Ground Temperature Changes Research Articles

Estimation on settlement of precast tower footings along the Qinghai–Tibet Power Transmission Line in warm permafrost regions

In order to mitigate frost jacking of the foundations, most of the towers in permafrost regions along the Qinghai–Tibet Power Transmission Line from Golmud, Qinghai Province to Lhasa, Tibet Autonomous Region, China were installed on precast or cast-in-place footings. However, the monitoring data showed that these footings were suffering more from settlement rather than heave due to the settlement of the warm and ice-rich permafrost under the footings. In order to estimate the long-term settlement of these footings, a series of numerical simulations were conducted for predicting the changes in ground temperatures under the precast footings in the coming 50years, taking three mean annual ground temperatures (MAGTs) of permafrost (−0.5, −1.0 and −1.5°C), two moisture contents of foundation soils (20, 35 and 55%), two embedding depths of footings (3.7 and 5.8m), and the most intense scenario of climate warming (linear rate of +0.052°C/a) into account. Then, the settlement processes of the foundation soils were calculated by using the layer summation method in which the thaw consolidation of permafrost soils as well as the compression of plastic frozen soils under the footings were considered. The computation results show that due to climate warming and disturbances of the ground surfaces, major settlement of the foundation soils would occur after 20 or 30years of operation. Additionally, the compression of plastic frozen soils under the footings could considerably contribute to the total settlement of foundation soils. Furthermore, embedding depth of the footings would have a significant effect on both thermal and mechanical stability of the footings. When the embedding depth is set at 3.7m, thawing of the permafrost beneath the footings would always happen in warm (MAGT>−1.0°C) permafrost areas during the next 50years, and the settlement of foundation soils could exceed 20cm for all calculated conditions by the end of the 50th operating year. When it is 5.8m, however, thawing of the permafrost would take place only in very warm (MAGT>−0.5°C) permafrost areas, and the settlement of foundation soils would be less than 20cm by the end of the 50th operating year.

The research station “Vaskiny Dachi”, Central Yamal, West Siberia, Russia – a review of 25 years of permafrost studies

The research station Vaskiny Dachi on the Yamal Peninsula was established in 1988. Activities aimed at monitoring of permafrost and related environmental features under a relatively low level of nature disturbances caused by gas field development. Cryogenic processes that may affect the environment and their structures have been of primary interest. Landslides are the most common cryogenic processes in Central Yamal in general and also in the proximity of the station. Field surveys of numerous landslides, analysis of their dependence on climatic parameters and their fluctuations resulted in novel classification of cryogenic landslides based on mechanisms of their development. Dating by radiocarbon and dendrochronology allows the separation of cycles of landslide activation. Cryogenic landslides control the development of other processes, such as thermal erosion, river channel erosion and thermokarst. It also affects topography, vegetation pattern, geochemistry of vegetation, ground water and soils. As a result, permafrost parameters, specifically active layer depth and ground temperature, moisture and ice content in the active layer, depend indirectly on landsliding. Monitoring within the framework of the main programs of the International Permafrost Association, such as Circumarctic Active Layer Monitoring (CALM, since 1993) and Thermal State of Permafrost (TSP, since 2011), play an important role among the research activities. From the collected data one can conclude that ground temperature increased on average by about 1 °C since the 1990s. At the same time, active layer fluctuations do not exactly follow the air temperature changes. Spatial changes in ground temperature are controlled by the redistribution of snow which is resulting from strong winds characteristic for tundra environments and the highly dissected relief of Central Yamal. Temporal variations rather depend on air temperature fluctuations but the rate differs in various landscape (environmental) units. While the spatial distribution of active layer depth depends on lithology and surface covers, temporal fluctuations are controlled by ground temperature, summer air temperature, summer precipitation, and in general may contravene climate warming due to specific combination of all factors.

Ground-dwelling arthropod community response to native grassland conversion in a temperate desert of northwestern China

Oases are common in desert regions of northwestern China and are major sites for human settlement. The implementation of oasis conservation planning has led to afforestation with appropriate shrubs and trees in the native grasslands surrounding inhabited oases. However, little is known about how this Land use change from native grassland to shrub and tree plantations influences the composition of ground-dwelling arthropod communities and the performance of their different trophic groups. To address this, we measured activity density, taxon richness, and relative abundance of four different ground arthropod trophic groups (spiders, beetle predators, beetle herbivores, and beetle detritivores) and several environmental variables affecting arthropod distributions (vegetation cover, ground temperature, soil moisture, soil properties, and leaf litter) along an experimentally established land use change gradient of a mature shrub (Haloxylon ammodendron) planation, a mature poplar (Populus gansuensis) plantation and a mature pine (Pinus sylvestris) plantation, as well as a native grassland from which all cultivated systems were converted. We found that converted shrub plantation had much lower activity density of predatory, herbivorous, and detritivorous beetles; similar activity density of spiders; and similar taxa richness of all four trophic groups relative to the native grassland. However, converted forest plantations regardless of tree species had much higher activity density of spiders, lower activity density of the three beetle groups, much higher richness of predatory beetles, and lower richness of herbivorous and detritivorous beetles. We also found a change in the composition of the ground arthropod community that was largely driven by changes in ground temperature and leaf litter mass. We conclude that conversion of native grassland to shrub and tree plantations can significantly affect ground-dwelling arthropod communities, reducing the activity of ground-dwelling beetle assemblages while increasing that of ground-dwelling spider assemblages. These findings are important for conserving native arthropod diversity in desert ecosystems.

Simulation on Ground Temperature Change of GSHP System in Severe Cold Regions

For the case of ground-source heat pump in severe cold regions in winter, the heat transfer situation of the ground and ground heat exchanger was dynamically simulated according to the statistics of a project in Changchun to analysis the change of the ground heat, which provided references for the initial design and operation and management of the ground-coupled heat pump in severe cold regions.

Small slope tilts caused by meteorological effects and vital processes of trees on a wooded slope in Hidegvíz Valley, Hungary

Long-term measurements were carried out to investigate the relationship between ground tilts and variations of meteorological (temperature, precipitation) and hydrological (soil moisture content) parameters in the area of the Sopron Mountains, on a wooded slope of the Hidegvíz Valley, Hungary. The connection between surface tilts and the vital processes of the trees was also studied on the basis of the reference evapotranspiration calculated for the study area. Long- and short-term variations were separated. A long-term ground temperature change of 1°C caused a 4 μrad tilt in the SE direction. Short-term temperature effects can be neglected. The fluctuation of temperature around the freezing point caused tilts of about 10 μrad °C−1. The soil water content variation had the largest effect on the ground tilt (0.5 μrad mm−1). Its contribution to the total ground tilt in the investigated period was about 70 μrad (65% of the total tilt of 107 μrad) toward the SSE. The contribution of the wind speed to the ground tilt was about 20 μrad m s−1 toward the SSE depending on the water content of the soil. The wind did not cause a permanent ground tilt. The magnitude of the daily tilt variations in the active growing period of trees, from March to October, is 1–2 μrad while in the dormant period (with no canopy) the tilt variations were less than 0.4 μrad. The admittances between the evapotranspiration and the ground tilts were 0.3–0.5 μrad mm−1 and 0.1–0.2 μrad mm−1 in the active and dormant period of the trees, respectively. These small effects superimposed on each other can significantly contribute to slope failures. The results of this study provide information which can be useful in the modelling of landslide movements and for the mitigation of landslide hazards.

Microclimate under agrivoltaic systems: Is crop growth rate affected in the partial shade of solar panels?

Agrivoltaic systems are mixed systems that associate, on the same land area at the same time, food crops and solar photovoltaic panels (PVPs). The aim of the present study is to assess whether the growth rate of crops is affected in the specific shade of PVPs. Changes in air, ground and crop temperature can be suspected due to the reduction of incident radiation below the photovoltaic shelter. Soil temperature (5cm and 25cm depth), air temperature and humidity, wind speed as well as incident radiations were recorded at hourly time steps in the full sun treatment and in two agrivoltaic systems with different densities of PVPs during three weather seasons (winter, spring and summer). In addition, crop temperatures were monitored on short cycle crops (lettuce and cucumber) and a long cycle crop (durum wheat). The number of leaves was also assessed periodically on the vegetable crops.Mean daily air temperature and humidity were similar in the full sun treatments and in the shaded situations, whatever the climatic season. On the contrary, mean daily soil temperature significantly decreased below the PVPs compared to the full sun treatment. The hourly pattern of crop temperature during day-time (24h) was affected in the shade. In this experiment, the ratio between crop temperature and incident radiation was higher below the PVPs in the morning. This could be due to a reduction of sensible heat losses by the plants (absence of dew deposit in the early morning or reduced transpiration) in the shade compared to the full sun treatment. However, mean daily crop temperature was found not to change significantly in the shade and the growth rate was similar in all the treatments. Significant differences in the leaf emission rate were measured only during the juvenile phase (three weeks after planting) in lettuces and cucumbers and could result from changes in soil temperature. As a conclusion, this study suggests that little adaptations in cropping practices should be required to switch from an open cropping to an agrivoltaic cropping system and attention should mostly be focused on mitigating light reduction and on selection of plants with a maximal radiation use efficiency in these conditions of fluctuating shade.

Creep closure rate of a shallow salt cavern at Gellenoncourt, France

Cavern creep closure rate was recorded in the SG13–SG14 salt cavern of the Gellenoncourt brine field operated by CSME at Gellenoncourt in Lorraine, France. Cavern compressibility and the evolution of cavern brine temperature first were measured. In this shallow cavern (250-m, or 800-ft, deep), which had been kept idle for 30 years, cavern-brine thermal expansion can be disregarded. To assess cavern closure rate, a 10-month brine-outflow test was performed, followed by a 6-month shut-in test. During the tests, brine outflow or pressure evolution is influenced by atmospheric pressure changes, ground temperature changes and Earth tides. From the average pressure-evolution rate, it can be inferred that the steady-state cavern closure rate is slower than 10−5/year or 3×10−13/s.

Relevance of magnetic properties of soil in the magnetic observatories to geomagnetic observation

Annual geomagnetic variations with a maximum amplitude of 5 nT, and in phase with ground temperature variations at a depth of 1–2 m, were observed in the baseline values of fluxgate magnetometers installed at three JMA magnetic observatories. A possible origin of the annual variations is a change in magnetization of the soil due to changes in ground temperature. In order to examine the effect of temperature changes on soil magnetization, we measured the magnetic properties of soil samples collected at the JMA observatories. Magnetization of soil samples in a magnetic field of 0.05 mT ranged within 0.05 × 10−3−1.6 × 10−3 A m2/kg and the temperature dependence of magnetization ranged within 0.3 × 10−6−14 × 10−6 A m2/kg °C, except for a sample having an extraordinarily strong magnetization. Based on the measured magnetization, and their temperature dependence, of samples from Memambetsu, which shows the largest values among the samples from the three observatories, we determined the distribution of the geomagnetic field and its annual variation produced by soil magnetization. The maximum amplitude of annual variation in the geomagnetic field is 7 nT, which is consistent with the observed annual variation of the baseline value of the magnetometers.

Recent Advances in Mountain Permafrost Research

ABSTRACTKnowledge of the thermal state of mountain permafrost has greatly increased since 2007 with the establishment of numerous new monitoring stations around the world. Data collected at these sites have pointed to longer‐term changes in ground temperatures, which seem to have increased during the last two to three decades in cold permafrost, while in ground close to 0°C the near‐surface ice content has restricted warming and similar trends are not apparent. Modelling of mountain permafrost has developed greatly, driven by general circulation models or gridded temperature maps, through both predictive methods and spatial equilibrium and transient approaches. The spatial resolution of climate parameters, which is normally much coarser than the spatial heterogeneity of alpine environments, presents a major problem for modelling studies. This is a fundamental challenge for future research. Copyright © 2013 John Wiley & Sons, Ltd.

Some engineering geological effects of drought: examples from the UK

Most countries experience periodic dry spells/droughts and climatologists predict these may become more severe and of longer duration in the future. Whilst ground movement associated with shrink/swell is well known, other implications of changes in the general climatic conditions are less often considered by the construction industry. Having discussed the effect of shrink/swell in open field and wooded areas, the pressures involved in re-hydration, the significance of desiccation cracks for slope stability and the influence of dry and moist periods on road construction, the paper highlights how a change in ground water level and/or temperature can induce the development of ground sulphates and cause irreversible heave in lime-stabilised ground.

The study of the climate in the past and the climate change in mainland portugal using geothermal data has started in 199

The study of the climate in the past and the climate change in mainland portugal using geothermal data has started in 199. Reconstruction of ground surface temperature (GST) history from temperature logs measured in a 200 m deep borehole located 5 km away from the town of évora in portugal, indicates a warming of 1K since the second half of the nineteenth century to the middle of the 90s of the twentieth century, increasing considerably in the last 10 years. Results of the reconstruction (based on a functional space inversion – FSI – method) are compared with air temperatures recorded at the lisbon meteorological station since 185. The air temperature time series display a warming trend with the amplitude about 1K for the same period. The coupling of the air and ground temperature changes and their downward propagation by heat conduction was confirmed by repeated logging in November 2003, .7 years after obtaining the first temperature log. The method can be used in paleoclimatic studies in Antarctica as well as in areas with permafrost.

An Assessment of Changes in Kunzea ericoides var. microflora and Other Hydrothermal Vegetation at the Wairakei–Tauhara Geothermal Field, New Zealand

Hydrothermal ecosystems are of high conservation and scientific value, but they are sensitive to external perturbations that result from development. This study examines the composition of vegetation at four plots at the Wairakei-Tauhara geothermal field, New Zealand, using the Scott height-frequency method, ground temperatures at 0.1- and 1-m depth, soil pH, and photographic surveys. It highlights the response of plant communities, in particular that of Kunzea ericoides var. microflora, in terms of composition, structure, and biomass index values, measures changes in ground temperature, as well as provides baseline data against which to compare future changes. It was found that optimal growing conditions for K. ericoides var. microflora are at temperatures above background conditions with a slightly acidic pH. Plots with cooler, less acidic conditions support more diverse plant communities, which also promote the establishment of invasive species. This suggests that the largest threats to thermotolerant vegetation in New Zealand, including K. ericoides var. microflora, are further decreases in ground temperature because the establishment of invasive species may result in thermolerant vegetation being out-competed in hydrothermal ecosystems. Recognising and understanding the ecological diversity and dynamics of hydrothermal ecosystems, as well as acknowledging the competing interests between development and conservation, is key to the management and protection of these areas.

Borehole temperatures and climate change: Ground temperature change in south India over the past two centuries

Seventy‐five borehole temperature‐depth profiles in south India, located between 8° and 15°N, are analyzed to infer past changes in surface ground temperature. Solutions for a linear surface temperature change indicate average warming of about 0.9 ± 0.3°C over the past 127 ± 25 years at the 95% level of confidence for the entire data set, albeit with considerable geographic variability. Some sites in a restricted region exhibit surface ground temperature cooling during the last 50 to 100 years while a number of other borehole sites show large surface warming amplitudes in the range 1–3°C with onset times during the last few decades to less than a Century. Such rapid changes may represent effects of local land use changes superimposed on the long‐term climate change. Results of borehole analysis do not support a latitude effect in climate change. A set of 28 meteorological surface air temperature (SAT) records, distributed in the three major climatic provinces (Interior Peninsula, West Coast and East Coast) in south India yield an average warming trend of 0.6 ± 0.2°C/100 years over the period 1901–2006 for which records exist. Combined analysis of borehole temperatures and SAT data yields a long‐term, pre‐observational mean temperature (baseline) 0.6 ± 0.1°C lower than the 1961–1990 mean SAT. With an additional 0.35°C of warming beyond the 1961–1990 mean, the total warming from the ∼1800 baseline is 0.95°C. Given multiple uncertainties, we consider the 0.9°C of warming from borehole temperature inversion and 0.95°C of warming from the hybrid borehole temperature‐SAT analysis to be consistent if significant warming occurred in the 19th Century, prior to the onset of SAT records. The present data set together with the set of 70 temperature profiles in India analyzed earlier constitute an extensive documentation of climatic warming for the low latitude region 0°–20° N that was previously under‐sampled in global geothermal climate change studies.

Numerical modeling of permafrost dynamics in Alaska using a high spatial resolution dataset

Abstract. Climate projections for the 21st century indicate that there could be a pronounced warming and permafrost degradation in the Arctic and sub-Arctic regions. Climate warming is likely to cause permafrost thawing with subsequent effects on surface albedo, hydrology, soil organic matter storage and greenhouse gas emissions. To assess possible changes in the permafrost thermal state and active layer thickness, we implemented the GIPL2-MPI transient numerical model for the entire Alaska permafrost domain. The model input parameters are spatial datasets of mean monthly air temperature and precipitation, prescribed thermal properties of the multilayered soil column, and water content that are specific for each soil class and geographical location. As a climate forcing, we used the composite of five IPCC Global Circulation Models that has been downscaled to 2 by 2 km spatial resolution by Scenarios Network for Alaska Planning (SNAP) group. In this paper, we present the modeling results based on input of a five-model composite with A1B carbon emission scenario. The model has been calibrated according to the annual borehole temperature measurements for the State of Alaska. We also performed more detailed calibration for fifteen shallow borehole stations where high quality data are available on daily basis. To validate the model performance, we compared simulated active layer thicknesses with observed data from Circumpolar Active Layer Monitoring (CALM) stations. The calibrated model was used to address possible ground temperature changes for the 21st century. The model simulation results show widespread permafrost degradation in Alaska could begin between 2040–2099 within the vast area southward from the Brooks Range, except for the high altitude regions of the Alaska Range and Wrangell Mountains.

광섬유 센서 내장형 텐던을 이용한 그라운드 앵커의 장기 장력모니터링을 위한 온도보상

그라운드 앵커공법은 현재 우리나라에서 가장 일반적으로 사용되는 사면보강공법들 중 하나이다. 앵커로 보강된 사면의 안정성을 장기간 확인하기 위해서는 그라운드 앵커의 긴장력을 측정하는 것이 매우 중요하다. 그러나 현재 현장에서 주로 사용되는 스트레인게이지 및 V/W타입의 로드 셀은 전자기파에 의한 노이즈 발생이 크고 습기 또는 수분의 영향으로 인해 측정값에 오차가 발생할 수 있으며 자기열화 등으로 장기간의 모니터링에 한계가 있다. 또한 앵커의 개별 텐던에 발생하는 미세한 변화를 정확히 감지할 수 없는 단점이 있어 이를 개선할 수 있는 방안으로 광섬유 센서를 이용하여 강연선의 변형률을 측정할 수 있는 광섬유 센서 내장형 텐던이 개발되었다. 이 광섬유 센서 내장형 텐던은 단기간의 앵커 장력 측정에 성공적으로 적용된 사례가 보고되었으나 장기간에 걸친 장력 변화를 측정하기 위해서는 온도에 의한 광섬유 센서의 변형률을 보상하여야 한다. 이 논문에서는 광섬유 센서 내장형 텐던을 이용하여 그라운드 앵커의 장력모니터링 시 지중온도 변화에 의한 영향을 보상하는 실용적인 방안에 대하여 기술하였다. 먼저 실내실험을 통하여 광섬유 센서 내장형 텐던의 온도반응계수(<TEX>${\beta}^{\prime}$</TEX>)를 <TEX>$2.0{\times}10^{-5}/^{\circ}C$</TEX>로 결정하고 실제 현장에 설치된 광섬유 센서를 이용하여 깊이별 지중온도 변화값을 측정하였다. 연구 대상지역(여수)의 기상청 지중온도 측정 결과 자료와의 비교를 통하여 결정된 온도반응계수(<TEX>${\beta}^{\prime}$</TEX>)를 이용한 광섬유 센서 내장형 텐던의 온도반응 성능을 검증하였다. 최종적으로 광섬유 센서 내장형 텐던을 이용하여 실제 사면에 설치된 인장형 앵커와 압축형 앵커의 계절별 긴장력을 모니터링하고 기상청 지중온도 측정자료와 온도반응계수를 이용하여 온도보상을 실시하여 기존 V/W타입의 로드 셀 측정 결과와 비교하였다. 제안된 광섬유 센서 내장형 텐던의 온도반응계수와 기상청 지중온도 측정결과를 이용한 앵커의 온도보상 방법에 의해 측정된 긴장력 모니터링 결과가 계절에 따른 지중온도 변화에 상관없이 로드 셀 결과와 일관성 있게 비교되어 제안된 온도보상 방법이 매우 실용적이며 합리적인 것으로 나타났다. Ground anchor method is one of the most popular reinforcing technology for slope in Korea. For the health monitoring of slope which is reinforced by permanent anchor for a long period, monitoring of the tension force of ground anchor is very important. However, since electromechanical sensors such as strain gauge and V/W type load cell are also subject to long-term risk as well as suffering from noise during long distance transmission and immunity to electromagnetic interference (EMI), optical FBG sensors embedded tendon was developed to measure strain of 7-wire strand by embedding FBG sensor into the center king cable of 7-wire strand. This FBG sensors embedded tendon has been successfully applied to measuring the short-term anchor force. But to adopt this tendon to long-term monitoring, temperature compensation of the FBG sensors embedded tendon should be done. In this paper, we described how to compensate the effect in compliance with the change of underground temperature during long-term tension force monitoring of ground anchors by using optical fiber sensors (FBG: Fiber Bragg Grating). The model test was carried out to determine the temperature sensitivity coefficient (<TEX>${\beta}^{\prime}$</TEX>) of FBG sensors embedded tendon. The determined temperature sensitivity coefficient <TEX>${\beta}^{\prime}=2.0{\times}10^{-5}/^{\circ}C$</TEX> was verified by comparing the ground temperatures predicted from the proposed sensor using <TEX>${\beta}^{\prime}$</TEX> with ground temperatures measured from ground thermometer. Finally, temperature compensations were carried out based on <TEX>${\beta}^{\prime}$</TEX> value and ground temperature measurement from KMA for the tension force monitoring results of tension type and compression type anchors, which had been installed more than 1 year before at the test site. Temperature compensated tension forces are compared with those measured from conventional load cell during the same measuring time. Test results show that determined temperature sensitivity coefficient (<TEX>${\beta}^{\prime}$</TEX>) of FBG sensors embedded tendon is valid and proposed temperature compensation method is also appropriate from the fact that the temperature compensated tension forces are not dependent on the change of ground temperature and are consistent with the tension forces measured from the conventional load cell.

Modeling of the Second Indirect Effect of Anthropogenic Aerosols in East Asia

AbstractThis study investigated the second indirect climatic effect of anthropogenic aerosols, including sulfate, organic carbon (OC), and black carbon (BC), over East Asia. The seasonal variation of the climatic response to the second indirect effect was also characterized. The simulation period for this study was 2006. Due to a decrease in autoconversion rate from cloud water to rain as a result of aerosols, the cloud liquid water path (LWP), and radiative flux (RF) at the top of the atmosphere (TOA) changed dramatically, increasing by 14.3 g m-2 and decreasing by −4.1 W m-2 in terms of domain and annual average. Both LWP and RF changed most in autumn. There were strong decreases in ground temperature in Southwest China, the middle reaches of the Yangtze River in spring and autumn, while maximum cooling of up to −1.5 K occurred in the Chongqing district. The regional and annual mean change in ground temperature reached −0.2 K over eastern China. In all seasons except summer, precipitation generally decr...

Geothermal climate change observatory in south India 1: Borehole temperatures and inferred surface temperature histories

Temperature–depth profiles measured in boreholes contain records of changes in surface ground temperature over the past few centuries. We have recently set up a geothermal climate change observatory at the Choutuppal campus of National Geophysical Research Institute (17.29 °N, 78.92 °E) to measure subsurface temperature changes on annual to decadal timescales and quantify how well they track surface temperature changes. The site is located about 60 km to the east of Hyderabad in south India, in a designated reserved forest land and far from potential urban heat islands. In April 2009, two boreholes were drilled to depths of 210 m and 21 m respectively after careful site selection to minimize perturbations to the subsurface temperatures on account of groundwater flow in the borehole, large thermal conductivity contrasts and rugged topography. Temperature measurements in the two holes are being carried out periodically. Analysis of equilibrium temperature–depth profile in the 210 m deep borehole reveals at least two ongoing events that started during the past Century: (i) surface ground warming of 0.5 ± 0.1 °C over the past 92 ± 7 years, and (ii) a more recent cooling of ∼1 °C over the past ∼39 years, probably representing local changes to surface vegetation caused by the presence of a thicker grass cover throughout the year inside the campus since 1967 AD compared to the short cropping of grass outside it. The inferred surface ground warming is consistent with estimates from temperature measurements in three other boreholes (170–300 m deep) distributed in a 10 × 5 km 2 area in the vicinity of the observatory (mean: 0.5 ± 0.1 °C over the past 93 ± 21 years), and is characteristic of the Interior Peninsula region of south India.

Repeat temperature measurements in boreholes from northwestern Utah link ground and air temperature changes at the decadal time scale

Borehole temperature profiles provide a record of ground surface temperature (GST) change at the decadal to centennial time scale. GST histories reconstructed from boreholes are particularly useful in climate reconstruction if changes in GST and surface air temperature (SAT) are effectively coupled at decadal and longer time periods and it can be shown that borehole temperatures respond faithfully to surface temperature changes. We test these assumptions using three boreholes in northwestern Utah that have been repeatedly logged for temperature over a time span of 29 years. We report 13 temperature‐depth logs at the Emigrant Pass Observatory borehole GC‐1, eight at borehole SI‐1 and five at borehole DM‐1, acquired between 1978 and 2007. Systematic subsurface temperature changes of up to 0.6°C are observed over this time span in the upper sections of the boreholes; below approximately 100 m any temperature transients are within observational noise. We difference the temperature logs to highlight subsurface transients and to remove any ambiguity resulting from steady state source of curvature. Synthetic temperature profiles computed from SAT data at nearby meteorological stations reproduce both the amplitude and pattern of the transient temperature observations, fitting the observations to within 0.03°C or better. This observational confirmation of the strong coupling between surface temperature change and borehole temperature transients lends further support to the use of borehole temperatures to complement SAT and multiproxy reconstructions of climate change.

Heat transfer in a tower foundation with ground surface insulation and periodic freezing and thawing

Insulation can be used over the foundation of ground structures to protect them against cyclical freezing and thawing damage. However, if the structure is composed of metal, heat transfer through the structure can have significant thermal effects on the foundation (i.e., causing ground temperature changes). This paper presents analytical and experimental studies on thermal effects of a metal tower in a power transmission line foundation, particularly when the foundation is protected with ground surface insulations. The results indicate that the metal tower has seasonally variable effects on temperature variations in the tower foundation. Although ground surface insulation can reduce the temperature variations in the foundation, it cannot prevent adverse thermal effects of the metal tower. In this paper, other protective techniques are proposed to develop more effective thermal protection for tower foundations.

Relationships between permafrost distribution and surface organic layers near Esso, central Kamchatka, Russian Far East

AbstractUnique boreal forest, consisting mainly of sparse larch (Larix cajanderii), creeping pine (Pinus pumila) and birch forest (Betula ermanii), occurs above the lower elevational limit of discontinuous permafrost of about 500 m above sea level in the area around Esso, central Kamchatka (∼56°N). Permafrost is present beneath surfaces covered by Sphagnum or creeping pine, but is absent beneath birch forest. Thermal conductivities in mid‐September are low in Sphagnum (0.07–0.19 W/(m·K)) and in the thick (13–20 cm) litter layer beneath creeping pine‐covered areas (0.06–0.09 W/(m·K)). Seasonal changes in the subsurface ground temperatures beneath creeping pine show that the surface litter prevents ground temperature increases at depth in summer, resulting in a thin active layer (several decimetres). The surface organic layer appears to be the most important factor controlling the presence or absence of permafrost in this area. Copyright © 2008 John Wiley &amp; Sons, Ltd.