensional optimal interpolation of the satellite data produces fields of surface height anomaly and temperature. These data are provided to the MODAS synthetic profile routine to predict subsurface temperature and salinity fields compatible with the surface observations and local climatological statistics. Available in situ measurements may be assimilated at this stage. A sound speed field calculated from the temperature and salinity estimates provides the basis for additional acoustical applications. MODAS products, evaluated by comparison with finely sampled surveys, show significant improvement over estimates from static climatologies. [This work was funded by the Space and Naval Warfare Systems Command (SPAWAR) and the ONR through the Advanced Data Fusion Center Support and the On-Scene Tactical Ocean Forecast Capability projects (SPAWAR, Program Element 603207N) and the MODAS Improvements and the Prediction of Coastal Buoyancy Jets projects (ONR, Program Element 602435N).]

Assimilation of TOPEX/Poseidon altimetric data in a primitive equation model of the tropical Pacific Ocean during the 1992–1996 El Niño‐Southern Oscillation period

Four years of TOPEX/Poseidon data (October 1992 to October 1996) are assimilated into a high‐resolution primitive equation model [Gent and Cane, 1989] of the tropical Pacific Ocean. The assimilation method used is a degraded version of the Singular Evolutive Extended Kaiman filter approach [Pham et al., 1998] in which the reduced order basis is fixed. The along‐track TOPEX/Poseidon sea surface height residuals are introduced in the model every 3 days. Initialization of the model runs appears to be crucial. This is particularly true for the 1992–1996 period, which is characterized by several El Niño and La Niña events and exhibits quite anomalous climatological behavior. An in situ database dedicated to this period was built and used to initialize the model properly. The simulation results with and without assimilation were compared with expendable bathythermograph and Tropical Atmosphere‐Ocean in situ observations. The impact of sea surface height assimilation is observed both on the surface and subsurface temperature and velocity fields. The deficiencies of the free model in terms of means and variability structures are significantly reduced. More importantly, the evolution of the model fields over time is considerably improved by the assimilation. These supposedly more realistic assimilated four‐dimensional fields are used to investigate the mechanism responsible for the 1992–1996 warm pool replenishment and depletion. This approach provides insights into the combined role of zonal and meridional transports in balancing volume changes in the warm pool.

Dynamics of the Subsurface Temperature Field Caused by Mining-Related Groundwater Management

The subsurface temperature field was studied on a set of 46 borehole logs measured in the vicinity of uranium deposits in the Bohemian Cretaceous Basin. Vertical variations of the steady state temperature and the temperature gradient are governed by thermal conductivity which strongly varies in dependence on lithology. Large departures from undisturbed temperature detected in many holes are associated with uranium mining. A positive anomaly is observed in leaching fields where large amounts of acid are injected into the uranium-bearing Cenomanian. A negative anomaly is linked to the operation of hydraulic barriers which enclose the mining area and helps to contain pollution by pumping clean water into the Cenomanian aquifer. The spatial distribution of the observed temperature anomalies helps to map the migration of the fluids used in both processes.

A Numerical Investigation of the Subduction Process in Response to an Abrupt Intensification of the Westerlies

Abstract A three-dimensional ocean general circulation model, forced by idealized zonal winds, is used to investigate the effect of an abrupt intensification of westerly winds on the subduction process. Four experiments are carried out: 1) a control experiment with standard wind stress forcing, 2) an intensified winds experiment with wind stress that is larger in the region of the westerlies than the control, 3) an increased surface cooling experiment, and 4) an experiment with both intensified wind stress and surface cooling. Experiments 2 through 4, which contain surface anomalous forcing, are run from the steady state obtained in experiment 1, the control experiment. The results obtained for each of these runs are compared to the control experiment. A subarctic tracer injection experiment is also carried out to verify the differences in the subduction process of each of these experiments. In the wind stress intensified experiment, an examination of the subsurface temperature field shows that negative t...

Ground surface temperature as a function of slope angle and slope orientation and its effect on the subsurface temperature field

Variations of the mean annual ground surface temperature (GST) extrapolated from 7 temperature–depth profiles measured in boreholes located in a forest in the Krušné Hory Mountains, Czech Republic, were related to the elevation and the slope attitude (angle and orientation) of the surface. A two-dimensional linear fit of the GSTs to the annual sum of the total sun radiation (obtained from the slope angle and orientation) and to the elevation yields factors of 0.0040°C/(kWh m −2 year −1) and −0.0040°C/m, respectively. The last factor is close to the value of −0.0047°C/m found by Kubı́k (1990) as the lapse rate of the annual soil temperature at a depth of 50 cm for the former Czechoslovakia. The GST variability due to the slope attitude amounts up to 1.1°C in the investigated data set. Three-dimensional model calculations for a hilly terrain typical for the mountainous regions of Central Europe reveal appreciable differences in distortion of the subsurface temperature field caused by considering or ignoring the investigated GST dependence on the slope attitude.

Transient thermal effects below complex topographies

The topographical perturbation of steady-state subsurface temperature fields has been an important issue in geothermal interpretations throughout the past century. This paper reports a numerical study, which considers the possible influence of terrain topography on transient temperature signals. Typical morphological situations over wide areas in central Europe affect most likely that same depth range which also contains the temperature signals resulting from the most interesting ground surface temperature changes (i.e. during the last 200 years). The evaluation of the interaction is performed on a synthetic sinusoidal topography with varying wavelength and amplitude. Vertical profiles (i.e. temperature logs) were extracted from these numerical forward 2-D calculations. Thereby, the error could be estimated by comparing ground surface temperature time-histories inverted from temperature logs both with and without topographic correction. The results show that a topographic correction of temperature data is absolutely necessary to achieve a consistent inversion result. Even rather flat topographies with 20-km wavelengths and 100-m amplitudes may introduce topographical effects which confuse the inversion process. On the other hand, the palaeoclimatically induced temperature signal persists even in rough topographies and will show correct inversion results when data are adequately treated. Only extreme situations cause a lateral interference of these transient signals with depth. The results from such 2-D synthetic models have been confirmed by an analysis of a real situation. The example chosen is the area surrounding the German Continental Deep Drilling (KTB) project. The area is situated in a moderately undulating surface topography with maximum altitude variations of the order of 250 m. The additional 3-D simulation demonstrates that a strong topography-dependent variation of the transient temperature signal can occur even at greater depths. The introduction of corrections for topography influence, reduces apparent differences in profiles from different locations in the surroundings of the KTB site to a maximum of 0.2 K.

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.