Articles de revues : « Soil Moisture Temperature Coupling »

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Yuan, Qing, Guojie Wang, Chenxia Zhu, Dan Lou, Daniel Fiifi Tawia Hagan, Xiaowen Ma et Mingyue Zhan. « Coupling of Soil Moisture and Air Temperature from Multiyear Data During 1980–2013 over China ». Atmosphere 11, n^o 1 (26 décembre 2019) : 25. http://dx.doi.org/10.3390/atmos11010025.

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Soil moisture is an important parameter in land surface processes, which can control the surface energy and water budgets and thus affect the air temperature. Studying the coupling between soil moisture and air temperature is of vital importance for forecasting climate change. This study evaluates this coupling over China from 1980–2013 by using an energy-based diagnostic method, which represents the momentum, heat, and water conservation equations in the atmosphere, while the contributions of soil moisture are treated as external forcing. The results showed that the soil moisture–temperature coupling is strongest in the transitional climate zones between wet and dry climates, which here includes Northeast China and part of the Tibetan Plateau from a viewpoint of annual average. Furthermore, the soil moisture–temperature coupling was found to be stronger in spring than in the other seasons over China, and over different typical climatic zones, it also varied greatly in different seasons. We conducted two case studies (the heatwaves of 2013 in Southeast China and 2009 in North China) to understand the impact of soil moisture–temperature coupling during heatwaves. The results indicated that over areas with soil moisture deficit and temperature anomalies, the coupling strength intensified. This suggests that soil moisture deficits could lead to enhanced heat anomalies, and thus, result in enhanced soil moisture coupling with temperature. This demonstrates the importance of soil moisture and the need to thoroughly study it and its role within the land–atmosphere interaction and the climate on the whole.

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RAMARAO, M. V. S., J. SANJAY et R. KRISHNAN. « Modulation of summer monsoon sub-seasonal surface air temperature over India by soil moisture-temperature coupling ». MAUSAM 67, n^o 1 (8 décembre 2021) : 53–66. http://dx.doi.org/10.54302/mausam.v67i1.1142.

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The influence of soil moisture on the sub-seasonal warmer surface air temperature anomalies during drier soil conditions associated with break spells in the Indian summer monsoon precipitation is explored using observations. The multi-model analysis of land surface states and fluxes available from the Second Global Soil Wetness Project (GSWP-2) are found useful in understanding the mechanism for this soil moisture-temperature coupling on sub-seasonal timescales. The analysis uses a soil moisture-temperature coupling diagnostic computed based on linear correlations of daily fields. It is shown that the summer surface air temperature variations are linked to intraseasonal variations of the Indian monsoon precipitation, which control the land-climate coupling by modulating the soil moisture variations. Strong coupling mainly occurs during dry soil states within the summer monsoon season over the transition zones between wet and dry climates of central to north-west India. In contrast, the coupling is weak for constantly wet and energy-limited evaporative regimes over eastern India during the entire summer monsoon season. This observational based analysis provided a better understanding of the linkages between the sub-seasonal dry soil states and warm conditions during the Indian summer monsoon season. A proper representation of these aspects of land-atmosphere interactions in weather and climate models used for sub-seasonal and seasonal monsoon forecasting could be critical for several applications, in particular agriculture. The soil moisture-temperature coupling diagnostic used in this study will be a useful metric for evaluating the performance of weather and climate models.

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Miralles, D. G., M. J. van den Berg, A. J. Teuling et R. A. M. de Jeu. « Soil moisture-temperature coupling : A multiscale observational analysis ». Geophysical Research Letters 39, n^o 21 (novembre 2012) : n/a. http://dx.doi.org/10.1029/2012gl053703.

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Feng, Xiaohang, Xia Zhang, Zhenqi Feng et Yichang Wei. « Analyzing moisture-heat coupling in a wheat-soil system using data-driven vector autoregression model ». PeerJ 7 (11 juin 2019) : e7101. http://dx.doi.org/10.7717/peerj.7101.

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Soil temperature and moisture have a close relationship, the accurate controlling of which is important for crop growth. Mechanistic models built by previous studies need exhaustive parameters and seldom consider time stochasticity and lagging effect. To circumvent these problems, this study designed a data-driven stochastic model analyzing soil moisture-heat coupling. Firstly, three vector autoregression models are built using hourly data on soil moisture and temperature at the depth of 10, 30, and 90 cm. Secondly, from impulse response functions, the time lag and intensity of two variables’ response to one unit of positive shock can be obtained, which describe the time length and strength at which temperature and moisture affect each other, indicating the degree of coupling. Thirdly, Granger causality tests unfold whether one variable’s past value helps predict the other’s future value. Analyzing data obtained from Shangqiu Experiment Station in Central China, we obtained three conclusions. Firstly, moisture’s response time lag is 25, 50, and 120 h, while temperature’s response time lag is 50, 120, and 120 h at 10, 30, and 90 cm. Secondly, temperature’s response intensity is 0.2004, 0.0163, and 0.0035 °C for 1% variation in moisture, and moisture’s response intensity is 0.0638%, 0.0163%, and 0.0050% for 1 °C variation in temperature at 10, 30, and 90 cm. Thirdly, the past value of soil moisture helps predict soil temperature at 10, 30, and 90 cm. Besides, the past value of soil temperature helps predict soil moisture at 10 and 30 cm, but not at 90 cm. We verified this model by using data from a different year and linking it to soil plant atmospheric continuum model.

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Dharssi, I., B. Candy et P. Steinle. « Analysis of the linearised observation operator in a soil moisture and temperature analysis scheme ». SOIL Discussions 2, n^o 1 (1 juin 2015) : 505–35. http://dx.doi.org/10.5194/soild-2-505-2015.

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Abstract. Several weather forecasting agencies have developed advanced land data assimilation systems that, in principle, can analyse any model land variable. Such systems can make use of a wide variety of observation types, such as screen level (2 m above the surface) observations and satellite based measurements of surface soil moisture and skin temperature. Indirect measurements can be used and information propagated from the surface into the deeper soil layers. A key component of the system is the calculation of the linearised observation operator matrix (Jacobian matrix) which describes the link between the observations and the land surface model variables. The elements of the Jacobian matrix (Jacobians) are estimated using finite difference by performing short model forecasts with perturbed initial conditions. The calculated Jacobians show that there can be strong coupling between the screen level and the soil. The coupling between the screen level and surface soil moisture is found to be due to a number of processes including bare soil evaporation, soil thermal conductivity as well as transpiration by plants. Therefore, there is significant coupling both during the day and at night. The coupling between the screen level and root-zone soil moisture is primarily through transpiration by plants. Therefore the coupling is only significant during the day and the vertical variation of the coupling is modulated by the vegetation root depths. The calculated Jacobians that link screen level temperature to model soil temperature are found to be largest for the topmost model soil layer and become very small for the lower soil layers. These values are largest during the night and generally positive in value. It is found that the Jacobians that link observations of surface soil moisture to model soil moisture are strongly affected by the soil hydraulic conductivity. Generally, for the Joint UK Land Environment Simulator (JULES) land surface model, the coupling between the surface and root zone soil moisture is weak. Finally, the Jacobians linking observations of skin temperature to model soil temperature and moisture are calculated. These Jacobians are found to have a similar spatial pattern to the Jacobians for observations of screen level temperature. Analysis is also performed of the sensitivity of the calculated Jacobians to the magnitude of the perturbations used.

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Zhang, Ziyuan, Xiao Chen, Zhihua Pan, Peiyi Zhao, Jun Zhang, Kang Jiang, Jialin Wang et al. « Quantitative Estimation of the Effects of Soil Moisture on Temperature Using a Soil Water and Heat Coupling Model ». Agriculture 12, n^o 9 (2 septembre 2022) : 1371. http://dx.doi.org/10.3390/agriculture12091371.

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Soil moisture is not only an essential component of the water cycle in terrestrial ecosystems but also a major influencing factor of regional climate. In the soil hydrothermal process, soil moisture has a significant regulating effect on surface temperature; it can drive surface temperature change by influencing the soil’s physical properties and the partitioning of the available surface energy. However, limited soil temperature and moisture observations restrict the previous studies of soil hydrothermal processes, and few models focus on estimating the impact of soil moisture on soil temperature. Therefore, based on the experiments conducted in Wuchuan County in 2020, this study proposes a soil water and heat coupling model that includes radiation, evaporation, soil water transport, soil heat conduction and ground temperature coupling modules to simulate the soil temperature and moisture and subsequently estimate the effects of soil moisture. The results show that the model performs well. The Nash–Sutcliffe coefficient (NSE) and the concordance index (C) of the simulated and measured values under each treatment are higher than 0.26 and 0.7, respectively. The RMSE of the simulation results is between 0.0067–0.017 kg kg−1 (soil moisture) and 0.43–1.06 °C (soil temperature), respectively. The simulated values matched well with the actual values. The soil moisture had a noticeable regulatory effect on the soil temperature change, the soil surface temperature would increase by 0.08–0.43 °C for every 1% decrease in soil moisture, and with the increase in soil moisture, the variation of the soil temperature decreased. Due to the changes in the solar radiation, the sensitivity of the soil temperature to the decline in soil moisture was the greatest during June–July and the least in September. Moreover, the contributions of soil moisture changes to temperature increase under various initial conditions are inconsistent, the increase in sunshine hours, initial daily average temperature and decrease in leaf area index (LAI), soil density and soil heat capacity can increase the soil surface temperature. The results are expected to provide insights for exploring the impact mechanism of regional climate change and optimizing the structure of agricultural production.

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Schwingshackl, Clemens, Martin Hirschi et Sonia I. Seneviratne. « A theoretical approach to assess soil moisture–climate coupling across CMIP5 and GLACE-CMIP5 experiments ». Earth System Dynamics 9, n^o 4 (17 octobre 2018) : 1217–34. http://dx.doi.org/10.5194/esd-9-1217-2018.

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Abstract. Terrestrial climate is influenced by various land–atmosphere interactions that involve numerous land surface state variables. In several regions on Earth, soil moisture plays an important role for climate via its control on the partitioning of net radiation into sensible and latent heat fluxes; consequently, soil moisture also impacts on temperature and precipitation. The Global Land–Atmosphere Coupling Experiment–Coupled Model Intercomparison Project phase 5 (GLACE-CMIP5) aims to quantify the impact of soil moisture on these important climate variables and to trace the individual coupling mechanisms. GLACE-CMIP5 provides experiments with different soil moisture prescriptions that can be used to isolate the effect of soil moisture on climate. Using a theoretical framework that relies on the distinct relation of soil moisture with evaporative fraction (the ratio of latent heat flux over net radiation) in different soil moisture regimes, the climate impact of the soil moisture prescriptions in the GLACE-CMIP5 experiments can be emulated and quantified. The framework-based estimation of the soil moisture effect on the evaporative fraction agrees very well with estimations obtained directly from the GLACE-CMIP5 experiments (pattern correlation of 0.85). Moreover, the soil moisture effect on the daily maximum temperature is well captured in regions where soil moisture exerts a strong control on latent heat fluxes. The theoretical approach is further applied to quantify the soil moisture contribution to the projected change of the temperature on the hottest day of the year, confirming recent estimations by other studies. Finally, GLACE-style soil moisture prescriptions are emulated in an extended set of CMIP5 models. The results indicate consistency between the soil moisture–climate coupling strength estimated with the GLACE-CMIP5 and the CMIP5 models. Although the theoretical approach is only designed to capture the local soil moisture–climate coupling strength, it can also help to distinguish non-local from local soil moisture–atmosphere feedbacks where sensitivity experiments (such as GLACE-CMIP5) are available. Overall, the theoretical framework-based approach presented here constitutes a simple and powerful tool to quantify local soil moisture–climate coupling in both the GLACE-CMIP5 and CMIP5 models that can be applied in the absence of dedicated sensitivity experiments.

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Berg, Alexis, Benjamin R. Lintner, Kirsten L. Findell, Sergey Malyshev, Paul C. Loikith et Pierre Gentine. « Impact of Soil Moisture–Atmosphere Interactions on Surface Temperature Distribution ». Journal of Climate 27, n^o 21 (24 octobre 2014) : 7976–93. http://dx.doi.org/10.1175/jcli-d-13-00591.1.

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Abstract Understanding how different physical processes can shape the probability distribution function (PDF) of surface temperature, in particular the tails of the distribution, is essential for the attribution and projection of future extreme temperature events. In this study, the contribution of soil moisture–atmosphere interactions to surface temperature PDFs is investigated. Soil moisture represents a key variable in the coupling of the land and atmosphere, since it controls the partitioning of available energy between sensible and latent heat flux at the surface. Consequently, soil moisture variability driven by the atmosphere may feed back onto the near-surface climate—in particular, temperature. In this study, two simulations of the current-generation Geophysical Fluid Dynamics Laboratory (GFDL) Earth System Model, with and without interactive soil moisture, are analyzed in order to assess how soil moisture dynamics impact the simulated climate. Comparison of these simulations shows that soil moisture dynamics enhance both temperature mean and variance over regional “hotspots” of land–atmosphere coupling. Moreover, higher-order distribution moments, such as skewness and kurtosis, are also significantly impacted, suggesting an asymmetric impact on the positive and negative extremes of the temperature PDF. Such changes are interpreted in the context of altered distributions of the surface turbulent and radiative fluxes. That the moments of the temperature distribution may respond differentially to soil moisture dynamics underscores the importance of analyzing moments beyond the mean and variance to characterize fully the interplay of soil moisture and near-surface temperature. In addition, it is shown that soil moisture dynamics impacts daily temperature variability at different time scales over different regions in the model.

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Yang, Yugui, Dawei Lei, Haibing Cai, Songhe Wang et Yanhu Mu. « Analysis of moisture and temperature fields coupling process in freezing shaft ». Thermal Science 23, n^o 3 Part A (2019) : 1329–35. http://dx.doi.org/10.2298/tsci180519130y.

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The temperature change of frozen soil wall and the evolution characteristics of the specific heat capacity are analyzed. The frozen soil cylinders form surrounding freezing pipes at initial freezing stage, and the temperature field of frozen soil presents a non-linear decrease. With the increase of freezing time, the radius of the frozen soil cylinder increases and a frozen soil wall is enclosed. After freezing 30 days, the thickness of the frozen soil wall is obtained as 1.7 m. After freezing 250 days, the thickness of frozen soil wall increases to about 11.0 m.

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Teng, Yun Chao, Zhen Chao Teng, Yu Liu, Xiao Yan Liu, Ya Dong Zhou, Jia Lin Liu et Bo Li. « A Review of the Research on Thermo-Hydro-Mechanical Coupling for the Frozen Soil ». Geofluids 2022 (21 mars 2022) : 1–11. http://dx.doi.org/10.1155/2022/8274137.

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This paper reviews the history of the research development on the coupling mechanism of the multiphysical field, e.g., thermo-hydro-mechanical (THM), for frozen soil. The objective is to deepen the current understanding of the theories and mechanism of multiphysical field coupling in the frozen soil and the dynamic changes in the temperature, moisture, and stress fields during soil freezing. A new differential equation of the coupling of temperature field and moisture field is proposed. Based on the DiscreteFrechetDist algorithm, a fitting method of evaluating a curve is proposed. The paper is expected to help understand the soil freezing process in cold regions and enhance the innovativeness of the research methodologies dealing with multifield coupling for the frozen soil.

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Berg, Alexis, Benjamin R. Lintner, Kirsten Findell, Sonia I. Seneviratne, Bart van den Hurk, Agnès Ducharne, Frédérique Chéruy et al. « Interannual Coupling between Summertime Surface Temperature and Precipitation over Land : Processes and Implications for Climate Change* ». Journal of Climate 28, n^o 3 (1 février 2015) : 1308–28. http://dx.doi.org/10.1175/jcli-d-14-00324.1.

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Abstract Widespread negative correlations between summertime-mean temperatures and precipitation over land regions are a well-known feature of terrestrial climate. This behavior has generally been interpreted in the context of soil moisture–atmosphere coupling, with soil moisture deficits associated with reduced rainfall leading to enhanced surface sensible heating and higher surface temperature. The present study revisits the genesis of these negative temperature–precipitation correlations using simulations from the Global Land–Atmosphere Coupling Experiment–phase 5 of the Coupled Model Intercomparison Project (GLACE-CMIP5) multimodel experiment. The analyses are based on simulations with five climate models, which were integrated with prescribed (noninteractive) and with interactive soil moisture over the period 1950–2100. While the results presented here generally confirm the interpretation that negative correlations between seasonal temperature and precipitation arise through the direct control of soil moisture on surface heat flux partitioning, the presence of widespread negative correlations when soil moisture–atmosphere interactions are artificially removed in at least two out of five models suggests that atmospheric processes, in addition to land surface processes, contribute to the observed negative temperature–precipitation correlation. On longer time scales, the negative correlation between precipitation and temperature is shown to have implications for the projection of climate change impacts on near-surface climate: in all models, in the regions of strongest temperature–precipitation anticorrelation on interannual time scales, long-term regional warming is modulated to a large extent by the regional response of precipitation to climate change, with precipitation increases (decreases) being associated with minimum (maximum) warming. This correspondence appears to arise largely as the result of soil moisture–atmosphere interactions.

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Diro, G. T., et L. Sushama. « The Role of Soil Moisture–Atmosphere Interaction on Future Hot Spells over North America as Simulated by the Canadian Regional Climate Model (CRCM5) ». Journal of Climate 30, n^o 13 (juillet 2017) : 5041–58. http://dx.doi.org/10.1175/jcli-d-16-0068.1.

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Soil moisture–atmosphere interactions play a key role in modulating climate variability and extremes. This study investigates how soil moisture–atmosphere coupling may affect future extreme events, particularly the role of projected soil moisture in modulating the frequency and maximum duration of hot spells over North America, using the fifth-generation Canadian Regional Climate Model (CRCM5). With this objective, CRCM5 simulations, driven by two coupled general circulation models (MPI-ESM and CanESM2), are performed with and without soil moisture–atmosphere interactions for current (1981–2010) and future (2071–2100) climates over North America, for representative concentration pathways (RCPs) 4.5 and 8.5. Analysis indicates that, in future climate, the soil moisture–temperature coupling regions, located over the Great Plains in the current climate, will expand farther north, including large parts of central Canada. Results also indicate that soil moisture–atmosphere interactions will play an important role in modulating temperature extremes in the future by contributing more than 50% to the projected increase in hot-spell days over the southern Great Plains and parts of central Canada, especially for the RCP4.5 scenario. This higher contribution of soil moisture–atmosphere interactions to the future increases in hot-spell days for RCP4.5 is related to the fact that the projected decrease in soil moisture caused the soil to remain in a transitional regime between wet and dry state that is conducive to soil moisture–atmosphere coupling. For the RCP8.5 scenario, on the other hand, the future projected soil state over the southern United States and northern Mexico is too dry to have an impact on evapotranspiration and therefore on temperature.

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Koster, R. D., S. P. P. Mahanama, T. J. Yamada, Gianpaolo Balsamo, A. A. Berg, M. Boisserie, P. A. Dirmeyer et al. « The Second Phase of the Global Land–Atmosphere Coupling Experiment : Soil Moisture Contributions to Subseasonal Forecast Skill ». Journal of Hydrometeorology 12, n^o 5 (1 octobre 2011) : 805–22. http://dx.doi.org/10.1175/2011jhm1365.1.

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Abstract The second phase of the Global Land–Atmosphere Coupling Experiment (GLACE-2) is a multi-institutional numerical modeling experiment focused on quantifying, for boreal summer, the subseasonal (out to two months) forecast skill for precipitation and air temperature that can be derived from the realistic initialization of land surface states, notably soil moisture. An overview of the experiment and model behavior at the global scale is described here, along with a determination and characterization of multimodel “consensus” skill. The models show modest but significant skill in predicting air temperatures, especially where the rain gauge network is dense. Given that precipitation is the chief driver of soil moisture, and thereby assuming that rain gauge density is a reasonable proxy for the adequacy of the observational network contributing to soil moisture initialization, this result indeed highlights the potential contribution of enhanced observations to prediction. Land-derived precipitation forecast skill is much weaker than that for air temperature. The skill for predicting air temperature, and to some extent precipitation, increases with the magnitude of the initial soil moisture anomaly. GLACE-2 results are examined further to provide insight into the asymmetric impacts of wet and dry soil moisture initialization on skill.

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Liu, Di, Guiling Wang, Rui Mei, Zhongbo Yu et Huanghe Gu. « Diagnosing the Strength of Land–Atmosphere Coupling at Subseasonal to Seasonal Time Scales in Asia ». Journal of Hydrometeorology 15, n^o 1 (1 février 2014) : 320–39. http://dx.doi.org/10.1175/jhm-d-13-0104.1.

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Abstract This paper focuses on diagnosing the strength of soil moisture–atmosphere coupling at subseasonal to seasonal time scales over Asia using two different approaches: the conditional correlation approach [applied to the Global Land Data Assimilation System (GLDAS) data, the Climate Forecast System Reanalysis (CFSR) data, and output from the regional climate model, version 4 (RegCM4)] and the Global Land–Atmosphere Coupling Experiment (GLACE) approach applied to the RegCM4. The conditional correlation indicators derived from the model output and the two observational/reanalysis datasets agree fairly well with each other in the spatial pattern of the land–atmosphere coupling signal, although the signal in CFSR data is stronger and spatially more extensive than the GLDAS data and the RegCM4 output. Based on the impact of soil moisture on 2-m air temperature, the land–atmosphere coupling hotspots common to all three data sources include the Indochina region in spring and summer, the India region in summer and fall, and north-northeastern China and southwestern Siberia in summer. For precipitation, all data sources produce a weak and spatially scattered signal, indicating the lack of any strong coupling between soil moisture and precipitation, for both precipitation amount and frequency. Both the GLACE approach and the conditional correlation approach (applied to all three data sources) identify evaporation and evaporative fraction as important links for the coupling between soil moisture and precipitation/temperature. Results on soil moisture–temperature coupling strength from the GLACE-type experiment using RegCM4 are in good agreement with those from the conditional correlation analysis applied to output from the same model, despite substantial differences between the two approaches in the terrestrial segment of the land–atmosphere coupling.

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Gou, Qianqian, Changsheng Shen et Guohua Wang. « Changes in Soil Moisture, Temperature, and Salt in Rainfed Haloxylon ammodendron Forests of Different Ages across a Typical Desert–Oasis Ecotone ». Water 14, n^o 17 (28 août 2022) : 2653. http://dx.doi.org/10.3390/w14172653.

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Soil water and salt movement during the freeze–thaw period facilitate soil and water conservation and agroecological environment maintenance in the desert–oases transition zone of the Hexi Corridor; however, our understanding of soil salinization and the shifting water, heat, and salt states in soil ecosystems of Haloxylon ammodendron forests at different ages is poor. We analyzed the soil moisture, temperature, and salinity characteristics of Haloxylon ammodendron forests of different ages in the Hexi Corridor of Northwest China and determined their coupling. Our results indicated that shallow (0–120 cm) soil temperatures significantly correlated with air temperatures. With increased forest age, the soil freezing period shortened and the permafrost layer shallowed. Changes in soil temperature lagged those in air temperature, and this lag time increased with forest age and soil depth. With increases in forest age and planting years, the water in the shallow soil layer gradually declined, and the surface aggregation of salt increased. In deep soils (120–200 cm), both soil moisture and salinity increased with the number of planting years. Accordingly, the clay layer and deep root system of Haloxylonammodendron greatly influenced the transport of soil water and salt; and temperature is a key driving force for their transport. Thus, water, temperature, and salt content dynamics were synergetic.

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Deru, Michael P., et Allan T. Kirkpatrick. « Ground-Coupled Heat and Moisture Transfer from Buildings Part 1–Analysis and Modeling* ». Journal of Solar Energy Engineering 124, n^o 1 (1 mai 2001) : 10–16. http://dx.doi.org/10.1115/1.1435652.

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Ground-heat transfer is tightly coupled with soil-moisture transfer. The coupling is threefold: heat is transferred by thermal conduction and by moisture transfer; the thermal properties of soil are strong functions of the moisture content; and moisture phase change includes latent heat effects and changes in thermal and hydraulic properties. A heat and moisture transfer model was developed to study the ground-coupled heat and moisture transfer from buildings. The model also includes detailed considerations of the atmospheric boundary conditions, including precipitation. Solutions for the soil temperature distribution are obtained using a finite element procedure. The model compared well with the seasonal variation of measured ground temperatures.

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Catalano, Franco, Andrea Alessandri, Matteo De Felice, Zaichun Zhu et Ranga B. Myneni. « Observationally based analysis of land–atmosphere coupling ». Earth System Dynamics 7, n^o 1 (14 mars 2016) : 251–66. http://dx.doi.org/10.5194/esd-7-251-2016.

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Abstract. The temporal variance of soil moisture, vegetation and evapotranspiration over land has been recognized to be strongly connected to the temporal variance of precipitation. However, the feedbacks and couplings between these variables are still not well understood and quantified. Furthermore, soil moisture and vegetation processes are associated with a memory and therefore they may have important implications for predictability. In this study we apply a generalized linear method, specifically designed to assess the reciprocal forcing between connected fields, to the latest available observational data sets of global precipitation, evapotranspiration, vegetation and soil moisture content. For the first time a long global observational data set is used to investigate the spatial and temporal land variability and to characterize the relationships and feedbacks between land and precipitation. The variables considered show a significant coupling among each other. The analysis of the response of precipitation to soil moisture evidences a robust coupling between these two variables. In particular, the first two modes of variability in the precipitation forced by soil moisture appear to have a strong link with volcanic eruptions and El Niño–Southern Oscillation (ENSO) cycles, respectively, and these links are modulated by the effects of evapotranspiration and vegetation. It is suggested that vegetation state and soil moisture provide a biophysical memory of ENSO and major volcanic eruptions, revealed through delayed feedbacks on rainfall patterns. The third mode of variability reveals a trend very similar to the trend of the inter-hemispheric contrast in sea surface temperature (SST) and appears to be connected to greening/browning trends of vegetation over the last three decades.

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Ford, T. W., A. D. Rapp, S. M. Quiring et J. Blake. « Soil moisture–precipitation coupling : observations from the Oklahoma Mesonet and underlying physical mechanisms ». Hydrology and Earth System Sciences 19, n^o 8 (21 août 2015) : 3617–31. http://dx.doi.org/10.5194/hess-19-3617-2015.

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Abstract. Interactions between soil moisture and the atmosphere are driven by the partitioning of sensible and latent heating, through which soil moisture has been connected to atmospheric modifications that could potentially lead to the initiation of convective precipitation. The majority of previous studies linking the land surface to subsequent precipitation have used atmospheric reanalysis or model data sets. In this study, we link in situ observations of soil moisture from more than 100 stations in Oklahoma to subsequent unorganized afternoon convective precipitation. We use hourly next generation (NEXRAD) radar-derived precipitation to identify convective events, and then compare the location of precipitation initiation to underlying soil moisture anomalies in the morning. Overall we find a statistically significant preference for convective precipitation initiation over drier than normal soils, with over 70 % of events initiating over soil moisture below the long-term median. The significant preference for precipitation initiation over drier than normal soils is in contrast with previous studies using satellite-based precipitation to identify the region of maximum precipitation accumulation. We evaluated 19 convective events occurring near Lamont, Oklahoma, where soundings of the atmospheric profile at 06:00 and 12:00 LST are also available. For these events, soil moisture has strong negative correlations with the level of free convection (LFC), planetary boundary layer (PBL) height, and surface temperature changes between 06:00 and 12:00 LST. We also find strong positive correlations between morning soil moisture and morning-to-afternoon changes in convective available potential energy and convective inhibition. In general, the results of this study demonstrate that both positive and negative soil moisture feedbacks are important in this region of the USA.

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Ford, T. W., A. D. Rapp, S. M. Quiring et J. Blake. « Soil moisture–precipitation coupling : observations from the Oklahoma Mesonet and underlying physical mechanisms ». Hydrology and Earth System Sciences Discussions 12, n^o 3 (25 mars 2015) : 3205–43. http://dx.doi.org/10.5194/hessd-12-3205-2015.

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Abstract. Interactions between soil moisture and the atmosphere are driven by the partitioning of sensible and latent heating, through which, soil moisture has been connected to atmospheric modification that could potentially lead to initiation of convective precipitation. The majority of previous studies linking the land surface to subsequent precipitation have used atmospheric reanalysis or model datasets. In this study, we link in situ observations of soil moisture from more than 100 stations in Oklahoma to subsequent unorganized afternoon convective precipitation. We use hourly, high resolution NEXRAD radar-derived precipitation to identify convective events, and then compare the location of precipitation initiation to underlying soil moisture anomalies the morning prior. Overall we find a statistically significant preference for convective precipitation initiation over drier than normal soils, with over 70% of events initiating over soil moisture below the long-term median. The significant preference for precipitation initiation over drier than normal soils is in contrast with previous studies using satellite-based precipitation products to identify the region of maximum precipitation accumulation. We sub-sample 19 convective events occurring near Lamont, Oklahoma, where soundings of the atmospheric profile at 06:00 and 12:00 LST are also available. For these events, soil moisture is strongly, negatively correlated with the level of free convection, planetary boundary layer height, and surface temperature changes from 06:00 to 12:00 LST. We also find strong, positive correlations between morning soil moisture and morning-to-afternoon changes in convective available potential energy and convective inhibition. In general, the results of this study demonstrate that both positive and negative soil moisture feedbacks to the atmosphere are relevant in this region of the United States.

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Berg, Alexis, et Justin Sheffield. « Soil Moisture–Evapotranspiration Coupling in CMIP5 Models : Relationship with Simulated Climate and Projections ». Journal of Climate 31, n^o 12 (juin 2018) : 4865–78. http://dx.doi.org/10.1175/jcli-d-17-0757.1.

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Soil moisture–atmosphere coupling is a key process underlying climate variability and change over land. The control of soil moisture (SM) on evapotranspiration (ET) is a necessary condition for soil moisture to feed back onto surface climate. Here we investigate how this control manifests itself across simulations from the CMIP5 ensemble, using correlation analysis focusing on the interannual (summertime) time scale. Analysis of CMIP5 historical simulations indicates significant model diversity in SM–ET coupling in terms of patterns and magnitude. We investigate the relationship of this spread with differences in background simulated climate. Mean precipitation is found to be an important driver of model spread in SM–ET coupling but does not explain all of the differences, presumably because of model differences in the treatment of land hydrology. Compared to observations, some land regions appear consistently biased dry and thus likely overly soil moisture–limited. Because of ET feedbacks on air temperature, differences in SM–ET coupling induce model uncertainties across the CMIP5 ensemble in mean surface temperature and variability. We explore the relationships between model uncertainties in SM–ET coupling and climate projections. In particular over mid-to-high-latitude continental regions of the Northern Hemisphere but also in parts of the tropics, models that are more soil moisture–limited in the present tend to warm more in future projections, because they project less increase in ET and (in midlatitudes) greater increase in incoming solar radiation. Soil moisture–atmosphere processes thus contribute to the relationship observed across models between summertime present-day simulated climate and future warming projections over land.

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Zhou, Dong, Xiao Duo Ou, Li Ming Wang et Guan Yong Yue. « Analysis of the Coupling of Heat and Moisture of the Soil under Circulating Action of Temperature ». Advanced Materials Research 433-440 (janvier 2012) : 6356–62. http://dx.doi.org/10.4028/www.scientific.net/amr.433-440.6356.

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This article has used the equations of coupled heat-moisture anisothermal flow of the unsaturated soil, and conducted the numerical simulation coupling of heat and humidity by FLAC. By comparing the calculation result with the test result, it shows that the calculation result is close to the experiment result. The error is tending to be larger as the depth of the soil adds. The maximum error between the calculation and the experiment result is 1°C, and the smallest one is 0.1°C. Moreover due to the hysteresis of the heat transfer in the soil, the middle of the soil occurs temperature concentration phenomenon; Their trends of water migration variation are similar as the depth of the soil adds. The model of the coupling of heat and moisture is able to better simulate the change of heat and moisture of the soil under circulating action of temperature.

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He, Pengfei, Meng Xiong, Yanhu Mu, Jianhua Dong et Xinlei Na. « Experimental Study on Frost-Heaving Force Development of Tibetan Clay Subjected to One-Directional Freezing in an Open System ». Advances in Civil Engineering 2021 (13 janvier 2021) : 1–13. http://dx.doi.org/10.1155/2021/6626149.

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Frost heave of soils involves complex coupled interactions among moisture, heat, and stress, which can cause serious damage to cold regions engineering. In this paper, a series of one-directional freezing experiments were implemented for the Tibetan clay with rigid restraint in an open system. The varying characteristics of the temperature, frost-heaving force, and water replenishment during the freezing process were analyzed under different freezing temperatures (−5, −7, and − 9°C), dry densities (1.65, 1.7, and 1.75 g cm−3), and initial moisture contents (11, 14, and 17%) of the soil samples. It was concluded that the freezing of soil samples mainly occurred within 10–25 hours from the beginning of the experiment; hereafter, the soil temperatures tended to be stable. The development of frost-heaving force could be divided into three stages as slow increase, quick increase, and relative stable stages. Low freezing temperature, large dry density, and high moisture content were all the contributors to the frost-heaving process of the soil, which could increase the freezing depth, magnitude of the frost-heaving force, and amount of water replenishment. The variations in water replenishment from the open system corresponded to the three stages of the frost-heaving force but had time lags. The moisture contents at different layers of soil samples were measured after the freezing experiment. The results showed that the freeze part of soil samples experienced a significant wetting, while the unfrozen part experienced drying during the experiment. The degrees of wetting and drying were related to the freezing temperature, dry density, and initial moisture content of the soil samples. The experiment results could provide data support for theoretical study on moisture, heat, and stress coupling in freezing soil.

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Guo, Zhichang, et Paul A. Dirmeyer. « Interannual Variability of Land–Atmosphere Coupling Strength ». Journal of Hydrometeorology 14, n^o 5 (1 octobre 2013) : 1636–46. http://dx.doi.org/10.1175/jhm-d-12-0171.1.

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Abstract Recent studies in the Global Land–Atmosphere Coupling Experiment (GLACE) established a framework to estimate the extent to which anomalies in the land surface state (e.g., soil moisture) can affect rainfall generation and other atmospheric processes. Within this framework, a multiyear GLACE-type experiment is carried out with a coupled land–atmosphere general circulation model to examine the interannual variability of land–atmosphere coupling strength. Soil wetness with intermediate values are in the range at which rainfall generation, near-surface air temperature, and surface turbulent fluxes are most sensitive to soil moisture anomalies, and thus, land–atmosphere coupling strength peaks in this range. As a result, the “hot spots” with strong land–atmosphere coupling strength appear in regions with intermediate climatological soil wetness (e.g., transition zones between dry and wet climates), consistent with previous studies. Land–atmosphere coupling strength experiences significant year-to-year variation because of interannual variability of soil moisture and the local spatiotemporal evolution of hydrologic regime. Coupling strength over areas with dry (wet) climate is enhanced during wet (dry) years since the resultant soil wetness enters into the sensitive range from a relatively insensitive range, and soil moisture can have stronger potential impact on surface turbulent fluxes and convection. On the other hand, land–atmosphere coupling strength over areas with wet (dry) climate is weakened during wet (dry) years since the soil wetness moves further away from the sensitive range. This results in a positive correlation between the land–atmosphere coupling strength and soil moisture anomalies over areas with dry climate and a negative correlation over areas with wet climate.

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Gevaert, A. I., D. G. Miralles, R. A. M. Jeu, J. Schellekens et A. J. Dolman. « Soil Moisture‐Temperature Coupling in a Set of Land Surface Models ». Journal of Geophysical Research : Atmospheres 123, n^o 3 (février 2018) : 1481–98. http://dx.doi.org/10.1002/2017jd027346.

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Guo, Zhichang, Paul A. Dirmeyer, Timothy DelSole et Randal D. Koster. « Rebound in Atmospheric Predictability and the Role of the Land Surface ». Journal of Climate 25, n^o 13 (1 juillet 2012) : 4744–49. http://dx.doi.org/10.1175/jcli-d-11-00651.1.

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Abstract Total predictability within a chaotic system like the earth’s climate cannot increase over time. However, it can be transferred between subsystems. Predictability of air temperature and precipitation in numerical model forecasts over North America rebounds during late spring to summer because of information stored in the land surface. Specifically, soil moisture anomalies can persist over several months, but this memory cannot affect the atmosphere during early spring because of a lack of coupling between land and atmosphere. Coupling becomes established in late spring, enabling the effects of soil moisture anomalies to increase atmospheric predictability in 2-month forecasts begun as early as 1 May. This predictability is maintained through summer and then drops as coupling fades again in fall. This finding suggests summer forecasts of rainfall and air temperature over parts of North America could be significantly improved with soil moisture observations during spring.

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Dong, Jianzhi, et Wade T. Crow. « The Added Value of Assimilating Remotely Sensed Soil Moisture for Estimating Summertime Soil Moisture-Air Temperature Coupling Strength ». Water Resources Research 54, n^o 9 (septembre 2018) : 6072–84. http://dx.doi.org/10.1029/2018wr022619.

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Schwingshackl, Clemens, Martin Hirschi et Sonia I. Seneviratne. « Quantifying Spatiotemporal Variations of Soil Moisture Control on Surface Energy Balance and Near-Surface Air Temperature ». Journal of Climate 30, n^o 18 (8 août 2017) : 7105–24. http://dx.doi.org/10.1175/jcli-d-16-0727.1.

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Abstract Soil moisture plays a crucial role for the energy partitioning at Earth’s surface. Changing fractions of latent and sensible heat fluxes caused by soil moisture variations can affect both near-surface air temperature and precipitation. In this study, a simple framework for the dependence of evaporative fraction (the ratio of latent heat flux over net radiation) on soil moisture is used to analyze spatial and temporal variations of land–atmosphere coupling and its effect on near-surface air temperature. Using three different data sources (two reanalysis datasets and one combination of different datasets), three key parameters for the relation between soil moisture and evaporative fraction are estimated: 1) the frequency of occurrence of different soil moisture regimes, 2) the sensitivity of evaporative fraction to soil moisture in the transitional soil moisture regime, and 3) the critical soil moisture value that separates soil moisture- and energy-limited evapotranspiration regimes. The results show that about 30%–60% (depending on the dataset) of the global land area is in the transitional regime during at least half of the year. Based on the identification of transitional regimes, the effect of changes in soil moisture on near-surface air temperature is analyzed. Typical soil moisture variations (standard deviation) can impact air temperature by up to 1.1–1.3 K, while changing soil moisture over its full range in the transitional regime can alter air temperature by up to 6–7 K. The results emphasize the role of soil moisture for atmosphere and climate and constitute a useful benchmark for the evaluation of the respective relationships in Earth system models.

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Mei, Rui, et Guiling Wang. « Summer Land–Atmosphere Coupling Strength in the United States : Comparison among Observations, Reanalysis Data, and Numerical Models ». Journal of Hydrometeorology 13, n^o 3 (1 juin 2012) : 1010–22. http://dx.doi.org/10.1175/jhm-d-11-075.1.

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Abstract This study examines the land–atmosphere coupling strength during summer over subregions of the United States based on observations [Climate Prediction Center (CPC)–Variable Infiltration Capacity (VIC)], reanalysis data [North American Regional Reanalysis (NARR) and NCEP Climate Forecast System Reanalysis (CFSR)], and models [Community Atmosphere Model, version 3 (CAM3)–Community Land Model, version 3 (CLM3) and CAM4–CLM4]. The probability density function of conditioned correlation between soil moisture and subsequent precipitation or surface temperature during the years of large precipitation anomalies is used as a measure for the coupling strength. There are three major findings: 1) among the eight subregions (classified by land cover types), the transition zone Great Plains (and, to a lesser extent, the Midwest and Southeast) are identified as hot spots for strong land–atmosphere coupling; 2) soil moisture–precipitation coupling is weaker than soil moisture–surface temperature coupling; and 3) the coupling strength is stronger in observational and reanalysis products than in the models examined, especially in CAM4–CLM4. The conditioned correlation analysis also indicates that the coupling strength in CAM4–CLM4 is weaker than in CAM3–CLM3, which is further supported by Global Land–Atmosphere Coupling Experiments1 (GLACE1)-type experiments and attributed to changes in CAM rather than modifications in CLM. Contrary to suggestions in previous studies, CAM–CLM models do not seem to overestimate the land–atmosphere coupling strength.

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Orlowsky, Boris, et Sonia I. Seneviratne. « Statistical Analyses of Land–Atmosphere Feedbacks and Their Possible Pitfalls ». Journal of Climate 23, n^o 14 (15 juillet 2010) : 3918–32. http://dx.doi.org/10.1175/2010jcli3366.1.

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Abstract In some regions of the world, soil moisture has a typical memory for atmospheric processes and can also feed back to the latter. Thus, a better understanding of feedbacks between soil moisture and the atmosphere could provide promising perspectives for increased seasonal predictability. Besides numerical simulations, statistical analysis of existing GCM simulations or observational data has been used to study such feedbacks. By referring to a recent statistical analysis of soil moisture–precipitation feedbacks in GCM simulations, the authors illustrate potential pitfalls of statistical approaches in this context: (i) most importantly, apparent soil moisture–precipitation feedbacks can often as well or even better be attributed to the influence of sea surface temperatures (SSTs) on precipitation and (ii) the discrepancy between different GCMs is large, which makes the aggregation of individual model results difficult. These aspects need to be carefully evaluated in statistical analyses of land–atmosphere coupling. Results for soil moisture–temperature feedbacks complement the precipitation analysis.

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Levine, Paul A., James T. Randerson, Yang Chen, Michael S. Pritchard, Min Xu et Forrest M. Hoffman. « Soil Moisture Variability Intensifies and Prolongs Eastern Amazon Temperature and Carbon Cycle Response to El Niño–Southern Oscillation ». Journal of Climate 32, n^o 4 (février 2019) : 1273–92. http://dx.doi.org/10.1175/jcli-d-18-0150.1.

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El Niño–Southern Oscillation (ENSO) is an important driver of climate and carbon cycle variability in the Amazon. Sea surface temperature (SST) anomalies in the equatorial Pacific drive teleconnections with temperature directly through changes in atmospheric circulation. These circulation changes also impact precipitation and, consequently, soil moisture, enabling additional indirect effects on temperature through land–atmosphere coupling. To separate the direct influence of ENSO SST anomalies from the indirect effects of soil moisture, a mechanism-denial experiment was performed to decouple their variability in the Energy Exascale Earth System Model (E3SM) forced with observed SSTs from 1982 to 2016. Soil moisture variability was found to amplify and extend the effects of SST forcing on eastern Amazon temperature and carbon fluxes in E3SM. During the wet season, the direct, circulation-driven effect of ENSO SST anomalies dominated temperature and carbon cycle variability throughout the Amazon. During the following dry season, after ENSO SST anomalies had dissipated, soil moisture variability became the dominant driver in the east, explaining 67%–82% of the temperature difference between El Niño and La Niña years, and 85%–91% of the difference in carbon fluxes. These results highlight the need to consider the interdependence between temperature and hydrology when attributing the relative contributions of these factors to interannual variability in the terrestrial carbon cycle. Specifically, when offline models are forced with observations or reanalysis, the contribution of temperature may be overestimated when its own variability is modulated by hydrology via land–atmosphere coupling.

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Yang, Zesu, Qiang Zhang, Yu Zhang, Ping Yue, Liang Zhang, Jian Zeng et Yulei Qi. « Hydrothermal Factors Influence on Spatial-Temporal Variation of Evapotranspiration-Precipitation Coupling over Climate Transition Zone of North China ». Remote Sensing 14, n^o 6 (17 mars 2022) : 1448. http://dx.doi.org/10.3390/rs14061448.

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As a land–atmosphere coupling “hot spot”, the northern China climate transition zone has a sharp spatial gradient of hydrothermal conditions, which plays an essential role in shaping the spatial and temporal pattern of evapotranspiration-precipitation coupling, but whose mechanisms still remain unclear. This study analyzes the spatial and temporal variation in land–atmosphere coupling strength (CS) in the climate transitional zone of northern China and its relationship with soil moisture and air temperature. Results show that CS gradually transitions from strong positive in the northwest to negative in the southeast and northeast corners. The spatial distribution of CS is closely related to climatic hydrothermal conditions, where soil moisture plays a more dominant role: CS increases first, and then decreases with increasing soil moisture, with the threshold of soil moisture at 0.2; CS gradually transitions from positive to negative at soil moisture between 0.25 and 0.35; CS shows an exponential decreasing trend with increasing temperature. In terms of temporal variation, CS is strongest in spring and weakens sequentially in summer, autumn, and winter, and has significant interdecadal fluctuations. The trend in CS shifts gradually from significantly negative in the west to a non-significant positive in the east. Soil moisture variability dominates the intra-annual variability of CS in the study regions, and determines the interannual variation of CS in arid and semi-arid areas. Moreover, the main reason for the positive and negative spatial differences in CS in the study area is the different driving regime of evapotranspiration (ET). ET is energy-limited in the southern part of the study area, leading to a positive correlation between ET and lifting condensation level (LCL), while in most of the northern part, ET is water-limited and is negatively correlated with LCL; LCL has a negative correlation with P across the study area, thus leading to a negative ET-P coupling in the south and a positive coupling in the north.

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Xinchun, Liu, Kang Yongde, Chen Hongna et Lu Hui. « Hydrothermal Effects of Freeze-Thaw in the Taklimakan Desert ». Sustainability 13, n^o 3 (26 janvier 2021) : 1292. http://dx.doi.org/10.3390/su13031292.

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The Taklimakan Desert, also known as the “Sea of Death”, is the largest desert in China and also the world’s second largest remote desert. The road crossing the Taklimakan Desert is the longest desert road in the world and has been the center of the Silk Road since ancient times. Based on field observation data (November 2013 to May 2014) collected from the Tazhong and Xiaotang stations, we studied the interannual and diurnal variations of soil temperature, soil moisture content, and surface heat fluxes during different freezing and thawing periods. The annual and daily changes of soil temperature, soil moisture content, and surface energy fluxes at different freezing and thawing stages were analyzed. We illustrated the coupling relationship between water and heat in freezing-thawing soil in the Taklimakan Desert. We established a coupling model of soil water and heat during freezing and thawing. During the soil freezing period, the soil temperatures at different depths generally trended downward. The temperature difference between the Tazhong station and the Xiaotang station was 4~8.5 °C. The freezing time of soil at 20 cm depth occurred about 11 days after that at 10 cm depth. The effect of ambient temperature on soil temperature gradually weakened with the increase of soil depth. With the occurrence of the soil freezing process, the initial soil moisture contents at 5 cm, 10 cm, 20 cm, and 40 cm depths at the Xiaotang station were 6%, 10%, 29%, and 59%, respectively, and those at the Tazhong station were 5%, 3.6%, 4.4%, and 5.8%, respectively. As the ambient temperature decreased, the freezing front continued to move downward and the liquid soil water content at each depth decreased. The desert highway is closely related to the economic development and prosperity of southern Xinjiang. Therefore, it is important to maintain and inspect the safety and applicability of freeze-thaw zones and avoid casualties from vehicles and personnel.

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Berg, Alexis, Benjamin Lintner, Kirsten Findell et Alessandra Giannini. « Soil Moisture Influence on Seasonality and Large-Scale Circulation in Simulations of the West African Monsoon ». Journal of Climate 30, n^o 7 (avril 2017) : 2295–317. http://dx.doi.org/10.1175/jcli-d-15-0877.1.

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Prior studies have highlighted West Africa as a regional hotspot of land–atmosphere coupling. This study focuses on the large-scale influence of soil moisture variability on the mean circulation and precipitation in the West African monsoon. A suite of six models from the Global Land–Atmosphere Coupling Experiment (GLACE)-CMIP5 is analyzed. In this experiment, model integrations were performed with soil moisture prescribed to a specified climatological seasonal cycle throughout the simulation, which severs the two-way coupling between soil moisture and the atmosphere. Comparison with the control (interactive soil moisture) simulations indicates that mean June–September monsoon precipitation is enhanced when soil moisture is prescribed. However, contrasting behavior is evident over the seasonal cycle of the monsoon, with core monsoon precipitation enhanced with prescribed soil moisture but early-season precipitation reduced, at least in some models. These impacts stem from the enhancement of evapotranspiration at the dry poleward edge of the monsoon throughout the monsoon season, when soil moisture interactivity is suppressed. The early-season decrease in rainfall with prescribed soil moisture is associated with a delayed poleward advancement of the monsoon, which reflects the relative cooling of the continent from enhanced evapotranspiration, and thus a reduced land–ocean thermal contrast, prior to monsoon onset. On the other hand, during the core/late monsoon season, surface evaporative cooling modifies meridional temperature gradients and, through these gradients, alters the large-scale circulation: the midlevel African easterly jet is displaced poleward while the low-level westerlies are enhanced; this enhances precipitation. These results highlight the remote impacts of soil moisture variability on atmospheric circulation and precipitation in West Africa.

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Ye, Zhi Qiang, Xue Song Mao et Min Ye. « Moisture-Thermal Coupling Model for the Temperature Calculation of the Permafrost Subgrade ». Applied Mechanics and Materials 204-208 (octobre 2012) : 1580–85. http://dx.doi.org/10.4028/www.scientific.net/amm.204-208.1580.

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Water and heat conditions and their interactive affections are the key factors for the frost damages of highway engineering. In order to understand the moisture and thermal movement of subgrade soil deeply, a moisture-thermal coupling model has been developed for analyzing the temperature distribution in the permafrost subgrade of highway. The model takes into account both the effects of heat generation, internal conduction and convection, and the moisture movement to accurately predict the temperature evaluation. The theoretical calculations are compared to in-situ test results for the Qinghai_Tibet Highway and shown to be in great agreement at accuracy and precision. The coupling model can serves for the prediction of the frost depth of permafrost subgrade, further prevent the highway engineering from damages.

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Hauser, Mathias, René Orth et Sonia I. Seneviratne. « Investigating soil moisture–climate interactions with prescribed soil moisture experiments : an assessment with the Community Earth System Model (version 1.2) ». Geoscientific Model Development 10, n^o 4 (20 avril 2017) : 1665–77. http://dx.doi.org/10.5194/gmd-10-1665-2017.

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Abstract. Land surface hydrology is an important control of surface weather and climate. A valuable technique to investigate this link is the prescription of soil moisture in land surface models, which leads to a decoupling of the atmosphere and land processes. Diverse approaches to prescribe soil moisture, as well as different prescribed soil moisture conditions have been used in previous studies. Here, we compare and assess four methodologies to prescribe soil moisture and investigate the impact of two different estimates of the climatological seasonal cycle used to prescribe soil moisture. Our analysis shows that, though in appearance similar, the different approaches require substantially different long-term moisture inputs and lead to different temperature signals. The smallest influence on temperature and the water balance is found when prescribing the median seasonal cycle of deep soil liquid water, whereas the strongest signal is found when prescribing soil liquid and soil ice using the mean seasonal cycle. These results indicate that induced net water-balance perturbations in experiments investigating soil moisture–climate coupling are important contributors to the climate response, in addition to the intended impact of the decoupling. These results help to guide the set-up of future experiments prescribing soil moisture, as for instance planned within the Land Surface, Snow and Soil Moisture Model Intercomparison Project (LS3MIP).

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Mei, Rui, Guiling Wang et Huanghe Gu. « Summer Land–Atmosphere Coupling Strength over the United States : Results from the Regional Climate Model RegCM4–CLM3.5 ». Journal of Hydrometeorology 14, n^o 3 (1 juin 2013) : 946–62. http://dx.doi.org/10.1175/jhm-d-12-043.1.

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Abstract This study investigates the land–atmosphere coupling strength during summer over the United States using the Regional Climate Model version 4 (RegCM4)–Community Land Model version 3.5 (CLM3.5). First, a 10-yr simulation driven with reanalysis lateral boundary conditions (LBCs) is conducted to evaluate the model performance. The model is then used to quantify the land–atmosphere coupling strength, predictability, and added forecast skill (for precipitation and 2-m air temperature) attributed to realistic land surface initialization following the Global Land–Atmosphere Coupling Experiment (GLACE) approaches. Similar to previous GLACE results using global climate models (GCMs), GLACE-type experiments with RegCM4 identify the central United States as a region of strong land–atmosphere coupling, with soil moisture–temperature coupling being stronger than soil moisture–precipitation coupling, and confirm that realistic soil moisture initialization is more promising in improving temperature forecasts than precipitation forecasts. At a 1–15-day lead, the added forecast skill reflects predictability (or land–atmosphere coupling strength) indicating that that model can capture the realistic land–atmosphere coupling at a short time scale. However, at a 16–30-day lead, predictability cannot translate to added forecast skill, implying that the coupling at the longer time scale may not be represented well in the model. In addition, comparison of results from GLACE2-type experiments with RegCM4 driven by reanalysis LBCs and those driven by GCM LBCs suggest that the intrinsic land–atmosphere coupling strength within the regional model is the dominant factor for the added forecast skill at a 1–15-day lead, while the impact of LBCs from the GCM may play a dominant role in determining the signal of added forecast skill in the regional model at a 16–30-day lead. It demonstrates the complexities of using regional climate model for GLACE-type studies.

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Jach, Lisa, Thomas Schwitalla, Oliver Branch, Kirsten Warrach-Sagi et Volker Wulfmeyer. « Sensitivity of land–atmosphere coupling strength to changing atmospheric temperature and moisture over Europe ». Earth System Dynamics 13, n^o 1 (24 janvier 2022) : 109–32. http://dx.doi.org/10.5194/esd-13-109-2022.

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Abstract. The quantification of land–atmosphere coupling strength is still challenging, particularly in the atmospheric segment of the local coupling process chain. This is in part caused by a lack of spatially comprehensive observations of atmospheric temperature and specific humidity which form the verification basis for the common process-based coupling metrics. In this study, we aim at investigating where uncertainty in the atmospheric temperature and moisture affects the land–atmosphere coupling strength over Europe, and how changes in the mean temperature and moisture, as well as their vertical gradients, influence the coupling. For this purpose, we implemented systematic a posteriori modifications to the temperature and moisture fields from a regional climate simulation to create a spread in the atmospheric conditions. Afterwards, the process-based coupling metric convective triggering potential – low-level humidity index framework was applied to each modification case. Comparing all modification cases to the unmodified control case revealed that a strong coupling hotspot region in northeastern Europe was insensitive to temperature and moisture changes, although the number of potential coupling days varied by up to 20 d per summer season. The predominance of positive feedbacks remained unchanged in the northern part of the hotspot, and none of the modifications changed the frequent inhibition of feedbacks due to dry conditions in the atmosphere over the Mediterranean and the Iberian Peninsula. However, in the southern hotspot region in the north of the Black Sea, the dominant coupling class frequently switched between wet soil advantage and transition zone. Thus, both the coupling strength and the predominant sign of feedbacks were sensitive to changes in temperature and moisture in this region. This implies not only uncertainty in the quantification of land–atmosphere coupling strength but also the potential that climate-change-induced temperature and moisture changes considerably impact the climate there, because they also change the predominant atmospheric response to land surface wetness.

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Lavender, Sally L., Christopher M. Taylor et Adrian J. Matthews. « Coupled Land–Atmosphere Intraseasonal Variability of the West African Monsoon in a GCM ». Journal of Climate 23, n^o 21 (1 novembre 2010) : 5557–71. http://dx.doi.org/10.1175/2010jcli3419.1.

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Abstract Recent observational studies have suggested a role for soil moisture and land–atmosphere coupling in the 15-day westward-propagating mode of intraseasonal variability in the West African monsoon. This hypothesis is investigated with a set of three atmospheric general circulation model experiments. 1) When soil moisture is fully coupled with the atmospheric model, the 15-day mode of land–atmosphere variability is clearly identified. Precipitation anomalies lead soil moisture anomalies by 1–2 days, similar to the results from satellite observations. 2) To assess whether soil moisture is merely a passive response to the precipitation, or an active participant in this mode, the atmospheric model is forced with a 15-day westward-propagating cycle of regional soil moisture anomalies based on the fully coupled mode. Through a reduced surface sensible heat flux, the imposed wet soil anomalies induce negative low-level temperature anomalies and increased pressure (a cool high). An anticyclonic circulation then develops around the region of wet soil, enhancing northward moisture advection and precipitation to the west. Hence, in a coupled framework, this soil moisture–forced precipitation response would provide a self-consistent positive feedback on the westward-propagating soil moisture anomaly and implies an active role for soil moisture. 3) In a final sensitivity experiment, soil moisture is again externally prescribed but with all intraseasonal fluctuations suppressed. In the absence of soil moisture variability there are still pronounced surface sensible heat flux variations, likely due to cloud changes, and the 15-day westward-propagating precipitation signal is still present. However, it is not as coherent as in the previous experiments when interaction with soil moisture was permitted. Further examination of the soil moisture forcing experiment in GCM experiment 2 shows that this precipitation mode becomes phase locked to the imposed soil moisture anomalies. Hence, the 15-day westward-propagating mode in the West African monsoon can exist independently of soil moisture; however, soil moisture and land–atmosphere coupling act to feed back on the atmosphere and further enhance and organize it.

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Hirsch, A. L., A. J. Pitman, J. Kala, R. Lorenz et M. G. Donat. « Modulation of Land-Use Change Impacts on Temperature Extremes via Land–Atmosphere Coupling over Australia ». Earth Interactions 19, n^o 12 (1 octobre 2015) : 1–24. http://dx.doi.org/10.1175/ei-d-15-0011.1.

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Abstract The role of land–atmosphere coupling in modulating the impact of land-use change (LUC) on regional climate extremes remains uncertain. Using the Weather and Research Forecasting Model, this study combines the Global Land–Atmosphere Coupling Experiment with regional LUC to assess the combined impact of land–atmosphere coupling and LUC on simulated temperature extremes. The experiment is applied to an ensemble of planetary boundary layer (PBL) and cumulus parameterizations to determine the sensitivity of the results to model physics. Results show a consistent weakening in the soil moisture–maximum temperature coupling strength with LUC irrespective of the model physics. In contrast, temperature extremes show an asymmetric response to LUC dependent on the choice of PBL scheme, which is linked to differences in the parameterization of vertical transport. This influences convective precipitation, contributing a positive feedback on soil moisture and consequently on the partitioning of the surface turbulent fluxes. The results suggest that the impact of LUC on temperature extremes depends on the land–atmosphere coupling that in turn depends on the choice of PBL. Indeed, the sign of the temperature change in hot extremes resulting from LUC can be changed simply by altering the choice of PBL. The authors also note concerns over the metrics used to measure coupling strength that reflect changes in variance but may not respond to LUC-type perturbations.

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Wang, Weile, Bruce T. Anderson, Nathan Phillips, Robert K. Kaufmann, Christopher Potter et Ranga B. Myneni. « Feedbacks of Vegetation on Summertime Climate Variability over the North American Grasslands. Part I : Statistical Analysis ». Earth Interactions 10, n^o 17 (1 septembre 2006) : 1–27. http://dx.doi.org/10.1175/ei196.1.

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Abstract Feedbacks of vegetation on summertime climate variability over the North American Grasslands are analyzed using the statistical technique of Granger causality. Results indicate that normalized difference vegetation index (NDVI) anomalies early in the growing season have a statistically measurable effect on precipitation and surface temperature later in summer. In particular, higher means and/or decreasing trends of NDVI anomalies tend to be followed by lower rainfall but higher temperatures during July through September. These results suggest that initially enhanced vegetation may deplete soil moisture faster than normal and thereby induce drier and warmer climate anomalies via the strong soil moisture–precipitation coupling in these regions. Consistent with this soil moisture–precipitation feedback mechanism, interactions between temperature and precipitation anomalies in this region indicate that moister and cooler conditions are also related to increases in precipitation during the preceding months. Because vegetation responds to soil moisture variations, interactions between vegetation and precipitation generate oscillations in NDVI anomalies at growing season time scales, which are identified in the temporal and the spectral characteristics of the precipitation–NDVI system. Spectral analysis of the precipitation–NDVI system also indicates that 1) long-term interactions (i.e., interannual and longer time scales) between the two anomalies tend to enhance one another, 2) short-term interactions (less than 2 months) tend to damp one another, and 3) intermediary-period interactions (4–8 months) are oscillatory. Together, these results support the hypothesis that vegetation may influence summertime climate variability via the land–atmosphere hydrological cycles over these semiarid grasslands.

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Chen, Ajiao, Huade Guan, Okke Batelaan, Xinping Zhang et Xinguang He. « Global Soil Moisture‐Air Temperature Coupling Based on GRACE‐Derived Terrestrial Water Storage ». Journal of Geophysical Research : Atmospheres 124, n^o 14 (27 juillet 2019) : 7786–96. http://dx.doi.org/10.1029/2019jd030324.

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Wang, Licheng, Jinxin Lu, Ronglei Zhou, Gaohui Duan et Zhongming Wen. « Analysis of Soil Moisture Change Characteristics and Influencing Factors of Grassland on the Tibetan Plateau ». Remote Sensing 15, n^o 2 (4 janvier 2023) : 298. http://dx.doi.org/10.3390/rs15020298.

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Soil moisture is an important component of the soil–vegetation–atmosphere terrestrial hydrological cycle and is an important factor affecting terrestrial ecosystems. In the context of extensive vegetation greening on the Tibetan Plateau (TP), it is important to investigate the effect of vegetation greening on soil moisture to maintain ecosystem stability and protect the sustainability of ecological restoration projects. To evaluate the effect of vegetation greening on soil moisture on the TP, the spatial distribution and trends of soil moisture and vegetation on the TP were analyzed using GIMMS NDVI data and ERA5 soil moisture data from 1982 to 2015. The effects of grassland NDVI, precipitation, and temperature on SM were also explored using multiple regression apparent and SEM. The main results are as follows: from 1982 to 2015, both grassland NDVI and SM showed a stable increasing trend. Precipitation was the most important factor influencing SM changes on the TP. In the context that vegetation greening is mainly influenced by temperature increase, vegetation plays a dominant role in SM changes in soil drying and soil wetting zones. In this paper, the climate–vegetation–soil moisture coupling mechanism of grasslands on the TP is investigated, and the related results can provide some theoretical references and suggestions for global ecosystem conservation and the sustainable development of ecological restoration projects.

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Kumar, Sanjiv, Matthew Newman, David M. Lawrence, Min-Hui Lo, Sathish Akula, Chia-Wei Lan, Ben Livneh et Danica Lombardozzi. « The GLACE-Hydrology Experiment : Effects of Land–Atmosphere Coupling on Soil Moisture Variability and Predictability ». Journal of Climate 33, n^o 15 (1 août 2020) : 6511–29. http://dx.doi.org/10.1175/jcli-d-19-0598.1.

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AbstractThe impact of land–atmosphere anomaly coupling on land variability is investigated using a new two-stage climate model experimental design called the “GLACE-Hydrology” experiment. First, as in the GLACE-CMIP5 experiment, twin sets of coupled land–atmosphere climate model (CAM5-CLM4.5) ensembles are performed, with each simulation using the same prescribed observed sea surface temperatures and radiative forcing for the years 1971–2014. In one set, land–atmosphere anomaly coupling is removed by prescribing soil moisture to follow the control model’s seasonally evolving soil moisture climatology (“land–atmosphere uncoupled”), enabling a contrast with the original control set (“land–atmosphere coupled”). Then, the atmospheric outputs from both sets of simulations are used to force land-only ensemble simulations, allowing investigation of the resulting soil moisture variability and memory under both the coupled and uncoupled scenarios. This study finds that in midlatitudes during boreal summer, land–atmosphere anomaly coupling significantly strengthens the relationship between soil moisture and evapotranspiration anomalies, both in amplitude and phase. This allows for decreased moisture exchange between the land surface and atmosphere, increasing soil moisture memory and often its variability as well. Additionally, land–atmosphere anomaly coupling impacts runoff variability, especially in wet and transition regions, and precipitation variability, although the latter has surprisingly localized impacts on soil moisture variability. As a result of these changes, there is an increase in the signal-to-noise ratio, and thereby the potential seasonal predictability, of SST-forced hydroclimate anomalies in many areas of the globe, especially in the midlatitudes. This predictability increase is greater for soil moisture than precipitation and has important implications for the prediction of drought.

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Genxu, W., H. Hongchang, L. Yuanshou et W. Yibo. « Impacts of changes in vegetation cover on soil water heat coupling in an alpine meadow, Qinghai-Tibet Plateau, China ». Hydrology and Earth System Sciences Discussions 5, n^o 4 (4 septembre 2008) : 2543–79. http://dx.doi.org/10.5194/hessd-5-2543-2008.

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Abstract. Alpine meadow is one of the most widespread grassland types in the permafrost regions of the Qinghai-Tibet Plateau. The transmission of coupled soil water heat is one of the most important processes influencing cyclic variations in the hydrology of frozen soil regions, especially under conditions of changing vegetation cover. The present study assesses the impact of changes in vegetation cover on the coupling of soil water and heat in a permafrost region. Soil moisture (θv), soil temperature (Ts), soil heat content, and differences in θv−Ts coupling were monitored on a seasonal and daily basis under three different densities of vegetation cover (30, 65, and 93%) upon both thawed and frozen soils. Regression analysis of θv vs. Ts plots under different levels of vegetation cover indicates that soil freeze-thaw processes were significantly affected by changes in vegetation cover. With decreasing vegetation cover upon an alpine meadow, the difference between air temperature and ground temperature (ΔTa−s) also decreased. A decrease in vegetation cover also resulted in a decrease in the Ts at which soil froze and an increase in the temperature at which it thawed; this was reflected in a greater response of soil temperature to changes in air temperature (Ta). For ΔTa−s outside the range of −0.1 to 1.0°C, root zone soil-water temperatures showed a significant increase with increasing ΔTa−s; however, the magnitude of this relationship was dampened with increasing vegetation cover. At the time of maximum water content in the thawing season, the soil temperature decreased with increasing vegetation. Changes in vegetation cover also led to variations in θv−Ts coupling. With increasing vegetation cover, the surface heat flux increased, along with the amplitude of its variations. Soil heat storage at 20 cm depth also increased with increasing vegetation cover, and the downward transmitted of heat flux decreased. In addition to providing insulation against soil warming, vegetation in alpine meadows within the permafrost region also slows down the response of permafrost to climatic warming via the greater water-holding capacity of its root zone. Such vegetation may therefore play an important role in conserving water in alpine meadows and maintaining the stability of engineering works constructed within frozen soil of the Qinghai-Tibet Plateau.

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Vogel, Martha M., Jakob Zscheischler et Sonia I. Seneviratne. « Varying soil moisture–atmosphere feedbacks explain divergent temperature extremes and precipitation projections in central Europe ». Earth System Dynamics 9, n^o 3 (30 août 2018) : 1107–25. http://dx.doi.org/10.5194/esd-9-1107-2018.

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Abstract. The frequency and intensity of climate extremes is expected to increase in many regions due to anthropogenic climate change. In central Europe extreme temperatures are projected to change more strongly than global mean temperatures, and soil moisture–temperature feedbacks significantly contribute to this regional amplification. Because of their strong societal, ecological and economic impacts, robust projections of temperature extremes are needed. Unfortunately, in current model projections, temperature extremes in central Europe are prone to large uncertainties. In order to understand and potentially reduce the uncertainties of extreme temperature projections in Europe, we analyze global climate models from the CMIP5 (Coupled Model Intercomparison Project Phase 5) ensemble for the business-as-usual high-emission scenario (RCP8.5). We find a divergent behavior in long-term projections of summer precipitation until the end of the 21st century, resulting in a trimodal distribution of precipitation (wet, dry and very dry). All model groups show distinct characteristics for the summer latent heat flux, top soil moisture and temperatures on the hottest day of the year (TXx), whereas for net radiation and large-scale circulation no clear trimodal behavior is detectable. This suggests that different land–atmosphere coupling strengths may be able to explain the uncertainties in temperature extremes. Constraining the full model ensemble with observed present-day correlations between summer precipitation and TXx excludes most of the very dry and dry models. In particular, the very dry models tend to overestimate the negative coupling between precipitation and TXx, resulting in a warming that is too strong. This is particularly relevant for global warming levels above 2 ∘C. For the first time, this analysis allows for the substantial reduction of uncertainties in the projected changes of TXx in global climate models. Our results suggest that long-term temperature changes in TXx in central Europe are about 20 % lower than those projected by the multi-model median of the full ensemble. In addition, mean summer precipitation is found to be more likely to stay close to present-day levels. These results are highly relevant for improving estimates of regional climate-change impacts including heat stress, water supply and crop failure for central Europe.

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Fairbairn, David, Patricia de Rosnay et Philip A. Browne. « The New Stand-Alone Surface Analysis at ECMWF : Implications for Land–Atmosphere DA Coupling ». Journal of Hydrometeorology 20, n^o 10 (1 octobre 2019) : 2023–42. http://dx.doi.org/10.1175/jhm-d-19-0074.1.

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Abstract This article presents the “screen-level and surface analysis only” (SSA) system at the European Centre for Medium-Range Weather Forecasts (ECMWF). SSA is a simplification of the operational land–atmosphere weakly coupled data assimilation (WCDA). The goal of SSA is to provide 1) efficient research into land surface developments in NWP and 2) land reanalyses with land–atmosphere coupling. SSA maintains a coupled forecast model between assimilation cycles, but the atmospheric analysis is not performed; rather, it is forced from an archived analysis. Hence, SSA is much faster than WCDA, although it lacks feedback between the land and atmospheric analyses. A global sensitivity analysis was performed over one year to compare the WCDA and SSA systems. Prescribed proxy 2-m temperature/humidity screen-level observation errors were approximately doubled in the soil moisture data assimilation, thereby reducing the average size of the root-zone soil moisture analysis increments by about 60%. The systematic impact of these changes on the WCDA surface and near-surface atmospheric dynamics was effectively captured by SSA, although the short-term impact was underestimated. Importantly, the SSA forecast verification scores accurately reflected those of WCDA: atmospheric 1–10-day temperature/humidity forecasts were degraded in the tropics and lower midlatitudes up to about 700 hPa. The soil moisture analysis performance was not significantly impacted. These results endorse SSA as an NWP research tool and confirm the role of assimilating proxy screen-level observations in the soil moisture analysis to improve weather forecasts. Appropriate use and limitations of SSA are considered.

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Gasparin, Suelen, Marx Chhay, Julien Berger et Nathan Mendes. « A hybrid analytical–numerical method for computing coupled temperature and moisture content fields in porous soils ». Journal of Building Physics 42, n^o 1 (3 août 2017) : 68–94. http://dx.doi.org/10.1177/1744259117720644.

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This work is devoted to proposing a hybrid numerical–analytical method to address the problem of heat and moisture transfer in porous soils. Several numerical and analytical models have been used to study heat and moisture transfer. The complexity of the coupled transfer in soils is such that analytical solutions exist only for limited problems, while numerical solutions can deal with more realistic ones but at a higher computational cost. Therefore, we propose to implement analytical solutions where variations of temperature and moisture content are known to be almost nonvarying, while the numerical solution is implemented in the remaining region, near the boundaries. The coupling between solutions is performed assuming the continuity of both fields and fluxes at each interface. This strategy allows assuring the physical phenomenon occurring at the interface. Numerical experiments are performed, showing the accuracy, the efficiency, and the great potential of the method regarding applications in nonlinear soil problems.

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Genxu, W., H. Hongchang, L. Guangsheng et L. Na. « Impacts of changes in vegetation cover on soil water heat coupling in an alpine meadow of the Qinghai-Tibet Plateau, China ». Hydrology and Earth System Sciences 13, n^o 3 (13 mars 2009) : 327–41. http://dx.doi.org/10.5194/hess-13-327-2009.

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Abstract. Alpine meadow is one of the most widespread grassland types in the permafrost regions of the Qinghai-Tibet Plateau, and the transmission of coupled soil water heat is one of the most crucial processes influencing cyclic variations in the hydrology of frozen soil regions, especially under different vegetation covers. The present study assesses the impact of changes in vegetation cover on the coupling of soil water and heat in a permafrost region. Soil moisture (θv), soil temperature (Ts), soil heat content, and differences in θv−Ts coupling were monitored on a seasonal and daily basis under three different vegetation covers (30, 65, and 93%) on both thawed and frozen soils. Regression analysis of θv vs. Ts plots under different levels of vegetation cover indicates that soil freeze-thaw processes were significantly affected by the changes in vegetation cover. The decrease in vegetation cover of an alpine meadow reduced the difference between air temperature and ground temperature (ΔTa−s), and it also resulted in a decrease in Ts at which soil froze, and an increase in the temperature at which it thawed. This was reflected in a greater response of soil temperature to changes in air temperature (Ta). For ΔTa−s outside the range of −0.1 to 1.0°C, root zone soil-water temperatures showed a significant increase with increasing ΔTa−s; however, the magnitude of this relationship was dampened with increasing vegetation cover. At the time of maximum water content in the thawing season, the soil temperature decreased with increasing vegetation. Changes in vegetation cover also led to variations in θv−Ts coupling. With the increase in vegetation cover, the surface heat flux decreased. Soil heat storage at 20 cm in depth increased with increasing vegetation cover, and the heat flux that was downwardly transmitted decreased. The soil property varied greatly under different vegetation covers, causing the variation of heat conductivity and water-heat hold capacity in topsoil layer in different vegetation cover. The variation of heat budget and transmitting in soil is the main factor that causes changes in soil thawing and freezing processes, and θv−Ts coupling relationship under different vegetation fractions. In addition to providing insulation against soil warming, vegetation in alpine meadows within the permafrost region also would slow down the response of permafrost to climatic warming via the greater water-holding capacity of its root zone. Such vegetation may therefore play an important role in conserving water in alpine meadows and maintaining the stability of engineering works constructed within frozen soil of the Qinghai-Tibet Plateau.

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Lv, Shaoning, Bernd Schalge, Pablo Saavedra Garfias et Clemens Simmer. « Required sampling density of ground-based soil moisture and brightness temperature observations for calibration and validation of L-band satellite observations based on a virtual reality ». Hydrology and Earth System Sciences 24, n^o 4 (17 avril 2020) : 1957–73. http://dx.doi.org/10.5194/hess-24-1957-2020.

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Abstract. Microwave remote sensing is the most promising tool for monitoring near-surface soil moisture distributions globally. With the Soil Moisture and Ocean Salinity (SMOS) and Soil Moisture Active Passive (SMAP) missions in orbit, considerable efforts are being made to evaluate derived soil moisture products via ground observations, microwave transfer simulation, and independent remote sensing retrievals. Due to the large footprint of the satellite radiometers of about 40 km in diameter and the spatial heterogeneity of soil moisture, minimum sampling densities for soil moisture are required to challenge the targeted precision. Here we use 400 m resolution simulations with the regional Terrestrial System Modeling Platform (TerrSysMP) and its coupling with the Community Microwave Emission Modelling platform (CMEM) to quantify the maximum sampling distance allowed for soil moisture and brightness temperature validation. Our analysis suggests that an overall sampling distance of finer than 6 km is required to validate the targeted accuracy of 0.04 cm3 cm−3 with a 70 % confidence level in SMOS and SMAP estimates over typical mid-latitude European regions. The maximum allowed sampling distance depends on the land-surface heterogeneity and the meteorological situation, which influences the soil moisture patterns, and ranges from about 6 to 17 km for a 70 % confidence level for a typical year. At the maximum allowed sampling distance on a 70 % confidence level, the accuracy of footprint-averaged soil moisture is equal to or better than brightness temperature estimates over the same area. Estimates strongly deteriorate with larger sampling distances. For the evaluation of the smaller footprints of the active and active–passive products of SMAP the required sampling densities increase; e.g., when a grid resolution of 3 km diameter is sampled by three sites of footprints of 9 km sampled by five sites required, only 50 %–60 % of the pixels have a sampling error below the nominal values. The required minimum sampling densities for ground-based radiometer networks to estimate footprint-averaged brightness temperature are higher than for soil moisture due to the non-linearities of radiative transfer, and only weakly correlated in space and time. This study provides a basis for a better understanding of the sometimes strong mismatches between derived satellite soil moisture products and ground-based measurements.

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Song, Hyo-Jong, Craig R. Ferguson et Joshua K. Roundy. « Land–Atmosphere Coupling at the Southern Great Plains Atmospheric Radiation Measurement (ARM) Field Site and Its Role in Anomalous Afternoon Peak Precipitation ». Journal of Hydrometeorology 17, n^o 2 (26 janvier 2016) : 541–56. http://dx.doi.org/10.1175/jhm-d-15-0045.1.

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Abstract The multimodel Global Land–Atmosphere Coupling Experiment (GLACE) identified the semiarid Southern Great Plains (SGP) as a hotspot for land–atmosphere (LA) coupling and, consequently, land-derived temperature and precipitation predictability. The area including and surrounding the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) SGP Climate Research Facility has in particular been well studied in the context of LA coupling. Observation-based studies suggest a coupling signal that is much weaker than modeled, if not elusive. Using North American Regional Reanalysis and North American Land Data Assimilation System data, this study provides a 36-yr (1979–2014) climatology of coupling for ARM-SGP that 1) unifies prior interdisciplinary efforts and 2) isolates the origin of the (weak) coupling signal. Specifically, the climatology of a prominent convective triggering potential–low-level humidity index (CTP–HIlow) coupling classification is linked to corresponding synoptic–mesoscale weather and atmospheric moisture budget analyses. The CTP–HIlow classification defines a dry-advantage regime for which convective triggering is preferentially favored over drier-than-average soils as well as a wet-advantage regime for which convective triggering is preferentially favored over wetter-than-average soils. This study shows that wet-advantage days are a result of horizontal moisture flux convergence over the region, and conversely, dry-advantage days are a result of zonal and vertical moisture flux divergence. In this context, the role of the land is nominal relative to that of atmospheric forcing. Surface flux partitioning, however, can play an important role in modulating diurnal precipitation cycle phase and amplitude and it is shown that soil moisture and sensible heat flux are significantly correlated with both occurrence and intensity of afternoon peak precipitation.

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